Useful Stuff

Engine Breathing


Some pointers to standard Minor breathing arrangements.
*  The earlier cars had a pipe pointing straight down on the tappet chest cover which was the inlet for engine breathing.
*  The outlet was via the pipe on the rocker cover to the air.
*  The Oil Filler Cap on these engines should be solid ( i.e. NO wire filter in it.)
*  The 'straight down' pipe was found to leak oil, so was later changed to a swan's neck shape which stopped a lot of the leakage.
*  Later engines had a different system where the breather pipe on the tappet chest went straight to either a valve device on the inlet manifold and then to the carb.  Or, straight to the carb so this was now the outlet and necessitated a change in the Oil Filler Cap which now had a wire filter in it and had become the breather inlet.

So the rules are:-
*  If your engine breathes into the air filter it should have a 'solid' oil filler cap.
*  If it breathes into the carb the filler cap should have the wire filter in it and the rocker cover should not have a breather pipe on it.
*  These filter type caps are supposed to be changed every 12,000 miles but can be thoroughly cleaned with a good de-greaser etc.
*  If the revs rise considerably when the filler cap is removed then the wire filter is clogged up.

Hope this helps...

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