new engine c169 no oil pressure

I just rebuilt a C169 engine for a 1954 Int 300 Utility.

Fired it up, had only 10 lbs oil pressure. Took oil pump off, cleaned everything, gear lash within specs, reinstalled, now no oil pressure at all!

What-up? Anyone?

Have you checked the oil pressure regulator?

The only "regulator" is the pump.

Hopefully you put the original gasket(s) back in that determine the clearance between the gear and the bottom plate. The bottom plate could be warped or damaged-it can be sanded flat, or if necessary, replaced. New engine--same oil pressure gauge or a different one? If same, did it work right in the other engine?

What is the rod & main bearing clearance? New cam bushings?

Thank you for the correction.

Was the engine block dipped in a hot tank? Some pipe plugs may have been removed during the cleaning and were not installed in the rebuild. Hal
PS: Look for any oil dripping from the bell housing or from the front of the engine.

Thanks everyone for responding. I'll answer all the questions one at a time.

The block wasn't hot-tanked. I cleaned it out personally, didn't remove any plugs, bushings, or anything like that from the inside of the block, or the outside.

Main crank seals front and back sealed good- no oil leaks.

Main bearings were 10 over, tight, just like we like ‘em. Rod bearings within specs, new cam bushings. Everything tight, tight tight.

I cleaned the oil pump, and made sure the gasket was there and still in good shape. Checked all the clearances, condition of the gears, the clearance between the gears and the housing, the gear lash, etc, etc. The only pressure regulator, like you said, is in the pump, and it’s preset, non-adjustable.

New information: When the oil pump didn’t make any pressure at all, I installed a completely different oil pump, one known to be working. Problem is still there. More on this in a minute.

Oil pressure gauge in known working condition. Just to make sure, I installed a brand new oil pressure tube and a new gauge.

OK, so I am stumped. Here’s what is happening. When I crank the engine, I have good flow through the filter housing. If I run the engine and remove the oil pressure tube, oil shoots up in the air about three feet. I tried putting my finger over the hole, and I couldn’t feel any pressure there at all. The pump should make 50-60 psi- if it was doing that I think I’d have a hard time keeping the oil from squirting out. But I can keep the oil in the motor with my finger, easy.

So, I have a really good flow, but no pressure. Here is my thought process: I have a working oil pump, but somewhere in the block, the oil is short-circuiting the journal system and returning to the pan. The big question is where? I wonder to myself, “How is the oil getting from the pump into the block? Could this junction (between the oil pump outlet and the journal inlet in the block) be the place where the oil is just dumping back into the pan without pressurizing the system? There aren’t any gaskets or o-rings to seal the oil pump into its socket in the block. The outlet of the pump is just below the drive gear- (driven by the cam). What keeps the oil from just running down the outside of the pump and not going into the oil passages?”

I know a guy here in town with a Ford 8N- has the exact same problem. He can’t make oil pressure- replaced the oil pump, etc, etc… so two different old tractors, same problem.

Thanks everyone, for your help!

I know this is frustrating, I had same exact problem with a rebuilt Cub, but unlike you I had the block dipped and the machine shop left out an oil galley plug hole behind the cam gear. Really made me think I was going crazy when I could see oil flowing but no pressure.

I"d say that your oil pressure relief valve in the oil pump is stuck partially open. Or the oil pressure regulating spring is weak or broken. You are correct when you say there is no adjustment there but the valve could be scored or just plain stuck. Make sure it works freely and check the spring for breakage etc.

The filter is not full flow, it has a restrictor in the bolt (IIRC) that allows modest amounts of oil to bleed into the filter then back into the block through the filter boss base. If the metering hole is wrong, or out of place there is the problem. If you are sure the pressure regulators are working, and the filter orifice is OK (checked from outside) I would pull the pan, put a laundry tub under the engine, and pressurize the system from the oil pressure sending unit threaded hole. Using just a hand pumped oil can, may work. Look for hemorrhaging in the galleries and from the filter housing. return. Jim

Jim, thanks for the suggestion- that is very helpful and I will try it asap.

Behind the cam gear huh? Well, I may have to tear this thing down again anyway, so I'll keep an eye out. The good news is, when i figure this out, hopefully I'll be able to help someone else who has the same problem.