Tuesday, November 22, 2005

Cam Chain Tensioner reset or rebuild

submitted by Dan

Re-Setting Cam Chain Tensioner

Here is a view of a new cam chain tensioner disassembled for reference.

photo courtesy JamesC

This a rare condition but never the less happens, the tensioner gets stuck at its maximum position causing the over tensioning of the cam chain not to mention the awful noise the engine emits while the chain slack is forced to rattle at the wrong location.

This may also cause undue wear on the two cam gears and single crank gear that drives this chain. Normal chain and gear replacement interval is 30000km.

photo courtesy JamesC

The above symptom occurred on my F4 and is fairly straightforward to rectify.

The side fairings and belly pan should first be removed followed by the front nose cone, the electrical covers and air tubes. This clears way to loosen the top radiator fixing screw on the left side and allowing the radiator to be released and moved forward giving just enough room to access and dismantle the cam chain tensioner. The cam chain tensioner is located between cylinders two and three by the exhaust manifold.

photo courtesy JamesC

First stage is to undo the centre screw (10mm). Undo it all the way, take care not to let it go it as it is spring loaded and will eventually come out including the spring, a small rod and a washer.
Next undo the two screws (8mm) securing the tensioner body and prise it out of the block by rotating it back and fourths while pulling outwards, it will feel a bit stiff due to the rubber ring washer but eventually come out.

Once the tensioner is out you will clearly see the mechanism, it is designed as a ratchet with teeth and a spring loaded stop so once the arm reaches its optimum position with the help of the long spring, there it stays (now I understand why the complete assembly costs £125).

To reset, release the stop and push the tensioner arm all the way in. That’s it.

The rest is in the re-assembly sequence, first replace the tensioner body back into the block and tighten up top and bottom screws to required torque (8Nm). Then insert the centre assembly spring, rod and not forgetting the washer. Tighten up to the required torque (8Nm).

[From the Factory Workshop Manual]:
""Lock the screw cap by hand till you feel the tensioner extend, then lock it with a 8 Nm torque
Acting this way the chain tensioner is adjusted."

Once assembled, start the engine and let the tensioner find its own setting as the chain slaps around for a few seconds after which all cam chain rattles will disappear and all will sound as it should.
Job done!

edited JamesC


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