Farmall Cub

I have a '50 Cub that has average oil pressure at first start-up but fades to almost nothing when 10 minutes of running. I thought the oil pressure gauge may be bad, after all it's only 63 years old, but after replacing it got the same results. Any ideas on what causes the oil pressure to fade?

Some engines with wear will exhibit this issue as they heat up; the clearances get a little larger in the bearings and the oil pressure will drop. Depending on how low it goes, and whether the engine shows other signs of wear (smoking exhaust, oil consumption, loss of power, etc.) you may be nearing rebuild time. But if it holds ok pressure and doesn't show too many other symptoms, you may can run it a good long while yet.

These old engines only need to have 7 lbs per 1000 rpms to run forever. So its not the best it could be but it will most likely be fine for quite awhile.

Romad50:

G'day to you. I would ten to agree with Rick's comments .. they sure make a lot of sense. I am not sure about the 7lbs but hey it sounds reasonable as well. One thing I would do is a compression test both dry and wet. See what numbers you get. Post them here and some combined wisdom may be able to offer you a few words.

In the meantimes, I would encourage you to follow the links below and spend a little time in the Owner's and Service manuals.

to Farmallcub.com Forum Family. And you have come to the right place for all things Cub related. If you click on the Site Rules, Regulations, & Important Information, it will point you to the Welcome Wagon wherein you will find links to many useful sites and topics. One of the most important resources are Owner's Manuals, Parts Catalogs and Service Manuals. The Cub Manual Server is the home of the jpg versions and the [url=http://www.farmallcub.com/[ Sorry, direct links to manual section is not allowed. ]/index.php]PDF Manuals[/url] -- well the pdf's of course Enjoy!.

It's hard to tell with the stock oil pressure gauge exactly how much pressure you do have.

If you have a Harbor Freight store nearby, stop in and pick up an oil pressure test gauge kit from the automotive section. The test gauge will give you an accurate reading of oil pressure in PSI. You can see where you start and where you end up after working the tractor for a while. It screws in right in place of the stock oil gauge and has a hose so you can hang the gauge from the gas cap and watch it while you drive.

Hello and welcome to the best Cub site on the web. Great bunch of guys with a wealth of practical knowledge about Cubs and mechanics in general.

Rick Spivey wrote:Some engines with wear will exhibit this issue as they heat up; the clearances get a little larger in the bearings and the oil pressure will drop. Depending on how low it goes, and whether the engine shows other signs of wear (smoking exhaust, oil consumption, loss of power, etc.) you may be nearing rebuild time. But if it holds ok pressure and doesn't show too many other symptoms, you may can run it a good long while yet.

For what it's worth I had the same symptoms as you except that my pressure gauge was reading right on the edge of the red zone, hot at idle, and about center gauge at operating engine speeds. Even though the tractor ran great otherwise, decent power, no knocks, etc. although it did smoke a bit under power, I felt I needed to check it out. I plasti-gauged the mains and the rods, they were all at or over the maximum allowable clearance. While your tractor may run a long time with low oil pressure, it will not with no oil pressure. I presume your oil pressure goes up at operating speeds.

Romad50 wrote:oil pressure at first start-up but fades to almost nothing

Even though my oil pressure was tolerable I wasn't comfortable with it. I went ahead and gathered up all the parts and gaskets after I determined which I needed (std. or oversized). I was lucky enough to only need standard sizes and it needed no machining. So I was able to replace the bearings and rings without splitting the tractor not to mention save the expense of shop labor. For me (and depending on your skills), it was well worth the effort to check it out before the engine was too far gone. The tractor has great oil pressure now, no smoke, and I think it's a little stronger as well. I took a bit of a gamble by not replacing the rear main seal (it wasn't leaking), however if you need a rear main seal then the tractor will need to be split.