blown plug and a hole in piston

[fiveOnick]

detonation usually will burn a hole in a piston, with 18cc domes you need race fuel. a air leak on the left side could be crank seal, bad or installed wrong, leaking base gasket, carb boot or gaskets. you definitly know one problem is the fuel, find the others before you ride again!!!

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Detonation does not simply just burn a hole in a piston without leaving other indications. I do not disagree that it should be on race fuel, infact it doesnt matter how high the exhaust port is. The higher it is the hotter the piston will be and the quicker it will detonate, with relevance to heat alone. There is more to it than compression. I have seen the crank seal burn a hole in the piston over and over and over. Either side can do it, but in my case the clutch side was the culprit because of that bearing failing. A lean condition does a cleaner job of burning up the engine. Detonation tears shit up. Look at the pics, this is detonation on alky. And there was not a hole in the top of the piston, nor was it caved or damaged from heat in the center at all.

He needs to post a pick of the piston, that would make troubleshooting much easier.

 

 

 

[ssanddemon]

This one is out of my old Ski-Doo Mach 1. I guess that last pass of 110mph in the dunes was too much for it. This sled wasn't jetted for sea level so it was running very lean as well as very hot, since sand doesn't cool the exchangers nearly as well as snow. If this is what Cadillac's piston looked like, I would say it was lean rather than detonating.

[dawarriorman]

This one is out of my old Ski-Doo Mach 1. I guess that last pass of 110mph in the dunes was too much for it. This sled wasn't jetted for sea level so it was running very lean as well as very hot, since sand doesn't cool the exchangers nearly as well as snow. If this is what Cadillac's piston looked like, I would say it was lean rather than detonating.

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But see thats the thing, if you are close to the edge of needing more octane, running lean can cause enough heat to start detonating. And once it starts, if you keep on the throttle, it keeps getting worse. And that could very well be his problem too.

 

Just out of curiosity, what fuel were you running when it did that?

[ssanddemon]

But see thats the thing, if you are close to the edge of needing more octane, running lean can cause enough heat to start detonating.  And once it starts, if you keep on the throttle, it keeps getting worse.  And that could very well be his problem too.

 

Just out of curiosity, what fuel were you running when it did that?

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Yup, I see your point, but this pic shows lots of heat around the rings, scuffing, and obviously the hole, but not the general pitting all over the piston face like we usually see with detonation. I think it's a textbook example of a lean but not detonating blown up piston. I was running this POS on crap gas, left over from the previous winter. Sled motors are real low compression so it takes a lot to make 'em ping; like an outboard boat motor.

[dawarriorman]

Yup, I see your point, but this pic shows lots of heat around the rings, scuffing, and obviously the hole, but not the general pitting all over the piston face like we usually see with detonation. I think it's a textbook example of a lean but not detonating blown up piston. I was running this POS on crap gas, left over from the previous winter.  Sled motors are real low compression so it takes a lot to make 'em ping; like an outboard boat motor.

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Outboards can have quite a bit of compression. I worked at a boat shop this past summer. There were some that had 180 lbs. I would say you have a combination of the two from that pic. Lean made it hot, enough to start detonating, and thats why the center of the piston burned up instead of the side. Once the piston started to burn the detonation went after the center of the piston. If you had been jetted right it never would have happened probably, cause it. It happens fairly often. Ive seen it on several boat motors where the carbs got clogged. Piston looked the same.

[fiveOnick]

It makes sense that an engine would start to preignite when it goes toward a lean state. But still the reason it is detonating is because it was too lean. One can lead to the other but not vice versa. My case was purely detonation, in fact the motor was rich. There is not sign of melt on the top of the piston because it was not lean and did not build up a concentration of heat in the center, as you said for the detonation to take over. It stripped all the porcelin off my plug, but all the metal is intact and looks sharp as a tack. The porcelin is obviously what beat the piss out of the top of my piston. If a motor is detonating for a longer period of time then the porcelin usually goes and does what it did to mine, if it only starts as the engine leans out then the plug usually just melts and you see the result. Not to mention you should hear detonation, hell I could hear it like crazy. Sounded like the engine was coming apart, I really feared for the boys if you know what I mean. For this case I would guess its not a question of whether the motor melted because it was detonating solely, but was it lean causing the resulting. The two look completely different as can been seen by both pistons pictured. If a picture of the piston could be posted I am sure the problem could be further broken down, otherwise all we can do is speculate.

[99Banshee]

....I dont know wtf you just said..but it sounds good to me