Pics of pistons

[Tom Sharpe]

A70Duster at aol.com wrote:

> << 10/4 to Greg. Go to http://www.mtco.com/~twsharpe/images/Piston2.jpg >>
>
> Question to Tom.
>
> Judging by the pin location in the oil rings, I assume that you have a SBC
> piston with a 6" rod.  I also assume with a custom setup like that, you
> gapped the rings.   Yes
>
> What compression was the engine and how was the engine used (daily driver,
> drag strip)??  Street thriller - had 5K miles on it when it failed.  10.25-10.29
> compression. New injectors and fuel pump - finally got power to 6K rpm w/o going
> lean.
>
> First, what did you gap the rings at?  <.035, zero gap second > From the damage,
> it looks like the top ring gap was too tight, the extra heat expanded/butted the
> top ring together
> and the weakest part of the piston broke off (valve relief to top ring lan)
> when the top ring was "seizing" in the bore.  <<  Maybe but....   Pistons
> ceramic coated along w/ combustion chamber also causes heat to flow to the top
> ring.  Problem was block distortion, the head studs were pulling the bores out
> of round. I don't have pictures but there are zebra stripes at the top of the
> bore next to the center head studs, about 1/2" wide shinny strip at the stud
> location w/ dark (non touching) areas on both sides about 3/8" wide followed by
> normal wear areas. These were in the top 3/4 - 1" of the bore - and it was
> bored/honed w/ torque plates.  Might have gotten by w/ 5.7 rods.....

Anyone want a block cheap.  Just wanted to say that finding the weak link is more
expensive than forged pistons.

>
> If that is the case, then blaming a hypereutectic for breaking like it did is
> like blaming a hand tighten rod bolt that failed.
>
> Looking at pic
>
> http://www.mtco.com/~twsharpe/images/Piston1.jpg
>
> it is more obvious that there are "detonation" imprints on the piston. << ???
> please explain >> Again
> assume a SBC, there is damage in the quench area.   Did you notice (audible)
> detonation/pre ignition?  No knock - 93 no-lead. Engine never saw full throttle
> under 3500 rpm.  some damage is crow bar marks getting the heads off --- I was
> in a hurry.

Advance curve was conservative - could make it knock by adding 6-8 deg. spark
advance.

>
> Did you have open chamber heads?  And did you know what the quench height was?

Brodix -8's,  deck was +.003 to +005 , quench was ~ .035  never touched the heads.
I've seen others w/ marks from the sonic flow towards the center of the CC.

>
> Sorry for the 20 questions.  I'd would rather learn from people's past
> experience.
>
> Thanks,
>
> Mike
>
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