Since 1951 the BMW twin has had a magneto ignition system. It is made
in such a way that can result in a different ignition timing for each cylinder.
some call this a double image, or split image. One cylinder might be
exactly correct and the other one might be many degrees off. This error
can most easily be seen with a timing light. It is possible to correct
this error and this is my attempt to describe it. I have avoided doing
this for the last two years for several reasons.
1. My experience is from a highly specialized shop background.
The procedures that we used can't easily be duplicated by an owner. The
perspective that I come from doesn't even exist these days for these old bikes.
Our primary goal was to get the bike operating as well as possible in the
shortest time possible. The bikes were common, not collectors items, as is
the case today. The mechanics were well trained and did these procedures
often. They developed a "feel" from doing it repeatedly. They could
recognize when something was different from normal. They had this "normal
feel" from the vast experience gathered in our shop. I must add that we
also had the legendary BMW mechanic, Bryan Hilton.
2. The procedure that we used is problematic, at best. This is
the procedure taught in the advanced BMW service schools. We could tell
that it was with great trepidation that we were told about this procedure.
We were astonished at being told by the factory service person to do this.
Few certified mechanics of that day learned this part. I abhor taking a
hammer to a BMW, especially delicate ignition parts, but that is what we did.
The first few times we were terrified to try this procedure. Later it
became fairly common and much of our procedure was successful because of our
experience. The possibility exists of breaking something, as once happened
on a /5, and it can be catastrophic, it was.
3. I am describing something from 30 + years ago. I have
basically ignored BMW for most of that time. I have always owned and
ridden one, but haven't been in the concentrated service environment since.
My memory is failing on many of these subjects. I am amazed at how many
things that were as easy as breathing, are now gone from my recall. With
tools in my hand I can still do some of them, but it is more autopilot, than
This is not for the faint hearted or the average mechanic, but only the
skilled or very adventurous one. Don't even try to hold me responsible for
the results. This writing will bring a lot of criticism from "experts" and
I understand that. Were these experts there, doing it on a production
basis? Feel free to ask politely, but as many of you have already discovered, I
don't suffer fools easily.
I will address the /2 (and earlier) and /5 (and /6 and /7) in different parts
because, while the procedure is similar, they are really different. I
haven't gotten around to the /5 and later procedures. Maybe one day.
The /2 magneto BMW (1951-69) ignition.
All timing inspection is done with a timing light. It is a strobe light
and it "senses" the spark and flashes a light. You may direct this flash
onto the flywheel. The flywheel has 3 marks. The first one to show
up is the "F" mark for high rpm. The next one is the "S" mark for idle
speed. The third is "OT" and is for adjusting the valves.
Not all timing lights will work on the magneto ignition of the /2.
Nearly all modern timing lights are inductive pick up and require 12 volts.
You may discover that your timing light that works great on cars just won't give
a consistent flash on your perfectly working /2 BMW motorcycle ignition system.
Try to find a light that works well at low rpm. When you find an
inconsistent flash, it has a good chance to indicate an error in ignition.
In the first few years of production (roughly up to about 1959) the flywheels
had the two timing marks made by a ball that was swaged into a hole in the
flywheel. It showed up well and was elegant.
Please send me a close-up picture of this ball. As a cost cutting
measure, the later flywheels just had a line stamped into the flywheel.
The lines were painted yellow and even when new they didn't show up well with
the timing light. I suggest that you mark the timing marks on the flywheel
with white paint. I just barely touch a slot screwdriver into a small can
of white paint and then touch the line on the flywheel. Be very careful to
not use too much paint, or it may run and be a real mess to clean up. Let
it dry some before you crank it up.
How much error is too much? That is up to you. We found little, if any,
improvement if the two marks are brought together from only 1/4" apart. We
took the limit to be somewhere from 1/4" to 3/8" before we would think about
fixing it. Let me caution here. You may see only one mark and think
all is OK. It could be that the other mark is so far off that you can't
even see it. That is not uncommon.
Ideally, you will see one "S" mark at idle and at midrange see one "F" mark
and no more. Often you will see two marks with some distance between them
at idle and two marks at full advance (about midrange) of about the same
distance. The error, or distance between marks, is more important at full
advance than at idle. The final indicator is the "F" mark. If it is
good and the "S" is a bit out, forget about it. It is one of those things
From an idle, slowly raise the rpm till the "S" mark disappears out of the
window. Just before midrange rpm the "F" mark should show up in the
window. You should only see one. Keep increasing the rpm another
1000 or so and see if the one mark, or two close together, stay there. You
may see one come and go and then another show up later. That could mean
that at idle, one of the "S" marks if so far retarded that you never saw it.
