Hi,
I can write a considerable amount here. I have a stock TR4A with about 10,000 on a rebuilt engine. It runs perfectly. However, about 3,000 miles ago a mechanic told me I needed the head resurfaced and a new head gasket to remedy an oil leak. So, the work was done.
Well, immediately thereafter (with a stock PCV and vented oil cap in place) the oil leaks started every where (and I mean every where!). Baffled for about a year, I then ran all sorts of diagnostics on the engine (compression, leak down, intake manifold vacuum, plug inspection, mpg) to figure this out (can you tell I stopped using that mechanic?). The engine starts, idles, runs, accelerates perfectly. All the diagnostics checked perfect including 180psi dry compression across all four cylinders.
What I eventually traced it down to was the shaved head led to increased compression (admittedly 180psi is at the very high end so I triple checked it with three different gauges - same result). Performance and throttle response are excellent but, this results in just that little bit extra blow-by the piston rings into the crankcase. The stock PCV system was marginal at best and, thus, was overwhelmed by this extra blow by. Eventually, the crankcase would pressurize with oil leaking everywhere. Same will happen if you have an older engine with tired piston rings which allows too much blow-by.
For the moment, I have a 1/2" hose venting off the valve cover, between the carbs and down to the chassis. I have a rubber plug over the connection on the intake manifold. Since then, I barely get a dime spot of oil after an hour of driving. Much better than the 3" to 4" puddles I was getting.
Like you, I am very into a stock set up. But, after fiddling with multiple new (from Moss) and old PCV valves with different internal springs etc. I have finally resolved myself that it will never work. So, for now I run the 1/2" vent hose. Ideally, and for emissions purposes, I would like to try and find a generic PCV valve (which is up to the task) and reconnect it. Note, it has to be a PCV valve designed to be connected to the intake manifold, not the carburetor. The intake manifold will reach upwards of 20-22" Hg vacuum and this needs to be properly metered by the PCV (otherwise you simply get a massive vacuum leak and the engine won't run).
Most PCV valves are designed to create a slight negative pressure in the crankcase (~3" Hg). This is to pull the hydrocarbon rich blow by out of the crankcase and route it back into the combustion chamber. The collateral effect of negative pressure in the crankcase is almost no oil leaks! What a wonderful thing!
As a final note, the '65-'67 PCV system was problematic to begin with. If you look at the TSA Service Bulletins (I have copies at home) there are at least a dozen in those years to the dealerships addressing these poorly designed PCV valves.
Hope that's not too much info. My advice is leave well enough alone. Also, if anyone out there has successfully fitted a generic PCV, I'd appreciate any info you have on make, part no, or specific application it came from.
Bob
PS: some of the racers here can say more but, this is exactly why most race motors run a vent hose into a catch can, no PCV valve can process the blow by from a high compression race motor.
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