How stiff should mechanical Type 4 Fuel Pump be?

Discussion in 'Mech Tech' started by Spacecowboyuk, Jun 18, 2022.

  1. As per title I have whipped a pump off my spare engine and I'm wondering if its possible to bench test it before installing it?
    20220618_100120.jpg 20220618_100131.jpg
     
  2. nicktuft

    nicktuft Supporter

    Don't know a way of testing it but if you think it's too stiff it could be that the diaphragm is dry.
    Try pouring some petrol into it and try again tomorrow.
     
    Spacecowboyuk likes this.
  3. davidoft

    davidoft Sponsor

  4. mikedjames

    mikedjames Supporter

    Its the constant return force behaviour of the spring that provides the fuel pressure, so to get at least 3.5 psi to regulate down to on the outlet when you let go, you need a fair push on the lever.

    You should be able to do a quick test by seeing if it sucks hard on the inlet if you push the lever in.

    But you cant tell if its leaking slightly until you make it work hard..
     
    Spacecowboyuk likes this.
  5. Going to rig it up to a jerry can. Stand by.
     
  6. So it does pump and suck but the lever seems to get stuck as well. I'll leave it with fuel in overnight. The old one pumps easily.

    It's almost as though the overflow vent thing is blocked stopping the lever returning. Eventually it returns back to its position.
     
  7. Zed

    Zed Gradually getting grumpier

    Take it apart, maybe you can make one good one out of your two, inspect the diaphram, grease the moving parts etc.
     
    snotty likes this.
  8. I thought about that but was apprehensive on the basis that there seems to be some kind of preload you need to apply when putting back together? Im unable to find any info on that process.
     
  9. mikedjames

    mikedjames Supporter

    It doesnt work properly, so you have nothing to lose. Take it apart carefully so as not to tear rubber. Take pictures if you cant remember how it all goes.
    Start with the wider outer ring of screws at the base, thats the pump diaphragm. If theres something wrong its probably under that you will find the crud or wear and tear.
    The operating lever is hooked over the operating pin from the pump diaphragm.
    The top bit I think is a cover over the pressure regulator bits.

    I took apart one of the T1 pumps that uses this style of construction off a Mexican engine, it was maybe a bit fiddly persuading the pin from the diaphragm back into the slot in the end of the operating lever with all the springiness around..

    Its just a pity that although SSP make a replacement T4 pump, the rebuild kits all seem to be for the T1 pumps..probably worth chatting to Heritage Parts who sell the SSP kit.
     
    Last edited: Jun 19, 2022
    Spacecowboyuk likes this.
  10. Update: left petrol in it overnight and it now moves and returns freely. Thanks for the suggestion @nicktuft.

    I'll go ahead with the install and take the original one apart to see what has failed.

    Should I grease/pack with grease the actuating arm before install or will the oil that drips in there do that?
     
  11. Old pump apart:
    20220619_190347.jpg 20220619_190543.jpg 20220619_190350.jpg 20220619_190400.jpg 20220619_190758.jpg 20220619_190914.jpg 20220619_191442.jpg 20220619_191519.jpg

    So as you can see the larger diaphragm has small cracks both sides. The smaller one has some kind of corrosion on it and inside the top section. I'm curious as to whether this can be fixed following the rebuild guide elsewhere on tlb:thinking:

    I'm also a bit perplexed by the vent/drain which looks to be quite dirty whereas the rest of that section looks to be clean. I never actually saw the pump leaking but my assumption was it came from the vent tube as the location on the ground matched it. What do you think?
     
  12. Zed

    Zed Gradually getting grumpier

    I think this split leaked when running. The vent tube is where they leak from when the diaphragm splits.
    [​IMG]
     
    jivedubbin and Spacecowboyuk like this.
  13. Close up of this crack too. Basically the bus sat for several months and started leaking spontaneously over the winter:

    Screenshot_20220619-210849_Gallery.jpg
     
  14. Zed

    Zed Gradually getting grumpier

    Answered your own question. :)
     
  15. 2 out of 2 then:thumbsup:
     
    Zed likes this.
  16. mikedjames

    mikedjames Supporter

    The drain would be constantly pumping dirty air in and out as the pump diaphragm goes up and down.
    The rust looks like its sat with a fair bit of water in it..engine left out in garden ?
     
  17. Engine is in the Bus. Its been sat over winter. Do you think the fuel tank has water in it? Also should I grease the actuating arm with vaseline or grease?
     
  18. mikedjames

    mikedjames Supporter

    You cannot really tell when the rust actually formed. It could be some time ago before you had anything to do with it. Maybe theres some matching rust in the tank, maybe that engine did sit around or get a lot of water in the fuel at some time.

    I think the rust is inside the fuel delivery area, where the pressure regulator/check valve part is at the top of the pump, so I would try and chip it out, to avoid risking it breaking off and getting into the carburettors or messing up the pressure regulation.

    For the hinge, you should use some general purpose grease, vaseline will melt and vanish. (it melts a bit above body heat .. )
     
    Last edited: Jun 20, 2022
  19. Fair enough. I won't be using this pump but fitting my spare but at least i know it will go again. Just need to do the repair in the link above.

    I'm sure I should go electric etc and I was going to. However, this pump has done the bus proud for many a decade so I'll happily continue the same for now albeit with my spare.
     

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