Sands Posted September 6, 2011 Report Share Posted September 6, 2011 What do you think about these pictures? Could it be detonation? The right spark plug is damaged. Quote Link to comment Share on other sites More sharing options...
252wheelieking Posted September 6, 2011 Report Share Posted September 6, 2011 Looks like detonation to me. Whats your set-up? Quote Link to comment Share on other sites More sharing options...
Sands Posted September 6, 2011 Author Report Share Posted September 6, 2011 Looks like detonation to me. Whats your set-up? 421 Cheetah Cub, 22cc domes ( live at sea level ), PWK39 178 jetted, VForce 3, +5º timming, Shearer SBIF. Quote Link to comment Share on other sites More sharing options...
252wheelieking Posted September 6, 2011 Report Share Posted September 6, 2011 (edited) What fuel are you using? Do a compression test to make sure your fuel has enough octane. Edited September 6, 2011 by 252wheelieking Quote Link to comment Share on other sites More sharing options...
Sands Posted September 6, 2011 Author Report Share Posted September 6, 2011 What fuel are you using? Do a compression test to make sure your fuel has enough octane. 98 octane. I didn't measure que compression after building the engine... It it happens to you, what would you do? New domes? New pistons? Quote Link to comment Share on other sites More sharing options...
Pasi S. Posted September 6, 2011 Report Share Posted September 6, 2011 Because you live here in Europe, I´m allmost 100% sure that your gas is not 98. Our Neste 98 is 87,2 to 87,7 MO and AKI is 93,2-> -Pasi S. Quote Link to comment Share on other sites More sharing options...
Rotax Raptor Posted September 6, 2011 Report Share Posted September 6, 2011 Take a magnet and check to see if you have any pieces of steel embedded in the top of your damaged piston. That almost looks like something is coming from your lower end and up through your transfers. Quote Link to comment Share on other sites More sharing options...
EvilBanshee Posted September 6, 2011 Report Share Posted September 6, 2011 Well it sure as hell aint lean! lol 22cc domes is more then enough for 98 octaine? I think it might be something eles. 91 pump fuel would do 22cc domes. Look like a piece of bearing or metal of some sort got in their and bounced around a few times. See if your rod bearing it getting loose or worn out. Quote Link to comment Share on other sites More sharing options...
pabansheematt Posted September 6, 2011 Report Share Posted September 6, 2011 Your running it out of fuel. Thats why the spark plug broke. It's to lean. Quote Link to comment Share on other sites More sharing options...
Sands Posted September 6, 2011 Author Report Share Posted September 6, 2011 Because you live here in Europe, I´m allmost 100% sure that your gas is not 98. Our Neste 98 is 87,2 to 87,7 MO and AKI is 93,2-> -Pasi S. In Portugal we have 95 and 98 octanes. Quote Link to comment Share on other sites More sharing options...
Sands Posted September 6, 2011 Author Report Share Posted September 6, 2011 Take a magnet and check to see if you have any pieces of steel embedded in the top of your damaged piston. That almost looks like something is coming from your lower end and up through your transfers. OK. Tomorrow I'll do that. Thanks for the help. Quote Link to comment Share on other sites More sharing options...
Sands Posted September 6, 2011 Author Report Share Posted September 6, 2011 Well it sure as hell aint lean! lol 22cc domes is more then enough for 98 octaine? I think it might be something eles. 91 pump fuel would do 22cc domes. Look like a piece of bearing or metal of some sort got in their and bounced around a few times. See if your rod bearing it getting loose or worn out. On both pistons? I would believe on it if it only happend on one cylinder... Quote Link to comment Share on other sites More sharing options...
Sands Posted September 6, 2011 Author Report Share Posted September 6, 2011 Your running it out of fuel. Thats why the spark plug broke. It's to lean. Maybe... If you were me, what would you do? New pistons or just tore it a little on the top? About the domes, I will certainly buy a new set. Quote Link to comment Share on other sites More sharing options...
252wheelieking Posted September 7, 2011 Report Share Posted September 7, 2011 I could be wrong but with 22cc domes for a 421 is suppose to be ran on race fuel. To be on the safe side, if I was you I would buy 24cc domes & run the pump gas that your getting from your local gas station. From the looks of it, it looks like your detonation from low octane. If your going to buy new domes try the 24cc domes. I dont think that your crank is shot from the looks of the piston & domes. You could pull the cylinder off & inspect the crank for piece of mind. Good Luck Quote Link to comment Share on other sites More sharing options...
EvilBanshee Posted September 7, 2011 Report Share Posted September 7, 2011 On both pistons? I would believe on it if it only happend on one cylinder... I dont think both sides are damaged? I Think hes just talking about one side. I know what lean looks like. Judging by those plugs she is FAAAATT. Quote Link to comment Share on other sites More sharing options...
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