Hole in piston. Lean or low octane?

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Knotical

Knotical

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Looking for a little help determining if my piston failure was caused be running lean or by low fuel octane. Anyone have pointers to tell one from the other?

G340rc running a ported Bartolone top and, quickdraw pipe and WT1257 carb. Fuel was 92 octane E10 with Amsoil Dominator mixed 25:1. Engine had a little over an hour on it.

Any input is appreciate.
 

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Can you show your spark plug? The next question is the oil, not familiar with the amsoil dominator, gonna Google it. OK it's available as a regular oil and a 2 stroke oil....you did get 2 stroke oil.... almost looks like something broke through causing hole. I recently blew up a raminator 49 cc most likely overheating, but mine broke piston ring causing no compression. Maybe show the combustion chamber/head too.
 
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kg5000 said:
Would the scoring on the sides of the piston indicate lean or wrong type of two stroke oil?
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I'd be surprised if the oil isn't good. I know people love to debate what the best oil is but I'm sure dominator is sufficient for these little engines.

I'm pretty sure lean damage tends to show most at the exhaust port side because of thermal expansion, so I'm leaning towards the scoring being from metal debris, but I'm totally open to someone more experienced teaching me otherwise
 
Says 2 stroke on bottle right. Not to concerned with fuel so much and how do you mix..... I use a chart to determine oil/fuel ratio and a mixing bottle that has marks to show amount.
 
Mick Mars said:
Can you show your spark plug? The next question is the oil, not familiar with the amsoil dominator, gonna Google it. OK it's available as a regular oil and a 2 stroke oil....you did get 2 stroke oil.... almost looks like something broke through causing hole. I recently blew up a raminator 49 cc most likely overheating, but mine broke piston ring causing no compression. Maybe show the combustion chamber/head too.
Click to expand...
 

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I thought I had heard a touch of pinging at idle, but I chalked it up to excessively lean running and I didn't hear it again after swapping out the plug and carb
 
Mick Mars said:
Says 2 stroke on bottle right. Not to concerned with fuel so much and how do you mix..... I use a chart to determine oil/fuel ratio and a mixing bottle that has marks to show amount.
Click to expand...
Yeah Dominator 2 stroke oil. Got it from my local dirt bike shop.

Mixed with a measuring cup for a 25:1 ratio. Just dumped into the gallon gas can and shook around pretty good
 
Doesn't look like a lot of oil in engine, take a look at my raminator thread, aye captain she can't take no more. You can see the black oil carbon build up on piston top. Your piston really clean. Looks like it's really lean. I'm not a expert but seems like you're mix not having enough oil. You mentioned new carb also, so it might not be tuned correctly either. Once one of the other good folks on here takes a look maybe they can give a better idea. Sorry but we've all been in your situation too . Hope you have better day with next one. I'm pretty curious about what others will think. You seem to have mixed correctly.
 
Mick Mars said:
Doesn't look like a lot of oil in engine, take a look at my raminator thread, aye captain she can't take no more. You can see the black oil carbon build up on piston top. Your piston really clean. Looks like it's really lean. I'm not a expert but seems like you're mix not having enough oil. You mentioned new carb also, so it might not be tuned correctly either. Once one of the other good folks on here takes a look maybe they can give a better idea. Sorry but we've all been in your situation too . Hope you have better day with next one. I'm pretty curious about what others will think. You seem to have mixed correctly.
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Thanks. I think I got carried away, I was thrilled to finally have it running after months and didn't do my due diligence tuning the carb properly.

I'll call it a painful lesson, save up to rebuild her and be more careful next time starting it out running nice and rich. Will double check my oil mix ratio too.

Will look forward to anyone else's input as well.
 
Also, y'all think the big end rod bearing is trashed after this?

I've already accepted replacing the top end, plus crank and wrist pin bearings, but if I could save 70 bucks reusing the crank and conrod that would be nice.
 
Knotical said:
I'd be surprised if the oil isn't good. I know people love to debate what the best oil is but I'm sure dominator is sufficient for these little engines.

I'm pretty sure lean damage tends to show most at the exhaust port side because of thermal expansion, so I'm leaning towards the scoring being from metal debris, but I'm totally open to someone more experienced teaching me otherwise
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Its more than sufficient. It's a motorsports racing oil, not weed eater / leaf blower oil. Its all I've been running for the last 6 years at 25:1 in my rc cars and my ported chainsaws.
 
Knotical said:
Looking for a little help determining if my piston failure was caused be running lean or by low fuel octane. Anyone have pointers to tell one from the other?

G340rc running a ported Bartolone top and, quickdraw pipe and WT1257 carb. Fuel was 92 octane E10 with Amsoil Dominator mixed 25:1. Engine had a little over an hour on it.

Any input is appreciate.
Click to expand...
Looks like it was ran lean. Either by improper adjustment or air leak. Are you still using the stock carburetor isolator that bolts between the cylinder and carb? There is no oil, no matter how rich its mixed, that can stop a too lean air fuel ratio from burning down an engine.
 
jeepfreak1972 said:
Looks like it was ran lean. Either by improper adjustment or air leak. Are you still using the stock carburetor isolator that bolts between the cylinder and carb? There is no oil, no matter how rich its mixed, that can stop a too lean air fuel ratio from burning down an engine.
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yeah stock isolator.

I think I must have been running it too lean. I was on the factory WT1257 high needle setting (about 2 turns out) but was running the modded engine and tuned pipe. Figured if it was too lean it would feel down on power... that was dumb
 
Knotical said:
yeah stock isolator.

I think I must have been running it too lean. I was on the factory WT1257 high needle setting (about 2 turns out) but was running the modded engine and tuned pipe. Figured if it was too lean it would feel down on power... that was dumb
Click to expand...
The stock isolators are prone to warping and leaning out the engine. As to the tune, those turns are yhe baseline. You need to tune it by ear. Its different depending on the fuel, oil, oil ratio, elevation, temperature ect. Best to turn the high out enough till will just slightly 4 stroke at full throttle and max rpm.
 
This is what one of my ported saws loojs like after 3 years of ansoil Dominator @ 25:1 and E free fuel. This saw has around 230-240 psi compression. 20250607_102951.webp20250607_102934.webp20250607_102916.webp20250607_102844.webpIMG_20231001_095307346~2.webp
 
jeepfreak1972 said:
The stock isolators are prone to warping and leaning out the engine. As to the tune, those turns are yhe baseline. You need to tune it by ear. Its different depending on the fuel, oil, oil ratio, elevation, temperature ect. Best to turn the high out enough till will just slightly 4 stroke at full throttle and max rpm.
Click to expand...
OK good to know. I'll swap out the isolator when I rebuild. Do you advise simply going with a stock replacement or something aftermarket?

Will be sure to get it good and rich next go around. Still don't have an ear for tuning since this hour of run time was most of the run time I've ever gotten out of this truck
 
"if" it was 25:1 then it was most likely lean. It is not from bad oil. Dominator is top shelf.
92 octane is plenty for these engines, they don't have enough compression to require any more.
Higher octane in an engine that does not need it provides no performance gain.
 
Mick Mars said:
Says 2 stroke on bottle right. Not to concerned with fuel so much and how do you mix..... I use a chart to determine oil/fuel ratio and a mixing bottle that has marks to show amount.
Click to expand...
Invest in a graduated cylinder , it is much more accurate than a measuring cup and allows you to fine tune your mixture if you choose to do so. Just do the math and adjust accordingly.

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