BMW motorcycle transmission (gearbox) service and repair |
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Of the 4 units (engine, transmission, drive shaft and final drive) in the BMW motorcycle drive train, the transmission is the least reliable. It is typical for a BMW transmission, using natural petroleum hypoid gear oil, to need repair in 50-75 k miles. Most make it to 50 k and most are opened up by 75 k miles. Yes, you can find the occasional transmission that violates these numbers, but I am giving the average. You don't need to believe me, ask any BMW motorcycle transmission re-builder about his experience. If you take a look at the sizes of gears and bearings and consider the horsepower, the unit should last far longer. It should last nearly forever. Most cars and trucks with a manual transmission go to the junk yard without ever needing a re-build. Why not our beloved BMW? I will try to explain some aspects of this unit. From time to time I will add to this page. If you like to print out a page for the shop, always check the "last edited" date at the bottom of the page to be sure that you are working from the latest version. Metal in the oil of a BMW motorcycle transmissionForever "they" have said that it is normal for the BMW transmission to have metal flakes in the oil. Does that make sense to you? I didn't think so. Ask a bearing engineer how much metal "should" be in the lubricant. I think that you will get a strange look. So, what are "they" talking about? Any metal in the oil is bad, but in the BMW motorcycle transmission, it is common. The source of the metal is from more than one place. The amount and size of the particles is important in predicting failure. While you can't completely stop the metal from getting into the oil, you certainly can do something about it. Drain your oil into a clean container and carefully examine the oil in the sunlight. You will see the metal swirl around and produce a "sheen". The magnetic drain plug (sport models only) will have "fuzz" or sludge on it. The rule of thumb is to pinch as much of the fuzz as possible between two fingers and rub them together. If you can easily feel the fuzz as sort of fine sand, that is bad. If the fuzz feels smooth, then that is good. (Learn to rub the fuzz and record your findings.) Well, maybe not good, but the bearings aren't coming apart soon. What is the problem here? Testing an unknown /6 BMW motorcycle 5 speed transmission on the bench, but this applies to any BMW motorcycle transmission.In evaluating and preparing a 5 speed transmission for sale on eBay, I had occasion to run a transmission thru the various tests. It was out of a 1974 R90/6 that had an engine failure while riding on the freeway. That only tells me that is was working well enough to ride it, but it may have been in need of a rebuild and I want to know as much as I can learn about it. I have photographed each step in my evaluation process. First step is to remove the magnetic drain plug and examine it. Since the transmission is out on the workbench, I am able to tilt it over on the front side and remove the drain plug.
This is how it looked right out of the case. The residual oil sort of "covers" the metal I want to inspect.
Here I have removed most of the oil by gently dipping it into solvent. I just wanted to get the oil out of the way to show the metal paste for this photo. I don't suggest that one needs to do this in normal maintenance. Then I wiped off as much as I could between my fingers and rubbed them together to see how the metal feels. It was pure paste and I could sense no particles. That is really good news.
In this photo I have also used a white piece of hand towel to clean the metal off as well as is possible.
I wiped my two fingers on this paper towel as well as I could and wiped off as much paste from the drain plug as well. I deposited it in one spot for the photograph. As you can see from the photo above this one, not all of the paste will come off by wiping. One just can't grab metal paste from a magnet. The good news is that no metal pieces are visible. This only serves to confirm my "finger test." I am only going to this much trouble to show readers, as I consider the finger test to be good enough and why waste this much time? Lets get it together and go riding.
Call me obsessive, but I won't put a plug back with any metal paste on it. I use my air gun to blast the magnet clean and it looks like this. Record this positive finding of the usual metal paste in your log book. Now I will drain the oil out, but I already know that I won't see any metallic swirl in the oil. This transmission hasn't run in about 2 years, so any metal would have settled out a long time ago. (If you want to see the most metallic swirl, drain it out after a long run while the oil is hot and little settling has taken place.) The oil was clean, as I expected. Note: If you ever find this same metal paste in any other place on your BMW, start planning on spending money.I forgot to take a picture of the front of the transmission before I started cleaning it off. It had the usual black clutch dust all over it. The good news is that it was as dry as a bone. That means that the input seal wasn't leaking. If the seal is leaking, you will observe a wet area under the seal. If the seal is leaking a bit more, then oil will actually get on the clutch plate and cause it to slip.
Check the ground/speedo cable bolt hole to make sure that it has good threads. They get stripped out easily from repeated use and over tightening.
One or both can break off, see below for the fix
I removed the shift lever for easier shipping. This shows the end that engages the shifting mechanism inside the transmission. One can easily see how it is splayed out and not only wider, but it has sharp edges. I would grind off the sharp edges, but leave the rest alone. The reason is that it is hard to insert this lever back into the transmission through the seal without risking damage to the seal.
Now it is safe to insert it back into the hole without risking seal damage.
The bolt that attaches the shift lever is quite long for only 6 mm in diameter. I am only showing it in case someone has a basket case.
The washer shown is actually a shim that is used to adjust the actuation of the neutral light. One may need more or less thickness to make it work correctly. I removed it for shipping, because it is exposed to damage when mounted.
I always test the switch if I have it out. Move the plunger from side to side and in and out while watching the meter. You are looking for any flaky action at all. It is really a good idea to just replace this rather cheap switch. If you once replace it with the transmission mounted in the bike, you will wish you had replaced it when the transmission was out. This shows the early /6 switch with the straight (vertical) terminals. This switch closed the circuit when the plunger is pressed in. The later switch (shown below) was closed when the plunger is in the natural (out) position. This occurred about in mid 75 to give it a more positive shift. The "kit" was a different drum with deeper indents for the spring loaded nylon roller that holds the drum in position for each gear.
These terminals are on a later /6 transmission. It shows the bent terminals which makes it easier to install the wires while the transmission is in place. Removing the kick start leverI also removed the kick start lever for ease in packing. This is usually quite a task if the kick start lever has been used very often. This info applies to all BMW motorcycle transmissions equipped with a kick start lever. Another reference is made of this below, near the bottom of this page.
