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:

[thstone]

Quick summary;

Engine failed at 136,000 miles due to a single lifter failure.

Full professional rebuild of engine including replacement of all 24 lifters with brand new lifters (and replaced all of the collateral damage).

Engine failed again within 500 miles of highway driving due to ... wait for it.... lifter failure.

Why? Lifter carrier was worn and excess tolerance was allowing the lifter to wobble ever so slightly. Slight wobble resulted in uneven stress causing failure.

Another full professional rebuild along with more collateral damaged parts replaced including another set of 24 brand new lifters but this time included two new lifter carriers.

Second time is the charm if you don't find the root cause of the failure on the first go around. Lesson learned.

[Smallblock454]

Hi thstone,

i think lifter means hydraulic lifter, right?

If the lifter carrier was worn, how was that repaired? As far as i know the lifter carriers are an integral part of the cylinder head. So did you overbore and use a kind of sleeve?

Or did you replace the complete cylinder head?

Thanks & regards
Markus

[Gilles]

Originally Posted by Smallblock454

As far as i know the lifter carriers are an integral part of the cylinder head. So did you overbore and use a kind of sleeve? Markus

Hello Markus,
I believe that the lifter carriers are bolted into the heads (between the heads and the cams), they look like cast aluminum egg crates
.

[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

[BYprodriver]

Maybe the backfire was caused by a failing fuel pump. Check fuel pressure!

[flaps10]

Originally Posted by Gilles

Hello Markus,
I believe that the lifter carriers are bolted into the heads (between the heads and the cams), they look like cast aluminum egg crates
.

This. Lifter carrier bolts to the head.

Markus, your English is much better than my german.

If a backfire trashed engines I would think that would be a very common failure.

[Smallblock454]

Thanks flaps10 and Gilles,

found the carrier in the parts catalogue (number 15). So there is bolt on a hydraulic lifter carrier for each cylinder head. Now i understand how this works and can be repaired.



Thanks & regards
Markus

[Gilles]

Originally Posted by flaps10

This. Lifter carrier bolts to the head.

Flaps,

Thanks for the correction (honestly..), sometimes my spanglish surfaces and goes undetected, and I noticed that after a couple of beers with tequila it just gets worse… LOL

[Paul]

I had the same problem with my 2001 2.7, bent valves everything still in time. Happened while trying to start the motor.

Sold the motor to Jake with a request to tell me what happened. Never got a answer that made sense (stretched timing chain) Page 7 of the short lived engine thread.