F650 Cam Chain FAQ
compiled & edited by Kristian #562
by Flash, HsN et al.
Please read the Disclaimer before attempting any work in this FAQ.
Last Updated: 22 March 2007, by Winter #1935
- So if it's making a Noise, what is the likely problem?
- Cam Chain Tensioner
- Symptoms of a Failed Chain Tensioner
- Do I need to remove that bolt to check the piston?
- Is the piston hydraulically actuated by engine oil?
- If the piston moves when I push on it does that mean that it is working okay?
- Is there any point at which the chain becomes so stretched that the tensioner will not take up enough slack?
- If it's not the Tensioner, what is it?
- Cam Chain
- Is there a way to check your chains while your engine is apart?
- How much trouble would it be to change the (endless) chain?
- How should I hold the Clutch Basket while the big nut is removed?
- I'm on a world trip and don't have the Tools/Experience to take off the Clutch Basket. Any Other (Temporary) Alternatives, like a Split Chain?
- What is Timing chain slap exactly?
- How much does a new Cam Chain cost?
- So How do I actually check the Timing Chain Wear Limit?
- Can the cam chain skip a tooth if there is too much slack?
- Does a loose cam chain wear faster?
- How often does the cam chain touch the rail?
For other related FAQs:
In a modern 4-stroke engine, the opening and closing of the valves are effectively controlled by the cams. The engine used in the F650 has two cams, and is commonly known as a Double Over Head Cam (DOHC) engine. The cams need to be kept in sync / driven by the engine - this can be done by gears, a cam belt, cam chain or something similar. Over time the cam chain can wear, and due to the forces inside the engine can result in the chain slapping against things. Thus some method must be used to keep tension on the cam chain to prevent it from slapping against things - the F650 engine uses cam chain and automatic cam chain tensioner. It is integrated into the oil circuit, which is used to provide hydrolic pressure to the tensioner.
When (for one reason or another) the cam chain is completely worn or the cam chain tensioner fails, klacking noises may be emmited from the engine. This FAQ should help identify if your cam chain or tensioner are causing the problem.
So if it's making a Noise, what is the likely problem?
- The tensioner may be shot, and replacement may fix it. While it is spring loaded, its tension is really dependent on oil pressure. If it happened worse while hot, you could be losing oil pressure. (How old/thin is the oil?) At idle, the manual says only 7psi or something (and that's what the check valve in the tensioner is for). If you are turning it over by hand, there's no oil pressure, therefore less tension on the chain, especially if the tensioner spring is old or the tensioner is stuck.
- Air can sometimes enter the cam chain tensioner, and prevent it from working effectively. Sometimes this will go away after a few seconds, and sometimes it will remain a problem.
- Check your valve clearances - if they are incorrect, fix them first.
- Another common noise mistaken for the cam chain tensioner is the automatic decompression release mechanism. This sound can come from the RHS of the upper part of the engine. See this image of the release mechanism (when the valve cover is removed).
|Cam Chain Tensioner Part Number|
|The hydraulic cam chain tensioner part number has been superceeded. This is the part that is supposed to be one part. When you go to adjust the valves, if it comes out in three parts, replace it.|
The old number 11 31 2 343 090 has been superceded by
the new number 11 31 7 686 731.
Cam Chain Tensioner
When you check your Valves or if you think you Cam Chain is slapping a bit and it's not the compression release sound (refer the Strange Noises FAQ) you might also like to check check your Cam Chain Tensioner. To do this you need to undo the Chain Tensioner, here: (Chain Tensioner Bolt Location), accessed from the LHS of the bike at the back side of the engine. There is a large 22mm Bolt. Undo this bolt. Note the Crush Washer should be replaced when reinstalling.
It is the same size as the Oil Drain Plug Crush Washer, or at least that washer fits, so if you have a spare one of those you could be in luck. Behind the bolt is a Steel Cylinder, which is the "Hydraulic Tensioner" itself. You can just pull it out to inspect it. The steel cylinder pushes up against the Chain Tensioner Guide. The BMW service manual "Engine Oil Circuit" diagram shows the chain tensioner as shown as being fed off the high pressure oil line. Elsewhere in the manual it's described as a "Hydraulic Chain Tensioner". Remove this cylinder so it doesn't drop onto the ground and score the sides of the cylinder.
The Chain Tensioner cylinder is a miniature hydraulic cylinder, acting as a
self adjusting unit on the cam chain guide, pressurized by the engine oil
pressure. If its tiny check valve is leaking slightly, it will reseat and allow
you to install the Large Bolt easily. If it's not leaking, it may seem too long
to re-insert and install the Large Bolt. You must de-pressurize it by looking
in the opening, finding the tiny ball bearing check valve, and pressing it open
with a pin to allow oil to leak out. This will allow it to shorten enough to
install the Large Bolt. If you think you have a problem with noise from a loose
cam chain, especially at start-up or low oil pressure, or find wear on the
chain guides, this is one of the parts to consider replacing.