My first attempt was using this battery terminal puller. It was not up to the task. Then I heated the aluminum lever up to around 300 F and still it would only move a little bit. In my BMW dealership, we had a stronger puller that was perfect for this job.
I resorted to using levers to lift the kick lever and shaft upwards, but not really trying to lever the part off of the shaft. Then I gave it dozens of fairly gently taps with a center punch in the center hole of the shaft. It is as if it was made for this. This is a two person procedure and my wife, Linda, is always willing to assist me. In this case, she was taking the picture, so I can't show the second person using the center punch and hammer.
This photo shows the normal wear on the BMW motorcycle /6 transmission kick start shaft. It is caused by the taper pin that secures the lever to the shaft. To minimize this damage, one must keep the nut on the pin tight. To test it, just grab the kick lever and try to move it up. That will rotate the taper away from the shaft and show any "play" that exists. The taper pin must be in the right way too, or the lever will hang way out when in the resting position. As the lever is removed, the bulged out part will slightly damage the lever.
The arrow points to the shiny spot on the shaft for the /6 BMW motorcycle transmission shift lever. It is actually larger at this point and the lever doesn't want to come off. While the shift lever can be pulled off, it won't go back on easily. The bulge on the shaft must be dressed down a bit for a nice fit.
The BMW motorcycle transmission input shaft spline wear is a major issue. It is well known that the splines must be lubricated at regular intervals with a high quality grease. I do not deal with how often and which grease is best. That is up to you. Here you can observe the spline wear. I took several photos attempting to show the wear pattern. All failed. By eye, one can see where the clutch hub internal splines wore against this shaft. None of the photos show it. In reality it doesn't matter except as a display on this page. This spline shows almost no wear at all. The odometer shows 82 k miles (about 130,000 km) and has evidence of tampering. The rest of the bike shows that it has a lot of miles on it, but has been in a good maintenance program. I can't believe that this shaft is the original one. I suspect that it has been replaced and doesn't have many miles on it. BMW motorcycle transmission shifting "bench test"When you do any work on a transmission you might want to test it for proper shifting before installing it in the bike. It may save you lots of work and time. You might want to test a totally unknown unit. You may want to test a unit before having it repaired to get a feel of what you have. Here is how we did it. (You may need a friend for that "third" hand.) 1. Mount it down to the bench somehow. You could tie it down to a milk crate and then put your foot on it to keep it in one place. We had the official tranny/engine stand for this. 3. Figure out a way to turn the input shaft. We used a modified clutch plate. We mounted a knob on the plate to use for turning it. You need to turn it as quickly as you easily can. Hand speed is ok. 4. You need to put some resistance on the output shaft. We used a piece of leather pushed/held against the flange. 5. Then shift it up and down through the gears. It was a surprise to us, but you can "feel" every defect or characteristic of shifting. It would be completely crazy to install a transmission that hasn't gone through a simple bench test. It is so easy to do and takes no special tools. I am showing it this way to show you that you don't need any fancy tools to do this very necessary test.
You will need to rotate the input shaft for this test. I use the clutch friction plate. If you haven't removed the clutch yet, maybe this is a good time to inspect the clutch. To avoid removing the clutch to get the plate, rig up something to turn the input shaft. A rubber hose of about 1" diameter and clamps will allow you to use your cordless drill. Just be sure to run it slowly. I turn the clutch plate by using the clutch rod in one of the holes. That is plenty fast enough.
The BMW motorcycle transmission to be tested must be held down really well. You may make a mounting bracket from angle iron and clamp it in a vise, but this shows one way to improvise. I use 30 + year old straps that mounted the motorcycle in the crate. Any old milk crate should work well. The only requirement of the ohmmeter is that I have alligator clips on the probe ends to fasten to the neutral switch. The clutch plate is mounted exactly the same direction as on the bike.
You will really need two people to test the BMW motorcycle transmission this way, but I manage with just myself. My wife, Linda, was nice enough to take the photo. I use my left ankle to apply pressure against the output flange. Without that pressure the shifting may be difficult and the transmission shifting test is invalid.
My right foot is holding me up. My left foot is holding the crate down and also applying pressure sideways against the output flange. My right hand is the motive power and turning the clutch plate. My left hand is operating the shift lever. I watch the meter to see if it show the neutral switch operating at the proper times. This might be a bit awkward the first time, but it can be done by one person. This one tested good. This 1974 BMW motorcycle /6 transmission was known to be hard to find neutral and that shows up in this test. While using this transmission, it is far easier to shift to neutral while rolling the last 10 feet before the full stop. Transmission appraisal conclusionThis transmission passed every test very well. I would have no problem installing this one and expecting good service out of it. The gear dogs and slider platesWhen removing the shafts, be sure to mark the slider positions. You will want to have it go back together with the slider in the same position/place. This will insure that the worn in parts are still together. If you were to elect to improve the matching, it is even more important to mark them. It is because of the method of production chosen by BMW. The gears are cast, the teeth cut and the dogs are not machined, but left with whatever precision that resulted. These gears are all /2, but the /5 is the same.
This is a typical BMW motorcycle transmission gear and the 6 "dogs" are faced up for view. What are dogs? They are the parts that engage the slider or shifting plate. The gear is free to rotate on the shaft and the slider "drives" the output shaft. The gear teeth can be used to define a "center" of the circle. The dogs can also define a center. The two centers should be identical. They are rarely the same. Only the teeth get precision treatment. The dogs just end up where ever they are cast. For casting, they are really good, but not good enough. A close examination of dogs on used gears will usually show that less than all 6 are being engaged. I have seen as few as 2 show evidence of serious wear. That means that all of the horse power is going through only two dogs. That is bad enough, but the situation is far worse. With only partial dogs engaging, the gear is cocked off to one side. With the gear cocked it wears far faster. That is reason for some, but not all of the metal in the oil.
