The Stovebolt Site Forums The Shop Area Engine Shop 235 Crankcase Ventilation

1957 3100, 235. I have read some contradictory information. Not here though! The only current ventilation on this engine appears to be the road draft tube. The oil filler cap is not vented. Twist and lock style. No other vents on the valve cover. Is this correct?
Or should the oil filler cap be the domed vented type? Thanks in advance for clarification.

Yes, the twist and lock filler cap should be screened and vented.
A newer one with the grommet will work.

Yes. The cap in the valve cover needs to be a vent type.

George

A road draft tube develops a suction at the end that hangs down into the airflow under the car, at speeds over 30 MPH. To get airflow through the engine, there must be an inlet somewhere. Early valve covers had slots, which also let dust into the engine. Later model valve covers without the vent slots need a vented oil filler cap with a dust filter built in. Engines with a PCV setup instead of a road draft tube had a tube from the "clean" side of the carburetor air cleaner to a nipple in the valve cover. That's called a "closed" ventilating system. California was one of the first places where the tree huggers demanded that no crankcase vapors could be vented to the atmosphere.
Jerry

Thanks! For the draft tube to work, air needed to get in there somewhere. I just hated to make assumptions. Thanks again!

My draft tube was clogged with carbon. I burned it out 👍

My old 235 had been dormant for many years as it sat in several barns and no telling where else it was till I got it, broke it free and put some miles on it. You can see a hose going in that valvecover cap in the pic. Cap is full of coarse stainless steel wool. It ran so much better after I put that vacumn to it 👍 .

PCV (positive crankcase ventilation) is the best thing you can do to upgrade these old engines. As Jerry stated, unless you've got some road speed road draft = crankcase oil diluted with fuel, blow by, etc. There is a reason pcv systems were being used in many applications before it was mandated by CARB (California air board) or DEQ.

One of the "unintended consequences" of mandating closed vent systems such as PCV was a dramatic increase in engine life between overhauls. One of the main byproducts of combustion is CO2, which is a good thing until some of it makes its way to the crankcase via blowby on a somewhat worn engine. CO2 + water vapor = carbonic acid (Coca Cola). Unless there's some sort of constant ventilation of the crankcase, the acids and other contaminants formed by combustion byproducts have a habit of eating engines for lunch. Filtered air pulled into the engine after it goes through the carburetor air filter also reduces abrasive wear from dust and other contaminants that road draft systems can allow to enter the crankcase.
Jerry

HI I ALSO DID a crankcase PVC on my 235 I will try my best to put some pictures below. I ran my pVC from blow by tube and then to exhaust manifold. On the valve cover I put a 3/8 hose to the air cleaner at the bottom of it.My question is should my valve cover hose be sucking in air or blowing it out ? It is blowing out a little blow by.

mikeg1955 -
There are too many serious mistakes to that installation to even begin to address. Why not just do it the way the factory did almost 70 years ago? The illustration has been posted repeatedly, and it's not difficult to make a clone of the OEM system.
Jerry

LOL okay Jerry thank you for telling me the truth. I did what I found on Youtube before I found this Forum. Is the crankcase okay. I wil try and find illustration with the post. thank you

Crankcase ventilation is not "rocket surgery". Air in, vapors out, sucked into the INTAKE MANIFOLD (not the exhaust!) All the monkey motion concerning the position of the PCV valve is to avoid suctioning liquid oil out of the crankcase in the process. A PCV is just a spring loaded one way valve that takes small sips of the vapors in the crankcase and valve cover, and burns the vapors by routing them into the gas flow in the intake instead of letting them escape to the atmosphere. It's essentially a calibrated vacuum leak, which needs to have the vapors it sucks from the crankcasae repolaced by filtered outside air, after the rocks, marbles, and bowling balls (and dust) get strained out by the air cleaner. The only tricky part is to match the airflow the valve allows to the size of trhe engine. If the PCV allows too much air to bypass the carburetor, the idle speed gets too fast, and/or the idle mixture too lean. Above idle speed, just about any PCV would work. However you choose to let it happen, position the PCV valve HIGH- - - -up near the valve cover gasket while it pulls vapors from the road draft tube hole, and plumb a fresh air inlet from the "clean" side of the air filter to the valve cover. How you go about doing that is subject to all sorts of personal interpretation. The OCD purists will insist on sourcing original equipment parts made somewhere in approximately the lifespan of Fred Flintstone. They're all wet, too! LOL!
Jerry

I chose to use non-vented filler cap with a grommet. Then I ran the hose from that (which is my intake spot) back to the clean side of my air filter. That way I'm not sucking in anything but air that has already been cleaned by the air cleaner. I added a small nipple to the underside of my air cleaner. Others may wish to do this differently. I'm just following all the closed circuit applications I've seen. Good luck. You can see what I did in another recent post here.

I found the V237 pcv valve worked well for the 235...really close to the right vacuum amount.

Also soon (as an experiment) I'm going to add a water/oil separator in the vacuum line (to remove water and oil before it gets to the intake manifold). No special reason...just curiosity. I'll let everyone know what I learn.

Hi Jerry after looking at my truck I did put my iine with the PVC valve into the intake below the carburetor, not the exhaust. so I guess my 3/8 vent tube that goes to the air cleaner is just in the wrong place ?
I really appreciate ypur time and patience with me. I saw the post with the gmc ventilation but haven't found it again yet. found it I am good on that. I will check my cap with the vent tube and make sure it is sealed.

Thank you

MikeG1955 "My question is should my valve cover hose be sucking in air or blowing it out ? It is blowing out a little blow by."

To answer your question as to whether your valve cover hose should be sucking in or blowing it out. The answer is yes. One or the other is happening at different engine loads.
A good indicator that this is true is that cars and trucks beginning in the '60s which all came with factory PCV systems had an open cell filter inside of the air cleaner at the end of hose that is the clean air supply for the PCV system.
This open cell filter would eventually be clogged up with crud from the crankcase.
One may wonder how, since the airflow should be in the opposite direction. Well it is during certain conditions, but goes in the opposite during other conditions.

thank you sir

A hard uphill pull with low intake vacuum and a fair amount of blowby will turn that air cleaner hose into a road draft tube. That's what usually causes crankcase vapors to end up in the air cleaner. It's one of the early warning signs of worn piston rings.
Jerry

Thank you for that information. I don't have any smoke from the tail pipe so I hope the rings are in fair shape. I just replaced the side rod cover gasket that was leaking pretty bad a quart of oil about every 1300 miles. Just did a oil change we will see how it does now. you have been a blessing Jerry, thank you