The tensioner is a hydraulic damper and they sometimes can get air bubbles in them that tops the damping effect and so the chain rattles. By taking it apart and filling it with oil you would have got rid of any bubbles in there and that may be all it was. If the tensioning piston is not worn (i.e. scored) and fits well in the bore in the cylinder then this may be ok and you have fixed the problem. If the chain is loose then this is another matter, there are specs for measuring the wear of the chain guides and the chain.
On the left is the new part (comes as one piece), on the right is the three parts it divides into when it goes bad.
On the left is the new one, the right is the bad one, which allowed the timing chain to "play". Both squeezed with same force, new on the left remains taught, old one on the right is lose, and therefore so was the timing chain
|Photos courtesy of Erin & Chris Ratay
Note that you can UNDO the Chain Tensioner Bolt with a ring spanner, but the Carbs can get in the in the way for torquing it up if you use long sockets. Here's a recommendation: "With a new washer, and using recommended sealer (Yamabond as a substitute for ThreeBond 1209), I just do mine by hand. Gingerly. I can't see that setup withstanding 40Nm forever. I think I can get a small torque wrench in there with some strange adapters, but it only goes to 30Nm, which is plenty as far as I'm concerned. You can easily tell if it leaks - looks like a good candidate for drilling and safety wire to me, good washer and sealer, and forget the 40Nm." Hombre sin Nombre.
Note! The tensioner is dependent on oil
pressure. If the Tensioner has failed, don't be alarmed it has happened before,
but take a minute to wonder why. At the very least I'd check to confirm that my
oil pressure warning light works. A more detailed check by the dealer (who
should have the right tools and fittings) might be to see that you have proper
oil pressure. Hombre sin Nombre.
|Removing the Tensioner on ABS equiped GS,Dakar,CS|
|On ABS equipped bikes, the ABS unit is located behind the engine in such a way it is difficult to remove the cam chain tensioner. Please see the GS Valve Shim Check and Change FAQ for more details on how to remove this bolt.
Symptoms of a Failed Chain Tensioner
- Clacking in the valves area, especially when the bike is hot. Valve clearances are okay.
- With the valve cover off (and engine off!), turn the engine over. If the cam chain makes a "swack" sound, the tensioner is bad or timing wrong.
- The cam chain tensioner should come out in a single piece when you remove it. If it comes out in pieces, it needs replacing.
- Loud knock, particularly noticable at engine tickover. It is a regular knock that does not go away as the revs increase. (There are other possible causes of such a noise).
- Knocking noise originating from the upper left side of the engine.
Do I need to remove that
bolt to check the piston?
Is the piston hydraulically actuated by engine oil?
- Yes. If you check your BMW service manual "Engine Oil Circuit" diagram you will see that the chain tensioner is shown as being fed off the high pressure oil line. Elsewhere in the manual it's described as a "hydraulic chain tensioner"
If the piston moves when I push on it does that mean that it is working okay?
- Yes. But it will be a little less stiff if you push the little ball bearing in and release the "valve"
Is there any point at which the chain becomes so stretched that the
tensioner will not take up enough slack?
- Yep, but you'll know. It'll start slapping against the front of the engine casing (See also the Strange Noises FAQ) and the guides will wear. Check them first. Otherwise I wouldn't worry about it. Check your Cams are not one tooth off. You need to check it with the CAM Chain Tension Bolt in Place.
If it's not the Tensioner, what is it?
- The real point of the whole thing - how stretched is the chain? Well, tell me how worn are the plastic guides? If they are badly worn (like eaten away to nothing), then there's likely no need to measure the chain. BTW, IF this is the case, when guides get eaten away THAT badly, those 2 ounces of abraded plastic have to end up somewhere - like in the oil filter, OR the oil tank intake filter, or in some very strange places. You might have low oil pressure because the oil filter bypass valve is open, or stuck or clogged with the cam chain guide material.
Is there a way to check your chains while your engine is apart?
- Can't be done. Tension requires oil pressure since the tensioner is
hydraulic. The tensioner is hydraulic - so will only be tensioned when the
engine is running.
How much trouble would it be to change the (endless) chain?
With the left cover off do you simply feed the chain up to the cams?
Do we have to remove the clutch basket to change the timing chain?
If so, any suggestions/tricks?
