24 bent valves

[Brett 986]

Hi all
Motor back together and running well, we dropped the sump and all was clear.
When I laid all the parts on the bench what we had was 12 exhaust and 2 intake bent valves. Only very slightly bent just enough to not to seat correctly.
There is evidence that the engine was running lean.
I laid out all the information I had and the mechanic had also done his own investigation with his Porsche peers. With the lack of distinct evidence of a failure we have put this damage down to a lean backfire the engine suffering a reverse rotation. The rotation was only slight just enough for the valves to kiss the Pistons.
One of the Chain guide tensioners was weak but still working so both were replaced. The tensioner could have some ownership in this affair but it is not conclusive.
I feel strange having pulled an engine to pieces and really fixed nothing, it certainly appeared to be an one off event.
Anyway if someone else has a similar problem I hope this string of comments can offer some help.
Thanks for everyone's thoughts
Cheers Brett

[thstone]

Originally Posted by Brett 986

...pulled an engine to pieces and really fixed nothing,...

You'll find the cause the second time around. At least I did with my engine.

[JayG]

Originally Posted by thstone

You'll find the cause the second time around. At least I did with my engine.

That's a comforting thought :ah:

[seningen]

Originally Posted by Brett 986

Hi all
Motor back together and running well, we dropped the sump and all was clear.
When I laid all the parts on the bench what we had was 12 exhaust and 2 intake bent valves. Only very slightly bent just enough to not to seat correctly.
There is evidence that the engine was running lean.
I laid out all the information I had and the mechanic had also done his own investigation with his Porsche peers. With the lack of distinct evidence of a failure we have put this damage down to a lean backfire the engine suffering a reverse rotation. The rotation was only slight just enough for the valves to kiss the Pistons.
One of the Chain guide tensioners was weak but still working so both were replaced. The tensioner could have some ownership in this affair but it is not conclusive.
I feel strange having pulled an engine to pieces and really fixed nothing, it certainly appeared to be an one off event.
Anyway if someone else has a similar problem I hope this string of comments can offer some help.
Thanks for everyone's thoughts
Cheers Brett

What year? The IMS sprocket on older cars is known to rotate. It is press fit.

Problem is -- you can't tell. I did one complete rebuild and ran and idled great.
Took it for a test drive and the first time I jumped on it, it christmas treed on me.
Bent valves -- all on one side.

Sure enough -- the IMS sprocket had rotated. That was an expensive lesson.

Mike