The BMW motorcycle slider plate.This is a "slider" or shifter plate found in a /2, /5, /6 and /7 BMW motorcycle transmission. It may have other names too, but the name is not important. This part drives the output shaft and selects one of two gears, or neutral. The outer groove that the shift forks ride in, have been machined. They have a center. The holes line up with the dogs on a gear and they must match. By examining the holes we can see the wear. The wear shows how well they match. It is common to find that less than 6 are driving the shaft. I have seen as few as two showing major wear. This will cock it off to one side, but in this case it isn't very important in adding metal to the oil. It may be important in shifting. One could consider that if the dogs are "off center" and the holes in the slider are also "off center", how do we know which is which? It is actually quite easy to tell. If the gear had only one dog "driving", that dog would drop into the slider and it would work. The dog would "visit" each of the 6 holes equally often over time. We would then see which of the 6 holes in the slider is worn more. The hole in the slider with the most wear is the one out of alignment. They should all show the same amount of wear. Lets consider the reverse situation. If the dogs were perfect and the holes in the slider were perfect, then we would see equal wear on all. If we have a perfect slider and imperfect dogs, then the holes in the slider would all get equal wear. Only the "driving" dogs would show wear. Examination of the slider and gear will show if there is unequal wear and therefore something is made off center. The dogs can be so far off that they carry too much power and snap off. Then the power shifts to the next dog and everything keeps going. It is possible to discover a broken off dog stuck to the magnetic drain plug. You can keep riding, but understand that the next dog is probably going to also break off eventually. I have seen three broken off and the bike was still running. This and other parts can be found in the bottom of the transmission. We had a slender long flexible magnet to shove into the fill hole and swish around across the bottom of the transmission. It was common to fish out some part. We put the owner on notice of impending transmission trouble. This way the owner could take care of it before it left him/her stranded.
The /2 BMW motorcycle transmission shift fork The shift forks are well made. They are precision ground and usually well done. One can usually reuse the forks. The factory made tools to reach down into the transmission and bend them into alignment. I only did that once and just swapped them after that. It is a very hard job, as the forks are made of super strong metal. A close examination of the upper and lower tips on any one fork will often show some uneven wear. That uneven wear shows that the forks were not in alignment. Later the /5 came out with almost the same transmission, with one very important exception. The bushings that mount the forks are made non-concentric. You can see that the mounting hole is off center.
The bottom end of the /5 bushing on the left and top end of the /2 bushing on the right. Sorry, but I mixed them up when taking the photo.
Each one flipped over, but still the opposite ends. The /5 bushing with the "nut" end for the adjusting wrench on the left. The /2 on the right. Can you see that the hole is "off center" on the /5 bushing? As one rotates it, the fork is moved from side to side compared to the sliding plate. This allows one very easy and exact adjustment of the plate. I highly recommend this upgrade to the /2 any time it is rebuilt. The part number for the bushing is 23 31 1 230 086. The shift forks are ground "off" a bit during manufacture and they tend to get worn down, during use, to fit. It is most common to see one tip show far more wear than the other one. I never found that to be a problem. There is a test for misalignment and if the forks pass that test, then I have never had a problem shifting.
This photo shows a tip of the BMW motorcycle transmission shifter fork riding in the groove of a slider. If the fork is out of alignment, then one tip is off to one side, the plate will be cocked to one side and it will bind up and make hard shifts. Over time, a lot of time, it will get ground off and may work better. It was not uncommon for the /2 BMW motorcycle transmission to be a bit stiff for the first 10,000 miles. The path through the gears of a BMW motorcycle /2 and /5 transmission
This photo shows the gears as they are located in the BMW motorcycle transmission case. I have removed all of the unrelated parts possible, for clarity. The lower shaft is the input shaft. The splines are on the left end and stick into the clutch plate. The middle shaft is one piece and is called the "cluster gear" and the "intermediate shaft." The upper shaft is called the "output shaft" by most. See the sliders are not engaged with any gear? That is because this is the neutral position.
The output (upper) shaft isn't shown as it isn't needed or desired for this demonstration. This is the path for first gear. The "right" slider has moved over to the right to engage first gear.
This is second gear. Now the "right" slider has moved left and engages second gear.
This is third gear. The right slider has moved back to neutral and isn't shown. The "left" slider has moved over to the right to engage third gear.
