Oil Pressure Variations

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Re: Oil Pressure Variations

Postby Jim Becker » Wed Jun 11, 2014 8:21 am

Ironlegs wrote:About hand lapping my Super A's oil pump housing plate...I'm getting the idea that abrasives are used to reduce the bolt flange thickness, thereby closing internal gaps with the pump's gears...let me know if this is the right idea.

Yeah, that is the general idea. The bottom plate started out with a flat surface. Lapping it will take out any warpage and remove any depression worn into it by the ends of the gears. It may reduce the end clearance of the gears.


Ironlegs wrote:There are very few decent running Farmalls in my region, NW PA, and no informed users and mechanics...everything is Kubota, Ford-New Holland and sheet metal lawn tractors.

That area along Lake Erie was covered with fruit and vegetable farms. It seemed like every one of them had an A or Super A. There have to still be some experts around if you look in the right place!
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Re: Oil Pressure Variations

Postby John *.?-!.* cub owner » Wed Jun 11, 2014 3:01 pm

Before you start reducing the clearance, use some plastic-gauge between the ends of the gears and the housing. The specs are in the service manuals. You may find the pump is ok, and you need to look at rod and crank bearings, or at the governor idler gear bushing instead.
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Re: Oil Pressure Variations

Postby Ironlegs » Thu Jun 26, 2014 1:18 pm

With the encouragement provided here, I removed my tractor's oil pan and pump and checked it. With Plastic-gauge, I determined the pump's gears to pump body bottom cover clearance was over 0.007 inches in the worst locations where the gears had rubbed against the lower cover's inside surface. The paper gasket sealing the lower cover was compromised during the work...it was made from rather thick paper. I had several very thin new pump cover gaskets, used together or separately to shim the cover to spec clearance with the pump gears...so I re-assembled with one of the thin gaskets and measured about 0.007 inches in the worst spot.

I honed the cover's inside surface by rubbing against 100 grit sandpaper. Most of the gear marks were removed. I did not detect any warping but did find minor uneveness due to the cover's manufacture. Re-measuring, the maximum end clearance was around 0.004 inches which is in-spec from the literature I have.

I am doing some other work on this tractor so I cannot report yet how the cover lapping and gasket change affected the oil pressure...I hope to follow-up on this in about a week. I'm really hoping to have about 35 psi cold start pressure and at least 20 psi warm, high speed pressure. If these changes give the improvement sought, I will split the FCub in the off-season (winter) and have a try at tightening it up.
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Re: Oil Pressure Variations

Postby Ironlegs » Mon Jun 30, 2014 8:52 am

Here are the performance numbers after replacing my tractor's rod and crank shaft bearings and lapping the inside of the oil pump bottom cover and replacing the cover gasket with a thinner gasket...using 30 weight motor oil:

1-immediately after a cold start: oil pressure around 45 psi
2-warm engine at idle: 28-30 psi
3-warm engine, high speed under load: 34-36 psi

As some of the fellows here suggested, most of the improved oil pressure was probably a result of tighter bearings. The oil pump improvements probably contributed to about 5-7 psi of the improvement.

I was elated when I got the engine started and noticed oil pressure topping 40 psi...over the twenty plus years I operated this machine, I never had oil pressure above 20 psi. I am encouraged to open-up the crank case of my FCub to replace the crank shaft bearings to get improvement in its oil pressure...after seeing what new pressure results, I can decide on whether to split the FCub to work on its oil pump.
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Re: Oil Pressure Variations

Postby Ironlegs » Wed Jul 16, 2014 7:54 am

Okay guys, here's the wrap-up on this topic: I lapped the Super A's oil pump bottom cover plate to something like 0.003 inches clearance with the pump gears...it was something like 0.007 before the lapping. I also replaced the crank shaft journal bearings and rod bearings and checked to make sure the block's oil passages were unobstructed (they weren't). New oil filter and SAE30W oil produced about 40 psi with no load, 1200 rpm right after a cold start. Once warm, the oil pressure remains above 30 psi for all speeds and loads. I'm very happy with the improvement and feel most of it is due to renewing the crank shaft bearings. Hand-lapping the pump helped...perhaps, ten percent of the improvement. Thanks to all for the guidance.
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Re: Oil Pressure Variations

Postby artc » Wed Jul 16, 2014 3:28 pm

just to add to Jim Becker's comments on the A/B/C/ super A oil pumps, you also want to look closely at any damage in the oil pump gear housing itself. i've seen a couple of oil pumps with worn shaft bushings, resulting in the oil pump gear hitting the housing. the worst one was from a 450 - i had to save it under the bench for show and tell, it was so trashed.
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