Pinking

Hello guys, I've had a major engine failure with my 3.0 L V6 (74 000 miles, timing belt changed at 50 000) resulting in pistons hiting the sparking plugs and so on.

Audi confirmed that bolts on the back of the timing belt roller (not the center bolt at the front) connected to the left camshaft had unscrewed by themselves leaving that shaft desynced, if I understand it correctly.

I'm now looking at a cost of $8 000 for getting another engine installed.

Does anyone know if there are any reasons a mechanic would loosen these bolts during a timing belt change or other Long Life service?
Trying to figure out if this could be a service mistake or if the screws weren't torqued enough/locked during assembly. Has anyone heard of this happening before?

4Rings::G2 boosted::

The camshaft gears are not keyed, they are press-fitted onto the end of the cams and there is a single large bolt in the end of the cam that keeps the tension so that the gear doesn't slip. If you follow Audi recommendation for changing the timing belt, it calls for setting the engine at TDC, using the cam lock bar to lock the cam gears in place, then undoing the cam bolts and pulling the gears forward until they are released from the cams. At this point the tension on the timing belt is released and it's easy to replace it. Personally I never pull the gears free when replacing the belts and with a bit of experience it's really not necessary to do that, but I can see a mechanic pulling the gears free and then either not torquing the bolts back correctly or possibly using an old bolt (I believe Audi calls for new bolts each time) and this causing the gear to slip, changing the cam timing and causing the damage you describe. This sounds like a service mistake to me.

4Driver4

Why can't you just change out the bent valves?

squidix9

But quite possibly a valve or two or three.

Just get a replacmeent head for the side that is bad. Ask on here and you'll likely find one for a maybe $100-150.

Give Chris a jingle at Force5 and see what he has in stock.

Even with parts and labor at a decent shop(not dealer), less than $1k

budpalumbo

Are you talking about the chain tentioner bolts? As far as the amount of damage is concerned, it you were at speed, the engine is probably junk. That engine seems like if the belt cuts loose at low speed will just bend valves, but if at high speed the valves break, and bust the pistons up. If a spark plug is smashed, a valve had to be loose in there. Take it to an indy shop and have a used motor installed. I just bought a 99 a4q avant that threw a belt(and an engine) for under 3k.

4Driver4

3.0 has no chains.

4Rings::G2 boosted::

I think he was referring to the cam chains

4Driver4

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4Rings::G2 boosted::

Gotya, somehow I thought the head design was similar to the 2.8, guess not

Whomever

There is a TSB on this. I just did a timing belt on my 3.0 and checked it out with a tech at Rockville Porsche / Audi (I had overheard him speaking of it earlier). There are 5 torx bolts on the back of the camshaft pulleys that need to be torqued to 15 NM.

Big drag: I don't quite understand why you can't address the head in question???