Replacing a Timing Chain, Guides, Tensioner, Sprockets...
on a BMW Airhead Boxer motorcycle engine.
This article is meant to be used, if required, with the cams article,
Replacing a chain (typically a job that includes one or both sprockets,
guides, tensioner, etc.) is actually not terribly difficult. For the vast majority of Airhead owners, it is likely 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. NOTE that camshaft removal may be needed, if you have an early Airhead, with the duplex chain, IF YOU NEED to replace the cam
No "precision" tools are needed for a "timing chain job", although you may need to borrow or otherwise obtain a few common tools. If you read this entire article completely through about THREE times, you will understand the process, and you CAN do it!
I am well-aware that there are considerable differences between SOME "guru's" and between those not in that category; AND, with the BMW factory service manual, in how to go about certain things. Unless you are doing a complete engine overhaul job, with removing pistons, cylinders, cam lifters, oil pump parts, etc.... and that means removing the clutch and flywheel, etc.....then you do not want to do it the BMW way.....unless you have to remove the camshaft to replace its sprocket (early models, with duplex chains). On early models a fair amount of work needs to be done to enable the cam to be removed to pull off and press on the camshaft sprocket. BMW installed continuous chains, that is, there were no masterlinks, thus the sprockets would be removed together. This is a huge PIA. So, since the camshaft sprocket does not wear much, perhaps 3 times slower wear than the crankshaft sprocket, it is seldom replaced, but how do you remove the old chain? You use a bolt cutter, which probably means removing the front wheel for access by the bolt cutter; OR, you use a high speed rotary tool with a cut-off disc (or, grind away one of the rivets in the old chain, and press it through!)...and the replacement chain type you REALLY want is the one WITH a master-link!!
A proper chain replacement job will always involve a new bearing
(something I disagree with a few folks about), new guide/follower shoe (on 1979+), new tensioner, usually a tensioner piston spring (pre-1979)...and usually a new crankshaft sprocket. It might include a new camshaft sprocket, but they wear much more slowly than a crankshaft sprocket.
Although you will be replacing the chain itself, IT DOES NOT USUALLY, with exceptions, stretch lengthwise much. Usually a truly bad chain indicates rather high mileage with typically VERY worn sprockets (at least the crank sprocket is very worn) which cause a lot of jerkiness in chain operation. Typically a FEW mm is all the chain really stretches when they are replaced, during a 'timing chain job'. There ARE exceptions, and I HAVE seen very worn chains. What USUALLY wears is the guides/tensioners, the crank sprocket, and eventually the cam sprocket. Just replacing the chain is not recommended by me, although some have certainly done that, and in many instances it will quiet down the timing chest and 'cure' timing ills, for some time. DO IT RIGHT, replace ALL the badly worn parts.
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. No matter what year or model, if you do not read this entire article through thoroughly, and understand what is going on, will be done, etc., you will probably have troubles.
I usually recommend folks either purchase everything they could possibly need; or, better for your wallet, just wait until inspecting things after you have the timing chest casting removed.
For an extensive treatment of replacing a duplex chain, etc., here is an article by Brook Reams, with lots of photos:
INSIDE THE TIMING CHEST:
Note the differences between the two photos shown further down. The first photo is of the 1979 and later SIMPLEX chain (one row of chain rollers). Notice also the flat end of the camshaft, with a slot, used to drive the canister ignition 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. In the first photo, the tensioner on the right side is HYDRAULIC; and there is an added GUIDE not on the earlier models, on the LEFT side (as viewed). The second photo is of the PRE-1979 DUPLEX chain (two rows of chain rollers). Notice the chain tensioner differences, and lack of a left side (as viewed) guide. In that version as the chain, 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. That metal shows up in the pleats of the paper oil filter, and lets you know it is nearing time for a timing chain job. Note the camshaft nose differences.
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 MAY NOT; but definitely gives better long-term-mileage stability to
the ignition timing. The valve timing is also considerably more stable.
Here is something not discussed except by professional wrenches. The problem the same, for both chain
types, ALL years. The chain tensioners are not positioned, nor shaped, for the best tensioning, & after some miles, while the tensioners do not appear worn-out from their material all disappearing, wearing-out is the actual effect. As I noted earlier, what wears is not all that much the chain itself, it doesn't wear much & any rollers wear or over-all stretching is USUALLY quite modest. What DOES wear is the guide on the later model & tensioner wear for both models at their contact point.
The effect is that
wear moves the contact point for the tensioner. 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. Ignition timing irregularities happen, worse on the pre-1979, but eventually noticeable on the 1979 and later. If the carburetors are out of synchronization, the whipping is worse. Further:
The timing of the valves opening & closing changes. The camshaft is RETARDED from the original design point; this means the engine will not develop its designed torque & power curve. The ignition timing gets sloppy too. The guide and tensioner are just not as perfectly designed as they could have been. IMO.
