Crankcase blow-by


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Crankcase blow-by

Tim I have a '84 316 w/ an Onan b43e motor. Oil has filled up the air cleaner box. Before I tear the engine down for a rebuild is there something simple to check that is causing this? Compression is right up there at 113&102. Spec is 75-115. Thanks for anyting that save me from a rebuild now.
Dave Tim - A couple of ideas for you to check. It's possible the oil sending unit has an internal crack (very common). This allows oil to leak and then it is pulled toward the back of the engine and up into the air cleaner canister.

Another item to check is the crankcase tube coming up into the air cleaner. If the media inside is gone, oil gets sucked up through that. Could also be the reed valve under the valve cover is bad. The reed valve acts as a check valve. Once it goes, oil can easily be sucked up through the vent tube.

Finally, take a long wooden dowel and run the tip of it around the flywheel. If you pick up a lot of goo from oil and dirt mixing together, it may be an indication the rear main seal is bad. Oil from this leak can also get pulled up into the air cleaner canister.

Good luck - Dave

fred Also front crank seal could be leaking


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