a Timing Chain
on a BMW Airhead Boxer motorcycle engine
Understanding chain operation; advice &
hints on replacing it & associated parts.
****This article is meant to be used with the cams.htm article!!
© copyright, 2014, R. Fleischer
Replacing a chain (and typically that job includes one or
both sprockets, guides, tensioner, etc.) is not overly difficult. For the vast majority of airhead owners, it is,
perhaps, the most complex job that is likely going to be done by THEM. That is because most owners will not tackle a transmission overhaul, rear drive overhaul, crankshaft removal, camshaft removal, etc.
No precision tools are needed for a "timing chain job".
A proper chain replacement job will always
involve a new bearing, new guide/follower shoe (on 1979+) and new tensioner,
and usually a tensioner piston spring (pre-1979)...and usually... or often... a new
crankshaft sprocket. It might include a new camshaft
sprocket (they wear much more slowly than a crankshaft
sprocket). If you DO have to replace the
camshaft sprocket, that brings about some additional complexity, which I discuss later herein.
***It is very important that you read this article completely through, AT LEAST TWICE, before beginning work. This is particularly so if you have a 1977 or 1978 model, where there can be confusion if you need to replace a camshaft sprocket.
***If you have plenty of time, you will want to inspect the parts before you decide to order anything.
INSIDE of the TIMING CHEST:
Note the differences between the two photos shown further down.
The LEFT photo is of the 1979 and later SIMPLEX chain (one row of chain rollers). In the LEFT photo, the tensioner on the right side is HYDRAULIC; and there is an added GUIDE on the LEFT side.
The RIGHT photo is of the PRE-1979 DUPLEX chain (two rows of chain rollers).
Those are hardly the only differences. Notice the chain tensioner in the RIGHT photo.
In the RIGHT photo, as the chain and sprocket and SPRING LOADED tensioner wears, the chain can flop around a fair amount, and will begin to wear metal, as noted by the red line and arrow I added to the photo. Note the camshaft nose differences. The 1979 and later flat nose camshaft drives the ignition timing unit located in a CANISTER, through an offset tang. That the slot in the camshaft is offset is not clear in the photo. With the new style camshaft nose and associated ignition canister, there is MUCH less chance for timing errors and no chance of a bent cam nose.
Because of the differences, the chain does not whip about
nearly as much on the 1979 and later models TO BEGIN WITH, that is, even with NEW parts.
This theoretically should lead to longer sprocket and chain life, but it does NOT, or, that has been my experience;
gives better long-term-mileage stability to the ignition timing.
The valve timing is also considerably more stable.
NOTE that this is complicated by some other 'things'. The problem is basically the same, for both chain types. The chain tensioners are not positioned, nor shaped, for the best tensioning, and after some miles, while the tensioners are not appearingly worn-out from their material all disappearing, that wearing-out
is the actual effect. I will explain this. What wears is not the chain itself, it doesn't wears much inside the roller area, and its stretch is quite minimal. What DOES wear is the guide on the later model, and the tensioner wear at the contact point, which moves the contact point for those items. The early model
with the tension shoe and no guide, wears similarly. As the GUIDE and/or TENSIONER wears, probably within 50K miles, the tensioning is lessened enough due to the moving of the contact point, that the chain starts whipping around enough to be heard from various effects, including irregular idling. Ignition timing irregularities happen, worse on the pre-1979, but eventually noticeable on the 1979 and later.
Summarizing: the chains don't wear much, but the combination of chain, sprockets, guide and/or tensioner, etc., create some noise, especially at engine idle
RPM, and it can be relatively loud if the carburetors are out of synchronization. Timing of the valves opening and closing changes due to camshaft jerkiness and
effective chain stretch due to wear on the sprockets and tensioner/guide. The wear of the items means that the camshaft is RETARDED from the design point, and this means the engine will not develop its designed torque and power curve. The ignition timing gets sloppy from, firstly, the chain guide/tensioner initial wear (after which these are not all that effectual at tensioning the chain as previously noted). Note that the wear of the crankshaft sprocket becomes rather noticeable and eventually, much later usually, on the camshaft sprocket. The guide and tensioner are just not as good, nor, especially as perfectly designed, as they could have been. All in MY opinion, of course.
The leaf spring on the duplex chain can be bent with heat applied, to lessen the effect, that is, to create a better positioning/pressure position, but I am not supplying the information, as it is tricky to do properly, and it is perhaps best not for amateurs to modify the spring....nor the guide (that has been done too). You can also destroy a spring by wrong application of heat.
