Loosing oil pressure when warm.

Ehud

Member
Hello everyone,

I'm working on a '52 8n, I thought we were finished but about ten minutes into bush hogging for the first time the oil pressure was down to less than 10 psi. Cold its running about 35 psi. I just did a fresh oi/filterl change with Mobile Delcac 15W40 (my local store was out of Shell Rotella). I looked at the oil pressure relief plunger and someone has already stretch out the spring and the plunger has a pretty good groove around the tip, so I'll replace both of those. A few months ago I cleaned out all the oil lines and replaced the guage so I don't think that's it. Dry I'm getting 115, 110, 110, 105 (1-4) on the compression, wet I got 130, 135, 110, 130. I'm including pics of the plugs, they have less than an hour of use and a lot of that time was adjusting the carb, I gapped them per the ford manual. I don't see any oil in the coolant, I don't see any signs of water in the oil. I'm guessing dropping the oil pan is next? Looking at oil pump kits online this pump is like nothing I've seen before, what am I looking for?

This is our first tractor ever, we got it from a guy that claimed to have no mechanical ability and he admitted to overheating it once. We have replaced/repaired every system on the tractor so far but we were hoping to not have to rebuild the motor, that's a little beyond my skill level.

Thanks for your advice!
mvphoto59911.jpg

mvphoto59912.jpg
 
FYI, plugs wires, coil and cap were replaced as a kit from here, points and condenser were electronic so I left them.
 
Low oil prressure at hot idle is a (very common) indication of excessive clearances in the rotating assembly and/or oil pump.

Dean
 
The oil pumps on these old machines are different. I just got through with a tractor split on my '41 9n and while I was
there,checked the clearances on the main and rod bearings. It's not too hard with a concrete floor and a hoist and an engine
stand helps. I have worked on lots of motors in the past and this was pretty easy.
 
Is there a really good rebuild writeup somewhere? I've never done one before and I need all the help I can get.

Since the bearings are not in a rebuild kit would it be OK to replace them without an entire rebuild? The compression numbers aren't fantastic but they are in spec I believe.
 
Is there a really good rebuild writeup somewhere? I've never done one before and I need all the help I can get.

Since the bearings are not in a rebuild kit would it be OK to replace them without an entire rebuild? The compression numbers aren't fantastic but they are in spec I believe.
 
(quoted from post at 20:55:04 08/06/20) Is there a really good rebuild writeup somewhere? I've never done one before and I need all the help I can get.

Since the bearings are not in a rebuild kit would it be OK to replace them without an entire rebuild? The compression numbers aren't fantastic but they are in spec I believe.

You can replace main and/or rod bearings without doing a full overhaul. Just drop the oil pan and they are right there. Rod bearings
are easier - just unbolt the caps and install new shells. Mains require rolling the upper half shell in around the crankshaft which can be a bit of a challenge. If you go that route make sure you get the proper undersize for the shells. The size is usually marked on the back of the old ones and rods may be a different undersize than the mains.

My guess is your problem is bearings not oil pump but once you are there dont skimp - do the pump as well.

TOH
 
Yes you can just do the bearings. Did you verify the oil pressure with a hand held gauge or are you going by the dash gauge? I do not know your level of skill, but if you haven't done this before it can be somewhat tricky. Proper engine work is time consuming and detailed. You will need a good book. The one we use is James Haldermann Engines: Theory and Servicing. You want to number all main and rod caps as they are removed because they were align bored and honed. That means they need to go back in the same position and direction as when new.
 
Plugs are a tad rich turn mixture in 1/4 turn. When is the OP at 10 is it at idle are full throttle...

The OP relief valve is not you issue..
 
Thanks for all the info, I don't get home for another week but I'll drop the pan and see what I can get done (at least get parts ordered).

ASE - I used the dash guage, it's a new guage and I cleaned out all the external oil tubes. I don't have an external guage but I could probably borrow one. I am good at taking stuff apart and putting it back together, I have no idea about checking bearing clearance, setting valve clearances etc. I'll look up that book though and see what I can figure out.

Hobo - that is at about 80% throttle. Thanks for the carb tip!

TOH - I agree, with the pan off I may as well replace what I can reach. [/i]
 
Just be aware that it is not just dropping the pan! the front axle has to be swung out of the way. block under the trans and keep it safe. learn how to use plastigage to check for bearing clearances.
 
(quoted from post at 14:41:40 08/07/20) learn how to use plastigage to check for bearing clearances.

That process is different when the crankshaft is hanging loose under the engine. To get an "accurate" measurement you need to place a jack under the crankshaft and use it to push the crankshaft up fully against the engine side bearing shells. Letting it hang unsupported will get you an inaccurate (undersize) measurement.

TOH
 
(quoted from post at 15:00:13 08/07/20)
(quoted from post at 14:41:40 08/07/20) learn how to use plastigage to check for bearing clearances.

That process is different when the crankshaft is hanging loose under the engine. To get an "accurate" measurement you need to place a jack under the crankshaft and use it to push the crankshaft up fully against the engine side bearing shells. Letting it hang unsupported will get you an inaccurate (undersize) measurement.

TOH
Works good on connecting rods tho! I would do nothing unless I had the engine on an engine stand. By the time you get the pan off, it is not that much more to remove the engine and put it on an engine stand!
 
Much thanks again both of you, I never would have consideted pushing the crank shaft up into the engine for an accurate measurement. I don't have an motor stand, just basic tools fit the most part.

I did some research on the plastiguage looks pretty straight forward. Looks like I can grab an engine stand for less than $100.

I was looking into a rebuild and it looks like if I have a machine shop clean and check the block and head I think I can put it back together. Adjusting the valves and checking the bearings look like the most complicated parts. Is there something I'm missing?
 

I built many engines on a table... The first shop I worked at did several engines a week they never used a stand. The first engine I put on a engine stand around 1977 I tipped it over so went back to a table. I did not use a stand till about 2000 and that was because it was Ford 460 I was not man enough the rassel it... Once I leaned how to use a stand I did like it tho... : )
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top