This is fourth gear. The "left" slider has moved over to the left to engage fourth gear. BMW motorcycle transmission bearingsThe BMW motorcycle transmission specifies using C3 bearings. That means "loose" fit. Check the "play" of the gears on the output shaft, they are quite loose on the bushings. All of this "looseness" is necessary to allow the gears to "center" themselves and try to distribute the power equally through all 6 dogs. The uneven wear is evidence that it wasn't "slop" enough to work. The metal in the oil is evidence of wear. Where exactly does this wear come from? The most wear is usually on the helically cut 4th gear on the input shaft. It gets all of the horsepower, all of the time. It is also 4th gear, the one used most of the time. The other 3 gears are straight cut. Over time, the input gear on the input shaft (4th) becomes undercut. Then it really makes noise and sheds metal. The next source of metal is the other gears. Next is from the kick starter sector gear. See those very fine "wires" that show up in the oil? They are bits sheared off of the second tooth. More info below. Change the oil oftenThe best single thing that you can do for your transmission is to change the oil often. That flushes out the metal. The /2 sport models were supplied with a magnetic drain plug. If you have a 55-69 R50 or R60, then your drain plug has no magnet. Get one. The next is to use synthetic oil, as it seems to about double the bearing life. When you have it rebuilt, have it done properly. The factory has changed the spec for shaft end play. In my opinion, the later spec (.004" cold) is still a bit loose. The /2 is tolerant of end play, but the /5 and later transmissions are not. (That is because they changed the clutch splines) Lots of people can change bearings, but few know how to really rebuild one of these units. Don't try the stupid method shown in the factory shop manual for measuring the shaft end play. More below. These gears shown here are slightly used and as good of a set as I have ever seen. They will not be offered on ebay, but will eventually be for sale on my site under the used parts section. Typical failure mode for a /2 motorcycle transmissionI will describe a common failure mode of the /2 drive train. The first symptom is often a slipping clutch. The clutch is found to have oil on it. The oil can only come from the input shaft seal on the transmission. Contrary to common belief, an engine rear main bearing seal that is leaking can't put oil onto the clutch. The transmission oil migrates forwards along the shaft, or inside the shaft and onto the clutch. Replacing the seal will do nothing to stop the leakage. The real culprit is "often" that the bearing on the transmission input shaft has gotten loose. The seal can't do its job if the shaft is moving around. The failure of the input bearing commonly can be from one, or more, of three factors. 1. The bearing can go out from misalignment of the transmission. When a transmission is installed into a /2, it is very important to align it. When the transmission input shaft is running out of center with the crankshaft, the much smaller transmission bearing is the one that will fail first. Misalignment also causes premature wear of the clutch disc and shaft splines. 2. The bearing can fail from old age and put metal in the oil. More info on that above. 3. The rear main bearing on the crankshaft will start to fail. It can fail in a variety of ways, but as it gets loose it may make little or no noise. It can be hard to detect in the early stages. The small input bearing is just not enough to "hold" the moving crankshaft. The transmission input bearing will fail quickly. That allows the oil to leak past the seal and onto the clutch. Because of the importance of centering (aligning) the transmission to the engine, we wouldn't rebuild a transmission that was out of a bike. It is understandable that an owner would pull the transmission out and reinstall it to save money. The total labor to remove and install is usually under an hour, so not much is saved. I felt that I couldn't warranty my work if someone else was installing the transmission. Ask your rebuilder about his policy. You may have to ship it off to one of the few good rebuilders and that means that you must install it later. Learn how to align it. I will never forget one rebuild job. The customer brought in his transmission with a bad input bearing. I refused to rebuild it because I hadn't removed it and appraised the bike. He offered to bring in the bike so that we could install it. I reluctantly agreed. Upon installing his rebuilt transmission, we discovered that the rear main bearing was "growling" very badly. The new clutch and rebuilt transmission were all for nothing. The bike wasn't worth an engine job. Had he just brought the whole bike in for appraisal, he would have saved a ton of money. We were both very unhappy about the result. Just because it was the owners fault, didn't make it any easier for either of us to accept. The earliest symptom of a failing rear main is hard to detect. A very quick exam will "tend" to indicate the possibility of eminent failure. Remove the rubber timing hole plug. Originally they were white, but I think that only black is available now. Operate the clutch lever several times while watching the flywheel very closely. If you see any flywheel movement at all, you may have trouble. Some people just can't see small movements that are critical. Sometimes a small movement is evident with a badly failing main bearing. Sometimes a crank will have a lot of movement and the bearings will last tens of thousands of miles, but that is rare. Sometimes a bearing will make obvious noise and not have much float. This simple test isn't a for sure thing, but is generally indicative. I must add that it is important to have seen many of these to start to get the "feeling" of how much visible movement is tolerable and how much is "way too much" movement. If you also see the flywheel move a bit up or down when the clutch is pulling in, that is always a failed bearing. We saw a few of these failure on early /2, but the ones manufactured in the mid and late 60s were really bad. The R50/2 and the R60/2 were the worst. That is due to the flex in the crankshaft. Why it got worse during that era of bike was an interesting question. We were never able to pin down the exact reason for a far greater failure rate during those years. The R69S barrel roller bearing was so much stronger and allowed for crank flex, so it failed at a much lower rate. That was in spite its 50% greater horsepower output. Many failed in the first 30 k miles. I had one customer that had his R69S lower end fail in 6,000 miles. During those last days of the /2, I started having much less success with lower end rebuilds. Finally I stopped doing it. Once, I ordered three new R60/2 crankshafts from Germany. Two of them were defective and out of spec. Rebuilding a new crank is rather depressing. This story goes on, but many of the /2 transmission jobs were related to crank troubles. Are all /2 BMW motorcycle transmissions the same?The technical aspects of all twin transmission are the same. They have the same gear ratios for all solo bikes. They are almost completely interchangeable. In this case, one must lump them into two groups. The later sport models, R50S and R69S, used a different air cleaner. That air cleaner was more open and allowed a bit more flow. The R50, R60, R69, R50/2, and R60/2 used an air cleaner that had a choke lever. Both types of air cleaner mounted in the same way, by a long bolt through the middle. The choke type air cleaner was kept oriented by a roll pin that was mounted into the transmission case. It must be removed to mount the sport type air cleaner. The holes on each side of the transmission top for the chrome carb tubes are slightly different for the R50/R60 and the R69/R69S. The sport bikes have a ridge that locates the rubber bushing that mounts the chrome tube.
Slightly below the center of the picture is the locating roll pin for the choke type air cleaner. A /2 BMW motorcycle transmission jumping out of gearThere can be a few reasons for a /2 BMW to jump out of gear. This is only one of them and a rather odd finding. A customer came in for a tune and happened to mention that the transmission would often jump out of third gear. It had done this for a long time and he hadn't noticed any pattern to it. My test ride confirmed it and found that the shifting didn't feel correct. Further inspection showed that someone had installed the shift lever with the wedge pin upside down. That made the lever rotate a bit on the shaft and that was enough to allow the lever to hit the exhaust pipe on down shifts. The exhaust pipe wouldn't allow the full travel of the lever on a down shift from 4th gear. That meant that the gear didn't get fully engaged with the shifter plate. Sometimes it worked and sometimes it jumped out of gear. I can only surmise that someone had installed the transmission without the lever installed. Later they had to install the lever and the pin could only go in from the top. If one carefully inspects the lever it seems to have been designed for the pin to go in from the top. A review of my old books and photos show it both ways. I suspect that BMW designed it to go in from the top, the logical way. A close look at the lever shows that it has a "flat" where one would expect the nut and washer to go. Later they found that a certain percentage wouldn't stay in gear due to the lever hitting the exhaust pipe. Rather than redesign the lever they just switched the pin and solved the problem. Some of you are asking "What difference does the direction of the pin make?" The pin is tapered, or a wedge. As it goes in, it gets tighter. Also, it forces the shift lever to slightly rotate a bit "clockwise" on the shaft. If the pin is put in (incorrectly) from the top, that forces the lever to be a bit counterclockwise on the shaft. This few degrees of difference is enough to put the lever lower so that it can hit the exhaust pipe on a downshift. Such small details as this are the difference between success and failure on a BMW. Attention to detail is very important.
