What should happen when I plug the breather?
The engine should labor and die as crankcase pressure builds up. Due to the particular construction of the 617, the shutoff diaphragm gets pushed on just as if you put a vacuum on its other side. (All pressure is relative.) It is used as a poor-man's blowby test, and was shown me by the dealership service manager (though I'd heard of it before that). If it dies quickly the engine is in poor shape, though the converse is not true. The crankcase ventilation system has to be intact, you see. If it's leaky elsewhere the pressure can't build up, and it can masquerade as an unworn engine. Also, high blowby need not be a permanent condition, if it's due to carbon build-up. -- Jim
