41 Farmall H oil pump

How to check body gears backlash on a Farmall H oil pump?
Is it the clearance between the two drive gears where gear teeth contact, do I use a dial indicator?

There are no specs on the clearance between the gear teeth. The important thing is if they are worn smooth. The clearance that is critical is between the outer edge of the gear and the housing s(measure with feeler gauge) along with end clearance of gear to cover.

The shaft wears bad on those pumps and sometimes the stud idler gear runs on. This will give you excessive clearance between between gear and housing.

The reason clearance between gear teeth is not critical is that under pressure while operating, the driving gear teeth will be fully engaged with the idle gear and if smooth will seal the oil. If they are worn rough then oil will leak through between the gear teeth. This is normally not a problem. I have replaced many a worn out shaft which always came with new gear installed and used the old idler gear to obtain proper oil pressures.

Replacing spring and plunger was just something we always did when repairing a pump. Make sure plunger is same diameter top to bottom on H or M gasoline engines as some other models used a plunger with a slightly smaller diameter on closed end of plunger. Parts books were screwed up years ago and some of them wrong plungers got into the system. Saw it twice in my years. Gives you about 45 psi tops with wrong plunger where correct on gives near 70 psi.

Whats more important is the clearance at the bottom of the pump between the gears and the bottom plate. It's like 0.001 to 0.002 between the gears and bottom plate(don't quote me). You should buy the factory gasket for this, they are half as thick as what is sold on this site. The bottom plate needs to be smooth and flat. On the last one I refurbished I spent hours with a flat block of steel and wet or dry sand paper getting it so. Last I check you could buy a replacement but they were pretty spendy. You can check the clearance with plastigage which you can get an most auto parts stores.


OTJ