Look at the pin and it's insertion from the bottom. That is the correct way. It is hard to change, as the frame is in the way.
Closely look at the head of the pin. This pin has undergone a hard hit and gotten smashed. It was so hard that it slightly mashed some of the aluminum on the shift lever too. While I had owned this NOS (new old stock) transmission for over 30 years, it had always been in it plastic wrapper. I have no idea of how or when this happened. I sold it recently and in packing it up I cut my finger on the damaged shifter pin. Removing the /2 (and /5) BMW motorcycle shift leverLoosen the nut and back it off until the surface of the nut is flush with the end of the bolt. Use a brass drift to tap the bolt loose in the hole. Since the mounting bolt is a tapered pin, it can really get jammed in place. The brass is so that you won't damage the bolt/pin. Once the pin is loose, it can be removed. Now gently rotate the shift lever while pulling on it. Use lots of oil. When new, the shift lever would easily slide onto the shaft. The tapered pin has now spent a lot of time trying to distort the shaft. Over time, it is common for the shaft to be sort of mushed around and some of the metal goes into a recess of the lever. If effect, the shaft is now "larger" than when new. With the lever in place there is no way to fix it until the lever is removed. The softer lever will take some damage during this removal. With the lever removed, smooth off the shaft so that the lever goes on and off easily. The shafts seem to have more damage when the tapered pin has been left loose for some time. If you find a loose lever, always secure it properly. Eventually the pin will be useless and need to be replaced. I have never had to replace a shaft. BMW motorcycle kick start lever installation
This is the same NOS transmission. The transmission is slightly tilted in that picture as the kick lever isn't vertical. It shows the correct installation of the pin. I have seen them installed backwards too. It results in the kick lever sticking out too far and it is in the way. It also results in not allowing the kick lever having it's full throw during starting. I have only seen this error once. It is important to protect the kick lever as it is very expensive to replace. I am told that they are no longer available from BMW. Some after market replacement is available, but is of poor quality.
This is the kick start lever pin. It is a wedge. It has never before been off of the transmission. The ridge is normal. That is where it hits the "flat" on the shifting shaft. It is important to keep this pin tight. Any looseness results in it being able to hammer back and forth on the shaft. Soon, something is ruined. The biggest reason for the kick lever to break is from hitting the frame. Normally a rubber bumper is there to cushion it, but the rubber breaks off and owners often didn't replace it. Big mistake. Additional damage often happens inside the rear cover and that is expensive. Keep the rubber bumper in good condition. It is one of those items that should be kept as a spare, while you can still get it. See examples below.
This one had been on a R51/3 and the "V" notch was caused by the old style kick lever. The later lever, started on the R25/3, has a wider surface contact area.
This is the usual "about to fail" bumper. Get your spare purchased.
This one is slightly used and still good.
The bumper with special fasteners. See the black paint? That was normal for the early /2, not cad plate.
Special fasteners alone. /2 and /5 BMW kick starter gear informationOwner abuse causes damage to the kick start sector gear. Two forms of abuse are common. Often the rider "jumps" on the lever to start the bike. (Avoid this by keeping the bike in good tune. One in good tune can be started by using a hand on the kick lever.) The gears may not be meshed, hit and lock up. This chips off a tiny piece of metal that is now in the oil and may circulate in the bearings. The tooth finally wears away too. The correct way to use the kick start lever is to gently engage it and push the engine through till it gets up on compression. Then lift the lever up a bit, but not to the top, keep the teeth engaged, then give it your best kick. The second form of abuse is neglect. The /2 kick start rubber bumper must be kept in good condition to protect the sector gear. It is normal for the /5 kick start lever to bottom on the foot peg rubber.
See the first tooth, the one on the right? It starts out as only a partial tooth and gets beaten down even more. You can even see some damage to the second tooth, but not much. This sector gear is still in rather good condition. I have seen them with the second tooth looking almost like the first one and the third one damaged too. That damage makes a lot of metal in the oil. Learn proper kick start procedure.
Here is another view of the same gear. You can see that the second tooth has some metal taken off of the tip. Not good.
This gear is the one that the sector gear engages. It can get ruined too and isn't available from BMW. I believe one aftermarket source exists. See the shaft on which the gear rides? That is the shaft that comes loose and falls into the transmission. More info below.