The duplex chain leaf spring can be bent with heat to lessen the effect; creating a better positioning/pressure position. I'm not supplying the information, as it is tricky to do properly & it is 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 it in other places in this article, this is a good time to mention something. The casting with the horizontal cylindrical part, located above the crankshaft nose, contains a piston and a spring. The purpose is to regulate the oiling system pressure. It does this by releasing oil through a hole, if oil pressure is too high. When the engine oil is cold (or rpm high enough, engine oil cold or not), plenty of oil comes out of this regulating hole. This oil is what lubricates the hard-working chain, sprockets, and guide and/or tensioner, depending on model. Because of this design, which is 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, and if the engine bearings are worn. Low rpm at idle causes less oil to come out the exit hole of the pressure regulator. 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. Oil pressure is lessened at lower rpm first as the engine bearings wear. There is less and less oil coming out of the oil pressure regularo to lubricate the timing chest items, and particularly so at a slow idle rpm....and very much so with the oil thinned from being hot.
The engines can be adjusted to idle very slowly due to the inherent smoothness of a boxer engine, especially with a heavy flywheel like on the earlier motors. Slow idling is not a good thing for these motors. Original Owners books and some factory literature said idling at 800 rpm was OK (paraphrasing the information). 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, and I have always advocated using a higher rpm when adjusting the carburetors, the factory did not then mention the oiling system advantage. We pro wrench's understood, long before BMW ever published anything about idling rpm being too low (well, they said that obliquely, simply recommending a higher rpm). MY recommendation has always been: Tune your Airhead so that, with a fully-warmed engine (from a RIDE of 10 miles minimum), 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: http://bmwmotorcycletech.info/tach.htm
Later single chain timing chest, called a SIMPLEX chain.
Early dual chain timing chest, called a DUPLEX chain.
|WARNING!.....you can NOT see the timing marks that BMW stamped into the metal of the sprockets. I recommend that when replacing a chain & sprocket, especially the crankshaft sprocket, that you mark the new sprocket so that when it is fitted with the new bearing, you can SEE THE MARK. The duplex chain photo, above, has such a white mark added.|
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, externally adjusted.
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 screws (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 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 the most 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 wear that gives free-play, tries to 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, whether or not the throttle is being moved.
The steady-throttle jerky AMOUNT is worse as rpm is DEcreased to idle due to wear. The forces are usually considerably worse on one side of the sprocket gear pockets due to the more constant crankshaft pulling direction on the chain; but, depending on how the bike was ridden, and 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 also 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. Typically one must replace the camshaft sprocket once per every second or third crankshaft sprockets. You do NOT want to replace the camshaft sprocket unless you have to.
The engine rotates in only one direction during operation, clockwise as facing from the front. As the engine rotates, the chain on the pulling side of the sprockets, the left side facing from the front, will be more taut, and the other side more loose. 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. If you look at the simplex (1979 and later) system in the photo, you will also see that the shoe on the left side is effective primarily when the throttle is being backed off, as the left side is the side the crankshaft sprocket applies PULLING force to.
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 DIMINISHING. 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 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, and always at lower idle the pressure is lower. 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. Another thing that occurs, and is usually also overlooked by the long-time owner, as it is ever-so-gradual, is an increasing high rpm vibration.
It is entirely possible that either or both crankshaft sprocket 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, and this can be hardness as well as the fact that the larger size spreads the forces between more teeth. 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 this 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. As the ATU rotates, the points do not typically have the exact same GAP and timing 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 really poor ATU needs fixing, as does a badly bent cam tip if noticeable by excessive timing variation. A dial indicator is used to measure the runout. 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 noisy timing chest area is an indication.
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 the sprockets and chain as an assembly was NOT a pleasant job. Today, master-linked chains are used for both Duplex and Simplex chains. You may or may not be able to get a master-linked duplex chain at your BMW dealership; but you should be able to at one of the Independents. 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....BUT....doing it will be a PIA....far more than you may think, considering how the sprocket is pressed onto the cam, and the early woodruff key at the back end.
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; and, a guide added. 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, I suspect variances in rider driving habits, besides heat treatment of sprockets....PLUS the wear on the tensioner/guides.
AS NOTED: 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 with bolt cutters or a high speed grinding or cutting tool. You can certainly grind off the riveted heads on a link and push the shafts through.
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; large rpm changes with jerkily done shifting;...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; and folks should use the brakes more, the engine braking less.
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.
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.
