Triumph Repair: Crankcase Air Leaks on TR4A, crankcase pressure, hg vacuum

Question
Hi Howard,

On a '66 TR4A, is it possible that excessive air leaks in the crankcase seals (rear main, timing chain cover, etc.) could cause the PCV to close (since this would act just like a massive vacuum leak)? The car is equipped with a Smiths pancake PCV connected from the valve cover to the intake manifold.  

The car runs fantastic and checks out great with 180psi dry compression across all four cylinders, 20" Hg vacuum at intake manifold and nice, clean, dry spark plugs.  I am fairly certain I am not getting excessive blow by, yet I still get crankcase pressurization (evidenced by oil leaks). I suspect the PCV is closing and what little blow by I have is causing the pressurization.

Thanks

Bob

Answer
Hi Bob,
Excessive oil leaks can be caused by excess crankcase pressure or by leaking gaskets and seals or both. That large PCV valve usually works very well if the diaphragm is good and the pin on the valve is clean and seating well.

If a gasket were to be so open as to not allow any air in the crankcase the air would be entering all the time and oil would not be able to exit and you would have a air intake leak (if the PVC valve had also failed)

If you have oil leaks you need to run a dry and a WET compression test to test for ring blow-by which is the usual cause of oil leaks, especially with such a high DRY compression test.

Howard