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My 1955 M38A1 is missing all of the components that make up the crankcase ventilation system. How important is this? Does/will this affect how my Jeep runs? Thanks

It is reasonably important. The how is up to you.

Unlike 2 stroke engines we do not want to pressurize the crankcase. It costs us both in power and economy.

The original L134's were vented straight overboard through a draft tube pointed down the left side of the engine towards the ground.

The PCV valve was the beginning of smog rules for us. We then just recycled the vented crankcase pressure across the top of piston and out the exhaust pipe.

So you folks in California, Tucson, Phoenix and other big urban areas with heavy duty smog laws and smog inspections you will have to use the PCV valve.

The necessary plumbing is cheap and easily procured so there's no real good reason not to plumb your M38A1 they way it was suppose to be.
If you just do not like PCV valves then buy an old used draft pipe setup. Draft tube A-1061. The gaskets are the same.

thanks for the information. As always very beneficial.

Without the crankcase ventilating you will get foamed oil in most of the engine.When you check the oil fill pipe you can easilly see the foamed oil sticking to the pipe.Unavoidably it is the same through the passages that the oil travels.This foamed oil becomes gummy as time goes by clogging the whole oil passages and poor lubrication busts the engine.