Blow-By

What a mess blow-by makes, an oily firewall, underside of hood and even on fenders. We install breather pipes or steel wool and even rags to slow it down.  What causes it?  I’ve heard a lot of theories but I didn’t have a clue.

Recently while running a new engine on a test stand, I experienced rough idle and a lot of blow-by.  I was really puzzled.  Rechecking the timing and carburation didn’t help.  My first thought was to tear the motor down.  While doing this I noticed exhaust burns on the manifold gasket.  I took the manifolds to the milling machine and cut them flat.

After reassembling the motor and running it on the engine stand, I was delighted to discover that the problem was solved.  No more blow-by and a smooth idle.

This tech tip was provided by AJ Pennington and was printed in the July 2003 “A” Quail Call.

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