Well I finally got my motor apart and I could not believe my eyes. Whoever had the motor before me had it rebuilt. Its been bored 40 over, and has forged pistons. Well, the only thing wrong with it is a bent valve and ONE piston. The piston cracked in half seperating the top half from the bottom, this saved the rod from doing any damage. I made it out lucky. All I have to do is get my crank turned and a rebuild kit. Probably be better off with a 400 crank

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Bright red 87 GTA with 350 tuneport. Basic mods such as K&N filter, Flowmasters, Wells MAF, TPIS air foil, Accel 8.8mm plug wires with , Accel distributor cap and rotary buttons.Gutted cat. B&M Shift kit, 100HP shot Nitrous, soon to change over to carburator.

 

I'd have to admit that's one failure mode I've never heard of before. I assume you'll replace all the pistons.

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82 Berlinetta, orig V-6 car. Rescued w/86 LG4/TH700R with all harnesses, sensors, ECM, etc. 2.73 open. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, exhaust, paint, etc.).
57 Bel Air, my 1st car. Currently 396 .030 over, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

I only saw a piston failure like that ONCE before- in my Tractor's 12 HP Briggs and Stratton!!

Here's what causes it- PISTON SLAP! Little garden tractor engines tend to get a lot of "taper" worn into their bore, allowing the piston to rock around in there pretty good. Eventually, and I couldn't tell you exactly why, the piston separates top from bottom around one of the oil rings. And fortunately, nothing else usually gets damaged (you really dodged a bullet not ventilating the block!)

Forged pistons also fit more loosely in their bores to begin with, making the problem worse. Have the machine shop check out the bores for taper REAL CAREFULLY while they are in there.


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94 Firebird Formula M6- No options but Z rated tires. No mods over $10. 13.5@105.
79 Malibu "beater" w/junkyard 400 SBC, tweaked QJet 4bbl, finally a decent set of heads, a few other tricks. A maddening 13.000001 @ 108 on the motor with little traction. No nitrous runs with the new heads yet.
Grandma's old 78 Malibu (33K miles!) soon to have the powertrain from the 79 put in it.

"One of the last remaining QJet tuners on Planet Earth!"