F12 fuel pump

[handcrank]

Is there a way to check the fuel pump for proper operation when it's on the bench?

 

[Fritz Maurer]

Yeah with the bowl on it , it should hold vacuum, although this is not a 100% requirement since the pump is gravity fed. Clamp it in a vice and operate the lever and see what it does. Dont clamp it by one of the bolt holes, it may break off.
When installing it to the tractor , turn the engine so the fuel pump push rod is all the way retracted. You should be able to feel the rod contact the lever and start to move the diaphragm. If not , try it without the gasket. If the rod now makes contact, you can install the pump without a gasket, with just a light coat of RTV on the block. Sometimes the push rod will wear down and wont move the diaphragm far enough. If at this point you still dont have contact, the push rod is too short and will have to be lengthened. Carefully drill a hole in the end of the pump end, and tap it for a 8-32 pan head screw. Then if this turns out to be too long, just grind a little off the head of the screw until you get the required clearance.

 

[rustred]

These pumps require the push rod to be the proper length. Its was the same deal as the old flathead Ford engines. U had to put a weld bead on the end to make up for wear. Had to do the sand on my w-12 to make it pump. As long as the valves and diaphragm inside are good then that is most likely the problem.

 

[Ron W]

What's the pushrod length?

 

[handcrank]

I don't know what you mean when you say it should hold vacuum with the bowl on it. I have the tractor timed on tdc on number one cyl.would the push rod be retracted all the way at this time?if it is I should feel a little resistance when I install it. Correct? Bear with me, this is all new to me, many thanks.

 

[rustred]

push the lever by hand and stick your thumb over the inlet hole it should suck you thumb in and stay there. if no suction the diaphram is toast. those fuel pumps you could by the kit for but i highly dought it now. also those fuel pumps are scarce as hens teeth already.

 

[rustred]

i dont remember as i did have that measurement. i usually go by the wear amount and just give her a bit of weld bead on the end. then grind it down flat or a bit convex. 1/8 longer may do the trick.it dont take much.

 

[SadFarmall]

I found an old post here and on a couple of other forums. I think the correct length is exactly 7".
SadFarmall

 

[Charlie M]

You cans still buy kits for the pumps. I've bought a couple for my F14 - had the diaphragm go bad a couple of times.

 

[Fritz Maurer]

I really dont know what the crankshaft position would be when the fuel pump push rod is on low cam. Thats an excellent piece of information I never thought about! You can bet Im gonna find that out for future reference. You are also correct about feeling resistance as the pump draws close to the block.
You can also gain a couple mm of stroke if the mounting face of the pump is flat. In many cases, the bolt holes of the pump flange are bent towards the engine. This is because the gasket compresses more under the bolts than the rest of the flange. File it down until you have an unbroken ring of bright metal all the way around the flange . Within limits, I prefer a worn out push rod, as this allows me to screw the pump directly to the block with no gasket. This makes it impossible for the flange to warp again. If you are using a gasket be careful not to over-tighten, one hand with a 1/4 inch ratchet is plenty.

 

[rustred]

The fuel pump runs off the camshaft essentric. .

 

[Oldiron29]

Not really a way to test on bench as you need fluid to see if check valves work.
I set up a small starter tank on my hood for working on these tractor so you can gravity feed gas to carb and get engine running.
Than you can put a rubber hose on the exit side of fuel pump and see if you get a good stream of fuel out of pump before you hook it back to carb. Also a tractor that has sat for some time, it helps to have a bowl drain on the carb so after cranking you can check to see if you have fuel at the carb. It could take 20 cranks to get fuel up to carb and it will not start if it is not there.