- With the left cover off, you have to be able to get the chain over the
crank sprocket. That means you must pull the gear off the end of the crank. You need to pull the clutch basket to do that. But since you might as well USE gravity instead of fighting it,
after you've removed the clutch basket, drop the cam chain down from the top
instead of trying to feed it up. One item we found interesting while in there
from my shift fork replacement is that with the cam carriers out you CAN lower
the cam chain to where it loses contact with the crank sprocket and lose cam
timing if you are not careful. If I were Rotax, I would have included a little
cast ridge to keep that from happening.
- It is a continuous (endless) chain. You cannot
simply remove the valve cover, attach new chain to old, and snake it through,
then close the new chain links, unless you have a SPLIT chain.
- An endless chain would be more secure. The
clutch basket should not be too difficult to get apart, you need to lock the
inner and outer basket/hub together, there is a special tool which has inner
splines (the steel plates) and outer lugs (clutch plates) on it. If you had a
spare steel disc you could make one. Undoing the big nuts would be the biggest
problem but this should not be a problem for a reasonable workshop.
- Here is the Clutch Basket. To the Left of it
is the Timing Gear:
- Take a look at the picture below:
- See that gear behind the nut the wrench is on?
That gear is the primary drive and meshes with the outer gear teeth of the
clutch basket. You'll need to remove the basket in order to remove the gear
behind the nut that the wrench is on in the picture. With slack in the chain,
the chain will drop down low enough to remove the gear. Then you can remove
the chain out the top and drop the new chain down from above. "Reassemble in
reverse order," as they say.
- Make sure you Loctite everything up when reassembling.
How should I hold the Clutch Basket while the big nut is removed?
- Put the bike in gear and have your assistant STAND on the rear brake If
you don't like that, a clutch tool is easily made out of a few old plates. Drill
a hole or two in the stack and stick nail(s) through the hole(s). Refer the
Clutch Plate Springs FAQ for details.
I'm on a world trip and don't have the Tools/Experience to take off the Clutch Basket. Any Other (Temporary) Alternatives, like a Split Chain?
- Sometimes a method of repair is to fit a split chain and as you say
snake it through and use split link to join it up again. You have to make sure
you have the exact number of links and ensure that the split link is 100%
secure. This is not an uncommon form of repair. There are spring clip master
link cam chains substitutes available for most bikes/BMW's - it's just a matter
of finding out who makes them and what to order.
What is Timing chain slap exactly?
- If the check valve within the cam chain tensioner leaks/depressurizes
when the bike sits for an extended period, the chain will loosen. No problem as
long as it extends and tensions properly when running and there is oil pressure.
The tensioner is easy to replace if it leaks too easily. People that remove it
and scratch it, dirty it or crush it have had this problem. Inspect your left
side plastic cam chain guide. If it is badly worn or chewed you will have chain
stretching or lack of tensioner travel. When the timing chain stretches
excessively, the plastic guides usually show wear first. The Tech Data chart in
the Classic Service Manual (p11.8) gives: Timing Chain wear limit, distance from
sealing face to chain tensioner piston: 9.5mm. Sure you can drop the chain off
the bottom sprocket - no big deal, that's what the crankshaft set screw is for,
as long as the cam sprocket timing marks line up when you reassemble. Dropped it
down several times - the only annoyance is when you drop it and it hooks onto
the sprocket teeth and seems to be shortened - you have to disengage it with a
How much does a new Cam Chain cost?
- I checked the dealer and the chain is $108.00 the guides are $14.00
each. (Dec. 2001)
So How do I actually check the Timing Chain Wear Limit?
- The Wear Limit Distance from sealing face of plug to piston of chain tensioner 9.0mm (0.35in) for the GS and 9.5mm for the Classic
- You don't need to have the Valve Cover off for this work, but it helps, because you can inspect the Chain Guides. The Front Guide can definitely be removed.
- Just like checking the wear on your chain and sprockets, check the teeth on the cam sprockets, and take a measurement of say 10 links of the chain at various intervals around the chain. If the length of 10 links varies too much, you may have uneven chain stretching. Inspect the chain for damage.
- Push hydraulic chain tensioner (4) in the direction of the tensioner rail in the guide on the cylinder, until resistance to movement is felt.
- Measure distance (A) from the sealing face to the chain tensioner piston.
- If the wear limit, distance "B", is exceeded, first inspect the tensioner rail and the two guide rails for score-marks and renew them if necessary.
- If a part has to be renewed, repeat the measurement procedure described above. If the wear limit has been exceeded, the timing chain must be renewed.
Can the cam chain skip a tooth if there is too much slack?
- This is unlikely on an F650. If it is making excessive noise, the tensioner is broken, plain old wear, it may happen. However if you have left it so long the chain has skipped a tooth, then you deserve whatever mess you end up with.
Does a loose cam chain wear faster?
How often does the cam chain touch the rail?
- All the time (if the cam chain tensioner is working correctly)