wcheung

Something is wrong with my 97 A8 : engine sounds like there is a slipping belt or tight bearing when revved.
Car at dealer already. Could be bad/worn cam-followers. Will know by tomorrow.

Anyone here had similar problems ?

PaulW

I don't know what a cam follower is. There are two bearings and rollers on the serpentine belt that could make noise, or the damper that helps keep tension on the serpentine belt (it's a little shock absorber) could be bad or the ecentric pulley that controls tension on the belt could of slipped somehow, but unlikely.

Could also be the same things inside the timing belt cover with the components in there, basically exactly the same, two rollers, one ecentric pulley and one damper.

Here's a pictures of the two rollers and ecentric pulley and the timing belt cover that has the damper on it. The one roller that you see on the cover is plastic, the other is at the bottom of the engine (these are for the serpentine belt). The ones inside the TB cover (old ones, second picture) are metal. Look at the timing belt post below and you can see the ones inside the cover.

Paul

<img src="http://pictureposter.audiworld.com/22012/tb11.jpg">

<img src="http://pictureposter.audiworld.com/22012/tb12.jpg">

skiracer

I don't think that a bad/worn lifter would make the sounds you are describing- the typical sound a bad lifter makes is a distinct clicking sound. I think Paul is on the right track with his ideas on belt bearings- the sounds you are describing are more likely to be caused by a spinning/rotating part. Keep us informed as to what the dealer finds.

wcheung

Dealer came back and told me the cam works on these metal blocks that pushes the valves. They told me I need new valve 'blocks', total 32 pcs. Will cost around US$2000 !

skiracer

So these engines use "solid" lifters, not hydraulic. That makes the valve train more responsive and better able to handle high RPMs, which is a good thing. It also means that they wear out and must be replaced at some unknown interval. $2000 sounds about right for a job of this size- if it is like most solid lifter arrangements, each lifter must be custom fitted to to the valve/cam combination. Having done a valve job on my '68 E-Type (solid lifters), it is a biggie. This is another reason to use the very best engine oil you can find and change it at conservative intervals- it is the only way to reduce the wear on these parts!! Looking at an explosion of the engine, it does use solid lifter "buckets" just like my Jag. The cams must be removed from the head in order to replace these. The followers themselves are $32 each discount (over $1000 in parts!), and the labor will be extensive! If they do the job, be sure that they replace the valve stem seals (will cost a little more, but since you have already paid for them to get that far into the engine, you may as well have it done) and all the other cam/vavle cover seals. Good luck, and keep us informed of the progress/results. I'm still suprised that the sounds you described are the result of worn cam followers. Oh well, live and learn :-)

wcheung

My A8 is now at the dealer's flagship workshop for more detailed diagnosis......