My 1980 Spitfire 1500 still has blowby after the rebuild. It could be
because I lapped the valves instead of machining it. Usually cars have
some sort of crankcase venting that burns the secondary mess through
the carburettor, one comes from the valve cover and the other through
the bottom of the engine block and feed through the carb. But mine
has only the valve cover venting to relieve the backpressure. If I
put the oil cap on, the pressure through the crankcase causes oil to
spew out of every nook and cranny including the dadgum dipstick hole
placed next to the exhaust causing a smoky mess at high rpm.
You usually figure out your rpm is high when people start honking behind
because the smoke is causing them to gag. One of the main causes of this
backpressure is that I have Webers and the large venturi is, as far
as the engine is concerned, uncool. I do have the valve cover vented
to the carburettor but it is not enough to relieve the pressure.
So my question is, how do get rid of this backpressure and how come
the bottom of the block does not have some form of venting? The pistons
do create some pressure in the crankcase because of the downward motion
that must be vented. Is this an oversight? somehow I don't think so. I
would like to keep the Webers and the oil cap on because it is creating
an unsightly mess. The car has no emissions rig attached.
Best Wishes
Zahid
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