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

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?

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The old number 11 31 2 343 090 has been superceded by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

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?
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?

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?

  1. Push hydraulic chain tensioner (4) in the direction of the tensioner rail in the guide on the cylinder, until resistance to movement is felt.
  2. Measure distance (A) from the sealing face to the chain tensioner piston.
  3. 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.
  4. 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?

Does a loose cam chain wear faster?

How often does the cam chain touch the rail?