Hole in piston

[xcentric5]

Motor is freshly rebuilt about 3 hours on it. I thought i fowled a plug while riding it. Removed the plug and seen it messed up, after that did a compression test no compression at all. Found out that piston has a huge hole in it. Any thoughts on what could of happened. It had brand new 65mm wiseco piston and it has a 4 mil stroker crank. Could it have been from riding it for about 45min to an hour with a fowled plug? Also it doesnt appear to be hitting the plug becuase the prong is not smashed against the center of the plug.

[supersider]

Motor is freshly rebuilt about 3 hours on it. I thought i fowled a plug while riding it. Removed the plug and seen it messed up, after that did a compression test no compression at all. Found out that piston has a huge hole in it. Any thoughts on what could of happened. It had brand new 65mm wiseco piston and it has a 4 mil stroker crank. Could it have been from riding it for about 45min to an hour with a fowled plug? Also it doesnt appear to be hitting the plug becuase the prong is not smashed against the center of the plug.

 

i had same problem it caused from being way to lean!!!!!!!!

[Screaming Yellow Zonker]

Yup that is detonation. Causes: lean condition, too much timing, to low of octane fuel and or excessive engine heat (beyond normal).

 

did someone forget to rejet for the 4mm?

[someone82]

Air leak = lean out condition = hole in piston; did you leak down the motor after it was rebuilt?

[xcentric5]

Yup that is detonation. Causes: lean condition, too much timing, to low of octane fuel and or excessive engine heat (beyond normal).

 

did someone forget to rejet for the 4mm?

 

I put 100 octane fuel in it. Definitely could be from running to rich. I just got thing on wednesday dont know if the previous owner forgot to rejet. Such crap huh had it for less then a week and i got a hole in my cylinder. thanks for the help.

[AKheathen]

that's not from running rich. what was your squish? what is the dome size? ported, spacer plate, or cut domes? what does the other side look like? could've developed an airleak somewhere

[Rodneya]

Yup that is detonation. Causes: lean condition, too much timing, to low of octane fuel and or excessive engine heat (beyond normal).

 

did someone forget to rejet for the 4mm?

 

 

That is not from detonation, but preignition probably caused by an air leak. What does the other side piston and plug look like?

[xcentric5]

That is not from detonation, but preignition probably caused by an air leak. What does the other side piston and plug look like?

 

The other piston is totally fine no scratches and rings are also fine.

[AKheathen]

so, no pitting, on the other? what's the squish?

[xcentric5]

so, no pitting, on the other? what's the squish?

 

Yea no pitting on the other cylinder. I'm going to do a squish test after i receive the new piston. Whats a good squish clearance?

[Rodneya]

You need to find the cause of the meltdown before rebuilding or it will happen again.

Air leaks, blocked jets or running the float bowls dry at WOT can cause this.

[AKheathen]

well, that varies from build to build. but, .050-.055 is a nice, conservative/safe squish, whereas some push smaller than .030 and you get piston slap below .020. generally, you shoot around .035-.045. what size domes you run, or you have a cut stock head?

[crustydemon]

I also had the same thing happen caused by a partially blocked main jet but you really should have done a leak down test before you tore it down just to verify if you had an air leak or not. Check your carbs over real good and post your jet sizes, did you notice any cracks in your intake on that side, was everything tight? If your jetted right on the edge of lean, a small air leak is all it takes.

This happened within 5 min of riding.

[xcentric5]

well, that varies from build to build. but, .050-.055 is a nice, conservative/safe squish, whereas some push smaller than .030 and you get piston slap below .020. generally, you shoot around .035-.045. what size domes you run, or you have a cut stock head?

 

The head was reshaped for the extra stroke.

[xcentric5]

I also had the same thing happen caused by a partially blocked main jet but you really should have done a leak down test before you tore it down just to verify if you had an air leak or not. Check your carbs over real good and post your jet sizes, did you notice any cracks in your intake on that side, was everything tight? If your jetted right on the edge of lean, a small air leak is all it takes.

This happened within 5 min of riding.

 

My jet sizes are 340 for the mains and 30 for the pilots with the 2nd notch on the needle. No cracks on the intake and everything was tight when i was taking it off. Yea im really kicking myself for not doin a leak test before i took it all apart.