Tomas Wallin
Charter Member
Yes, and most likely because of the glowing spark plug...
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What caused my melted piston?
- Thread starter Tomas Wallin
- Start date
Yes, and most likely because of the glowing spark plug...
MikeyFIN
Competitor
Why did it start to detonate in the first place... if you lose a plug the one cylinder just dies and gives no energy to ignite anything.
So what raised the cylinder temp up to detonation?
A loose plug itself doesn´t do that IMO because it´s a blown engine..it doesn´t suck air as the intake is pressurized so therefore the A/F ratios didn´t go lean until the temp of the combustion chamber got uncontrollable.
MikeyFIN
Competitor
Tomas Wallin
Charter Member
Because of the plug not beeing able to transfer enough heat to the head and got too hot, same thing as running with too hot plug heat range.
At 175 psi, an MSD won't jump a .100" plug gap. .070" will barely run.
MikeyFIN
Competitor
Detonation can loosen the Spark plug.... by itself.
Believe me on this one the loose plug is not the issue here Id say it got loose because the detonation gave a hit on the threads. We´re talking of a 10 times pressure peak and force to the threads compared what they usually take.
Was it the first run after winter ?
Believe me on this one the loose plug is not the issue here Id say it got loose because the detonation gave a hit on the threads. We´re talking of a 10 times pressure peak and force to the threads compared what they usually take.
Was it the first run after winter ?
MikeyFIN
Competitor
That´s what I meant...therefore I agree with you that the loose plug wasn´t the cause but the head had an air pocket...
Tomas Wallin
Charter Member
It was the first run a few days after a 15 hour dyno session.
MikeyFIN
Competitor
Aka the same thing as a first startup... unless you kept the water in the engine while installing it back in the boat...
Tomas Wallin
Charter Member
What's the chance of an air pocket with free flowing water, dumps through two barely 1" dumps. Water temp was around 60F. Don't know the water pressure though more than it beeing more than 10PSI since that's where my warning light goes away.
Tomas Wallin
Charter Member
Nope, didn't drain it. Anyways, Idled for 10-15minutes, warm up passes at 3000 to maybe 4500rpm for 10-15 more minutes before the wot runs.
Tomas Wallin
Charter Member
The exhaust valve seat was loose... But I had to pry it loose.
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MOBILEMERCMAN
Founding Member / Competitor
Two things not mentioned yet.. Water pressure less the 15 lbs is trouble. This should be closely monitored. Exhaust could have a pin hole in it. Not enough to collect and rust but, enough to change compression.
MOBILEMERCMAN
Founding Member / Competitor
After 15 hours on the dyno what changed besides water pressure and exhaust ? Fuel?
MikeyFIN
Competitor
Valves looks good so no blowby´s on the seats that´s what I was after.
I stick with the air pocket issue.
Not an ignition crossfire like Daredevil hinted as a timing problem ?
Those seems to be the only 2 reasons which could lead to detonation IMO as the plug hasn´t blued or anyother part to speak of.
I stick with the air pocket issue.
Not an ignition crossfire like Daredevil hinted as a timing problem ?
Those seems to be the only 2 reasons which could lead to detonation IMO as the plug hasn´t blued or anyother part to speak of.
Tomas Wallin
Charter Member
The 10PSi light goes off at around 20-30mph so I guess it should be higher than 15PSI at 80mph+
MikeyFIN
Competitor
On a long term cooling issue yes.
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