While I get into something in other places in this article, this is a good time to mention it. The cylindrical part above the crankshaft nose contains a piston and a spring. The purpose is to regulate the oiling system from excessive pressure. It does this by releasing oil through a hole, if pressure is too high. When the engine oil is cold and/or rpm, engine oil cold or not, is high enough, plenty of oil comes out of this regulating part. This oil is what lubricates the hard-working chain, sprockets, and guide and/or tensioner, depending on model. Because of this design, which is basically perfectly OK, the various parts noted can be deprived of lubrication, or deprived of enough lubrication (which is also a cooling medium for the parts), if the idle RPM is too low. The situation is worse if the engine oil has thinned from being fully warmed...
or quite hot from high speeds, or the oil is of poor quality, etc. Low rpm at idle causes less oil to come out the exit hole. As the timing chest parts wear, the parts need additional lubrication, and don't get it if the idle rpm is not high enough. As the motor bearings, etc., wear, more oil passes by/through them, lessening oil volume, and oil pressure is usually lessened at lower rpm first as things wear.
The engines CAN be idled very slowly due to the inherent smoothness of a boxer engine, together, especially, with a heavy flywheel like on the pre-1979 motors. Slow idling is not a good thing for these motors. The factory came out with a Service Bulletin for the later models, specifying a higher idle speed, I think I remember the SI saying 950 to 1050 or something like that, but the factory gave the reason as being for better carburetion adjustments (and throttle response at the JUST off-idle position).
While true, the factory did not mention the oiling system. We pro wrench's understood, long before BMW ever published anything about idling rpm being too low.
MY recommendation has always been: have your Airhead tuned so that, with a fully-warmed engine, the idle is between 950 and 1100. I usually try for about 1025 on the engine tachometer. BTW...you can check the calibration of your tachometer rather easily by several means, the information is on this website, or, ask about it on the Airheads LIST on the Internet. Here is a link to my article: tach.htm
Your BMW Airhead motorcycle's engine has a crankshaft located in the middle of the engine, and that crankshaft drives the lower located camshaft via a chain. A chain and guide is used rather than gears, otherwise a method for adjusting the mesh of gears would be needed over the life of the gears and associated bearings. Gears can be very noisy, especially if not totally immersed in an oil bath. Gear mesh engagement methods to keep them properly aligned, and quiet, can be hard to do... especially considering the expansion rate of the aluminum case...and using gears would reverse the direction of rotation of the camshaft unless an extra gear was used as an intermediate idler. Thus, using gears generally adds complexity. BMW could have designed the engine for an intermediate gear or some other way and even had the
camshaft rotate in the opposite direction, compared to the
crankshaft, but for several reasons, did not. I have
wondered about that...including the effects on vibration modes.
I have also speculated on why BMW did not include an adjustable
idler sprocket, and a better guide/tensioner system.
The chain is located between the engine casting and the timing chest middle casting, and is hidden from view even if you remove the timing chest outer cover where the alternator is located. The crankshaft nose has a sprocket and a bearing pressed onto it. A 'sprocket' is a type of gear that meshes with chain rollers. When you remove the 2 or 3 bolts (3 on early models) that hold the outer cover onto the timing chest, you will see ignition components affixed to the camshaft, and at the crankshaft you will see the alternator. Nearly everything you see will have to be removed to do a "timing chain job".
Assuming you now removed the timing chest middle casting, you would
see that the chain travels from a smaller crankshaft sprocket to a larger
one located below on the camshaft, and then back to the crankshaft sprocket. The ratio of the sprocket sizes is such
that the camshaft rotation is
exactly half that of the
crankshaft. The crankshaft is the driving force (well, PULLING force!!) via the chain for the camshaft.
ONE side of the 'pockets' of the crankshaft sprocket have the most
force on them when the
throttle has the engine applying power, and the other side of the
chain roller sprocket pockets have force when the throttle
is being backed off due to the load of the engine and drivetrain; the transition from throttle on to throttle off causes jerkiness in the system. The chain, with any sort of real free-play, tries to whip back and forth with throttle
up-down (on-off) movement.
The engine rotates in only one direction
during operation, clockwise as facing from the front.
engine rotates, the chain on the pulling side of the sprockets,
the left side facing from the front, will be taut, and the other side looser.
