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, 2013, R. Fleischer
Replacing a chain (and typically includes one or both sprockets, guides, 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. That is because most owners will not tackle such as a transmission overhaul, rear drive overhaul, and engine crankshaft removal, camshaft removal, etc. The timing chain job is somewhat complex, but simpler than them. 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, perhaps
unexpected 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 these two photos.
The LEFT photo is of the 1979 and later SIMPLEX chain (one row of rollers.
The RIGHT photo is of the PRE-1979 DUPLEX chain (two rows of 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.
In the LEFT photo, the tensioner on the right side is HYDRAULIC; and there is an added GUIDE on the LEFT side.
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. There is MUCH less chance for timing errors, certainly almost zero from a bent cam nose.
Because of the differences, the chain does not whip about
nearly as much on the 1979 and later models.
This theoretically leads to longer sprocket and chain life (I am not convinced); but definitely gives better long-term-mileage stability to the ignition timing.
The valve timing is also considerbly more stable.
Timing chain; cam sprocket, crankshaft sprocket & other parts:
What are they? Where are they? What do they do? What happens when they wear out?...and do they? and how?
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 pressured 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
camshaft to 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
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 two or 3 bolts 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. Everything you see, and more, will have to be removed to do a "timing chain job".
Assuming you had the timing chest casting removed, 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. As you face from the front, the chain direction of travel is clockwise. 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 chain, with any sort of real free-play, could whip back and forth with throttle up/down (on-off) movement. This is made worse by the fact that the loading of the valves, springs, and valve gear in general, is NOT smooth, in regards to the cam and its cam lobes. Thus, the camshaft is a jerky load onto the chain, sprockets, and crankshaft. The jerky-ness AMOUNT is worse as rpm is DEcreased, partly due to inertia. The result of this jerky movement is that you may well have SPROCKET wear and you can SEE if either sprocket is excessively worn, by a visual inspection. The forces are worst on one side of the pockets due to the more constant crankshaft pulling direction on the chain; but, depending on how the bike was ridden, and many other factors, the wear could be more even. For the camshaft sprocket, the sprocket size distributes the forces over a wider area, and there are other things, which one needs mathematics on, to explain the difference in wear forces......and it is possible that the sprocket is of harder material...so the camshaft sprocket is not replaced as often...and might even last several chains and crank sprockets. For the nerdy types amongst you, typical wear is that one must replace the camshaft sprocket once per every 2 or even 3 crankshaft sprockets.
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. 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 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). Other things that can make the noise worse are hot thin engine oil and/or low oil pressure (additional effect on pressured tensioner, 1979+ models). The resultant effect is 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, explained later herein.
NOTE! 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 much 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. There is a way to fix that, with a small brass hammer, but that is not the main point of what I want to say here. When the tip is bent, and you can NOT see this with your eyeball, 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 for both ATU timing lobes. This will result in a dual-image when using a strobe lamp on the flywheel and will result in vibration, often at one or more narrow ranges of RPM. This type of problem is often WRONGLY interpreted as carburetors being out of perfect 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 change is some advance unit WEAR, and even irregularity in the grinding of the cam lobes. BMW at one time recommended 'stoning' those 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. Quite noisy chains are a giveaway.
NOTE, AGAIN, that 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 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 devices.
The forward end of the crankshaft has not only
a sprocket and bearing, but also the alternator
From the beginning of the /5 series, through 1978, the chain was DUPLEX (two sets of rollers in width). The original chain was an ENDLESS type; that is, no clip and master link was used. The chain was installed together with the sprockets, all as an assembly. For the average person, as well as the shop pro, doing that was a slightly unpleasant job. Today, master-linked chains are used for both Duplex and Simplex chains. You may or may not be able to get one for the duplex chain at your BMW dealership. You CAN install both sprockets and chain, at the same time, on a pre-1979 engine, with the help of a buddy, and having the correct technique....thus, you CAN use a non-master-linked chain.
In 1979 BMW made a considerable number of changes, one of which was to use a SIMPLEX chain (one set of rollers in width), and they also changed the method of tensioning the slack in the chain; that is, a new hydraulic method was incorporated. At that same time a master-link system was incorporated. The master-link makes the chain easier to replace; no sprocket removal needed. Many will cuss during replacing the master link. If you follow the hints and advice in this article, you will find that installing the master link is not as difficult as you may have heard. There seems to be no cut and dried viewpoints about whether the duplex sprockets last longer than the simplex sprockets.
chain stretches (some small amount anyway), from normal use. The amount of
stretch is actually usually very small, is almost entirely in the chain
rollers area and not the side plates, and what is typically
called a sloppy or worn chain is really USUALLY the much higher amount of
wear on the crankshaft sprocket. 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. Thus, one
concludes that chain wear does happen, but it is very minimally the sideplates,
and more the internal roller innards, but still small.
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.
