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Airtight Crankcase

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RJS

RJS

Jedi Warrior
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On a 1966 TR4A, does the crankcase need to be airtight for the PCV to function properly?

As some of you may know, I have a slight crankcase pressurization issue with my engine. The TR4A runs a PCV from the valve cover to the intake manifold. The PCV is supposed to modulate the vacuum from the intake and create a gentle vacuum in the crankcase, thereby venting the crankcase.

What I am wondering is if the seals/gaskets are shot (oil pan, valve cover, timing chain, fuel pump, etc) is it possible that this permits high flow through the PCV but never generates enough vacuum in the CC since so much air is leaking in? Then, the high flow causes the PCV to close resulting in the CC pressurization I am experiencing.

Thoughts, comments??

Bob
 
IMO, the TR4A PCV system was simply a poor design. It totally ignored what happens at full throttle with all engines, and at part throttle with engines that are a bit 'tired'.

If it were simply bad seals as you describe, then you would not get the slight vacuum in the crankcase. But with no vacuum in the crankcase, the seals would not leak! The PCV valve should still allow as much flow as it would anyway (the flow is regulated mostly to prevent leaning out the mixture too much) and, when the flow is not enough (like at full throttle when there is no manifold vacuum), the result is pressure in the crankcase.
 
IMHO you have a blow-by problem that is over whelming the PVC valve,as Randal says its a border-line thing at best.You might do a leak down test on the compression to try to detect broken rings, but you might as well start saving for the new jugs and slugs.....
MD(mad dog)
 
I can chime on on this one! My TR4A was leaking like a sieve when we put the EFI on it. There is no way that thing could ever be airtight with the dipstick the way it is. Anyway, we tried a conventional PCV valve between the EFI manifold and the valve cover, but it still leaked. I took the valve out, but instead inserted a Harbor Freight inline airline filter (for airtools). It is clear so you can see in, and it collects oil if it gets sucked out of the engine, but lets the air through. It has a metal screen inside, which I hope is sufficient for a flame arrestor. I may stuff it with stranded metal sometime just to be sure.
The intake pulls a vacuum on the line, keeping the oil from flowing out the labyrinth seal around the rear crankshaft. So far, this seems to be working pretty well. There is only a negligible amount of oil in the filter after driving maybe 200 miles with it on there, and running a few more hours than that in my garage.

Dan B
S. Charleston, WV
66 TR4AIRS EFI
80 TR7 DHC
 
Thanks Gents,

I think the best option is a leak down test when she comes out of winter storage in the spring. I have about 7500 miles on a rebuilt engine and this pressurization issue started about 1000 miles ago.

What's odd is that engine runs perfect in every other way. 180 psi dry, 200psi wet compression across all 4 cylinders (with such consistent pressures, I highly doubt a broken piston ring in one cylinder), dry white looking plugs, 20" Hg intake vacuum at idle and it starts & runs with excellent power and throttle response. 22 mpg. So, for the moment, I am venting the valve cover to the atmosphere and it runs great, NO oil leaks. Make no mistake, the engine runs perfect except for the pressurization when the stock PCV is connected.

What I suspect is b/t 10% to 20% leak down is occurring (which is acceptable range) but, it's just that too much for the marginal OEM stock PCV to handle.

If leak down is 20% or better, I won't touch it. 20% to 30% who knows. Over 30% I'll open 'er up for a look.

Bob
PS: here are my suspicions on what may be happening:
1. stuck rings
2. overly rich mixture caused bore wash and glazed cylinder walls
3. mechanic "re-planed" cylinder head a couple years ago. Not sure how much he took off but, could it raise compression which resulted in an increased volume of blow-by? I've heard that high compression engines have much more blow-by
 
Wasn't there a thread on here about this issue and the solution was to install the TR3 breather pipe instead of the PCV set-up or maybe I saw that on a different forum? Would it work? Same engine?
 
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