This is what a rear cover looks like just after it has been removed. Check the shaft to be sure it is tight. Some do a preventative procedure. Either drill a hole in the center of the shaft on the outside and mount a bolt and washer. That prevents the shaft from falling into the transmission case. A few like to weld the washer onto the shaft. /2 transmission noiseSometimes a /2 will have quite a rattle in the transmission when hot and at an idle. Pull the clutch lever in and the noise will go away. That rattle may be indicating a serious problem or a transmission that is out of alignment. The /2 transmission must be aligned after it is installed. The /5 and later transmissions are OK. The noise is coming from the error between the input shaft and the clutch hub splines. In time, this can wear the splines on both parts. Here is how to align it. Slightly loosen the 4 fasteners of the transmission to the engine. Keep them close to finger tight. You only want the transmission to be able to move freely. As a test, grab the transmission, by hand and move it around. Start the engine and run the rpm up to between idle and mid range. Pull the clutch lever in several times. With it held in, reach down and tighten up a couple of the fasteners. Now it is in alignment. It centers itself. Tighten them all up. As usual, they don't require much torque. They only hold the transmission in alignment. Test it for noise again. If it is still there then you may have a more serious problem. A poor state of tune will cause you to hear this same noise. One reader recently reported that he had to actually ride it around the block, then tighten the bolts. That fixed the noise. The late /2 gear selector plate and the "BMW clunk"The BMW motorcycle is famous for shifting with a clunk. It often concerns those new to BMW. By changing ones personal habits while shifting, it is possible to greatly reduce the clunk. The clunk is caused by large heavy parts that are spinning at different speeds and then being forced to mesh together. It doesn't sound good and it isn't good. That clunk will cause some wear on the shifting dogs over a long period of time. Metal is getting pounded off of parts and some of it may get into the bearings. Not good. When the bike is cold, one must not waste too much time going from neutral into first gear. If one is too slow, then the parts stop turning and they can jam up and just not shift. If it is too fast, then one will get the clunk. Find the "in between time" that is just right. A hot engine means that the transmission will also have hot oil. That means that when the clutch is pulled in, the parts will spin for a longer time. For the rider, a hot bike means pulling in the clutch lever and waiting a bit longer before shifting into first. More info on shifting. In 1968 BMW came out with the telescopic forks. The frame wasn't proper for the new forks, but it did serve as a test bed for the /5. With the telescopic forks was the final admission that BMW was no longer made for a sidecar. They no longer welded on the sidecar mounts. The rear tire was increased in size and the final drive ratio changed to accommodate the larger tire. The flywheel was lightened to make it rev up better for smoother shifting and sportier riding. A change was made inside the transmission to reduce the false neutrals.
This is the old plate and you can see the "detents" for each gear. On the left side are three detents. The lower one is for 1st gear, the next is neutral and the 3 rd is for second gear. The next two at the top are for 3rd and 4th gear. The area between the detents is of even height. If the selector happens to get in between the detents, it will just sit there, often in what is called a "false neutral."
This "newer" type of selector plate (1968 & 69) had already been installed, so I just had to photograph it in place. The position is different, but you can still see the three detents near the bottom. At about 7 O'clock is 1st gear. It is a deep detent. Next is a shallow detent and that is neutral. It is now in neutral, as you can see the part shoved into the detent. The other detents are all deep too. The part between detents isn't of even height. The selector is greatly discouraged to sit anywhere between detents. It is "encouraged" to drop into one or another. A "false neutral" is discouraged by this new scheme introduced in 68. I prefer the older type. That gives the rider the option of deciding how much time is used up when shifting. By taking some time between shifts, one can shift very quietly and avoid/reduce the clunk. The new way just forces it into the next detent and it will make a clunk. Since the flywheel is lighter, a careless shift will make less cluck than before. The 68 and 69 transmissions are very hard to shift quietly, while the older ones can be "learned." A big time "no-no"It is possible to really mess up the transmission by loosening a certain bolt. On the top of both the /2 and /5 transmission are two bolts that take an Allan wrench. They are recessed into the case and are about flush. These hold the shifting forks in place. The only time that these can be adjusted is when the transmission is being repaired. If either or both of these are loosened while the transmission is together and the bike is ridden, you will have big trouble and even safety could be an issue. The shifting forks could come loose enough to allow the bike to get into two gears at once and things will come apart in rather dramatic ways. It is even possible, but not likely, to crack the case. It is likely that the transmission would be turned into junk that may not be cost effective to rebuild. On both transmissions the bolts are under the air cleaner.
The /2 transmission This shows the two bolts that mount the shifter forks on the inside of the transmission.
The /5 transmission This shows the two shifter mounting bolts just like the /2 transmission. See the horizontal sheet metal piece and it's mounting bolt in the center? It holds the two halves of the air cleaner box down. The famous "clunk" of BMW transmissions, or gear changing on a BMW motorcycle.This is an old letter to the /5 United group about some transmission questions. It certainly could use some editing. Maybe later on. The clunk (bad noise) happens when the two parts that must meet, are going different speeds. As one part grabs the other we hear a nasty noise and even feel it. Don't let anyone tell you that that is normal, or OK. It is common, but it isn’t the best thing and can be reduced. Let me ask you this; if you have a piece of metal and you hit it as hard as you can with a hammer, will it stay as nice as long as if you had given it a gentle tap? For those of you that say "yes," stop reading here and start looking for a good transmission repairman. The factors are usually only a few. If you pull the clutch lever and "wait".............. then shift, it will MAYBE be in the proper range of time. One part begins to slow down and eventually gets in the ballpark of the speed of the other part and presto a "click" rather than a clunk. If you "wait" too long then it may not even shift at all, or it may feel as if it shifted and quickly pops out of gear. It was never fully in gear. With experience you will learn to "feel" a good shift. One factor in the "wait" is the condition of the clutch. I have seen clutches that didn't release enough and then the "wait" is useless. It will cluck, no matter what. It may be badly out of adjustment and wouldn’t release. It is about the same as not getting "pulled in" far enough. Check the freeplay. The end of the clutch lever should have about 3/8" of freeplay. Cold transmission oil has more drag, or friction and as the temperature increases, the "waiting time" decreases. On a cold tranny I have just learned to wait longer. t helps a lot to "pre-load" the shift lever a bit before going into first. Move the shift lever down until it "hits" and hold some pressure, pull the clutch, "wait" and add pressure. It really helps a lot on the other shifts. Its even possible, on most BMW transmissions, to shift without the clutch and get the "click" if one gets really good with the timing and preload. Important /5 "fix"The /5 has a trait that isn't very nice. The shaft that the kick start idler gear rides on (photo above) has a tendency to come loose. It is a shrink fit (it was cast in) in the aluminum cover and shouldn't come loose. Soon after it comes loose it may fall "into" the transmission. This can really cause trouble. As usual, the solution is to fix it before it locks up the transmission and ruins it. A common fix is to remove the transmission, drill a hole in the center of the pin and Locktite a bolt and flat washer in the hole. The washer must be larger than the pin and keeps the loose pin from falling in. Now it will only leak some oil. At this point the kick starter should be used only in an emergency. Simple BMW motorcycle transmission tool for spacing the shafts.Don't ever try to space the shafts by the method shown in the factory shop manuals. Eventually the factory came out with a tool to hold the shafts. I think that you can buy one from Ed Korn. It is easy to make a tool from an old cover to use for holding the shafts and bearings in place. It is usually easy to find an old cover that has the clutch arm bosses broken off. Have it machined off to make the tool. Hand sand the bearing mounts a bit so that they are a slip fit and you are done.