The first thing to try is a new advance unit. In those days that seldom
helped out at all. I remember that fewer than 10-20% were due to a faulty
unit, but we always tried that first. Several times we found that a new
bike would have the timing marks well out of any spec. I certainly wasn't
going to tell BMW that the brand new advance unit, on a brand new machine, was
"worn out" and expect much sympathy.
At first I tried to find the error with a dial indicator to see what was
"running out". A couple of times I found a bent camshaft nose. I
attacked the first one by hand dressing it down to hold the mag rotor straight,
with the engine in the frame. It is very hard to take out the wobble and
still keep it trimmed up for a taper fit. It is much easier to just
replace the cam.
Usually we were unable to find the specific part that was "out" of spec.
The BMW service person just told us that it "happens" and to do this procedure
to correct it.
It is up to you to decide if you have an error or not.
After reading this, probably any error is acceptable, rather than go through all
of this. I have received many emails from owners who went to the trouble to
correct the difference in timing. All reported a large improvement in
smoothness of the engine.
Boring facts about the "what and why" of the ignition timing wear
The magnet is on the cam shaft, above the crankshaft. The crank drives
the cam with a set of gears, called timing gears. One gear is small, steel
and on the crankshaft. The other is aluminum and on the camshaft.
The wear process and it's implications must be discussed here because, by now,
they are all worn.
As the piston goes out towards the head, on compression, it finds resistance.
This resistance tries to push the head off of the cylinder. The cylinder
is firmly attached to the block. At the point of attachment the block is
being pulled outwards. The same thing is happening on the other side.
As the engine runs, the block is being pulled "wider". To get wider it
must get "shorter". As the block gets shorter the distance between the
crankshaft and camshaft decreases. This means that the gears get pulled
closer together. Another way of looking at it is that as the gears wear
smaller they also get closer together. They tend to self adjust. If
the only effect was that they wore smaller, then the gap between them would
increase. This increase would result in lots of valve clatter at low rpm.
It is common for an engine with 100 k on it to still have fairly quiet timing
gears. That is because the two shafts have also gotten closer together.
If we measure the play on slightly loose gears at different points of it's
rotation, we find that it is different. At places where the cam has
pressure, from the valve springs to go backwards, the space between gears is
increased, or the gap is bigger. The slack has gone back and forth so many
times that it increases the existing gap. At low idle speeds this can be
heard as a clattering sound. It goes away with an increase of only a few
hundred rpm. During this clatter, the timing suffers slightly and may be a
partial cause of the difference between cylinders at low rpm. It isn't the
major one though. Nothing can be easily done about this gear wear and it
turns out that it isn't important anyway. I just mention it to give an
idea of where some of the timing error may come from.
A worn advance unit cam lobe, or lobes, can add to the timing error.
That can be easily seen with close inspection of the cam surface. Replace
it. Try a "known" good unit and see if anything changes. Sometimes
the advance mechanism can be slightly sloppy on the magneto rotor snout.
It can get tightened down in slightly different places to change the timing
error. The locating pin up inside of the
advance mechanism cam can damage the rotor when it has been installed
incorrectly and tightened down. After this happens many times the rotor
tip is sloppy too. One can see this by turning the advance towards advance
or retard, while tightening the 6 mm bolt. Then check the timing.
Change the advance by tightening it in a different position. Check the
If the engine was perfect, with no gap in the timing gears, no slop in the
perfect advance mechanism, it could still have a timing error between cylinders.
Fortunately for us in the repair end, it didn't make any difference to us why,
we just fixed it. If you want to use hundreds of $$ of precision tools to
measure things, dozens of hours proving and fixing it and hundreds of $$ for
parts, be my guest. I will try to describe what we did in the shop to
correct the visible error in timing.
I won't go through the magneto timing procedure here. That is another
big discussion, with some self appointed "experts" having different opinions.
I think that Vech has it written up very well. Don't follow the factory
info, as it is wrong.
In our normal service, on a bike that we had never serviced before, we would
often discover that the magneto timing was off. Not the ignition timing,
but the magneto timing itself. The Germans call it "Abriz" and the Brits
call it "E gap." We would pop the rotor off of the camshaft and gently
reset it with the 6mm bolt only slightly tight. Use only
hardened steel for this rotor removal tool, such as
a cut-off drill bit. We would usually just pop the rotor loose with the
magneto in place. That saved labor. For the private owner, time
isn't as important. You should remove the magneto so that you can remove
the rotor fully and inspect it. Take a good look at the taper fit on both
the rotor and the camshaft. They should both be clean and dry.
Do not use any lube on the taper.
Now we come up with the obvious question, "How do we know which cylinder is
advanced?" It doesn't really matter to us. It can be measured, but it
isn't important. If you wanted to measure the points gap closely, you would
find that one lobe of the advance opened them more and than the other.
This translates to opening the points earlier. The fact that they open at
different times is the whole problem.
