[TR] Crankcase Evacuation System for TR3

Randall TR3driver at ca.rr.com
Sat Dec 21 13:55:27 MST 2013

> It all seemed like 
> a great idea
> until I realized that on a street car all that would happen 
> is that over time
> you would fill up your glass pack muffler with oil and 
> probably have a fire...

At least in theory, the fumes should be burned by the hot exhaust, so oil could not collect in the muffler.  I plan to try that
system myself, eventually.  Note that the valve is more important than just backfire prevention; it's a special valve that only
opens when the pressure is below ambient, and closes as the pulses of exhaust go by.  Otherwise, you would have exhaust blowing into
the crankcase.  You'll also want some sort of separator, to remove as much oil as possible from the blowby fumes.

>      It all got me thinking. What if you put a port in on the 
> crossover piece
> on the intake manifold? You would vent the valve cover and 
> crankcase to there
> and the engine vacuum would evacuate the crankcase. Has 
> anyone ever done this?

You have just described exactly the system used on TR4A, except it had a valve to limit the amount of vacuum and prevent reverse
flow.  (You really don't want to be sucking fuel/air mixture into the crankcase, every time you step on the throttle.)

> Does something bad happen if you do?

Yes.  Every time you open the throttle to accelerate, you get maximum blowby, but there is no manifold vacuum.  So the crankcase
winds up being pressurized and blowing oil out in other places (like the rear main seal).

The cure for that (and the way most American engines are plumbed) is to have a large diameter fresh air intake back to some place in
front of the carbs, so that any reverse flow at full throttle gets let out without building pressure, and sucked into the intake to
be burned.

> I am assembling a rebuilt engine now 
> and wondering if
> there is a way to improve it.

Make sure the rings gaps are the right size, the rings fit the pistons properly, and the cylinder walls are properly prepared.

>      And yes, I know that ideally there
> shouldn't be blow by coming out the oil cap on the valve cover.

It's actually normal to have a small amount, at idle.


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