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i had something like this last year it was like black carbon up on the bottom side of the piston and you could wipe it off with your finger i never did find the cause of it
 

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QUOTE (andysbanshee @ Jan 5 2009, 06:54 AM) index.php?act=findpost&pid=23977hes just running pump gas. not sure of the ratio. i did not see the piston.but he said it was carbon build up. he also said the he looses power on the top end. he said his reeds are fine and crank seals are fine. piston and cyl mikes ok no brokin rings.


I have torn down many of the lt500's. The pistons are usually dark on the underside, but not really built up with anything. If there is dark under the bottom ring then it is time for some rings or boring. The LT's are known to have sticking powervalves or the spring breaking and not letting the valve work correctly. A good setup 500 doesnt need the valve, we usually lock them down and remove the governer to keep from having issues.
 

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QUOTE (bubba297 @ Jan 5 2009, 06:56 AM) index.php?act=findpost&pid=23980I have torn down many of the lt500's. The pistons are usually dark on the underside, but not really built up with anything. If there is dark under the bottom ring then it is time for some rings or boring. The LT's are known to have sticking powervalves or the spring breaking and not letting the valve work correctly. A good setup 500 doesnt need the valve, we usually lock them down and remove the governer to keep from having issues.
The main bearings sometimes woller the bore in the cases and upgrades need to be done with them. It could be starting to suck crankcase oil, but the water pump usually leaks first, and on and on from there. Built correctly they can make good power.
 

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QUOTE (portworks @ Jan 5 2009, 06:06 PM) index.php?act=findpost&pid=24100The main bearings sometimes woller the bore in the cases and upgrades need to be done with them. It could be starting to suck crankcase oil, but the water pump usually leaks first, and on and on from there. Built correctly they can make good power.


Your right about the main bearings. We've sent a couple out to Trinity to have the cases machined and an insert put in. The biggest thing is just changing the bearings before they turn the motor into a big jackhammer. The have to get a little PM.
 

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ive torn down alot of honda motors with wisecos and noticed that black build up underneath the piston on almost every piston. i have 2 theories why its there: blow by is going past the rings and burning underneath, or the piston crown is getting hot and burning the oil underneath and it sticks to the underside. i havent figured out exactly what causes it
 
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