There are one or two 'shoes' that the chain rides against, that
are spring or hydraulically loaded, so to maintain some sort of
chain tightness. Otherwise the chain would really whip
around, especially from throttle on-off and/or shifting gears if
not perfectly synchronized, and the chain would be rather
soon be stretched and the sprockets well worn. I have mentioned, well above, how the guide/tensioners cause noises and timing irregularities. Note that, as
mentioned previously, when you back off the throttle (particularly if abruptly
backed-off), the drivetrain, via the road connection, etc., is trying to cause
the engine to rotate, rather than the power produced inside the engine, since
the power is OFF OR DIMINISHED.
Thus, the forces on the sprockets and chain are THEN put on the other side of the
sprockets teeth. Since MOST of the time the engine is producing
POWER when you are under way, and most miles are in cruise mode, the MOST wear is USUALLY on one side of the teeth.
Once wear on any of the parts is appreciable, the tensioner(s) can not maintain the chain taut enough. This is particularly noticeable at very low rpm...such as at idle speed...and MOST particularly noticeable when the carburetors are not properly balanced and synchronized. The result is NOISE (and typically unstable ignition timing, especially on pre-1979 models). Making the noise worse on all models is hot thin engine oil. On the 1979+ models noise can be made worse by low oil pressure due to the
oil-pressure operated tensioner, and, additionally, pressure is just about always lower with HOT engine oil, particularly on a worn engine. The resultant effects are less than ideal smoothness at idle, jerky ignition timing, particularly on points models (and most particularly on models before 1979 with the less than ideal points drive method)......and in any event, it all shows up, more or less, as double timing marks at idle rpm when using a strobe light at the timing hole on the side of the engine. There is also a loss in power, from retarded camshaft timing, but only slightly from ignition timing irregularities.
It is entirely possible that either or both crankshaft and camshaft sprocket hardness has varied during production, or even varied between the early double-roller sprockets (called a DUPLEX sprocket) and the single-roller type of sprocket (called a SIMPLEX sprocket).
Because of these various things, sometimes the crank sprocket does not need replacing when a chain and guide job is done. Only inspection will tell you. The cam sprockets do seem to hold up longer. AFAIK, no one has tested, or reported to me that they have tested, the hardness of the metal teeth on brand new sprockets.
On BMW boxer Airhead points bikes, there are TWO lobes on the Automatic Timing Unit (ATU). On the models up through the 1978 model year, the points and timing unit are mounted at the nose of the camshaft, and NOT in a canister like the later models. The forward part of the camshaft, that nose area, of NON-canister models, can be found bent at times. You will not see it with your eyeball. There is a way to fix this, with a small brass hammer, but that is not the main point of what I want to say here. When the tip is bent, the bent part may be only a fraction of a thousandth of an inch, to a few thousandths; then, as the ATU rotates, the points do not typically have the exact same GAP and timing place for both ATU timing lobes. This will result in a dual-image when using a strobe lamp on the flywheel and results in vibration, often at one or more narrow ranges of RPM. This type of problem is often WRONGLY interpreted as carburetors being out of synchronization, and sometimes as bad chain and sprockets. The Dyna dual-pickup electronic ignition will eliminate most double-timing, but the camshaft TIP is fixable. ONE OTHER cause for this sort of timing irregularity is some advance unit WEAR, and even irregularity in the grinding of the cam lobes and wear in the cam bearings. BMW at one time recommended 'stoning' those timing lobes to equality. Don't bother! But, a poor ATU needs fixing, as does a bent cam tip. NOTE also, that a worn timing chain, chain guides, and one or both timing sprockets, will ALSO cause double images and the same results. Usually a quite noise timing chest area is an indication. In almost all instances, if the cam tip is bent, the points gap will vary for the two lobes. The brass hammer 'fix' must be done carefully, not knocking off NOR DAMAGING the threaded cam tip, and use of a dial indicator on the smooth side surface of the cam tip will tell the story....and if you have fixed the problem. Do NOT try the brass hammer fix unless you KNOW what you are doing, have a dial indicator and know how to use it, ETC!!
The camshaft operates the cylinder head valves, the oil pump, and the ignition triggering.
