Triumph Repair: TR4A PCV, rubber diaphragm, crankcase pressure

Question
QUESTION: Hi Howard,

1966 TR4A which I have owned for 8 years. Never had oil leak problems until this summer. Then I got leaks from every where. I am pretty sure I traced it back to a clogged PCV causing crankcase pressurization.  I opened the PCV up and cleaned it but, now I an not so sure the spring and diaphragm inside were assembled correctly. Do you know and can you explain it? I checked several manuals but cannot find a diagram of this part.

Mine had the spring first in the bottom of the valve. Then the little metal disk with the pin sat on top of the spring with the pin pointing down (towards the vent hole in the bottom of the valve). Then the rubber diaphragm on top, then the metal lid. My main question, is the metal disk with the pin supposed to be attached/glued to the rubber diaphragm to keep it properly positioned?  Mine was not so the metal disk was able to float around inside the valve.

Thanks

Bob

ANSWER: Hi Bob,
You are correct as far as the components in order as I remember them. The metal disk that had the pin attached was held in line by several spines that were part of the case. The rubber diaphragm was just a rubber disk and was not attached to the metal disk with the pin attached. The spines of the case kept the pin in line. Be sure the small hole in the metal cover disk is open so that the diaphragm can be forced down when manifold vacuum pulls the diaphragm down.

The same PCV was used on early MGBs too and we use to clean them on certain mileage inspections. If you have cleaned it and the ports and you still have oil leaks, you may have excess crankcase pressure which comes from ring leakage. You should run a compression leak down test and / or do a dry and wet compression test. This checks for ring leakage. A PCV valve can only handle a small amount of ring leakage.

Howard

---------- FOLLOW-UP ----------

QUESTION: Howard,

Quick follow-on question on this topic.  If the PCV is clogged resulting in crankcase pressurization (and leading to oil leaks from the engine) would I necessarily see this pressurization as excessive oil pressure on my gauge?  Or is crankcase pressurization different from oil pressure?

The reason I ask is b/c I am quite certain I had a bad PCV leading to crankcase pressurization and oil leaks. But, I never noticed any unusually high oil pressure.

Thanks

Bob

Answer
Bob, oil pressure on your gauge has nothing to do with crankcase pressure. Oil pressure on the gauge is the pressure built up by the oil pump trying to push oil past the bearings.

Crank case pressure is a normal pressure the builds inside the crank case from blow-by of combustion in the combustion chamber that leaks past the rings. If not relieved it builds so high it forces oil past many gaskets and seals and prevents the scraper rings and oil rings from removing excess oil off of the cylinder walls and thus the excess oil will burn and blow blue smoke out of the exhaust.
If the PCV valve is stopped up this will happen, or if the rings are bad, the PCV valve can not relieve the excess blow-by and the same thing happens.

If the PCV valve is not stopped up, you must do a dry and wet compression test to check the rings.
Howard