Look at the advance closely. It isn't symmetrical, off to one side of
the plate, it has the advance limit spring on it. Just make sure that you
can return the rotation of the advance to the same place
every time. You could paint a mark on it somewhere to make it more
obvious. Get the engine to the "S" mark. That is where the advance
is just about to open the points. Think about moving the rotor a bit
sideways to get it closer to the points rubbing block or farther from it.
If the rotor is moved closer to the rubbing block, then that cylinder will fire
earlier. If your magneto timing was perfect and you don't have a slightly
loose rotor, don't worry, it may still work. Decide which way you want to
"move" the rotor. Just pick a way and remember it.
I use a medium hammer and a brass drift. Put the drift against the 6 mm
bolt in the direction that will move it closer to or farther from the points
block. A point of theory here. If you
just happened to pick a direction at random, it could be 90 degrees to the
points block and the rotor could be moved a lot and result in no timing change.
It would hurt nothing, but why hammer on your BMW for no result. You could
assume that nothing was being moved, when it might be moving a lot. So
pick a direction, towards or away from the rubbing block, for your first hit.
If the rotor isn't very tight it will move much easier than if it is tight
and has been tight for a few years. The BMW service instructor told us
that the taper is "reseated" to correct the error and this is how it is done.
We were never able to confirm that the taper does reseat, but that is as good of
an explanation as any. If the rotor isn't very tightly seated on the cam
shaft, it shouldn't take very much of a hit. How much is too much? This is
where experience is very important. The good news is that the /2 parts
that you are hitting are so strong that they will take quite a bit of
punishment. I have never seen any damage to a /2 from this procedure.
The previous sentence doesn't apply to the /5 and later.
Maybe I can give an example of a "hit." If one is pounding a 16 penny nail
into new pine at the rate of about 3 or 4 hits to do the job, that is a hard
hit. I can't remember ever using that much force. The amount of hit
to "set the nail" in place so that it will stand by itself is a gentle hit.
The force that amateur carpenters use would probably take 10-12 hits and that is
about the max that should be needed. I always start with much less and
You might legitimately ask "Why not remove the advance and hit the rotor
shaft?" Only because we don't know what part is off and don't really care.
If one hits the 6 mm rotor bolt, everything is "adjusted" that is in the system.
After a hit or two, start the engine and check with the timing light.
Did the marks change or not. Caution; you
could have moved the rotor just enough from one side to the same amount of error
on the other side. You moved twice too far and the marks will make you
think that nothing moved at all. This isn't likely, but it could happen.
Probably nothing happened because you were very cautious and didn't hit it hard
enough to do anything. I don't blame you. Try again and check again
with the light.
If nothing seems to change and the rotor wasn't removed, then consider
removing it and reinstalling it lightly. If it is not fully tight and
nothing changed, maybe you didn't hit it hard enough. In any case, even a
mechanic with experience may need to hit it and check 6 to 8, or more, times to
get it where he wants it. I have had it in one hit, but more often it
takes more than the 8 attempts.
You may find that the distance between marks has increased. Return the
advance to your previously "calibrated spot" and hit it the other way. You
may find that things are in the way for the "other" hit. Rotate the engine
180 degrees and try again. It is very important to be able to know which
way you are hitting it so that you can change as need be. I have had to
"chase" the marks back and forth a few times to finally get it. I have had
a very few /2 where I couldn't move them at all. At least not with the
"hit" I was willing to give it.
You have it where you are willing to live with it. Now fully tighten
down the 6 mm rotor bolt. It doesn't need much tightening as it is a taper
fit. In fact you really don't want the bolt very tight. I have never
seen one come loose while running. More have been too tight. Test it
again and see if the marks stay once the rotor taper is fully seated.
Mounting the advance unit
The advance unit has a round peg that is supposed to align with a notch in
the rotor shaft. That is supposed to be a precise fit to keep the timing
in place and be repeatable. When all is new, the advance had a "slight"
amount of slack on the rotor shaft. The timing would vary slightly,
depending upon whether one would hold the advance in the clockwise or
counterclockwise position while tightening up the Allen bolt. Sometimes
the mechanic would only get it close and not really aligned. Then the
round peg would take a bit out of the end of the rotor and widen the notch.
That gives the advance even more slack and more possible error in timing.
My solution was to hold the advance with the play in the clockwise position of
its slack. That is the same direction of tightening the bolt. If you
always do that, then you will have repeatable timing when you remove and replace
the advance mechanism. I have seen many rotor shafts with several "new"
notches from someone having no clue as to the alignment peg and its purpose.
Soon the peg is smashed and won't fit the notch in the end of the shaft.