The forward end of the crankshaft has not only
a sprocket and bearing, but also the alternator
chain stretches some rather small amount from normal use. The amount of
stretch is VERY small, almost 100% of even that stretch is in the chain rollers area and NOT the side plates, and what is typically
called a sloppy or worn chain is typically the much higher amount of
wear on the crankshaft sprocket, plus the failure of the tensioner/guides to do a perfect job after a rather low number of miles. A removed chain from an
engine with fairly high mileage, compared to a brand-new chain,
may well look nearly identical in length. There will be
some differences noted, especially if twisting the chains which reveals play in the chain rollers. Thus, one could conclude that chain wear does happen, but it is rather small. In situations where the chain has been running in minimal lubrication often, .....perhaps due to too low an idle speed and thin hot oil and worn engine bearings......the sprockets and chain rollers WILL wear more, and the chain WILL have some goodly slop compared to a new chain. Since the chain is lubricated by the excess oil emitted from the oil pressure relief valve above the crankshaft sprocket, too low an idle rpm, with hot oil, is a NO NO.
NOTE: timing chains for all models are available with master links; not necessarily from BMW. Removing an old non-master linked chain is best done by cutting.
It is hard to give any type of firm mileage at which a chain, sprockets, guides, etc., should be replaced. It is also hard to give more than a few 'rules' to help reduce chain wear. Low idling rpm, poor quality oil, poor carburetor synchronization, excessive constant high rpm (yellow or red line), rapid on-off throttle movement...all these things accelerate wear on the timing chest parts (and sometimes elsewhere's). If shifting, especially downward, is done jerkily, with large excursions of rpm, that will accelerate wear. I suppose a decent argument could be made that blipping the throttle and downshifting one gear at a time, through all of them, as one approaches a stop sign, wears the sprockets, etc., more, than shifting all the gears just as one stops, maybe one blip only.
Chains/sprockets/etc., can be worn
excessively in 30,000 miles....or 150,000 miles.
Perhaps most bikes will signal a 'need for a timing chain job', from unstable ignition
marks as seen with a strobe lamp; or, from power loss, at around 80,000 miles. In reality, the guides/tensioner have worn, which leads to the other wear. The chain may well
start rubbing against the bearing carrier on the duplex models, and one may find some
metal particles in an engine oil filter that you properly should unroll for inspection at EVERY
oil filter change.
While not all that detrimental, they are a good indication of front crank bearing holder wear.
As previously noted, chain slop causes the ignition to jump around due to the irregular loading of the chain by the camshaft, and the timing will likely start having a difference BETWEEN the two cylinders, and this can cause vibration. It is entirely possible to find some plastic/hard rubber "chain guide" parts in the folds of the oil filter element (as noted one should disassemble filters at every filter change, and inspect all folds, inside, outside).....these may be tiny globules of melted plastic-like substance.
The 1978 and earlier models, as opposed to the 1979 and later models, do not sound the same when timing chain area components wear considerably, and only with considerable experience will someone know what the difference sounds like.
There is no really perfect method of positively
determining a chain and sprockets and tensioner/guide condition
without considerable labor in removing the front of the
For the canister ignition models (1979 and later), the split timing image at idle rpm tends to be a good clue as to worn chain and sprockets, as these models have a more precise method of the ignition triggering parts being driven from the camshaft. That is, the triggering of the ignition is more precise between left and right cylinders as the cam jerks about a bit. This is particularly so for the electronic canister trigger models (1981+) where one can be relatively certain that a split image (perhaps over 1/16" or certainly over 1/8") is due to chain and sprockets, as opposed to the 1979-1980 POINTS canister models where some irregularities in the points area cam nose and ATU can possibly cause even a bigger split image. Anything over 1/8" is ONE clue that a "chain job" MAY be necessary. At 1/4", you really do need to find out what the problem is. SOUND at idle, hot engine and hot oil, is another clue....there may be a very distinct chain rattle noise. That noise might be quite noticeable to the average owner, at 900-1000 rpm, and less so at 1200 rpm. NOTE that careful synchronization of the carburetors is needed before proceeding too far with guesses about the chain and sprockets, guides, etc. Do not confuse the noise from rattles in the transmission (hot)....pull in the bars clutch lever to stop any such noise.
One of the test methods, that works pretty good, is to have the engine hot from a 10 mile+ ride, put the bike on the centerstand, and let the engine IDLE for a moment. Now, raise the throttle the tiniest amount, then back it off the tiniest amount. If the rattle noise disappears while the throttle was being raised, it is likely worn timing chest parts. For this to be a good test, you MUST synchronize the carburetors very precisely first.
In the models PRIOR to 1979, an even faintly bent
camshaft tip (which can happen for more than one cause, even over-tightening!) can cause a larger split in the timing image than noted above.
