A certified audi mechanic replaced the timing belt, rollers and water pump on my 2004 a4 3.0.

He used audi parts and audi tools including the proper cam clamps. I have confidence that he torqued everything correctly.

Everything started fine, and the car was driven locally for a few days. Then after about 8 hrs of total engine run time, the belt shredded longitudinally when after it rolled over the lower roller retaining lip and contacted the engine.

A straight edge was used to check roller alignment after it was apart. The only possible issue we found was the hydraulic tensioner arm appeared to be slightly canted toward the engine. This is going to be replaced when an entirely new timing belt kit is installed, but we are both hesitant to put the new kit in because there is nothing obvious that could have caused this problem and we don't want to do it a 3rd time.
He also checked for coked oil, gunk or anything else under the valve covers- nothing.

How did this happen?

 

if he didnt bolt the cam sprokets back properly that could of done, or the hydr. dampener didnt get replaced?

 

The hyd tensioner definitely did not get replaced. Only replacements were what came with the timing belt kit.

Shouldn't the tensioner have lasted longer than that, or do most people usually replace it along with the belt?

 

Sounds like the belt was either riding on the inner or outter edge of the water pump pulley at one point or another during its life. If the damper wasn't changed I can see there being enough slack to allow the belt to ride along the lip, this causing the tear you're describing within a short period of time.

I have re-used my damper once and when I had my 2.7T taken apart again, I was sure to change it. There was no way I was reusing it again for the third time. It's simply not worth the risk.

You said an Audi certified mechanic did the work - Was this at a dealership? I can't see them NOT replacing the damper and everything else under the sun for the ~$1500 or so they charge for a typical timing belt job on our cars. I also can't see them touching a timing belt kit you get off of ECS or another tuning place for fear of exactly this thing happening.

Also, you're going to need to verify that the timing did not get messed up when the belt was shredded.

 

dude as i see it those shops are all insured, tell them that they need to work something out or your going to seek legal aid, it is absolutely his fault. HE fucked up, have a look at the paperwork you signed and gave them. the shop probably didnt tighten the sprockets the same on both sides causing the leveling to be uneven that would cause the belt to hop over the lip if they were tightened properly this woul be almost impossible.

Ive even heard storys of dealers installing the relay on the outside of the tensioner and trying to run the car and ******* everythin up.

tell em to fix it for free OR your going to lawyer up.