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Old 02-23-2009, 07:56 PM
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Broken piston

recently i blew both head gaskets in my 350 and when replacing them i noticed the number 1 piston was melted. when i took it apart i found out the 3 and 5 piston were both broke between the rings about a 1/4th of the way around the piston was broke off about a quarter inch deep what caused this any ideas? could it be a bad set of pistons? they are the speed pro hyp. flats. with the coated skirts

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Old 02-23-2009, 09:27 PM
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Engine was ran way too hot, or with way too much ignition timing, or with too low octane rating gas, or a multiple combination of these reasons. Head gaskets don't just blow, you forced them to blow somehow. Better take a look at the bearings, too. I'd bet that the rod bearings don't look very good anymore. Nothing was wrong with the pistons, something was wrong with your set-up.
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Old 02-23-2009, 09:45 PM
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im not askin why the gaskets went i kno it got to hot but it didnt get to that extreme heat to melt and break 3 pistons could heat cause them to just break like that
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Old 02-24-2009, 01:50 AM
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Yes, overheating the engine will cause that kind of damage because the overheating results in detonation and pre-ignition of the intake charge. This is what melted the top of the piston and broke the others, not just the temperature of the motor. The chambers and valves get hot really fast when there is no water on the other side of the metal to carry away the heat. Just 15-20 seconds of run time under a load with no water can do it. Hypereutectic pistons have absolutely no tolerance for too much heat, they just break.
You will have to figure out the root cause of the overheating to totally know what went wrong. Why did it get hot? Why did the head gaskets blow? Did it go into detonation first for some reason (too lean, too much timing, too low octane for compression ratio?) and that is what blew the head gaskets?
Was the radiator bad?
Need more info on what was happening in the few minutes before it blew up? What other parts are in the motor?
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Old 02-24-2009, 07:39 AM
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Quote:
Originally Posted by Casperdude898
im not askin why the gaskets went i kno it got to hot but it didnt get to that extreme heat to melt and break 3 pistons could heat cause them to just break like that
The deonation cause the piston break. Deonation is like a sledge hammer hitting top of the piston when gas fired instead of pushing the piston down the bore.
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Old 02-24-2009, 08:01 AM
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Melted piston=

it happened due to "pre-ignition",,,
a part or area in the chamber got so hot it became a model airplane "glow plug",,,,
the gas was lit and expanding while the piston was still low in the bore=mega hot and instant "kaboom" under load,,,
that instant shock wave/pressure rise destroyed the other parts...
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Old 02-24-2009, 08:37 AM
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When the motor was allowed to go into detonation the combustion chamber and piston top over het. this excessive heat and shock cause the top piston ring to heat up and expand. When the top ring gap closes up tight from expansion it grabs the cylinder wall. Then the piston goes down the cylinder and the locked right rips the piston ring land off the piston.

Loss of coolant, restricted coolant flow, severly restricted exhaust flow, lean fuel mixture, low octane fuel, excessive compression ratio, excessive timing, hot heat range spark plugs, carbon buildup (glow) incorrect nitrous setup (lack of fuel or fuel octane) any or all will cause detonation and overheating. Run away priignition folllows (much like a neucleur melt down) which is premature autoself -ignition on the compression stroke against compression. (This is what destoys engines in seconds. reguardless of what piston is in it.) The result is burned holed piston.
Fix the problem/cause and rebuild the motor with larger top ring end gaps if the motor is used under heavy heat load, Towing, supercharged, nitrous, Extended WOT, Marine, racing. Hyper pistons run a little hotter than conventional cast piston and like larger ring end gaps. Many builders refuse to accept this and blame the piston for ringland failures.

This did not happen by itself. You or something you tried did something to cause this failure.
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