The one the left is a /6 broken cover and the one of the right has been made into a tool for measuring the shaft spacing.
A close-up of the above cover. I put the thickness and my name on it.
This BMW motorcycle transmission cover is for the /2.
A close up of a broken cover. I have no idea how both bosses broke off, as only the lower one usually breaks off. You should find a cover for very little. Have your friend machine it off. The BMW motorcycle input shaft is "stiff" after reassemblySometimes the input shaft will feel kind of stiff. This can be because the shaft and bearings are seated perfectly. Solution; warm it up and give the input shaft a medium hit. You will/should feel the change instantly. The problem would have taken care of itself once the bike got up to temperature, but who wants to risk that it might not free up later? Find out before you install your newly rebuilt transmission. How do you think that I learned that? The vent bolt on the /2 and /5The vent bolt mounts the ground wire (/5 and later) from the battery, holds the speedometer cable into the bushing and provides a vent for the transmission. Due to the fact that it must do a few things and the bushing is a bit odd, the result is often less than desired.
This shows the two types of BMW motorcycle speedometer bushing used over the years. They are interchangeable. I think that the one on the left with the "square groove" is for the /5. The one on the right has the "circular groove" and is for the /2. Let me know if this is in error. I prefer the one on the right as it is more deeply cut and allows for more error in bushing installation.
This is about how it should look as it goes into the BMW transmission. It must usually go all of the way down. The bushings vary in fit. Many are finger loose and some are quite tight. It is the tight ones that really cause the problems. I will address them in detail. This photo is really "telling" as it shows several things. Look closely at the hole for the vent bolt. See that it has no threads? They are stripped out. That is one of the reasons for writing this information. I want to show "you" how to prevent this from happening. I didn't even know that this one was stripped out until I took the photos. See how the bushing is rotated so that as the bolt goes into the transmission it will miss hitting the bushing? That is what you want. Look carefully at the far side of the bushing and you can just barely see where the end of the vent bolt has hit it. If that happens badly enough, it can cause the hole in the bolt to be mashed against the bushing and be covered up. It won't vent. If you think of the bushing from the top, consider that if it is rotated slightly counter clockwise then the bolt could hit it as it gets started in. That will damage the bolt threads. If the bushing is rotated slightly clockwise, then the bolt can hit the far side. That is what happened here, but only to a small degree. The bushing can be turned even more clockwise and block the bolt from hitting bottom easily. What the person installing the bolt will notice is that the ground lug isn't tight when the bolt is. The person then tightens the bolt even more and strips out the threads. I install the bushing so that the vent bolt doesn't touch the bushing at all. Of course it is possible that a previous owner or mechanic over tightened the bolt and ruined the threads already, like this one.
Correctly or incorrectly installed, it will look like this. I have shown no battery ground wire or speedometer cable, as this transmission is out of a bike. Oil leaking from the vent on the /2The early /2 bikes (55-62) had a type of speedometer drive gear that caused oil to leak out, or at least didn't stop it from leaking. In 63 BMW replaced it with a slightly modified gear that reduced any tendency to leak. It has a spiral groove cut into it. The groove collects oil and the spiral part "moves" it back downwards. With an open vent and the spiral gear the oil leak problem was fixed.
See the spiral groove shown on the right side? The ratchet on the kick start lever doesn't release fullyThe /2 kick start lever can show the symptom of not fully releasing. After one kicks it through it fails to return and makes a wrong noise. The lever may have to be returned to its normal resting position by hand. I had been unable to diagnose this fault, but my 15 year old genius mechanic Bryan Hilton figured it out in a few minutes and he had never even looked at a BMW transmission before. What happens is that the parts on the input shaft can migrate backwards slightly (to the right as shown in the photo below) over time and this puts more pressure on the spring, resulting in the spring becoming bound up.
This is an input shaft from a /2 BMW motorcycle transmission. Starting on the right end the parts are a washer, spring (not visible here) the kick start idler gear etc. The test is simple. The rear cover must be removed. With the rear cover removed the symptom won't be obvious. Learn how it should feel. Grab the kick start gear and rotate it. It will ride up (ratchet) and over its teeth and operation will be normal. Now you can duplicate what happens when the rear cover is mounted. Use a socket to compress the washer downwards and rotate the idler gear by hand the same as before. It should "ratchet" easily over the teeth as before.
From right to left; the end of the shaft that protrudes into the bearing that is in the rear cover, the washer, the small spring that is barely visible, the kick start gear with its ratchet teeth, the matching teeth and on the far left is the cushion spring. The ratcheting teeth are shown just as they are about to snap over each other. If it fails to do this, then the small spring is fully compressed and failing to allow the gear to move enough to ratchet. There are two ways to fix this, the easy one and to actually correct the problem. We have done both many times and can see no long term difference. The easy way is to just shorten the spring. The washer should be an interference fit on the shaft. Pry off the washer and remove the spring.
The spring is on the left, washer and a USA quarter for comparison Cut 1/4 of a turn off of the spring and try it. Sometimes we had to cut nearly a full turn off before it would allow proper ratcheting. We had good long term success with this method. One can also remove the input shaft and use a hydraulic press to push the parts the tiny bit back into place. If they moved once, they will move again. I am more comfortable with cutting a bit off of the spring even with the parts pressed back into place. This symptom is common just after a rebuild. The shafts are shimmed to reduce the end play and that allows the spring to become bound. It became our standard procedure to check for proper ratcheting before replacing the cover. If it hangs up even the slightest amount, it will be much worse when the transmission is back in place. The amount of end play allowed is a bit controversial. We shimmed them cold, down to almost zero play, certainly less than .004" allowed by the factory. Your factory manual may show a greater amount, but it was in error and reduced in later manuals. As the unit heats up the end play increases. If you are doing the work while it is hot, then allow the .004" and check it cold before you put the cover on. All that you care about is that the bearings aren't ever pressed together and in a bind. TemperatureA few of us took transmission oil temperature measurements. On an eighty degree day and an hour of riding, a /5 will show a temperature of around 160-165 degrees F, or 70-75 C. The temperature was taken with a probe style thermometer. Other BMW transmissions are similar. Protect your /6 BMW motorcycle transmission clutch boss from breaking off.