In fact only .001" of run-out on the cam tip will cause a
noticeable split image. That is usually fixable, the
fix is not part of this article, and it involves making sure the
bearing is not overly worn, and using a dial gauge on the
camshaft tip and hitting the tip with a small brass hammer in a
very careful manner. In some instances, the two lobed cam
that is part of the automatic mechanical timing advance mechanism
on the PRE-1979 models might need attention. Few, anymore,
'stone' those ATU cams! I do not recommend YOU hit the cam tip!
On the pre-1979 models, those just mentioned points are located, NOT supported by any outrigger bearing, at the nose of the camshaft, and that camshaft nose may be ever so slightly bent. In fact, only 0.0008" of run-out on the tip is the specification limit. Any run-out makes for different ignition timing between the two cylinders, as there are TWO lobes on the IGNITION cam, located in the camshaft tip area (part of the Automatic Timing Advance unit) and they are on different valve loading areas, and the lobes may be different anyway. Even if the run-out is quite small, there will be ignition timing discrepancies. The camshaft that operates the valves is an UNeven load on the chain, that makes the chain jerk about somewhat, more as the chain and sprocket teeth wear. That makes for even more of a spread dual timing image, a timing variation between cylinders, as seen on the flywheel with your ignition strobe light. Thus you can get ignition irregularities from more than one source, and if enough, you will not only get extra idling roughness, and maybe chain noise...
For the 1979 and later models, the cam tip type timing unit drive was abandoned and the1979-1980 canister points models and later electronic models all use an wide offset keyway that has a reasonable fit, and the drive is off a large flat nose of the revised camshaft. This reduces the split image problem from the points area by making the timing better controlled over the entire rpm range. On the 1981+ electronics models, the points were eliminated, and the timing is more precise than all the points models.Some books tell you that you must be careful to not get the canister drive 180° out of phase when installing the canister. Total rubbish! You can NOT get it out of phase, as the drive is OFFSET.
On any model, chain, sprockets, and guides/tensioner wear will cause ignition irregularities. 1/8" of split image distance is usually acceptable, but at 1/4", it is really time...past time!...to replace a chain and other parts. ...if the problem is not in the ignition unit. Excessive chain noise and/or fine flakes in the oil filter pleats is also a warning that it is time to think SERIOUSLY about a change of timing chain and associated parts.
Special 'hints & tricks of the trade:
If your motorcycle has the stock Bosch alternator and is a model that uses rubber diode board mounts, NOW is the time to order the solid metal mounts. It is much easier to install these VERY worthwhile metal mounts (Thunderchild or Motorrad Elektrik's are both good) during a chain job.
In 1979, coincident with the change to the canister ignition and the change from the duplex chain to a simplex chain, there was an incorporation of a spring loaded hydraulic damper for the chain. That spring is 68 mm long. See item #8, well below.
Purchase chains with a master link/clip so
that both sprockets and chain do not have to be removed and
replaced as an assembly, which is the method seen in much of the
various literature. BMW sells ENDLESS DUPLEX chains. Old
NON-master-linked (endless) chains were usually removed by high speed cutting tool or very
strong chain link cutter. Master link type of simplex chains may
already be installed. Use of cutting is completely acceptable...just keep
bits out of the engine.
****In general, for the SIMPLEX chains, the master link is installed from the REAR, but an old link is usually first installed partially from the front, and the chain ends held together by a zip-tie, and the new rear link is pushed forward, and that displaces the old link which was used as a guide.
For the DUPLEX chains, install from the FRONT.
For the chains, there are two types of clip methods. A single fishclip, to be installed in the correct direction (rounded end forward in direction of travel) and the type with two individual small ROUND clips.
There are some other chain bits and pieces available from such as for Mercedes cars, frankly it is not of much importance at this point....and I don't do this Mercedes stuff myself. I only mention it because some have done a chain job with these parts; where BMW at that time only offered an endless chain.
If the chain drive system becomes too loose it might flop around and eat away at the front main bearing housing, depositing aluminum metal flakes into your oil filter, not a good thing (but mostly not all that bad either) (you DO use large side-cutters, remove the filter end caps, and unroll the filter paper at each filter change, and fully inspect?). This happens more on the pre-1979 bikes with the duplex chain.A modest amount of chain slop is not really damaging, and you will hear the chain flopping around at idle rpm on a hot thoroughly warmed-up engine.
