cold start cam chain rattle

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passivepassat
Posts: 7
Joined: Fri Aug 26, 2011 7:25 pm
Passat model: b5.5 1.8t

cold start cam chain rattle

Post by passivepassat »

Hardly a new subject, but my AWT 1.8t, like many others, rattles its cam chain for a couple of seconds when started from cold. I know the perceived wisdom is that this is is due to oil drain from the tensioner allowing the chain to be slack until rising oil pressure refills the tensioner and that it's regarded as 'normal' and requires no action ( I think there's a VW Technical Bulletin saying as much) but I recently read a post on an Audi forum ( http://forums.quattroworld.com/a8/msgs/65935.phtml) suggesting an alternative explanation: At least some VW vvt tensioners have a spring loaded detent plunger in the bore of the lower tensioner piston (the adjusting piston) which locks the lower piston until oil pressure rises, releasing the detent. According to this theory, the rattle is actually due, not to chain thrash, but to failure of this detent mechanism, allowing rapid up and down movement of both pistons ( due to the alternate torsional loadings from the cam shafts) until the oil pressure in the tensioner stabilises the situation.
Does anyone know, ( from having dismantled a defunct one ) whether or not the AWT vvt has this detent plunger ?

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