Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Blow By on a fresh rebuild. Possible ?? PLEASE HELP. Pics inside
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Old 09-22-2008, 10:28 PM
powerrodsmike's Avatar
powerrodsmike powerrodsmike is offline
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Those compression readings are a bit low for a somewhat fresh motor, 170-200 is a good reading for a fairly stock, fresh motor. I'm guessing that either the rings didn't seat, or got gummed up with oil from the unbaffled pvc, or you have some loose valve guides, which let the valves get burned. Or maybe the valve seats got all gummed up from the oil, and they burned from trying to close on the carboned up smegma from burnt oil..As your problem occurred over time, I'd bet valves are the culprit.

You can put a couple of squirts of engine oil in the spark plug hole, and re test, if the compression comes up 10 or 20 PSI, that indicates rings are the prob, if the compression does not come up, then it says valves are leaky.

You can also make a poor man's leakdown tester to isolate or confirm/disallow those theories., Take the hose from the compression tester, connect it to your air compressor,(if you have one), then put the cylinder at exactly top dead center, with both valves for that cylinder closed...Put some pressure in the cylinder,(if the crank turns, reset it back on TDC and try again..sometimes I leave the breaker bar on the balancer bolt and jammed into the frame to keep the crank from turning), ..Once the cylinder has pressure, you can listen for the air leaks at the carb throat, with the throttle open,(intake valve is NG,) the crankcase,(listen with a tube at the oil return holes with your valve covers off, that will say rings), or at the exhaust port....(ex valve leaking).


None of this sound good.


Mikey
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Last edited by powerrodsmike; 09-22-2008 at 10:34 PM.
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