Detonation melted my piston..... but what caused the detonation?
05-22-2015, 07:25 AM
#51
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Join Date: Aug 2012
Location: Collierville, TN and Pickwick Lake
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To the OP, there's a complete 496 in the swap shop for less than $6,000. your exhaust should work. EFI, decent power, closed cooling, ready to drop in and go boating.
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05-22-2015, 08:08 AM
#53
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Just thought I would throw this your way... buddy of mine is selling a built 496. Never ran. He put alot of time and money into this. Great price.
http://www.offshoreonly.com/forums/s...-ignition.html
http://www.offshoreonly.com/forums/s...-ignition.html
05-22-2015, 09:06 AM
#55
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05-22-2015, 09:35 AM
#56
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i got on this thread late but this is my take on the failure.first off,the head gasket is not a multi layer steel gasket,it is a composite marine gasket with a stainless fire ring.even if it had a mls gasket it would have failed.i believe a lot of things were wrong causing the failure,the total timing was more than 31 deg,the fuel mixture was to lean,the spark plug was to hot and could not take enough heat from the combustion chamber and it might have been cross firing.if you put all these things together and lug the engine for more than a few seconds detonation will set in.continuing to run the engine after feeling the misfire did not help matters.a hyperutectic piston can not take detonation as well as a forged piston and that was also a factor in the failure.with the block being bored .060 over it is time to start over with another engine.it is a nice looking boat and worth cleaning up and installing a good engine.good luck with the project.
05-22-2015, 10:22 AM
#57
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I've installed a few Fel Pro MLS gaskets, Cometic MLS gaskets, as well as standard head marine gaskets, like the 17040, 17048, etc.
For one, you arent getting a true Multi layer steel gasket for 32 bucks each. If so, I'll buy them all day long at that price. Felpro and cometics are nearly 100 bucks a gasket for standard thickness, and cometics get very expensive as they get thicker. I know the interweb shows that 17040 as MLS type, but I've learned you cant always trust what the interweb says.
Only reason I am debating this, is because I'd hate for the OP to go thinking his problem was due to his RA finish on the block/heads, when in fact, he has other issues.
Like, for example. A gen 6 block, should not be using the 17040 gasket. The 17040 has the coolant hole that you do not want on a Gen 6 block. Why? because the coolant will from right in the front of the block, and right out the thermostat housing. Take a look at the pic of the front coolant holes on a 1071 MLS, and a 17040. This right here could have been his whole issue.
For one, you arent getting a true Multi layer steel gasket for 32 bucks each. If so, I'll buy them all day long at that price. Felpro and cometics are nearly 100 bucks a gasket for standard thickness, and cometics get very expensive as they get thicker. I know the interweb shows that 17040 as MLS type, but I've learned you cant always trust what the interweb says.
Only reason I am debating this, is because I'd hate for the OP to go thinking his problem was due to his RA finish on the block/heads, when in fact, he has other issues.
Like, for example. A gen 6 block, should not be using the 17040 gasket. The 17040 has the coolant hole that you do not want on a Gen 6 block. Why? because the coolant will from right in the front of the block, and right out the thermostat housing. Take a look at the pic of the front coolant holes on a 1071 MLS, and a 17040. This right here could have been his whole issue.
05-22-2015, 10:27 AM
#58
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Actually, just saw he has a Mark IV block, so that would not be an issue with the cooling holes. For some reason in my head, thought he had Gen 5/6 block....either way, its good info so I'll leave it here.
Last edited by MILD THUNDER; 05-22-2015 at 10:42 AM.
05-22-2015, 04:28 PM
#60
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I would still like to hear about the carb, what size of jets, power valve or blocked. I melted a ring landing myself on a brand new, not rebuilt engine with less than 40 hours. I used the carb off a 496 stroker I built, but jetted up a few sizes I thought. Took it apart and I bumped the rears and put the wrong ones up front and ended up jetting down.
