BMW /2 motorcycle transmission
Some years ago I was working with Blaise on 5 transmissions that he had. We spent the evening disassembling them and doing a complete autopsy on each. He was a fast learner.
Today he has opened his own business doing transmission work. If I needed transmission work on a BMW, I would go to him. He knows more than I ever did and he knows modern technology, where to get parts etc. One more thing, he is honest.
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.
Metal in the oil of a BMW motorcycle transmission
Forever “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.
Note: If you ever find this same metal paste in any other place on your BMW, start planning on spending money.
BMW motorcycle transmission shifting “bench test”
These photos show a later transmission than a /2. It is just for showing the bench test technique and matters none.
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 to be a 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.
The /2 gear dogs and slider plates
When 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 ensure 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.
This is a typical BMW motorcycle transmission gear and the 6 “dogs” are faced up for a 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 a reason for some, but not all of the metal in the oil.
The BMW /2 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 has 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.
Let’s 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. These and other parts can be found at 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 /2 motorcycle 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” or the “intermediate shaft.” The upper shaft is called the “output shaft.”
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 engaged 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 the third gear.
This is fourth gear. The “left” slider has moved over to the left to engage the fourth gear.
BMW /2 motorcycle transmission bearings
The BMW motorcycle transmission requires 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.
Change the oil often
The best single thing that you can do for your transmission is to change the oil often. That flushes out the metal. The /2 sports 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. (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.
Typical failure mode for a /2 motorcycle transmission
I 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 on the clutch plate. 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.
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 transmission 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.
The earliest symptom of a failing rear main is hard to detect. A very quick exam will “tend” to indicate the possibility of imminent failure. Remove the rubber timing hole plug. 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 failures 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 the bike is 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. Some 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 sports 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 sports 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 sports 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 transmission jumping out of gear
There 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 its 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 its 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 BMW motorcycle shift lever
Loosen the nut and back it off until the surface of the nut is flush with the end of the bolt. The flush surface allows the drift to hit a wider area and cause less damage to the end of the pin. 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. Heating the shift lever will make it easier to remove. 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 /2 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 its 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.
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.
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 an 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. Purchase your spare now.
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.
The special fasteners.
/2 BMW kick starter gear information
Owner 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 hand.)
The second reason is that the gears may not have meshed, they 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, as mentioned above.
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 see significant damage to the second tooth. This sector gear is still in a 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. See the shaft on which the gear rides? That is the shaft that works loose in the casting of the rear cover 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 noise
Sometimes 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 noise is coming from the centers not being the same 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 one’s 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, the oil too is cold and one must not waste too much time going from neutral into first gear. Pull the clutch lever in and shift immediately. 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. Practice makes perfect.
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 selector arm seated in 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 the /2 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 has been removed and 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. 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 famous “clunk” of BMW transmissions
This is an old letter to the /5 United group about some transmission questions. It totally applies equally to the /2.
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.
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 free play. The end of the clutch lever should have about 3/8″ of free play. Cold transmission oil has more drag, or friction and as the temperature increases, the “waiting time” decreases. On a cold transmission, 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 too. It’s 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.
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 Cycle Works. 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 photos didn’t copy and paste. I hope to learn how to fix it later.
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 input shaft is “stiff” after reassembly
Sometimes the input shaft will feel kind of stiff when you rotate it. This can be because the shaft and bearings are not 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.
The vent bolt on the /2
The vent bolt 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 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 speedometer cable, as this transmission is out of a bike.
Oil leaking from the vent on the /2
The 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 won’t come back up
The /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 backward 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.
The above paragraph most likely doesn’t explain this issue. Blaise and I have discussed this issue of the kick start lever not returning to the upward position. He is working on another avenue, so stay tuned to see what develops.
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, or reshape the spring to fit into the recess. 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.
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″ recommended 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.
This is from my long time friend, Rick Weber.
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 petroleum 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.