piston damage (new pictures)

[40cpe]

That description sounds like piston slap. The piston warms up and expands.

I think a rod knock would get louder as the oil thins out.

[billfish]

Thanks for the reply-If it is piston slap, what is the cause and can I live with it if it does not get worse?

[Mark's 37]

I would run it as it is. If the clearance is tight enough to keep it quiet after getting the engine to operating temp, shouldn't be too bad.

[Bluebell]

Did you measure the old and replacement pistons to compare sizes?
It sounds like piston slap, because it goes away when the piston expands in size , as it warms up. A wrist pin is a double click on float just above idle, while the big end is a deeper knock under load.
It's a bit of a shame getting this result after doing all the work.

[billfish]

It is a shame but the idea in the beginning was to do a complete valve job to correct several leaky exhaust valves, That part was a complete success. The replacement piston was checked and was the same size as the old one. It runs and sounds great after a few minutes so I guess I'll keep my fingers crossed and if it changes I know what I have to do. Not fun but not the end of the world.

I assume piston slap is caused by a sloppy fit in the cylinder?

[flatford8]

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Sorry to hear it wasn't a complete success but I admire your attitude towards the problem. I own 2004 XXX pickup that I paid alot of money for. On a cold winter morning here in Maine, when I start that truck it sounds God awful! Good luck with that great looking car..... Mark

[Frank Miller]

Because you put a piston in an old engine there may be just a bit more clearance. When an engine is bored it is done to the size of the new piston. Like others said as long as it goes away when armed up it should not be a problem. At least you know there is clearance there.