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 to replace the chain and other parts. ...if the problem is not in the ignition ATU 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, part 1:
If your motorcycle has the stock Bosch alternator and 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 during a chain job. The following places sell these, they are NOT expensive, they are all slightly different ones, they all work OK:
NOTE: There is an article on this website dealing with diode boards, grounding wires, and the solid metal mounts referred to above. Please read it! ESPECIALLY item 2 in the article. http://bmwmotorcycletech.info/diodebds&grdgwires.htm
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 ~ 75-77 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; and, I hope, some day, master linked types. 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....be SURE if doing any type of cutting or grinding that you plug the front holes into the engine with rags.
****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 rollers 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. NOTE that many install the link itself from the rear. A bit of practice and you can do it.
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 as a PRY tool....& 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 a bit retarded camshaft timing;....and using an old relaxed pressure spring is also not a good idea. Of course, your crank sprocket might be fine for reuse. While 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? Can YOU feel for bearing wear? The crankshaft nose bearing must be very smooth in operation. I again suggest you replace it. If it is irregular/rough, you will likely have both timing variations AND vibration.
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 front 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. I do it for both though. NOTE that I do not use BMW's centering tool (there are two of them, old and later seal sizes).
Centering the cover, at the camshaft seal, Tom Cutter method, which is somewhat different from what I do, but is good:
Try installing the cover (heat) and snug the bolts finger tight. Wait ten minutes for the cover to cool. Now LOOSEN all the bolts 1/4 turn. Then shift the bottom of the cover left-to-right at the cam. You will see that you can move the cover over a millimeter each way. The seal does not center the cover. Instead, the seal lip deforms to the off-center cover position, and quickly behind to leak copiously. Use a caliper to measure from each side of the cam to the points plate bore, and lightly tap on the cover to match the left and right measurements. That will give the seal the best chance for survival.
If you get a whirring noise after you are all done (typically heard at idle), there are two possible causes:
1. You installed an EnDuralast permanent magnet rotor, they have a fan, and they do make a bit of noise. You could temporarily install a conventional Bosch-type rotor and see if that fixes the whirring noise. If so, then there is no fix.
2. You failed to properly have the timing chest cover hot, and failed to criss-cross tighten the various screws/bolts. To fix this, first loosen the screws/bolts...all of them....maybe 1/4th to 1/2 turn. Then, heat the cover, at least all around the seal/bearing, but I do the whole cover, to fairly hot. Tighten all the screws/bolts in a criss-cross fashion, to 75 INCH-pounds (use an INCH-pound torque-wrench!). Tighten again when cold. Some use a bit more torque.
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.
I recommend that you be sure of no burrs in the slot...if so, clean them up.
I recommend that when replacing a chain and sprocket, especially the crankshaft sprocket, that you mark the new sprocket so that when it is fitted with the new bearing, you can SEE THE MARK!!! Do clean up the sprocket keyway too.
The crankshaft sprocket, at pistons 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 method, regarding 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 critical 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 time. This is CONTRARY to some other's advice. If you want to, use a gasket removing chemical. DoNOT injure the mating surfaces!
Repeating, sort-of, earlier information: 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. 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 1980 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. It may 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. As noted earlier, the spring for the hydraulic tensioner is 75-77 mm long. The original spring was 11-40-0-652-128 (obsolete number).The present number is 11-31-1-335-584.
This is NOT the same spring as used in the oil pressure release valve, located above the crankshaft sprocket. It is ~68 mm long and is 11-41-1-744-324.
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! There is an entire section in this article on installing the fishclip...just below a bit.
Installing the fishclip:
Plug the various engine holes with rags or painter's tape. Put an old white sheet under the bike, in case the fish clip or the two small clips types, falls or goes flying. The engine rotates clockwise so install the open end of the fish clip pointing the other way. Since there is sometimes confusion in some peoples mind about that, I suggest you rotate the rear wheel in the forward direction before you remove the old chain, etc....see what the rotation direction is. You want the engine at TDC (OT) for your work when lining up the sprockets anyway. Be sure that the tail of the fishclip (assuming you have a single fishclip type master link...there are also two-piece round clips types which are not concerned as to direction) 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. I again suggest you rotate the rear wheel (use 4th or 5th gear) in the forward direction, before you remove the chain, and ACTUALLY SEE the direction of rotation. Do NOT GOOF-UP on the master link fishclip.
It is, of course, assumed here that you are installing a type of chain that has a master link. Installing the single fish clip, or the two small clips, depending on what your new chain comes with, can be frustrating. You may find that use of some heavy grease on the clip(s) when installing them, say with a screwdriver tip to hold the greased clips, will be helpful. Do NOT get discouraged, take your time! Don't have the chain oily, that will help.
Method #1: Installing the link from the rear side.
The master-link type of timing chain is available with two types of clips that hold the master link in place. One type has two individual small clips, and the other type has the more common and conventional fish-clip, a one-piece item. I suggest you purchase the fish-clip type, it is considerably easier, over-all, to install. NO MATTER WHICH YOU USE, be SURE they are FULLY AND PROPERLY SEATED into the GROOVE on the masterlink. I usually suggest folks order several extra of these clips. They have a habit of 'getting lost' during the installation process.
