Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 M3W Fuel Pump Replacement

As promised, here are some pictures of a failed OEM 3W fuel pump that I dismantled.

here is the assembly, not many parts. there were no numbers nor manufacturer marks anywhere. the pump is clearly based on the old Walbro pump patents.
https://www.tm-img.com/images/2019/02/27/assembly.jpg

With the exception of one brush failing, all else was clean and in good condition. The damaged brush did not move freely in its' socket, I suspect that full contact with the commutator became less and less and arcing started to take the brush apart.
[img:left]https://www.tm-img.com/image/YPo6O[/img]

In this view, you can see the brush on the right was making normal and full contact. The yellow circle shows the tiny area where the damaged brush was making contact.
[img:left]https://www.tm-img.com/image/YPiEH[/img]

At this point, there is no way to know if this is the common failure mode. I will need to dismantle more failed pumps to see.
Next, I will put a thermocouple in the fuel return basket to see how hot the fuel actually gets. Walbro pumps are advertised to work in the temp. range of -40 to 155 degrees F.

wow... that is really lack of quality (I am being polite)

Looks like an aquarium pump, a shoddy one at that! It should not eat brushes.

Could there be a ground issue causing extra load on its motor?

Wow, that't really interesting - thanks for taking the time to share the info.

Thanks for that info Kolvites. It confirms what we thought and what the Land Rover Discovery people found with their pumps. It will be interesting to see if other pumps have failed in the same way or if other defects have caused failures.

DEI offers heat insulation tubing for this application that are complementary to their exhaust wraps: DEI

Nice analysis Kolvites! Wonderful to see actual failure cause analysis...

If that is the "typical" failure scenario, it would seem unlikely that fuel temperature would be a contributing factor, unless the pump is overheating. Which I guess could causes the brush springs to weaken, potentially leading to the brush arcing and failing.

Is Morgan still using these pumps or have they upgraded what they are putting into new M3W?

Kolvites has done us all a big favor by showing this failure.

It takes a lot of heat to take the temper out of a spring... around 750 degrees F. The molded plastic end caps seem to be made of nylon. Nylon melts around 300 degrees F. The molded caps would be melting long before the springs lost their temper.
I think the brush was sticking in its' cavity... just a guess.

As I said previously, I need to see more failed pumps.

This weekend, I will place thermocouples on the fuel pump body and in the fuel return bucket. If it ever stops raining here, I can take a long ride and record the results.

I think the only way to overheat the pump is to run it dry. And most likely, the bearings would begin to seize and cause an increase in the current demand causing the appearance that the motor over heated for other reasons. The fuel circulating through the pump should keep it well within it's safe operating temperature.

I believe that the theory of wrapping the fuel lines with insulation is a hold-over from the days of carburetors, when fuel lines ran close to hot engines and caused vapor lock. At atmospheric pressure, automotive fuels will boil at temps. between 100 and 400 degrees F. The wide range is due to the various additives used.
With fuel under 58 psi pressure, there is no chance of the fuel boiling and causing vapor lock. Higher pressure, higher boiling point. Lower pressure, lower boiling point.

And, with the fuel sloshing around in those big, heat-sink aluminum tanks, how can the fuel heat up so much to cause damage. Put your hand on the fuel tank after a long run... see if it's hot.

that failure is temp related... it is quality or lack of related