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I have an F54 Block that I had bored .020 over by Budlong Motorsports Albuquerque. They gave me a new set of pistons and I rebuilt the Block... after about 2 years I had a head gasket blow so I tore the whole block down after finding water in the crankcase. When I pulled the pan, I found that 3 of the pistons had the tabs broken off at the bottom of the skirt.
When I asked the builder what happened I received no response. Anyone have an idea as to what might have happened? I am planning on rebuilding.. push the bore out to 87 or 88... do I have to go with forged? Or can I stay with billet?
Btw... FYI this is not my first build nor my first Z car... this ‘71 is my 5th ZCar and I’m dropping the F54 back in... once I figure out what to do..
Thanks...
Sageman
 

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Geez, that's nasty. It sounds to me like there was something misfit about the rebuild at .020 over that caused the broken piston skirts.

With your experience, I assume you would have heard piston slap if the bore was too big. On a straight 6, I can't see the crank weights interfering with the bottoms of the piston skirts.

You might want to take a really good look at the breaks on those pistons, and at the ones that didn't break. I'm wondering about a manufacturing error.
 

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You were detonating long term, inaudibly and broke the skirts off, and eventually blew the head gasket.

Very Common

There is no reason to go oversize each rebuild, that's American Engine Technology, not Nissan. Get out a set of mics and you will see your bores haven't worn at all, and just need a deglazing.
 
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