There are AT LEAST TWO articles on doing timing chains on the Airheads.org website that may be helpful, and I suggest that you read them before doing any work, and after you remove the timing chest, review them again, and review my article you are reading right now.
Special 'hints & tricks' of the trade, part 2:
There is sometimes confusion over the alternator and camshaft seals used in the inner cover. All models use 11-14-1-255-011 (latest number is 11-14-1-337-654) alternator seals, both are 28 x 47 x 7 mm.
The camshaft seal up to models built in 9/1975 was 11-14-1-261-193, is 12 x 25 x 8 mm. It must not be used in later models, or there will be leaks. The later cam seal is 11-14-1-262-977. It has been superseded by 11-14-1-262-282, both are 20 x 32 x 7 mm.
If you wish, refer to my extensive camshaft article: http://bmwmotorcycletech.info/cams.htm
There is a lot of information, including more about the seals, ETC.
For the curious, the chain size is 3/8 x 7/32, both SIMPLEX and DUPLEX.
Crankshaft bearing: 07-11-9-981-722, and is 35 x 62 x 9 mm. 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 very fine grit abrasive cloth; I use silicon carbide paper, to round the sharp machined edges on the ID of the sprocket so it can't hang up while being installed. If the keyway slot has the slightest burr, file it off!...and clean the sprocket again.
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.
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.
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). I prefer bacon grease. I suggest you do NOT heat the oil in the house, use an electric hot plate (I put a flat piece of metal over it), OUTSIDE the house! 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, do what I do: put the sprocket in a can of oil, and heat the oil slowly on the stove. CAREFUL!! It is important NOT to let the sprocket get over 290°F or maybe 300°F. You can purchase 'sticks' that wipe a temperature sensitive coating on the sprocket. Use a 250°F type. My method: heat in oil on the hot plate or stove using a candy thermometer. Be prepared to remove the sprocket from the oil and install it ...BEFORE it can cool off. My method is to have the rearside of the sprocket downwards in the oil in a reduced height 3 pound metal coffee can. I have tongs to grab it, and a pair of LEATHER gloves, etc. Have EVERYTHING ready! 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. 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 the sprocket in that rear position...with some rearwards pressure, as it cools slightly. 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 tightened. Make sure you have the thick 8mm washers under the tensioner so it lays flat.
The proper method of installing a cam sprocket is 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 to 300°F in a metal oil container. Using a leather gloved hand, quickly install the gear, fully, and completely, in one movement. It is the same method as for the bearing and other sprocket, see above information. After cooling, remove the feeler gauge. You do want to end up with that .004"-.005" clearance.
12/04/2008: Revise entire article, incorporating previous updates & other items. This Revision did NOT change anything of material importance, EXCEPT to clarify details & provide better hints & advice. 09/21/2009: clarify some minor details
11/06/2009: Re-arrange order of some sentences and paragraphs, edit rather extensively for clarity; eliminate a lot of superfluous repetition.
02/05/2010: Add photo of 1979+ timing chest innards
06/28/2011: Add photo of /5 timing chest innards
11/06/2011: Remove method information hint on installing cam sprocket in situ. Add references to using article with the cams article.
01/07/2012: Minor clarification on installing fishclips/master link, and on nose bearing.
07/26/2012: Add note regarding ATU wear, uneven ATU lobes, and run-out on pre 1979 cam tips
08/02/2012: Clean up article for better presentation
08/15/2012: Clarify #7
10/09/2012: Update #5; minor other things updated including a few inconsequential typos; add QR code; add language button; update Google Ad-Sense code. Language button and associated script removed in 2013, due to browsers problems.
01/30/2013: emphasize and clarify fishclip installations.
10/19/2013: Change wording in sections on sprocket wear; make things easier to understand (?)..or, more accurately described, in those areas.
08/10/2014: Clean up article some. NO substantive details changes. A bit more in September.
11/26/2014: Update a few part numbers.
02/11/2015: Clarify some details on the fishclip/clips installation. Re-arrange a few things. NO substantive changes. Some emphasis and font changes also done where applicable.
02/25/2015: Add same notes, three places, on marking the gears for timing mark so can be seen with bearing installed.
07/--/2015: Add some more hints, including how to deal with the new gaskets.
08/05/2015: Minor cleanup and fix info on torquing the hot timing chest, repeating when cold. A few days later I made a few clarifications.
02/29/2016: Fix error in describing the 1979+ tensioner spring length, add part numbers for it; add the information on the oil pressure relief valve spring; clarify details.
04/04/2016: Updated entire article: meta-codes, layout, add table for the photos, fonts, colors, explanations, details. A considerable amount of repetitive information was removed.
©Copyright, 2014, R. Fleischer
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