Timing Chain Tensioner

[scbmw]

When i get the tensioner from bmw i have been told that there is a snap ring on it. What does this do and if this is removes will the spring and piston be released.

[cheesebox]

The snap ring keeps the plunger compressed inside its sleeve, which is where you want it to be when you install it. The ring fits in a deep groove on the piston, and when this is pushed into the sleeve, it snaps into a groove on the inside of the sleeve - just tight enough to keep the spring compressed and the piston retracted. It only takes a relatively small force to release it - eg dropping it! The whole assembly comes as a single part, and should be supplied with an oil sealing washer. You can take it apart but this would be daft if you've just bought it new. They're impossible to put back together by hand - you need to use a vice - as the spring inside is pretty stiff. The only reason you'd want to take it apart would be to clean out an old one if it had stiffened up. Once installed in the engine, you rev up to 3000rpm for 20 seconds - this makes the cam chain fly out with centrifugal force, and cam chain guide then exerts enough pressure on the tensioner to release the piston.

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