It would be helpful to know the engine type and model year. If it's a recent diesel, I have the following comments to make:

I have changed a number of cambelts on these engines - without any problems - but I do not observe VAG's recommendations for tightening the nut on this tensioner stud. It is my belief that the stipulated 20Nm + 45 deg is excessive and will lead to a weakening of the stud through plastic deformation. The stud is unfavourably dimensioned at M10 into the cylinder head, necked down stepwise to M8 in the tensioner, which is secured with a 15AF flanged M8 nut.

I believe this problem emerged when VAG changed to the otherwise exemplary Litens tensioner which requires a smaller fixing stud to accomodate the self-adjust eccentrics. The earlier tensioners used an unstepped M10 stud - VAG presumably fitted a stepped stud in order to avoid making changes to the head.

It is also interesting to note that Continenetal include a replacement stud in their kit, wheras VAG do not. Both kits include new nuts.

My own approach with this engine is to re-use the stud provided it is undamaged and provided there is no evidence of non-elastic deformation of the stud whilst the nut is being tightened. I then tighten the nut to 20Nm + 20 deg when the tensioner is correctly set.

These are my own findings and do not constitute a recommendation. I have found other instances of stipulated tightening torques on VAG vehicles which, in my view are inappropriate and will lead to failure on re-use. I believe this arises from VAG's reluctance to use locking washers of any type on any fixing, and to rely on fastener stretch to give preload. This is not good for parts which require repeated disassembly without renewal.

I wish you the best of luck in resolving this problem with VAG - you will need it. I have found their unwillingness to admit to the most blatant design errors to border on the unbelievable.

659.

Edited by 659FBE on 05/12/2012 at 11:26

Briefly, the cambelt tensioner is held to the engine with a stud (threaded rod) and a nut. There is mounting evidence that this stud is prone to breakage following a belt/tensioner change. My observation and that of another poster would suggest that the design is marginal.

When the stud breaks or yields, the belt tensioner releases the cambelt causing the engine valves to hit the pistons. This constitutes major damage which is very expensive to repair properly.

It is my belief that this situation could be avoided by revised maintenance procedures.

659.

I should have said the tightening torque/angle is on the cambelt cover not the cam cover - my mistake. Have a look next time you unclip a belt cover on an 8 valve engine.

Whichever way you look at it, this design is unforgiveably marginal and calculations will show this to be the case for a stud of this length unless special material is used. I have also seen examples of damage where the M10 thread enters the aluminium cylinder head - the threads in the head pull out.

Failure of this component is not an isolated occurance as this Forum indicates. I know why it fails and we all know the consequences. I am not impressed by VAG's apparent indifference to these failures.

659.

The garage are to blame, replaceing the stud is a must. pay the £1.40 for a new one no argument whos fault it is then.

i had my car back all or 5 mins with a new vw engine as result of mine brakeing the stud turns out seeing the stud it had not been screwed all the way into to had to the end of the thread as should have been there was a small amont of thread on the broken side. also when looking inside the tensioner, the stud was m8 and the tensioner was alot bigger DIA which had marks inside of it which looks like the belt snached. this was not as belt was in one bit.. as saying it was caused by then stud not being correctly fitted.

engine itself was trash head gone pistion top showed very hard indents of valves which the damaged rods. engine replaced !

all for a defective stud, or the way the stud was fitted to tight or as mine not tight enough

its not easy getting vw into saying it was there fault. it took 3 months to get them to do the work!

Is this the same VW Group engine that had the issues with the injectors ? I seem to remember that eventually VW agreed to replace those where the fault had arisen.

There are many vehicles thus equipped, VW Golf, Touran, Passat, many Audis A3,4 6 Seat Toledo, Altea, Altea XL, any Skodas ? so this issue is not unique to the Passat.