Low oil pressure when hot

I really need some help I have done plenty of searches but got no real answers. I just recently put new rings and bearings in my f-head and when it warms up it goes from 60 to 20 psi oil pressure. I have had this thing apart four times and rechecked bearing clearances and even tried a new set of bearings. The clearance is around .002 it is a little loose but .001 undersized bearings do not seam available any more. I never had any problem before and the old bearings had over .003 of clearance. My only hope now is that its the pressure relief valve. Someone please give me some info because without good oil pressure I can't drive it and I don 't have the money for a new engine.

 

what engine do you have? also what weight oil are you running? back in the day there was no such thing as multi viscosity motor oil, example 10w30. it would have been 30weight and so on. with the clearances you have given i would give straight 30 a shot and see what happens, 10 w 30 will get thinner when it gets hot, straight 30 will not. i have found it at advance auto in the shell line and non detergent

 

He wrote f-head, Kaiser-Willys F134.

There are some issues specific to the 134s IIRC. Something about the orifice size squirting on the cam gears? This engine has cam bearings too, which can be a source of low engine oil pressure.

When you write 20 psi, is that at idle or at speed? 20 psi at idle is plenty. A good rule of thumb is 10 psi per 1000 RPM minimum. Certainly the oil pressure will drop as the engine warms up, since the oil thins out. Have you done anything to the oil pump? What kind of oil filter setup do you have?

I'm not the expert on the F134, but there are many here that are. There's also good information on the CJ-3B page, here and in other tech articles: http://www.film.queensu.ca/cJ3B/Tech/OilPressure.html

 

i see that now

 

just a thought, been going over this in my head, from what i gather from your post it had good oil psi untill you had it apart, it has to be something not put back together right...... depending on how far you had it down only a few things come to mind, rod and main caps back in their orignal location/ orientation? gasket in place for the oil pickup? lube the bearings with bearing lube on assembly? any of this could cause the problem, especially with the bearings, they can fail prematurely if not put back together right, bearing caps have to go back exactly how they came apart, if you get them turned around it causes major problems and will need to be fixed, the rods will have to be reconditioned, and if it is the mains the block will have to be line bored to correct the problem. not saying thats the problem, but one that is easy to mess up on

 

FSM sez minimum oil press (safe) at idle is 6psi. 20 psi at 2000rpm and normal is 35 psi and the relief valve opens at 40psi.

 

At 2000 rpm oil pressure starts out at about 50 psi and when it warms up it goes down to just under 20 psi. On idle it goes from 20 psi to about 5 psi. All bearing caps are in the right position the mains were not taken apart. I changed rod bearings because I put new rings in it I found that the motor was rebuilt not to many miles ago but someone lined all the ring gaps up. Like I said no oil issue before and the clearances are tighter now than before. A new gasket was put on the oil pickup also. I had put a shim in the oil releif valve to see if that made a differance but there was no change. I am also running just a straight 30 weight oil.

 

If this is not a non problem, I have had the same problem ever since I have had my F head. It has about 50 psi cold, 25 psi warm and 6 psi at idle. I have not considered this a problem. Are you sure the problem was not too high an oil pressure before you tore the engine down?

 

Did you mike or plastigage the rods when you put them together? If the clearance is worse with the new bearings, that could be a reason.

 

I did plastiguage the bearings the new bearings have less clearance than the old ones.

 

its also in the way your oil pump was set-up when you installed it. I got one engine that runs 35 at idle, and another that runs 20 at idle when hot. Both freshly rebuilt.

 

Ok I went digging around the back shed and found a gear type oil pump it has two small gears in it instead of the trochoidal set up. I put it in and it has a steady 10 psi at idle and runs about 27psi at 2000 rpm. It does not look like the early syle f-head pump so I think it might be an aftermarket one. I'll drive it to work to see if it really worked. It ran at varied rpm in the garage for almost a half hour and the oil pressure stayed the same. I really hope this fixed it.