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Looking for thoughts on a valve seat failure and a recommendation for an engine builder/ machine shop in Orange County, CA.

After sitting for 10+ years I finally fired up my engine a few weeks ago. It sounded good for 10 minutes then I had a bad clatter in the valve train. At first it appeared to be a loose rocker but there was weird interaction with the valves of cylinder #4. I popped the head off and found that the exhaust seat had come loose!


While dancing around, the seat also made some deep marks on the piston head.


My gut tells me the piston is trashed and needs to be replaced. I have a friend that says I should repair the head and go as is. I don’t know if anybody on this forum has an opinion…. But, when is a “witness mark” a catastrophic failure in the waiting?

Please opine away....




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It's difficult to see from the photo how deep the impression is but if the piston is forged you can likely polish off the sharp edges and reuse it. I've seen worse. Forged pistons are very tough. I would definitely have it checked. If you can buy a single exact duplicate I would go that route because it's probably cheaper than paying a pro to rework and check that one.

I would be more concerned about the cylinder head(s). Valve seats typically don't just fall out. Cracked head, overheated, poor initial installation...?

It doesn't take long to damage bearings. You probably did not damage the rod but it's possible the bearing got pounded a little. Same for the small end.

If time or budget is an issue or you feel confident in the rest of the engine, you can deal with the piston top, have the head repaired, reassemble everything and likely be OK.

Or, go through the process of having both heads checked, removing the piston and rod and having them checked, serviced and assembled.


The piston is quite capable of absorbing that impact and surviving fine.

The only reason to be running a valve seat would be if that is an aluminum head? Do not have anyone install hardened seats into your iron Ford heads. You DO NOT need them. Ford uses a harder cast iron then other companies like GM.

I can't quite identify the head from that picture but it looks aluminum and resembles the exhaust port of the Ford Motorsport "high port" heads.

You want to verify that the connecting rod didn't get bent (I doubt that it did) and the rod bearing is ok.

Those seats used in those heads are the same as in the Chevy aluminum heads. They aren't the fancy "Stellite" like in the 427 Ford heads and because of the source, are inexpensive and fairly plentiful.

The issue is going to be if the cylinder head itself is showing signs of damage where the seat normally sits.

It is on the unusual side for them to come loose and fall out like that unless the head has an issue in that area. That's really going to be the main concern.

The design normally pulls the seat in, not push it out.

Those are dished pistons with, it looks like 61cc chambered heads? Is that engine a "stroker". Leave the piston if you can. Unless you are going to run 24hrs at Lemans, you will never see an issue with it.

Last edited by panteradoug

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