LTCMontana

I'm in Iraq. Car is in Montana. We've pulled apart many 2.5's and 2.7's but never my 968 motor.

Friend and mechanic had ordered a belt kit for my car and while driving it yesterday, he thinks the belt let go.

Isn't the 3L motor made so the valves won't hit the pistons?

RajDatta

No, it is an interference engine. Plenty here have gotten bent valves from this failure. The worst case scenario I have personally seen is all 8 of the exhaust valves getting bent. This was one of those cases where the timing belt was shearing its teeth off and the driver kept trying to start the car. So, a few teeth would shred and then the next set of teeth would grab hold of the lower cam pulley. This would keep happening and the top and bottom end would keep getting misaligned and in the end he ended up bending ALL his exhaust valves.
Like I said, this is the worst I have ever seen. Your situation might not be so bad if he stopped the car right away. Start with a compression check. This would tell you which cylinders have no compression and you can do the math from there on the damage you might be looking at.
Raj

LTCMontana

Raj,

"Other than THAT Mrs. Lincoln, how did you like the play?"

Thanks for the info though.

Guess the money for the repaint is headed for the engine.

mtcarrera

The car was cruising at 45 mph, probably 2000 rpm. Went off like a switch had been turned. It's gonna be what it's gonna be. Do I understand from the above post that only the exhaust valves make contact? Doesn't matter much, because I won't order parts until I survey the damage.

RajDatta

Not, not at all. I have seen intake valves bent as well. These pistons do have some valve relief but not enough to avoid damage. That was just an example of worst case scenario I have personally seen. I should have some pictures of damage on another engine I worked on. I will post some pictures.
Raj

RajDatta

Here is a picture of piston top with valve relief. I have the pictures of the head from this engine with bent valves at home. I will try to post them tonight.


Regards.
Raj

mtcarrera

Yeah, I expect that they're all hosed. Won't be able to get to it for a couple of weeks. Raj, the only aspect of this engine I've never worked on is the variocam apparatus. Any lessons learned?

Dave
1978 928 track car
Broken 968

RajDatta

To do variocam timing right, you need a set of dial guages, a j pipe to pressureize the tensioner and an air compressor. Nothing fancy like people will make you believe. The procedure is well documented in the owner's manual and most DIYer's should be able to handle it. If you are not that **** about getting the correct timing and are happy with your current timing/want to leave that part as is, you can either lock your exhaust cam pulley or mark the backing plate so when you reinstall everything, you atleast get your old timing back. That is the only tricky part.
The rest is fairly simple. I have plenty of pictures on this thread.
http://www.clubstuttgart.net/showthread.php?t=768
That head had destruction from a snapped cam chain as you see in one of the pictures. We had the head reburbrished with new valves, new guides and a 3 angle valve job, also swapped the tensioner pads, used a new chain (like we had a choice, lol).
20K plus miles and running strong.
Raj

RajDatta

I found the pictures of the head with all 8 bent exhaust valves.



Yuck!!

Much cleaner


Regards.
Raj