My '77 loses oil pressure after several rides... I fix it by removing the oil pressure sending unit and running air out, but I changed it to an aftermarket replacement that cannot be removed easily, no shoulders for a wrench. I am going to replace the check valve but I am skeptical.

 

your at the other end of the problem would be my guess - to me its sucking air into the pump and 2 places that can happen, THAT is a fitting or hose connection at the intake side of the pump - The pressure switch is the exhause side its after the pump gets oil not before - and or the gasket surface or the O Rings are hard as a rock causing the pump to suck air past them - if we were doing this i would use Pipe paste not the tape that is for toilet fittings, on all the connections - jz

 

+1 on jz's reply

 

Are you talking about the fitting on the intake side? The body o-ring and gasket are new, I am going to replace the check valve. Could that be the problem? I don't understand how it could suck air... assuming the fitting is sealed well. The service manual says to remove the sending unit allow 3 oz of oil to run out to remove air... shouldn't the air be removed in the crankcase? What am I missing?

 

The manual is talking about air inside the pump itself. The pump has to be primed by having air removed and replaced with oil before it can function. Most pumps, excluding self-priming pumps, are like this.

Back to the beginning, what is the indication that there is a loss of oil pressure?

Are you running an oil pressure gauge? If it is mounted at the rocker cover it will show pressure only when the oil is cold. Oil pressure gauges, to work with hot oil, must be attached directly to the oil pump.

 

After riding a few times when I start it cold the oil pressure light doesn't go off, and when I check it is pumping mostly air into the tank return. Now that I verbalized that I realize that if it is pumping air... it must be sucking air. So...

 

The oil going into the tank will be frothy. This is typical and is not a problem. Do you really have air being pumped? or just frothy oil?

If it really is pumping air then it is time to examine the oil line connections - two at the tank and two at the pump.

 

i re read this post and i have a Question

where did you get the oil light switch if its is not the correct one for the bike as you stated ( it has a different look and attachment )

if its not an Iron head spicific oil pressure switch the light will always be on -- jz

 

Yes it is the right sending unit it worked fine for some time. It just happens to be an Accel part as the factory parts are not avail...
I have very little oil being pumped, Volume is the key. I am going to check the supply lines next. One thing that troubles me is that the oil pump body has two O-rings, the larger one is die cut square. It has a much deeper groove than the one around the check valve so I am not convinced that it is sealing when assembled. It came from a James gasket set... I ordered another Accel o-ring from e-bay to compare them. I will be gone until next week. Thanks guys. Do you guys use Harley 50 weight oil or something else?

 

At idle only a small amount of oil is being returned to the oil tank. This is normal.