blow bye

[1450]

hi all today riding my 57 pan. a knocking noise started ? looked it over , sounds like the case so i took off the timing plug to listen for the knock and the blow bye looked like a air compressor with a cut hose so how much blow bye is there ?if any .it still runs good but the exhaust sounds different ? thx all i 'm thinking piston.

[duoglide58]

I don't have any help on the knock, but the "blow by" looking like an air compressor is exactly what it is. Even with no combustion gases leaking by the rings, the action of the pistons going up and down is basically an air compressor. Factor in a large crankshaft counter weight cutting through the oil and it is going to be an aerated mess since the timing plug is on the crankcase side. A better assessment of the blow by would be to look at the breather tube vent which is dampened by the air in the timng case and the breather timing valve.
Doug