The /2 and /5 clutch arm pivot pin was held in by a cotter pin. These models of transmission didn't have a problem with breaking off. With the advent of the /6 models, BMW elected to retain the pin with a sheet metal clip, or keeper. That is a view of the tranny cover before it breaks. See the pin that holds the clutch arm onto the cover? The keeper falls off, the pin comes loose and slides down a bit. Soon it is only sticking in the lower part. Next time that you operate the clutch the pressure breaks the boss off. The arm falls down and off of the bike. Sometimes the bearing parts also fall out. You will be riding without a clutch, if you know how, or walking. You will also be paying for a very expensive repair job. It can all be avoided by fastening the pin so it won't fall out if the little keeper disappears. I don't have a picture of the original type clip that fell out, but it wasn't flat. The later one is a real clip of spring metal and is flat. It stays in place. It is very hard to see on the bike, but one of the good ones is in the photo. Sometimes both ears would break off. This is when you will be very glad that you used safety wire to hold the arm from falling onto the roadway. In those cases it is impossible to say what exactly happened or what to do to prevent it. The broken boss(s) can be repaired by a welder. The transmission must come out for the welder to get in and weld it properly. I prefer to replace the pin with a bolt. The bolt must have a long part that isn't threaded. The bolt (pin) must be installed so that the head is at the upper end. Even if the Nylock nut falls off, the head will prevent it from falling through and off. Kick starter on the /6 and laterThe /6 came out in 1974 and had a kick starter. In 1975 it was dropped from the line, except as an accessory. The European models may have had them far longer than the ones made for US delivery. The question keeps coming up about how to add the kick starter to a existing bike. Don't bother, they didn't work well. To kick over a 900 cc motor the engineers had to give the kick starter a bigger mechanical advantage. The result is less throw. It turns the engine far less of one revolution. Everything must be perfect, including the rider's technique, to kick start one. If it is used from time to time on a bike in very good tune and the rider knows how to use it, then it can be useful. The transmission case was also not strong enough for the impact of repeated kicks. Even the "easier to kick" /5, had lots of trouble with the rear cover. Save yourself lots of expense and grief. Of the $500 that you were willing to spend on the kick start function, send me my $100 commission :-) Comments by John FalconerThe five speeds are good boxes but definitely had bad years and foibles. The first ones were notoriously bad - if you have one from '74 or so then I'd consider getting rid of it. The shift cams were flimsy, the case is not as strong as later models and many parts are NLA. From about '76 through '80 you get a box that is much better than the first five speeds and one which is still compatible with the flywheel/clutch assembly on your /5. The shift cams are improved and in '79 (I think it was '79) that the case was substantially stiffened. From '81 on, the input shaft was changed to accommodate the lightweight clutch so you can't use these boxes on your /5 unless you fit the lightweight clutch assembly in toto (and this poses a problem since the mounting hardware is larger diameter that the threaded holes on your /5 crank). A good change to any pre-82 box is to fit the latest (third distinct design) of shift cams. In late '80s BMW omitted a circlip which can allow a shaft to move in its bearing - this can be an expensive problem but shouldn't affect you if you're running the /5 clutch since those boxes won't bolt up anyway. If you can't trace the lineage of your gearbox a disassembly would quickly reveal it - and would also give you a chance to address one of the most common and easy-to-fix failures, that being the early wear of the plastic roller that follows the outer track of the large shift cam. You can replace it with the roller fitted to K75 gearboxes. If the roller is worn some of the symptoms you describe can ensue since the camplates don't get properly located to where they need to be with each gear selection. BMW motorcycle transmission oilOur experience with bearing life was that most transmissions failed between 50 k and 75 k miles. This has been hotly disputed on one of the motorcycle lists by more than one owner. One's own experience is important and part of a large data base. A shop sees a larger part of the whole data base. To be fair, I asked Rick Weber about this issue. He has been working on BMW motorcycles for the past 25 + years. He was starting as I was getting out of the business. Here are my questions and his answers, directly copied and pasted. On Tue, 19 Feb 2002 08:49:41 -0800 "Duane & Linda Ausherman" writes: Rick, The question came up recently on the /5 group list. "How long do the transmissions last?" I found that we were opening some of them at 50 k and most had been opened by 75 k miles. One guy responded by saying that in 250 k his had never been opened. I guess it could happen, but we never saw anything close to it. He also said that he got 225 k on his first set of valves. That is hard to believe. Did you get an impression of how long they lasted? A general idea of the range of miles. I didn't count the factory errors of too loose input shaft in 70 and 71 when we had to open almost all of them. We are thinking about bearing life mostly. Any words you might have would be appreciated, thanks. Sincerely, Duane Ausherman Hi Duane, The secret to long tranny life is using synthetic gear lube, Spectro is the one I've used and had the most experience with. Usually 50k to 75k seemed average life span for the bearings getting regular oil changes with petro based lubes. You can at least double that with synthetic. I had one customer who had used nothing but synthetic and wanted me to inspect his gearbox that had 135k miles on it, and never had been opened. I swear it looked like brand new inside, no gray sludge, no metal on the drain plug. The 4 speed gear boxes seem to go longer than the 5 speeds, so I'd think the 4 speed could have a longer interval between overhauls. Valves seem to last 60k to 80k miles. Rick |
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This page was last edited:
04/01/2006 - copyright
Duane Ausherman |