NOTE: The oil pressure relief plunger
must operate smoothly, and the spring in it should really be at least 68
mm long when relaxed...if not, install a new one. Many just automatically replace it. I do not.
Do all work
with the engine at the OT (TDC) mark!
LOOSEN the valves rather completely so pressure is off the camshaft lobes.
Remove the battery negative wire(s).
You MAY find that if the wheel (and lowers if you have a RT fairing) are removed, this is an easier job, but that is up to you; and it is certainly NOT necessary. MAKE NOTES on where the various bolts, etc. go as you remove them; some may be of different lengths.
Remove the front outer cover (three allen bolts on early models, two on later models, and DO notice the roll-pin at the bottom, it "locates" that outer cover).
Remove the ignition components and alternator components, etc.
After you have removed what is necessary, it is time to remove the inner timing chest casting; which I call the inner cover. You will have a number of allen bolts, etc., to remove. Keep track of what goes where!
You will have to heat around the alternator seal area in order to free the bearing from the inner cover. Try reinstalling a lower inner cover allen screw, and pull...tap with a plastic or other very soft hammer onto the area near the top. The cover should free up. I heat the cover relatively hot, and also specifically around the crankshaft ball bearing. This heating will have to be done again, when replacing the cover! The timing chest cover needs to be centralized about the camshaft, I do it hot. This is for the duplex models.
You may be replacing the crankshaft sprocket. Use of a BMW puller for the crank sprocket (removed after the chain and front bearing is removed) is wonderful if you want to get one or have access to one. It is NOT a must, and has problems, as tools sometimes do.
The crank nose/taper must be protected against damage of any kind. This can be a HARDENED (ONLY!!) screw/bolt. You can purchase or make a puller. Very good pullers are available from such as Motion Industries. I highly recommend that you use the BMW tool; or, a common heavy duty three jaw puller and remove the crank sprocket and the nose bearing all at one time....that is, together, as a pair. Briefly HEAT the sprocket and the center of the bearing before pulling them. Do NOT even think about reusing that bearing!!
If the flywheel is to be removed for any reason (removal is not needed to do a 'chain job'), be SURE to see and read: Flywheel removal warning, main seal, oil pump cover, oil pump, grabby clutch, crankshaft, BMW Airhead Motorcycles
The crankshaft sprocket, at OT (TDC), has its matching indicator line at 6:00; and the keyway will be at 9:00. At this same positioning, the camshaft sprocket has its own matching line and keyway both at 12:00, after the tensioner is in place. During your work; BEFORE the tensioner is in place, there will be a slight error in lining the marks up.
*****If you replace the cam sprocket, be SURE you get the correct one for YOUR YEAR AND MODEL. BMW changed the keyway position by 3° during a change in the 1977-1978 years, which amounted to, obviously, 6° of equivalent crankshaft change. Engines in USA bikes had this change FROM 1/1/1978. Thus, the duplex sprocket was available in two types. The timing was advanced to meet emissions rules. Since re-start of production occurs just after the factory summer vacation period, some 1978 production year models did not have the emissions camshaft. I had my own way of determining which camshaft was in the bike;...but, Tom Cutter posted a rather nice and easy way...and it is posted in an article on this website, the CAMS article, but I have included the pertinent paragraph here, just below. The method determines, easily, if the cam is symmetrical, or not. The earlier sprocket used from 1970-1977 was 11-31-1-250-253. The R60/7 1976 and 1977 cams have TDC-40-40-TDC timing. The R60/7 for 1978 has 6-34-46-6 timing when stock. The larger engines in 1977 had 10-50-50-10 timing, note that this is "symmetrical".....whilst the 1978 would give 16-44-56-4 timing. For those wanting lots more camshaft and sprockets information, see my cams article, article 60, subsection 7.
Here is Tom's
symmetrical camshafts, with some editing by me:
Remove the spark plugs and valve covers. Put bike in 5th gear and rotate the rear wheel in the forward direction until the EXHAUST valve rocker arm pushes the valve inwards and then JUST returns ALMOST all the way outwards. As you rotate the wheel (jerks work fine on the gear backlash for that purpose) and the exhaust valve starts to come back out, the intake will start to go in. This is the overlap phase. Lay a straight edge across the adjustment LOCKnuts, from the exhaust to intake rockers. Looking straight down on the rockers, and on the straight edge, from above, the straight edge will change angle relative to the valve cover gasket, as you turn the rear wheel. STOP when it is parallel. At this point, if OT mark is lining up in the window, the cam is symmetrical. If it is about 3/8" below the window, it is the advanced timing cam.
