ford 8n oil pressure (rebuild oil pump

sklundy · Feb 9, 2015

1953 Ford 8N

At first we had low oil pressure. It would start around 20psi and fall to 5psi. Then it wouldn't even make it to 20psi. Even so, it was not knocking. So we knew we needed to take a look -- fast.

I then rebuilt the oil pump, replaced the bearings that I could access while I was in there, and put everything back together. New gaskets. The oil pump pickup tube had to be welded, but I am pretty sure that is secure.

We started it up and got about 20psi. The tractor held at 20psi for a few minutes and then fell again. It has been without oil for a while, so we have "primed" it repeatedly.

We loosened the oil gauge a little until oil dripped out because there was definitely a bubble in the line going to the oil gauge. But now that has been resolved, and we are getting NO oil pressure.

It has since decided that KNOCKING is a good idea -- and not a subtle knock. Oil is not being circulated consistently, but each time we prime the oil pump, it gives us oil pressure.

The old bearings were NOT in bad shape, but we replaced the ones we could access with the oil pan off.

We primed the oil pump again and it was at 20psi once more. But again it fell to 5psi. While at 20psi, the knocking stops. It was NOT knocking before, even at low pressure.

We are using 20w40 oil with oil stabilizer.

Any thoughts?

John Smith8N · Feb 9, 2015

You have a pump problem for sure, and possibly excess clearances elsewhere when you started. A properly rebuilt pump that has a decent housing will not lose prime like yours. If it keeps losing prime, there's too much clearance in the oil pump itself so it can't keep enough of a film to prime itself when you start it again. You can have the pump rebuilt properly and try it again, but if the engine has started knocking the crankshaft clearances are already toast. The engine needs rebuilt.

87nassaublue · Feb 9, 2015

Hmm, I'm with John, you definitely have some clearance issues.

I have a few questions.
You said you rebuilt the oil pump. what do you mean by that?
What did you replace or re-machine?
Did you measure clearances in the pump to make sure they are in spec?
You said the pickup tube had to be welded. Why was that?
Is it possible you don't have a good seal on your pickup tube?

You say you replaced the bearings you could get to. Did you replace both halves of the bearings?

Did you replace the main bearings and the rod bearings?

Did you measure the journals on the crankshaft and make sure you have the right bearings?

If all these things are correct, you might still have bad cam bearings too.

FLAcharlie · Feb 9, 2015

FWIW I had a pickup tube problem after an oil pump rebuild, double-check that.

After my rebuild it worked great for just a few minutes and then oil pressure failed.

old · Feb 9, 2015

First off no such thing as 1953 8N last year they where made was 1952. In 1953 they came out with the Jubilee.
As for oil pressure the relief valve spring maybe weak or not set as it should be.

Den N Ms · Feb 9, 2015

87nassaublue,There are no cam bearings in an N engine,the cam runs directly in the cast iron block bore.Unless the bore was worn badly and the block was machined and had cam bearings installed at some point in the past.

teddy52food · Feb 9, 2015

What size bearings did you put in? What did the crank mike out at?

87nassaublue · Feb 10, 2015

Ahh yes, that would be something to check though. If it's worn, it will bypass oil pressure. I've run into that before on a v6.

aric Lundy · Feb 10, 2015

Blue,
we ordered an oil pump repair kit and sent it off to a fellow who works on old tractors to bore the bushing to the proper diameter. We didn't personally measure the clearances. I have the tool somewhere.

The pickup tube had brolen off, may have been welded previously But this time it seemed secure.

Only replaced the rod bearings, top and bottom and lubed them up before reassembly.

If i didnt replace the remaining bearings would that cause a problem with oil pressure?

We did not measure the journals though. that may be the issue. I hope not.

But when I initially primed the engine it began by knocking loudly then quickly gained around 20psi and the knocking receded holding 20psi for about 10 or more minutes.

I added quite a bit of oil while priming the engine, also replaced the broken gasket on the prime cap.

Another detail i noticed was that when i would increase the throttle the pressure would plumet then regain a little and stabilize slightly lower than the original psi.

TheOldHokie · Feb 10, 2015

(quoted from post at 16:54:35 02/10/15)
Blue,
we ordered an oil pump repair kit and sent it off to a fellow who works on old tractors to bore the bushing to the proper diameter. We didn't personally measure the clearances. I have the tool somewhere.

The pickup tube had brolen off, may have been welded previously But this time it seemed secure.

Only replaced the rod bearings, top and bottom and lubed them up before reassembly.

If i didnt replace the remaining bearings would that cause a problem with oil pressure?

We did not measure the journals though. that may be the issue. I hope not.

But when I initially primed the engine it began by knocking loudly then quickly gained around 20psi and the knocking receded holding 20psi for about 10 or more minutes.

I added quite a bit of oil while priming the engine, also replaced the broken gasket on the prime cap.

Another detail i noticed was that when i would increase the throttle the pressure would plumet then regain a little and stabilize slightly lower than the original psi.

[*:f6bdb445cc]New gears and bushing won't fix a worn oil pump housing.[*:f6bdb445cc]The knocking at startup stopping once you had oil pressure is not unusual[*:f6bdb445cc]Initial startup oil pressure is higher than running oil pressure because the cold oil thins out as it warms up and the pressure drops.[*:f6bdb445cc]You need to pressure check the pickup tube to make sure there are no leaks in the weld or tube, You also need to check teh seal on teh gasket.[*:f6bdb445cc]If the mains are worn replacing the rods will not fix pressure lost through the mains.[*:f6bdb445cc]Increasing the throttle should not cause a drop in oil pressure unless the engine stumbles. You should see just the opposite. If it the engine speeds up but oil pressure drops you likely have such low flow the bearings are getting starved as the RPM's push oil through them faster.[/list:f6bdb445cc]

Unlikely you are not going to fix any of this without taking the engine apart to measure clearances.

TOH

ASEguy · Feb 10, 2015

Too many questions. The only way I trust oil pressure readings is with a known good pressure gauge set. Unfortunately with your engine knocking, testing oil pressure is not plausible. Teardown is, UNLESS it's not knocking when you test it. Just out of curiosity did you check the bearing backing for an undersize number?

TheOldHokie · Feb 10, 2015

(quoted from post at 20:18:00 02/10/15) Too many questions. The only way I trust oil pressure readings is with a known good pressure gauge set. Unfortunately with your engine knocking, testing oil pressure is not plausible. Teardown is, UNLESS it's not knocking when you test it. Just out of curiosity did you check the bearing backing for an undersize number?

One would hope so since he replaced them ;-) Stock bearings on a reground crank will play heck with oil pressure and quite possibly make a racket. :idea:

TOH

ASEguy · Feb 11, 2015

Without knowing his skill level or the depth of his knowledge I don't know. I have learned not to assume when repairing which is not intended to be disrespectful in any way.

TheOldHokie · Feb 11, 2015

(quoted from post at 07:15:57 02/11/15) Without knowing his skill level or the depth of his knowledge I don't know. I have learned not to assume when repairing which is not intended to be disrespectful in any way.

I certainly wasn't offended and I think your question was an excellent one. It got me to thinking about possible reasons for the sudden appearance of a new knock and even worse oil pressure after the rebuilt oil pump was installed.

TOH

Ken(Ark) · Feb 11, 2015

As for oil pressure the relief valve spring maybe weak or not set as it should be.

20 psi cold and 5 psi hot sounds like the spring is not an issue .

ford 8n oil pressure (rebuild oil pump

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