996 / 997 Turbo Chain Rattle on Startup Explained
Channel: jasno
Date: 2022-10-20

First, let me state, I'm not a mezger expert, but I've now dug in enough now on this engine to have a decent understanding.  I've spent some time thinking and reading about why there is a rattle on startup and when I pinned my cams on my 997.1 Turbo I set out to see if I could see it in action, I think I have.

This video attempts to show why sometimes these mezger engines have chain rattle on startup and why you shouldn't worry about it.  When the engine is off, oil pressure drops and the chain tensioners (they are oil pressurized) don't have enough pressure on the chain guides to keep the chains taut from the force of the valve springs pushing on cams & cam sprockets, which in turn allows slack in the chain.  You can see this in action with the chain as it rotates around the exhaust cam sprocket.

Once pressure builds, the chain tensioners have enough pressure on the chain guides to hold everything taut, no slack or slapping around from the chain.

This is why when folks prime the oil pressure by pulling the fuel pump relay there is no noise, because pressure is built and the timing chain is held tight.  

The black tool I used to demonstrate this is the Timing Chain Tensioner Locking Tool that simulates the right oil pressure to the chain tensioners, and while isn't necessary to set the cam timing, it makes it easy to keep things all in place.

Let me know what you think!  Do I have this right, or did I get this wrong?