ac-c oil pump

Whenever my C Allis sits I have to prime the oil pump to get oil pressure. Once I prime it, it has good oil pressure till I shut if off.If it sets for more the a hour I need to prime the oil pump again.Is there a check valve in the pump? Did a major on the engine and before that oil pressure was always there when started. Need help

There is a check ball and spring in the hollow pump drive shaft but it job is not to hold oil in the pump for restarting, it is to restrict the flow of oil into the cam. The priming problem lies in one of two places. Worn/broken pump or an air leak in the pipe from the sump. How to fix a pipe problem is obvious. The pump problems can be fixed in the home shop if you are careful about going after it. Four things that are most often seen in the pump that can be fixed at home are: 1. If you installed that thick cover gasket supplied in most overhaul kits you need to remove it and get a proper gasket, or use none as I do and use a thin coating of sealant. 2. Grooves worn in the cover. If there is anything more than very light scratches in the cover you need to remove them. This is done on a flat (VERY flat) surface with various grades of sand paper or emery cloth from about 180 to 400 is fine enough. You place the paper on the flat surface and hold it down with one hand and work the cover back and forth with the other rotating it some as you work it. This is not rocket science but neither is it slap stick. You can ruin the cover in about 2 minutes by just slapping it back and forth on some sand paper on a semi flat surface! Hold it flat and work it back and forth carefully trying to avoid rocking it from edge to edge (this is the natural movement) If you are hand challenged take it to a machine shop. 3. Worn or broken and incorrectly installed blades. All manuals will show you the correct orientation of the blades. About 1/4 the ones I have taken down have one or both in backwards. 4. Collapsed or broken blade springs.
Occassionaly you will find pumps where the housing is worn too bad to be of use were the blades run, a few scratches wont cause problems but deep wear and rust pits are a problem, no fix but find another housing.This is uncommon in my experiance.
Last I knew, been 5 years since I worked on a B-125 you could get the blades and springs from AGCO and the cover gasket from them was correct. If reusing the old blades they will be worn on the edges and you will have enough clearance to use a very small amount of sealant for a gasket. If you use new blades it is likely you will not have enough clearance and either need to use a gasket, or sand them slightly to give clearance to eliminate the gasket, your choice.

I should have added that a bad gasket behind the pump, or loose pump will cause it to suck air also.

Thanks Butch,The only thing I did was to put a gasket on the pump cover.When took the pump off there was no gasket(no gasket for a reason) Will have to split the tractor and take a look.

The cover gassket is very very thin. I am not where I can get the actual thickness at the moment.

On my B I kept the old gasket. First of all, on dis-assembly I sanded the cover down flat and smooth, then used a small amount of valve grinding compound under the rotor and worked it by hand to smooth out the scratches in the pump body. That made the rotor slightly thinner, so I sanded down the pump body until I could put it together& tighten the screws down & it would lock up. Finally, I made a gasket from a similar piece of paper. I used one of those junk mail flyers that landed in my mailbox. The paper is nicer than notebook paper, and slightly thicker. When I was done, the pump would lock up & not turn without the gasket, but turn fairly easily with the gasket. I figure that"s just about the right amount of clearance. Good luck on your fix.