It is not uncommon for someone to over tighten the (6 mm Allen wrench)
bolt that the advance smashes down on the rotor nose so hard that it is
"mushroomed" outwards. This mushroom effect serves to jam the advance unit
and keep it from operating smoothly. Correcting this error means removing
the mag rotor and filing the mushroomed metal off. You can test it in your
hand by installing the advance unit and tightening the advance down to a normal
amount. Then check to see if the fly weights operate smoothly.
If your timing marks were 1/2," or more apart and you correct it, you will
feel a difference, at road speeds, in vibration and general smoothness.
Since writing this, I have received several emails from people who have been
scared off from trying this procedure. I don't blame you. I have
received 2 or 3 emails telling me how much the bike improved by this correction.
That makes it worth writing it up.
Alternatives for failed coils
In recent years the magneto coils are failing. A variety of rewound
coils can be purchased. One or more places are rewinding coils, so you
must send yours in. Some of the new and rewound coils are also failing.
A new modern system can replace the original system.
You may elect to go another direction and install a battery/coil back up
BMW Repair manual /2 ignition timing contradiction.
The subject has come up about where the timing curve should end on the /2
models. Specifically, at what rpm should the "F" mark finish it's advance.
Few of the /2 had a tachometer so it was kind of hard to have a number.
The bikes performed well with that timing curve. We had no ping with the
fuel available at that time. Pinging from poor fuel was corrected by
thicker base gaskets. This was usually found only in third world
countries. Pierre Michaud, of Canada, quoted a 1966 workshop manual with
the figure of full advance reached at 5800. Here is the story.
These are photos of the workshop manuals of two different years. I only
have these two years left. Plainly, they are in contradiction or some
change was made. A check of service bulletins may show something. If
any change of this magnitude occurred I would remember it well. We would
have had to alter our timing specs and watch for it on each individual bike.
No such thing occurred. Since the bikes do reach full advance mid-range I
suspect that the 1963 and later specs are in error. This surely wouldn't
be the first time that BMW specs have been found to be in error.
Would the bikes benefit with the later full advance? I have no experience
with that. It works just fine as is. It is reported that an
electronic ignition system for the magneto, made by Mz-B, uses the later figure.
Are they aware of this or just going by the newer workshop manual?
I posted an email to the Yahoo slash 2 list and one of the respondents stated
that I should include it on my site, so here it is.
I can tell you from a great amount of experience with this, just how we did
it. The F should come into the window in mid range, more rpm shouldn't
change it any, or much. When it did keep advancing we would just
examine and lube the advance mechanism. The problem would be gone.
If the F comes too early it is because of weak springs. If it comes too
late or is jerky then it is due to lack of lube or some part is causing
friction. If the mark is double then it is due to some misalignment of
something. Double marks show up better with the strobe on the advance than
on the flywheel in cases where the marks are way out. Not good and I have
a page on this issue. I always put the strobe light on the advance and
watched the weights during advance and retard. That is because the
flywheel doesn't have enough marks to "watch" it there. The weights can
make a big jump that isn't visible at the flywheel. The advance has a peg
to fit into a notch in the rotor. That "locates" it in one place.
Idiots tighten them down a bit out of alignment, sometimes way out and it won't
run. The notch in the rotor gets "hogged" out a lot. As I tighten
the bolt I rotate the advance against the direction of rotation. I think
it was clockwise. That is where it would go anyway if the bolt were a bit
loose. Just a small bit of insurance, but mostly it allowed me to put it
back the same way every time. The way that the advance is located while
bolt is tightened can change the timing a lot. The idea of it needing to
get to 5800 for full advance is shocking.
That engine would be screaming with no cooling in my enclosed shop. We
just didn't do that. We would take it up just past mid-range to see that
the F stayed in one place, but that is all. All of the tune up can be done
so quickly that a fan isn't needed.
In my opinion, the main reason for changing the advance limit spring is
because the old one is broken. The new ones didn't break during my time.
I never found a source for them. That was about late 1968 when I first saw
them, not back in 64. The old spring had almost no flex to it. The
newer one had considerably more flex and probably would change the curve
somewhat. I didn't care about that part as it mattered none to me. I
just tuned them. Often, when the old spring broke the timing went too far
advanced and the engine would over heat and seize and/or
hole a piston. That was fairly common
(especially on the R60) and so I watched for a broken spring carefully. I
even made up a few parts that weren't springs, but just metal stops and they
didn't break. I saw no problems result from using them. I hated to
throw away a perfectly good advance, just because of a broken
spring. I kept the old ones and by 1970, had several dozen in a box.
Many had broken springs. The ones with worn out fly weight pivots got
robbed of the
spring and I installed on another advance.
Due to my request for contradictory evidence below, I received info from
Klaus Wolter. I have visited his home on two occasions and respect him
highly. Basically, he did a real test of the advance
curve. He found that the advance curve changed slightly at the upper
end of the rpm range.
I will entertain any reasonable ideas or evidence on this issue.