WTF?? three torched pistons

[rjt500r]

Im sorry but Im really lost, in this post you say that the only thing that hasn't been changed out is the carb and cylinder .now your saying It cant be carb and the cdi hasn't been changed out. What parts are the common denominator that resulted in the three pistons having holes in them. The CDI ?

As far as engine components, yes only the carb and cylinder have been run on both engines. I don't believe the carb is the problem because it was on two other bikes and worked fine. Now the CDI which is mentioned here in a reply has also been on both engines. I know it has an air leak, the leak down test confirmed that the stator side crank seal is leaking air. The piston damage is unlike any piston i have seen damaged by lack of fuel. By the visual damage to the piston and plug it seems like the plug is acting like a blow torch and melting through the piston. I did not take any pics the last go around but when i pulled the jug off there were little balls of what used to be the top of the piston everywhere, as if you where cutting metal with a blow torch.

[Bowtie316]

Have you verified there are no obstructions in the exhaust pipe or silencer?

I would check for air leaks, compression ratio, squish, and verify timing before I jumped on and started riding again.  I had an Lt250r that burned holes in pistons like that, after the third one, I put it together with a stock piston and sold it.

[Jerry Hall]

I do not have time right now to explain what is going on.  You are missing something very basic that is causing some detonation,  then preignition and then run-away detonation and then then blowing a hole in the piston.

Use a timing light to check the ignition timing curve.



Were you riding the engine in the medium to high RPM range with the throttle position around 1/2 throttle opening or less?

Does the exhaust system have a spark arrestor?

Have you inspected your muffler for a broken core or anything that may be offering slightly more restriction than the original design intended?

An engine that is burning holes in the piston like you have pictured was talking to you telling you what it was getting ready to do.   Remember these sounds.  This is detonation.  Pre-ignition does not make any sounds.   Remember the sounds it was making intermittently the last 10 to 20 seconds before it quit.  This is intermittent detonation.  Remember the tone of the engine and sound the last 5 to 10 seconds before it quit.  This is run-away detonation and the engine is in the process of drilling the hole.  

The 10 minutes you rode the bike had nothing to do with the failure.  When you have something drastically wrong with the engine build or tune (air fuel ratio and or ignition timing) the above damage can be done it less than 30 seconds from the time the engine first began telling you what it was going to do, to the time that it did it.

[rjt500r]

i do not have time right now to explain what is going on.  You are missing something very basic that is causing some detonation,  then preignition and then run-away detonation and then then blowing a hole in the piston.

Use a timing light to check the ignition timing curve.



Were you riding the engine in the medium to high rpm range with the throttle position around 1/2 throttle opening or less?        Yes!!

Does the exhaust system have a spark arrestor?  No spark arrestor!!

Have you inspected your muffler for a broken core or anything that may be offering slightly more restriction than the original design intended? No i have not

an engine that is burning holes in the piston like you have pictured was talking to you telling you what it was getting ready to do.   Remember these sounds.  This is detonation.  Pre-ignition does not make any sounds.   Remember the sounds it was making intermittently the last 10 to 20 seconds before it quit.  This is intermittent detonation.  Remember the tone of the engine and sound the last 5 to 10 seconds before it quit.  This is run-away detonation and the engine is in the process of drilling the hole.  

The 10 minutes you rode the bike had nothing to do with the failure.  When you have something drastically wrong with the engine build or tune (air fuel ratio and or ignition timing) the above damage can be done it less than 30 seconds from the time the engine first began telling you what it was going to do, to the time that it did it.

 

there is no warning that detonation is happening. Arlan at led thinks this could be the risk of running av gas,as opposed to running race fuel, so this last time i ran 110 race fuel. No change, the only warning was just before it blows through the piston there is a 1/2 second raise in rpm's and then it's done.

[Jerry Hall]

there is no warning that detonation is happening. Arlan at led thinks this could be the risk of running av gas,as opposed to running race fuel, so this last time i ran 110 race fuel. No change, the only warning was just before it blows through the piston there is a 1/2 second raise in rpm's and then it's done.

I have never burned a hole in a piston that I was not given ample warning.......the problem was, I did not have the experience at that time to recognize what the engine was telling me.   I have made a lot of pistons look just like your pistons early in my career, before I learned to pay close attention to the slight changes in the sound of the engine and slight performance change as the process is set in motion.  

The AV-gas IS NOT THE PROBLEM unless the oil you are using is not mixing homogeneously.  Have you given your fuel the tried and proven "jar test"

I will ask this very important question again.   Were you cruising at medium to high RPM at partial throttle???

[Langbolt]

Do you have one of these attached to your motor ?

[rjt500r]

I have never burned a hole in a piston that I was not given ample warning.......the problem was, I did not have the experience at that time to recognize what the engine was telling me.   I have made a lot of pistons look just like your pistons early in my career, before I learned to pay close attention to the slight changes in the sound of the engine and slight performance change as the process is set in motion.  

The AV-gas IS NOT THE PROBLEM unless the oil you are using is not mixing homogeneously.  Have you given your fuel the tried and proven "jar test"

I will ask this very important question again.   Were you cruising at medium to high RPM at partial throttle???

Jerry, let me start with saying i appreciate you and all the others who have responded to my post offering info, suggestions and solutions. I do not in any way disagree or doubt anything you have said. I did answer your questions in my first reply they are at the end of your questions in the shaded box that was your original post. I apologize for the confusion. Yes i was riding at about half throttle at medium to high rpm.  
 
Let me also clarify the AV gas reference, Arlan did not imply that the AV gas was the cause of the detonation. He and i have had several discussions about the use of AV gas, while he believes it should work in my engine his feeling is it's marginal at best and pure speculation on his part that maybe i'm not identifying the detonation because of the AV gas.

I have not heard what i identify as detonation, pinging, knocking or rattle of any kind. Now i have only ridden this bike three times since i bought it in Feb each time less than ten minutes and each time with a piston failure. I'm not saying it's not detonating but that i have not recognized it was happening.

I also did a leak down and discovered an air leak at the stator side crank seal. I have replaced both seals, even though they are brand new and it has been holding 6lbs of pressure for the last two hours.

[xTHUNDERCATx]

how bad was that air leak? Was it not hold any pressure or how quick was the drop rate?

[rjt500r]

Do you have one of these attached to your motor ?

No i do not.

[rjt500r]

how bad was that air leak? Was it not hold any pressure or how quick was the drop rate?

It was real bad, it would leak out as fast as i pumped it in. I tore both covers off and i could then hear the air leaking out of the stator side seal.

[KASEY]

if that had that severe of an air leak,, refer back to my original post please,

[fearlessfred]

no need to reply to this ,but a leak that bad would have been noticed by anyone. You would not have gotten the idle to calm down. its only my opinion that the seal was damaged during the failure .An explosion entering the lower end could easily mess up some seals and I cant imagine why the new seals you had installed just before this failure would leak. .I wish the best of luck to you

[rjt500r]

no need to reply to this ,but a leak that bad would have been noticed by anyone. You would not have gotten the idle to calm down. its only my opinion that the seal was damaged during the failure .An explosion entering the lower end could easily mess up some seals and I cant imagine why the new seals you had installed just before this failure would leak. .I wish the best of luck to you

Well it did idle, there was no indication of an air leak. it started one kick it idled just fine.

[85drag250r]

was the spark plug loose each time the engine failed?

[rjt500r]

was the spark plug loose each time the engine failed?

No!