Kyosan Denki Fuel Pump Rebuild

[240L31]

As my electrical fuel pump installation failed due to too little flow, I decided to rebuild the stock mechanical fuel pump. I ordered OEM parts but still had a similar looking american fuel pump. As I was curious, I took it apart and pictured the differences.

Findings:
- Castings are identical
- Afermarket rubber diaphram looks better (there's a reinforcement webbing layer in the middle), T style plunger is identical in size
- Aftermarket main spring is slightly stronger (most likely as the OE one settled a bit)
- Aftermarket helper spring is slightly weaker (1.0mm vs. 1.2mm OE)
- Aftermarket valves are pressed in place and can't be changed. Additionally, the movable valve part is a rubber disk as opposed to a solid disk (OE)
- The aftermarket pump has a 8mm inlet and 6.5mm outlet - this is a big plus! As the fuel rail is 6.5mm and the fuel filter 8mm

All in all the aftermarket pump is a great parts donor!

 

[240L31]

Question to all: Could you check what is written at the bottom of your pump? I have one saying L20 and one KJ, for now I assume it is some batch code (as both my pumps are from a L24 engine)

 

[SacCyclone]

Are you using the GMB, or Carter, or Delphi fuel pumps from the states??
I have used the GMB several times and it has worked ok but I never tried to transfer the parts to a Nikki.
I purchased a rebuild kit for the Nikki from a chap in Canada a year or so ago but have not had a chance to rebuild one yet. I think his kits were about $50 each.
I have several Nikki / Kyosan pumps set aside for rebuild and will check for the numbers next week at the shop.
Mike

 

[240L31]

It's the GMB pump. I think the Nikki internals are different and spare parts (at least from Nissan) are NLA.

 

[Mark N]

If the PCDs of the top seal and the diaphragm are the same and you want to maintain the aesthetics of the Kyosan pump, you may just be able to swap out the valve carrier assemblies and make a Frankenstein pump.



I don't see the size of the inner support disc on the diaphragm having any effect on its operation as the diaphragm springs both look to be the same size.
Are the oil seals interchangeable?

 

[uk66fastback]

My original pump has nothing on the bottom ...

 

[240L31]

That's a Nikki pump.. Not kyosan

 

[uk66fastback]

Sorry, I need to read the threads more in-depth and with more concentration! I saw Nikki mentioned above, that’s my excuse ...

 

[AliK]

Really great write up!! Big thumbs up!

I have 3 pumps, when I can lift things again and able to move my parts bins about, I will report back.

I also have a new one which I took apart suspecting it had a broken diaphragm, but I found the same as you described - a very strong reinforced diaphragm.

Strangely though, the stock helper spring on mine was longer than the new one - go figure!

 

[SacCyclone]

I just checked on the rebuild kits I got from Canada and they are for the KOYSAN and DENKI fuel pumps at $55 shipped to the US.

The web site is new-datsun-parts.com

I just checked the web site and do not see a listing for the kit at this time. Sent them a email to check status.

Mike

 

[240L31]

That's where I bought my oem parts for the Kyosan pump. If I would do it again, I'd only buy the valves (and use the GMB rubber parts).

 

[SacCyclone]

Got a reply back from new-datsun-parts and they are still available....new price is $50 plus $24 shipping to the states. Best to buy multiples next time to save a little quan.
Mike

 

[240L31]

The little round gaskets below the valves are NLA. I measured them and had a few laser cut, looks like stock (and should be good enough for another 50 years).

 

[240L31]

If the PCDs of the top seal and the diaphragm are the same and you want to maintain the aesthetics of the Kyosan pump, you may just be able to swap out the valve carrier assemblies and make a Frankenstein pump.

I don't see the size of the inner support disc on the diaphragm having any effect on its operation as the diaphragm springs both look to be the same size.
Are the oil seals interchangeable?

I've read many, many times that the new replacement pump valves fail quickly. So I wouldn't recommend swapping the valve carrier. I agree, I think the size of the inner support disk doesn't matter, they are interchangeable. The OEM one features a centering ring for the spring but I'd say it is not really needed.

 

[240L31]

I had everything ultrasonic cleaned and sand blasted the cover and the middle part (not the bottom). New OEM valves and gaskets installed, should be good for another 50 years!

 

[uk66fastback]

Looks excellent Tim. So what's next, refit and then try it at the same engine speeds as the electric one and see how the feed is?

 

[240L31]

Yes, and it will work fine (as I already have a mechanical pump on this engine).

 

[SacCyclone]

So 2 years later, are we still using a GMB pump internals to rebuild Nikki and Kyosan fuel pumps??

I have 2 Nikki pumps that I would like to rebuild and put up on the shelf, maybe sell one.

Mike

 

[240L31]

My rebuild pump works flawlessly just don't use the gmb valves.