6. It is
that every teensy bit of the
original gasket be removed.
Use a sharp tool such as a single edge razor or Xacto knife of
the needed style. NOTE: It is often not appreciated
that the new gasket is specially treated. DO NOT use a sealant of
any kind....or the two surfaces will 'walk...or move' over
CONTRARY to some other's advice. If you want to,
use a gasket removing chemical.
NOT injure the mating surfaces!
When the cover has cooled, loosening the three sleeve nuts and the one cover bolt
some. Center the cam in its seal bore, using a caliper
to measure the distance from the cam to the edge of the hole on
each side...tap the cover (left-right) to center it. BMW
has a tool for this, but it does not fit real well. Failure to do this can result in cam seal
leaks. I usually actually do this with a warmed cover.
8. The 1979 and later models had a hydraulic chain tensioner. Just how much they helped, I am not sure. BMW had some other problems, and came out with a Service Information (bulletin) 11-014-80 (2015), entitled "Sealing Cap for Chain Tensioner Bore" which said that the sealing cap for the bore would now be punch-pricked in production; and, that for any motorcycles that came into a shop for service in that timing area, the caps should be staked at two places. The cap is 07-11-9-932-412, and note that the convex side (dome side) is OUT. This may be an obsolete part! This number has been checked against old fiche, and was accurate...at least in 1985! It will be found in the parts books as an obsolete lock plug, A16. Take a look at the photos or sketches of the main bearing holder. So, if you are in there, and yours does not have two punch pricks, add them, to ensure that they don't pop out. Mind the information on the spring, that has been mentioned previously.
9. Use Loctite BLUE on the inner stud bolts.
10. The installation of the master link plate and fish-clip can be frustrating. You may have to have a number of tries at it. Plug up the holes into the engine with clean rags. I will have more to say on the clip(s). HINT!......Installing the fish clips is a lot easier if you do NOT oil the chain!
LINK, or MASTER LINK: A small metal plate, usually in somewhat of a figure 8 or dogbone shape, with two permanently affixed metal rods.
PLATE: a metal plate, usually in the same shape as the above metal plate, with holes for those two rods
instead of having the rods.
FISHCLIP: A funny-looking single piece clip that fits in a groove on the two rods. SOME chain link setups
use SEPARATE round clips which are NOT directional. The FISHCLIP type of fastener MUST
be installed in the CORRECT direction. That direction is ALWAYS such that the round
closed nose is pointing in the same direction of chain travel. You already KNOW the
direction the chain moves in, right? If not, go back and re-read this article from the
beginning!!! I actually get into this just below, however I want you to understand what is
Method #1: Installing the link on the rear side. This is done on SIMPLEX (1979+) chains. Push some cloth into the 7:00 (+-) case hole at the cam gear area and tape over the hole. Arrange the chain so that you have the break right there at about 7:00. Install, maybe half way or tad more, the OLD master LINK, from the front. This will hold the chain together! Use some sort of tool to install the link from the rear, which then pushes the old link out as the new one is pushed forward. Install the link plate and clip on the front. The engine rotates clockwise so install the open end of the fish clip pointing the other way. Before doing anything more, double check that the crankshaft is still at OT, and that the crank and cam sprocket marks line up! As a double check on THAT, when the crank is at OT, its keyway is at 9:00, the cam keyway is at 12:00, and the marks line up.
If you cannot get the master link into the chain, using the 7:00 position, install in from the front, clips on rear; or, do the master link at a place other than 7:00.
Method #2: Install the master link itself from the front. This is done on DUPLEX chains that have master links. Then put the clip in from the rear. Try doing this at about 2:00 or 4:00 in the CAMshaft sprocket area. Some prefer 10:00. If you have a simplex chain and want to try to install from the front, OK by me.
No matter what you do, be sure that the tail of the fishclip (assuming you have a single fish type here...there are two-piece round clips types) is installed so the round nose is leading in the direction of rotation (CW facing front). Confused?... if the fishclip is on the left side as you face the front, the round nose of the fishclip points upwards; downwards if the fishclip is on the right side as you face the front.
There are some articles on doing timing chains on the airheads.org website that may help you install the clip(s).
There is sometimes confusion
over the alternator and camshaft seals used in the the inner
cover. All models use 11-14-1-255-011 alternator seals,
probably 28 x 47 x 7 mm...have not measured to confirm that size.