As wear proceeds on the chain, sprockets, etc,; which it does from the first startup of the engine on brand-new parts, the camshaft will begin to lag the designed timing relationship to the crankshaft. The timing of the camshaft itself will retard in relation to piston movement, and the ignition also is retarded. This wear occurs rather slowly, and it is usually not noticed by the rider that the power has been slowly reducing. The ignition is usually checked every thousand or 5000 or so depending on personal preference or because of model and year....and the timing setting is adjustable, so you will probably not notice the very tiny compensating changes one makes in ignition timing, made over many many miles. This is very especially so with points ignition. Thus, the ignition will remain more or less correct in relationship to the pistons and crankshaft markings for ignition purposes, but the valve openings and closings will lag, versus the pistons, and power is reduced.
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. The chain itself does not wear all that much...but....for both chain and sprockets, ETC!....... certainly lengthy low rpm idling is not good.... as the oil supply is reduced. The oil for the chain comes from the pressure release valve area above the chain. More later herein. Trying to adjust the carburetors for the lowest possible rpm for idle is a BAD idea due to diminished chain and sprockets oiling. Same for lengthy idling after the engine is warmed up. Rapid on-off throttle movement accelerates wear, as does excessive use of the highest rpm area. As a general rule for most things mechanical, wear tends to increase more exponentially than directly, from incremental increases in rpm, this is especially so at the higher rpm levels. 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 85,000 miles.
If the chain and sprockets wear enough, the tensioner(s) will not do a very good job and the chain will slop around, and may well start rubbing against the bearing carrier, and one may find some metal particles in an engine oil filter that you unroll for inspection at EVERY oil filter change.
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 (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 good 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).
In the models PRIOR to 1979, an even faintly bent
camshaft tip 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, the points are located, unsupported 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 runout 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). 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... but also some higher rpm vibration. This higher rpm vibration may trick you into thinking the carburetor throttle cables need synchronizing. You could get engine vibrations....at several rpm areas. All sorts of combinations of things are possible. A worn chain/sprocket can definitely cause poor idling.
For the 1979 and later models, the cam tip type timing unit drive was abandoned and the 1979-1980 canister points models and later models all use an offset keyway drive 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 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.
There are some special 'hints and tricks of the trade'. I will attempt to lay out all of these, that I know of.
You are probably familiar with the alternator and ignition triggering parts, as those are very easily at hand after removing the front outer cover. The bearings, sprocket gears, tensioner and chain, ETC., are located REARward of these parts, behind that timing chest area. You have to remove the outer parts and then the timing chest casting for access. If your motorcycle has the stock Bosch alternator and is a model that uses the 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; for the DUPLEX chains, from the FRONT. I am sometimes asked about whether or not the master link can be installed from the rear or front, if you wanted to, and can. It really makes no difference. What DOES make a difference is the direction you install the fishclip (for those types with one fishclip, not two individual small 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 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.
Besides the chain replacement, you will also have to replace the gaskets, seals, tensioner shoe(s), guide, the spring inside the damper piston, and usually the crankshaft sprocket and if so, that bearing. It is probably penny-wise, pound-foolish, to not replace parts as reuse, such as of an old rather worn crankshaft sprocket, will not only accelerate wear on your new chain, but the engine performance will suffer, as a worn crank sprocket gives poor ignition stability and lousy engine idling....and using an old relaxed pressure spring is also not a good idea. Of course, your crank sprocket might be fine for reuse. Whilst, for curiosity, most folks will check the crank nose bearing (or, for that matter, any such bearing) by 'feel' and 'rotated sound', and a crankshaft bearing may thusly check out OK; that bearing SHOULD, IN MY OPINION, BE REPLACED...why take the chance that its clearances are getting sloppy? The crankshaft nose bearing must be very smooth in operation. I suggest you replace it. If it is irregular/rough, you will likely have both timing variations AND vibration.
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.
Be sure to read the cams.htm article!
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!
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:
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!
7. When replacing the two seals, be sure the seal mounting surface is quite clean, and you can use a very fine grit sandpaper, cleaning afterwards, then oiling if you want to, before pushing the seals into position. The seals go flush to the surface (the alternator seal with front surface, do it from the front or rear with the casting on the workbench); the cam seal (install from behind) flush with the rear surface. When installing the cover heat the cover again around the seal area. Install it immediately before it cools down, and install lightly the 3 sleeve nuts and one cover bolt closest to the seal. 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.
Note: The cast cover must be heated to fit
over the crank bearing. While still hot, snug down the bolts, in a criss-cross pattern. 68 INCH-pounds is fine.
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 affixed permanently.
FISH CLIP: 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 rounded 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 going on.
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).
Earlier in this article I talked about the inner timing cover, heating it, ...and when replacing the cover it is important to heat it around the crankshaft area, where the bearing fits. If you do not do this, the cover likely will not go on FULLY over the bearing....so have the cover HOT!...and the instant you have it fully over the bearing, start tightening up the bolts!..., criss-cross pattern, about 68 inch-pounds.....that means you have to center things at the cam seal too as I have noted!....but that can be done later, after the cover cools, you can loosen the bolts. Think about all this, before you start the the installation of the cover! Otherwise, you have to heat, remove the cover, and start over. I noted, well above, what particular fasteners to lightly fasten down, for centering later.
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.
For the curious, the chain size is 3/8 x 7/32, both SIMPLEX and DUPLEX.
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, 2013, R. Fleischer
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