Can Dual mass flywheel cause cambelt tension bolt to snap?

[keithyt]

Hi, am new here and been looking through the threads, learnt a lot already! reason I am looking is I have a very bad position re my 2006 2.0 TDI sport, 160K miles.

About 6 weeks ago the car would not start and the local garage fitted a new fuel pump and cam shaft sensor. To do so they had to move top of cambelt and reset tension after. As soon as I got the car back there were was a shudder when accelerating, esp in 5/6 gear, this had not occurred before, there was also a lot of road noise that was not there before. I advised the garage and they suggested to check the tyres, I did, one was misshapen and I changed 3 in total and got tracking done. The affect of the shudder was still there (but not as noticeable with the new tyres) so I took it back to the garage who took car for a test drive and said it was the DMF deteriorating. I drove for another 2-3 weeks while weighing up if I should replace the DMF or bite the bullet and replace the car.

Then while driving the engine lost power and the cambelt tensioner bolt had sheared. As you can imagine the damage to the engine is severe. The garage who fitted the new fuel pump also replaced the cambelt 17K and 18 months ago, so it is quite recent. Now I think there is something they must have done wrong (over tightening maybe) to cause the tensioner failure. But they are saying it is likely that DMF being deteriorating would have been off centre and hitting the tension bolt causing it to fail.

So my questions if any one can help me are: Is it really possible for the DMF to damage the tensioner bolt so it fails completely? can the mechanic really come to a diagnosis on the DMF from 1 test drive? What other reasons could there be for the bolt to snap?

Really appreciate the benefit of anyone's experience who has come across this type of thing before. thx

[Crasher]

The reason the tensioner stud snapped is both it and its nut are one time only (TTY, Torque To Yield) fasteners that MUST be replaced each time they are released after the torque angle has been applied. This is why good and genuine cam belt kits include the parts. This problem is SO well known on the BKD engine that it is surprising anyone still makes this school boy error.

[keithyt]

Hi Crusher, thanks for that, looks like I am in for a hard time getting compensation for the damage this has caused. Do you have any links to sources that explain that the bolt and nut are use once only I can use with the garage to show they made the error? Anything by VW themselves would be brilliant. Or could you suggest where I can look for that type of document?

thanks again.

[Crasher]

It is mentioned in different parts of the VAG workshop manual which is confidential and so even if you got hold of a copy or print out, it would be inadmissible as evidence because you shouldn't have it, catch 22. Sometimes the text gives the torque (25Nm +45 degrees) and says replace the nut and stud, other sections for different cars with the same engine just say the torque spec BUT an accepted fact in the trade is that if a fastener shows an angle after a torque, it means those fasteners must be replaced and it is the rule we work to here, in fact that rule tends to be if you remove a bolt, you replace it, earlier today one of my techs was doing a CR TDI cam belt and put three new cam sprocket bolts in and torque + stretched them and then realised he hadn't double checked the timing which proved to be minutely out so we had to wait two hours for more new bolts. The tensioner stud is shown as being 10Nm torque in one section and 15Nm in another which is I presume means the torque a new stud should be set to in the head but this is highly confusing as the info for replacing the stud states it should be only nipped down with thread lock and that same info could confuse some people to set the tensioner nut at 10Nm or 15Nm. In a TPI of the subject, it also points out that a new stud should be installed so that the M10 to M8 transition chamfer is below the head surface so that the tensioner hole does not load up on this radius which causes the stud to break and that the hole in the head may need tapping out deeper to achieve this. The whole subject boils down to experience. It has been suggested that the stud only needs changing if the people who did the last belt overtightened it, but how on earth are you supposed to know that? SO, amongst those int trade and clued up owners it is getting very well known that the best course of action is to replace it, as the part costs £1.38 from VW and it alarms me that a trader does not know this.

[keithyt]

thanks again Crasher. I do not think because something is confidential it can be discounted as evidence. Do you know how I could get a copy? Online anyway?

[Crasher]

PM me your email and cars reg and I will send you what exactly applies to your car plus what else I can find on the subject.