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H oversize pistons and oil pressure

Z

Zachary Hoyt

Well-known Member
I have two questions that I'm wondering about. I dropped the
pan on my H today to make a new gasket for it and noticed that
it has the 3/7-16" replacement pistons. I've seen the Nebraska
results for stock H and I'm wondering if anyone knows how
much difference there is in displacement and HP oversize vs
stock. Also when I've been working it lately and the engine gets
warm the oil pressure drops a lot. Cold it is about 3/4 of the
way over to the right of the gauge but warm it gets down near
the red line and it makes me nervous. I don't know what weight
of oil it had, but I'm thinking of putting in 15w40 which I've seen
recommended on here. Is there anything I should look at while I
have the pan down that might have to do with the oil pressure?
Thanks very much for any advice.
Zach
 
As El Toro says, the cam bearings may be worn. Hard to check that without some teardown.

While you are in there, I would check a couple of rod and main bearings for wear and clearance. Pull the cover off the oil pump and check it for wear also.
 
Thanks for the advice. I don't have a micrometer, and I've never checked those kind of bearings. Is there a way to do it without a micrometer? How can I tell if the oil pump is in good order or not? I can pull the camshaft if I need to, and replace the bearings, although I'll try 30w oil first. Thanks for the advice.
Zach
 
Thanks for the thought. Do you have a thought about how risky it is to run the engine with low oil pressure? Would it be sensible to put an oil gauge in that reads numbers instead of just a range, or does it not matter? Thanks very much.
Zach
 
You use plastigage. Pull the cap, insert the gage put the cap back on, torque, remove the cap again and check the gage.

Gordo
 
As long as you have the pan off and some are telling you to check the end clearance on oil pump gears, check the shaft in pump. You can grab a hold of the gear and see if it moves side to side. Or put a feeler gauge between gear and body, no more than 6 or 7 thousands clearance for good hot oil pressure. The H and M were kind of hard on the oil pump drive shaft, have replaced a lot of them over the years.Luckily the housing is normally not worn or not enough to bother. Then take a look at the pressure relief valve plunger. If it has a step on the end you have wrong one which was supplied for a number of years, will also have lower full throttle oil pressure and low at low idle speed. I have found several of them over the years, in my own H also. I have replaced a lot of cam bearing on H tractors but never really saw one bad enough to cause oil pressure problems. Just routine replacement to get all clearances up to specs. Should have about 70 psi at high rpm.
 
Thanks, I'll do that. I've never done it before, so it will be a learning experience. I've got a lot to learn before I know my way around.
Zach
 
Thank you, I'll get into the pump and see what I can find. I have a spare one out of a parts tractor too, so I'll look at it as well.
Zach
 
(quoted from post at 19:03:24 03/22/10) Thank you, I'll get into the pump and see what I can find. I have a spare one out of a parts tractor too, so I'll look at it as well.
Zach
Click to expand...

Zachary, my 1950 H was doing the same as yours. Good oil pressure at start up and after a few minutes would drop to near zero. I did the oil pump trick, cleaned the sludge out of the oil pan, poured in fresh 15w-40 oil, and now the oil pressure never drops below 1/2 way on the guage. Even after working it hard for an hour or two. An added plus is that I also eliminated that constant, very slight, blue haze from the exhaust.
 
Thanks very much for the story. I got all of it except I'm not sure
about the oil pump trick you mentioned. Did you adjust the
innards of the pump, or was it something else you did?
Zach
 
(quoted from post at 14:41:54 03/23/10) Thanks very much for the story. I got all of it except I'm not sure
about the oil pump trick you mentioned. Did you adjust the
innards of the pump, or was it something else you did?
Zach
Click to expand...

I should have taken a few photos. Basically, I removed the pump from the engine, turned it upside down and secured it in a vise, and then removed the bottom cover. That cover gets warped over time, and the gasket no longer seals up, thus oil pressure is lost. I used a rather crude method of taking a large file to the surface of that cover and removing material until it was flat again. I then made a new gasket, put it together and reinstalled the pump. I really don't recommend this method to someone who is not familiar with using a file because if you don't hold the file just right, you will do more damage than good. I got lucky and it worked.
 
Thanks for the explanation. I have a pump out of a parts tractor
that looks better than the one in the tractor so I'll try that. The
cover on the one I was running has some wear into it from the
gears, and the other one doesn't. If the new pump doesn't help I'll
try what you did.
Zach
 
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