A8, 2.8, Petrol, 1997 - Cambelt tensioner fault

[bigtony]

Hi all, need your help on this one,

recovered in with timing belt snapped and had wrapped itself round the crank,
took both heads off and most of the valves had been bent.
rebuilt both heads with 30 new valves, new timing belt, tensioner roller and new damper and new water pump.

got it running fine but noticed when the engine got hot the timing belt becomes slack and starts to flap about ,
had a good look and it appears that the hydraulic damper is not holding the tension and retracts back in making the belt slack.
the only way to get it right again is to let it cool down and its all fine until it warms up again.

Ive installed the timing belt correctly as per ad instructions, used all genuine parts, the belt feels correctly tensioned when cold and when it gets hot it doesn't sound like its over tightened, it seems worse when you rev the engine , seems to make the plunger retract in quicker .

im at wits end with this, my local Audi dealer hasn't a clue. please help ,

 any thoughts appreciated.

[pgs]

Hi, you did turn the tensioner eccentric anticlockwise to push the plunger back and tension the belt?  otherwise it won't tension correctly.
Also this has to be done slowly to allow the plunger to go back.  It sounds like you are ending up with the plunger too far out when you have tensioned the belt

[bigtony]

engine code is ack.

and yep replaced the tensioner assembly.

Ive followed the correct procedure using autodata, the cam sprockets are loose when i tension it and im using the special tools too.
I feel im pretensioning the tensioner correctly as i use a torque wrench and apply the correct nm to the tensioner , carnt remember what the setting is.

do you think the belt is overtensioned? ,
the tensioner seems to retract when the engine hits full operating temp, while its warming up to 90 everything is going fine and the belt is at good tension.
The only thing i noticed today was that 1 of the cam pulleys doesn't seem to be running true so Ive got a new one to try,

thanks for your suggestions will keep working at it .

I know its an unusual problem. Ive done loads of these type of tensioners on other engines and makes and never had a problem like this. im so confused by it .

By the way i think i have read somewhere that a Audi engine has a problem with a hydraulic damper. anyone know what the problem is ? i think its on the 5 valve engine

[Gary s]

hi gary. yes the hydraulic tensioner has been replaced along with the roller, genuine audi parts, when im applying a tension to the belt im doing it at 15 nm, anti clockwise, does this sound right to you .?

Manual says "Prior to initial start-up of engine, pre-tension the tensioning roller as follows:
–   Apply torque wrench to hexagon socket of tensioning roller.
–   Turn (15 Nm) tensioning roller in tensioning direction to pre-tension the tensioning roller.
–   Tighten camshaft sprockets to 30 Nm.
–   Remove camshaft retainer -3391-. "

Just make sure your turning in the direction to tension belt. 

If still not looking good, you may have a faulty tensioner.

Regards

Gary

[auto79]

"when im applying a tension to the belt im doing it at 15 nm, anti clockwise, does this sound right to you"
elsa shows for that engine clockwise !

[bigtony]

hi all, thanks for all your replies, Ive stripped all the timing belt off and checked everything very carefully and found a problem with the tensioner roller , basically the center of the tensioner where the bolt goes through had a tight spot and wasn't turning fully freely, so i think the tension was set incorrectly and was slowly compressing the damper when it warmed up.The tensioner was a new genuine Audi part so bit annoyed to find it was at fault.Fitted new tensioner, warmed it up and all is well now.