Unlikely as it sounds, worn piston rings can pressurise the gearbox and blow oil out of an opening. I had this happen on a TM 125 motocrosser with oil blowing out of the gearbox breather. I didn't know the piston ring would wear out in a few hours use and could not understand what was going on.
When the mixture fires at the top of the stroke, some of the combustion gases can blow past worn rings and past the main bearing oil seals, which on the drive side will result in pressurised gearbox.
In the case of the TM, a new piston ring fixed the problem and it ran well again. Not saying that's the case here, but it's something else to consider.
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'00 Montesa Cota 315R
'13 Husaberg TE 300
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11-03-2014, 03:26 AM
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