Crankcase ventilation

chicklin · Post by **chicklin** » Wed Feb 01, 2012 4:54 pm

The PO removed all the vacuum and vent lines on my M38A1. The fitting for the crankcase vent on the driver's side has been plugged with an 1/8" pipe plug.

It seems to me this vent needs to be opened and this is where you'd normally find a road draft tube on a civvy truck. Is it enough to just pull the plug or should I run a short length of copper tube out and down below the frame to create a bit of vacuum from the air moving under the jeep?

Also, all the road draft tubes I've come across have been around 1 - 1 1/2" in diameter. A small copper tube in that 1/8" fitting wouldn't provide much ventilation. Can that entire assembly be removed and replaced with something more civilian for the time being?

oilleaker1 · Post by **oilleaker1** » Wed Feb 01, 2012 7:38 pm

You need positive crankcase ventilation. You can set it up civilian or military. The fuel pump type you currently have should be the deciding factor. Overpressuring the motor will cause oil leak problems. ( you'll have them anyway

) Tell us which fuel pump you have, and the diagrams are simple to follow. Parts are easily available. Your engine will run much better too! John

chicklin · Post by **chicklin** » Wed Feb 01, 2012 7:40 pm

Aftermarket non-vacuum fuel pump. I realize positive ventilation is better, overall, but a simple draft tube is better than no ventilation at all, right?

If I can set up a PCV system for cheap, that's fine, but I don't want to over-complicate things.

Post by **wesk** » Thu Feb 02, 2012 2:58 am

Your fuel pump type is not important. The same side valve cover mounted vent was used with either pump. The use of a dual vacuum/fuel pump simply adds a "T" to the vent plumbing so the vacuum pump can be included in the system. If you a single action fuel pump only then you forget the "T".

Same with the Fording system. If you don't want to include the fording system valves then just leave them out.

Here is what the left side of the M38A1 engine looks with a dual vacuum/fuel pump. The horizontal plumbing just above the pump with the 4" piece of 1/2" rubber hose is the side valve vent fitting, the black hose that replaces the fording valve, the PCV valve, then the 90 deg fitting and "T" that allows the vacuum pump tp tap into the system and from there the small tube runs around to the 1/8" pipe plug you have just below your carb.

Just below the carb you can see the metal tube and the "T" fitting used in the 1/8P threaded hole in the intake. A cap is used on the rear side of the "T" and that allows easy attachment of a vacuum gauge when you need one.

oilleaker1 · Post by **oilleaker1** » Thu Feb 02, 2012 6:21 am

Did the PO change distributor and carburator too? If he removed the vent lines from the distributor, you can cook your 24 volt coil also.

chicklin · Post by **chicklin** » Thu Feb 02, 2012 7:32 am

oilleaker1 wrote:Did the PO change distributor and carburator too? If he removed the vent lines from the distributor, you can cook your 24 volt coil also.

Yes, everything is switched out to 12v civvy for the time being.

chicklin · Post by **chicklin** » Thu Feb 02, 2012 7:34 am

Wes,
Thanks for the pics, that helps a lot. So, just to be clear, I could run a hose or tube from that vent fitting all the way around to the port in the intake manifold below the carb, putting a PCV valve somewhere in line, right? That's not going to cause a lean condition inside the manifold, is it?

Post by **wesk** » Thu Feb 02, 2012 9:50 am

You are correct.

If you are not in a hot climate the military coil will do ok. The primary purpose of the vent lines on the coil was to vent corrosive and explosive gases generated by the high voltages attained in the system. In extremely hot climates a tire coil will react poorly to the heat buildup when the vent tubes are not used.