replacing a fuel pump diaphragm

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davebern
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Joined: Mon Jul 02, 2007 12:31 am
Location: Australia

replacing a fuel pump diaphragm

Post #1 by davebern » Thu Mar 13, 2008 10:05 pm

In response to a few calls to detail my fuel pump diaphragm replacement, here is a brief how-to
(I'm sorry but I didn't take any pictures when I did it....)
1: Pull the pump off the bike and remove the top cover.
2: You need to remove the pivot pin. This is sealed by a hardened ball bearing pressed into each end. Mount the pump on an angle bracket and set it up on a mill or sturdy drill press. You need to drill out one ball bearing with a 4mm diameter CARBIDE end mill. It needs to be solid carbide not HSS. Once its drilled through you can then drive out the pivot pin, pushing the other ball bearing out ahead of it. Then you can drive out the ball bearing with the hole from the other side.
3: You can now pull the pump completely apart so you end up with the diaphragm assembly in your hand.
4: Because the diaphragm shaft has a headed end, you will need to make up a split collet so you can hold the shaft in a lathe. You then need to turn away the riveted head so the diaphragm and washers come off the shaft.
5: While the shaft is in the lathe, drill and tap the centre of the shaft so the new diaphragm can be held in place. I think I used an M3 or M4 tap.
6: Get a sheet of diaphragm material. I used "GOSS HANDI-GASKET GP12 Diaphragm sheet - Nitrile, Fabric reinforced" It's around 1mm thick. Trace the old shape onto the new sheet and cut it out.
7: Reassemble the sheet onto the rod with a wipe of fuel resistant sealer between the washers and screw it together. You'll need an appropriate washer under the screw to allow the assembly to compress a bit as you tighten it up.
8: Assemble the mechanism together and insert the pivot pin. Instead of sealing it with ball bearings, I filled the ends with epoxy, it will make removal a lot easier in the future.

And that's all there is to it! As I said, not a job for the beginner, but not hard if you have a small lathe and drill press in the shed.

let me know if anoyne else gives it a go!
Dave
'75 GL1000

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