Air in Engine

[Barrman]

I had the truck running probably 2-3 hours this weekend. All except the last 30 minutes or so were with the air system open and no pressure built up. Once I finished up the horn plumbing, it was able to build pressure. I noticed oil dripping from the valve cover mounted vent. Since I had just refilled the oil bath filter there on Friday, I figured I had it too full of oil and didn't worry about it. Then I turned the engine off and heard air leaking from the vent. I pulled the cap and some built up air came out. Cap back on and it was coming out the vent. I opened the tank valves and emptied the air tanks. No air at engine vent. Fire the truck up with the tanks open, turn it off and no air at vent.

I looked all over for a source of compressed air getting into the engine and couldn't find one. All the fording stuff is open and no direct lines from the air system to the engine. Except for the oil lines to the air compressor that is.

Is this a sign that my supposedly rebuilt air compressor is having severe blow by issues?

Thanks.

 

[WillWagner]

There should be a check valve at the tank to prevent air going back into the compressor. Maybe the fording valve is leaking.

 

[Barrman]

Nope, no check valve. Let me look through the manuals at home tonight and see if I am even supposed to have one. I didn't think of that with this problem, but I did go looking after somebody asked on here a week or so ago about the check valve and mine isn't there. I will look on my other M35 and see if it has one too.

 

[Barrman]

No check valves on either of my Gassers and none shown in the 1954 manuals.

I think I will add one because I can't imagine the rear main seal lasting all that long with air pushing oil past it. The truck hasn't leaked a bit sitting in the same basic spot for more than a month. I ran it for an hour or so with air in the system over the last few days and now my rear main is leaking.