The Fordson Tractor Pages Forum

Hi, I have a 1964 Super Dexta with the Simms mechanical governor fuel pump. When I pump the lift pump lever, fuel comes out of the pig tail vent tube. I did some research and it seemed like a ruptured diaphragm in the lift pump could be the issue.

However, after I removed the lift pump I could pump the lever and build pressure by blocking the outlet with my finger. The pressure holds, doesn't leak down. This makes me believe the lift pump is not the problem.

Where should I look now?

You might have to give the injector pump an overhaul, as it sounds there's a big leak in there.
Sandy

Billy26F5 wrote: ↑

Fri Sep 03, 2021 9:06 pm

You might have to give the injector pump an overhaul, as it sounds there's a big leak in there.
Sandy

That's what I was afraid the answer would be. I'm in the United States, how difficult is an overhaul on this pump?

Take the side plate off, start the engine and see if you can see diesel leaking down from any of the delivery valves, if you can see it running down in the pump then i'm afraid, as Sandy says you'll need a rebuild from a pump specialist
John

John b wrote: ↑

Fri Sep 03, 2021 9:13 pm

Take the side plate off, start the engine and see if you can see diesel leaking down from any of the delivery valves

You should only need to pump the lift pump given your problem.
Sandy

True!

Your problem is almost certainly the lift pump diaphragm despite what you say about how it behaved after you had removed it. If you had that amount of leak down from the pumping elements your engine would be extremely difficult if not impossible to start. Get an overhaul kit and rebuild the pump, I recently had the same issue with the lift pump on my 1962 Dexta and fitted an overhaul kit from www.injectionpumps.co.uk - the part number is BD17 , £13.55 for AC pump types MD, YD, YJ.

If you have the VP type lift pump the overhaul kit is BD26, £12.67, check out the shape of the diaphragm on your pump with the listing details.

For the extra cost I'd fit a new lift pump. I've overhauled them before, but for the time it takes I don't think its worth the effort. Remember time is money, even if you are doing this for fun

If you have to overhaul the pump professionally it cost me £500. Take a look at BundyBears shed. He has a load of videos on youtube and a couple on overhauling fuel pumps. I'll be doing my own in future.

If the tractor is fitted with an original genuine lift pump then I prefer to overhaul to keep the tractor original. Sometimes these spurious replacements have poorly shaped castings or threads not tapped properly on the pipe inlets, etc etc.

Bluebilly, I assume you mean £500 for an injection pump overhaul? All parts for the Simms minimec and SP 3 and SP 4 pumps are available at keen prices from www.injectionpumps.co.uk
With regard to this tractor, as I said if there was that amount of leak down from the pumping elements the tractor would be very hard to start, the issue is almost certainly the lift pump.

Thanks for the replies. I may have not given enough information in my original post. I bought this tractor about ten years ago, it did not run. The tractor had a lot of things wrong but the injection pump was in working condition and the lift pump had been replaced by the previous owner in an attempt to get it running.
I got it running, one problem it had was the fuel supply line leaked and the previous owner tried to repair them with black tape. There were "repairs" like this in many places.
I replaced the fuel line, all filters and fluids. New clutch, axle seals and brake linings. Rebuilt starter. Installed a thermostat. Once I was done the tractor ran great and has been trouble free for the last nine years.
Then, this summer I noticed when I pressed the lift pump manual lever the pigtail would drip fuel. Not a lot, but enough to concern me.

I'm going to try what was posted above, examining the delivery valves as I press the lever.
The lift pump does hold pressure when I stop the outlet with my finger. It was suggested on another forum I check if it will hold vacuum. I will test that today.

Thanks,
Terry

I filled the lift pump with fluid and worked the lever. The pump holds vacuum at the inlet and pressure at the outlet. I also removed the five screws and examined the diaphragm. I saw no ruptures and under the diaphragm was dry.
I put the lift pump back on the injection pump and pumped up pressure. No drips of visible leaks.
I removed the deliver cover from the injection pump and again, no visible leak.
Started the tractor with the cover off. At first, everything looked dry. Then with the tractor running I saw small bubbles near the base of the plungers.
I suppose this means there is wear in the plungers.
The tractor still runs very well. Should I just leave it and allow it to get worse? Or is there some preventive maintenance that I should do at this point?
I did change the oil in the pump. It came out mostly diesel and had a shimmery brass look.

If the engine starts and runs well then the injection pump elements MUST be in good condition, any leakage between the plungers and barrels would be most apparent at starting cranking speed, quite simply the injector pump would not deliver enough pressure to the injectors to operate the nozzles crisply enough to give a good start.

One thing that springs to mind, on the minimec pump the delivery valves are held in place with the knurled unions on the top of the pump onto which the injector pipes attach. The knurled unions are clamped together with clamps held by Allen screws, these are supposed to stop the knurled unions coming loose. Under the knurled unions are nylon sealing washers that seal the joint between the pump body and the delivery valves. Sometimes the knurled unions can loosen a bit without it being apparent, resulting in leakage from the delivery valves into the pump body and the cambox. Give these knurled unions and washers a good checking out. If you are seeing what looks like bubbles at the bottom of the pump elements it could be that fuel is running down the element from the delivery valve area and the vibration of the pump elements is causing the bubble effect in the leaking fuel.

If all this checks out OK and the engine starts and runs well then there is no major cause for concern.

Thank you Shep, I will check the area you suggested.
I used the tractor today to bushhog and it ran very well, so I don't believe I have a major problem. This tractor will outlast me I suspect.

To check the delivery valve holders you'll need a special spanner, tool no. CT.9054, to avoid damage. Torque to 33 lb ft.
Sandy

The special splined socket for the minimec delivery valve retainers is also available from
www.injectionpumps.co.uk but it is expensive, £49.72

Aside from the nylon sealing washer there is also an aluminium washer that seals the delivery valve holder to the pump body, this will be able to withstand fuel injection pressure.