PCV on a 1937 type Flathead?

ajmac

ajmac

Member
A friend has asked me to fit a PCV and block the road draft tube on a British Flathead which is the same as a 37. I am worried about doing this as it doesn't have a real rear crank seal so I think it will not function as intended....it will draw dirty unfiltered air from the bell housing past the slinger type seal into the unit rather than filtered air through the oil filler cap gauze. Any thoughts?

I guess the road draft system does the same thing and suffers the same problem, but in that case the engine isn't drawing crank case air directly into the cylinders.

Probably over thinking it, it will be fine.
 
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aj,
Most guys look to do this because of excessive blowby......in my experience.
What might 'work' is fitting a respectable piece of tubing from the fuel pump stand
to the air cleaner. A portion of the crankcase vapors would then be drawn into
the carburetor air stream and thence to the combustion chamber to be reburned.
I'm pretty sure your friend will not be happy with his idea as you have stated.
Charlie ny
 
I would think if you could attach a PCV to that breather in the front of the oil pan and run a PCV hose into intake manifold someplace, it would suck the air through the oil filler cap and down through engine and into the PCV and up into the intake. Probably kind of hard to hide the PCV hose. Walt
 
I put a PCV in my 36 engine with the labryinth rear seal, I have not started the engine so I cannot say from experience it will work. But I think it will because the concern about drawing air in through the rear seal exists in the original design with the road draft tube but there is no outcry about the side effects. Also, I have read that back in the day certain creative engine builders considered using the spinning flywheel as a supercharger due to the air movement it generated in the bell housing. This implies that there is a tendency for the bell housing to have a slight positive pressure, but again I have not read anything about dirt ingestion through that rear seal. Lastly, the volume of air that is displaced by a descending piston is matched by an ascending piston, this makes me think that while the air is certainly churning in the crankcase, it is not exchanging a large volume either in or out. If it were, either that seal would leak horribly or the crankcase would be full of clutch dust. What you have is an aerodynamically inefficient road draft slot that draws out a small volume when the car is moving. This suggests that the whole system is fairly pressure static and therefore a PCV should work. But I might be full of crap, I'll let you know when I get it started.
 
Charlie ny>>>What might 'work' is fitting a respectable piece of tubing from the fuel pump stand to the air cleaner.>>>

This is what's on my early 38 21-studder. A short-as-possible 1-inch id tube filled with stainless scouring mesh from the stand to the air cleaner canister. It entrains rather than sucks crankcase fumes down the carb throat. Does what it's supposed to do in the engine compartment. Nonetheless, a fiberglas screen is wrapped around pan draft a few times to filter out road boulders just in case it creates a crankcase vacuum. 8^)

Jack E/NJ

PS Works great at WOT when a PCV valve is ineffective.
 
Alistair,
Some of the wartime British and Canadian flatheads had a PCV fitted. These have a pan with no breather in the front corner, the PCV fitting is on the inlet manifold next to the generator directly above the stand pipe in the valve chamber. Other end is through a fitting below the carb. Was used on slinger type rear "seals" aswell as rope seal cranks.
Donaldson crankcase ventilator is the original one, similar to what was fitted on some jeeps.
Your into "green stuff" I'd think you should be able to dig one up.
Martin.
 
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