The camshaft seal up to models built in 9/1975 was 11-14-1-261-193. It must not be used in later models, or there will be leaks. The later cam seal is 11-14-1-262-977, is 20 x 32 x 7 mm.
If you wish, refer to my extensive camshaft article: cams.htm
For the curious, the chain size is 3/8 x 7/32, both SIMPLEX and DUPLEX.
Crankshaft bearing: For many years, this was number 07-11-9-981-722, and is 35 x 62 x 9 mm. The bearing number was been changed to 07-10-1-468-882. It is a common bearing, but you must get the correct GRADE. The bearing is: FAG16007-C3. Generic (but quality) bearings are OK, in correct grade.
Prepare any new sprocket
ahead of being installed. DO! use a stone or
crocus cloth to round the sharp machined edges on the ID of the
sprocket so it can't hang up while being installed!!!! I
prefer to round those edges much more than crocus cloth will do,
although I do 'polish' after my rounding work (I use silicon
carbide paper for that).
Have the valve gear well-loosened, as has been previously described...that will avoid the cam rotating.
Set the crank with the key at the 9 o'clock position, OT on flywheel will give this position, as noted.
Check that you have the sprocket going on in the right direction...there is a 'step' in the ID. The larger ID goes on first, then the tighter part.
Don't use anti-seize. Just oil the crank nose with a thin film of petroleum, not synthetic, motor oil. Old-timers, and maybe the factory, used tallow (which is fine). Heat the OILED sprocket evenly, until it JUST begins to smoke. This should be done on a hot plate, with a protective metal plate separating plate and sprocket. Do NOT overheat the crank sprocket, the heat-treatment from the factory may already be a bit on the soft side. If worried about the heating and using a thermometer, put the sprocket in a can of oil, and heat the oil on the stove. CAREFUL!!
It is important NOT to let the sprocket get over 290°F!!!
You can purchase 'sticks' that wipe a temperature sensitive coating on the sprocket. Use a 250°F type. Or, heat in oil on the hot plate or stove using a candy thermometer.
Grab the crankshaft sprocket with a pair of dry leather work-gloves. As quick as you can, slip the sprocket all the way onto the oiled (or tallowed) crank until it seats.
NOTE that you will need to ensure that the sprocket goes all the way onto the crankshaft. In order to ensure this, have ready a brass or lead hammer and some sort of sleeve made of brass. Tap the sprocket with those, IMMEDIATELY, before the sprocket cools off. Hold it there as it cools slightly.
Before you install the bearing, make a nice, visible timing mark with some white paint or White-Out, right on top of the faint sprocket scribe mark. You must heat the bearing with a torch from a distance, or use a close-by oven, or can of hot oil. DO NOT damage that bearing with a torch! Heat the bearing, oiled, until it smokes....or use the same oil can method as for the sprocket...or the temperature stick. Don't exceed 290°F or 300°F, and use a 250°F stick if using one. Put the bearing on quickly, and use the soft hammer and brass piece again. If the bearing or sprocket sticks part way on, you will need a piece of sized hard pipe and a quite big hammer and you risk doing more damage than good. DO the job with heat and cold: COLD crank; and HOT bearing and/or sprocket!
After all the rest of the chain, tensioner's
and everything else is in place, recheck that the OT mark is in
the timing window, the crank and cam timing marks are lined up,
and the tensioner shoe is free to move the piston in and out. The
follower shoe gets LIGHTLY pressed to the chain and the nut/bolt
you have the thick 8mm washers under the tensioner so it lays
The proper method of installing a sprocket is really to do it with the camshaft OUT of the engine. Removing a camshaft means having to remove the transmission, clutch, flywheel (or clutch carrier), and then removing the oil pump parts. If the camshaft is out, you can clamp its tail in soft vice jaws, nose upwards, lube the bearing flange, install a .004-.005" feeler gauge under the flange, on the cam shoulder. This will allow setting of the proper end-float of the cam. Install the key in the slot, and use a C-clamp to press the key in squarely and fully (replace key if sloppy fitting!!). Remove!! any roughness at the edges of the slot and on the ends of the bore. Heat the gear to 250°F in a metal oil container. Using a leather gloved hand, quickly install the gear, fully, and completely, in one movement. After cooling, remove the feeler gauge. You do want to end up with that .004"-.005" clearance.
© Copyright, 2014, R. Fleischer
Return to Technical
Articles LIST Page
Return to Homepage