Bent exhaust valves oh my!

[Trackrash]

I'm in the process of going through the heads on my rebuild based on a '78 SC motor.

After replaceing the guides and re-surfacing the seats I found that FOUR of my exhaust valves were bent!

The weird thing is there was no evidence of burning, pitting, or grooving of either the valves or seats. They all looked like nicely worn in parts.

AND, there is no evidence of any piston to valve contact.

To be honest one of the valves did have a dark area on the face, but the other three looked like they were properly seated all around the seat. The guides were at the wear limit but not totally shot.

Question; is this common or very weird?

This valve had about .015" run-out.

Here are two valves that apparently were fully seated, but show .010" run-out.

What the seats looked like.


Thoughts? BTW I have no history on this motor beside "it ran when pulled".
And I just ordered 6 new exhaust valves.

[cgarr]

How did it run?? I just got a set of 2.7 heads in that all looked fine but went to grind the exhaust valves and 2 had about the same run out as yours. No evidence of any contact, first one I came across like this besides the obvious bent over valve that hit the piston ones.

[Trackrash]

When I bought the motor it was on a pallet. So no history other than it "Turns freely"

The only other thing was it had back dated exhaust and oil lines and it probably came out of a wrecked long hood. Not that that makes a difference.

[Steve@Rennsport]

Someone missed a shift and tagged the valves with the pistons.

[Trackrash]

Originally Posted by Steve@Rennsport

Someone missed a shift and tagged the valves with the pistons.

And kept driving like it never happened....

That was my thought. Probably happened long before the motor was in my possession.

It's just weird that three of the four seemed to still be properly seated.

[Steve@Rennsport]

Originally Posted by Trackrash

And kept driving like it never happened....

That was my thought. Probably happened long before the motor was in my possession.

It's just weird that three of the four seemed to still be properly seated.

I see this fairly often with heads that are sent here for rebuild. Most people don't notice and/or don't want to spend the money to fix it properly.

Just another can that gets kicked down the road.

[DRACO A5OG]

holy poop, that sucks a cancer on their house!

[Trackrash]

Originally Posted by DRACO A5OG

holy poop, that sucks a cancer on their house!

Actually not a real big deal to replace all the exhaust valves, in the big scheme of things. Just glad I noticed, and new valves are a good thing.

[DRACO A5OG]

Yes, lucky you found it now vs later.

I am having my moments of cursing their children and children's children on my 964 Cam Swap. I mean what the fudge, how hard is it to get close to proper timing of 1.25MM. I found it to be 1.10MM and 0.85MM and all rocker shafts were miss-aligned, no wonder she was a lazy dog.

[crummasel]

Are you sure your jaw chuck really runs true?
To measure valve truth and roundness i would rather use a collet chuck on a lathe...

The one valve having a dark area on its seat surface may really be bent or not having rotated during operation on an out of round valve seat.

[chris_seven]

I would think that a 3-jaw scroll chuck would run out by around 0.003" at the worst .

A good quality chuck like a Pratt Burnerd may be 0.001".

It would be quite easy to check with something like a 3/8" drill centre gripped in the chuck to see what is happening,

[manbridge 74]

I would think .010 would be noticeable rolling the valve on something flat like plate glass.

[Trackrash]

Originally Posted by crummasel

Are you sure your jaw chuck really runs true?
To measure valve truth and roundness i would rather use a collet chuck on a lathe...

The one valve having a dark area on its seat surface may really be bent or not having rotated during operation on an out of round valve seat.

I took that into account. That chuck is close, but not perfect to be sure.

I put all my valves in that chuck just as a double check. All the intakes and two of the exhaust valves ran true.

I considered re-facing the two not so bad exhausts, but for <$30 a pop not worth taking the chance. Especially when Porsche says replace any bent valves.

Originally Posted by manbridge 74

I would think .010 would be noticeable rolling the valve on something flat like plate glass.

Yes the four bent valves wobbled noticeably.

[prschmn]

Not hard to bend exhaust valves due to weak tensioners either--the cams retard when on decel and bango.