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oil blowing out dipstick on ac 620 with 20 hp onan

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had the motor bebuilt on it an have mowed yard 3 times.the second time it started to blow oil out the dipstick.u can loosen the dipstick an there is so much pressure on it that it almost blows it out of your hand .what is causing this blowby an how do i fix it.

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Check your crankcase breather to be sure balls are not stuck, also remove breather hose from aircleaner intake hose. If you are getting excess crankcase pressure I would suspect faulty ring. Check spark plugs to see if either has oil buildup on plug.

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think i have found the problem.gasket on dipstis is worn an someone has put a rubber o-ring on it.if the dipstick is not in right place it leaves it loose enough for oil to blow out of it.i turned it till it got snug an ran engine for awhile .no oil blowed out .

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