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zKars

Weakness Revealed in the GMB and Spectra Mechanic Fuel pumps

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Posted (edited)

I've recently been through the wringer on mechanical fuel pumps. I LOVE the stock mechanical pumps and dearly wish to be able to use them more. Silent, plenty of volume to run triples etc up to 250 hp (my educated guess). Stock new pumps put out a CRAP load of volume even at cranking speeds. 

The cheap "offshore" GMB and Spectra fuel pumps that are out there that look like the stock Nikki/Ampco/Kyosan Densi  pumps have been reported here and elsewhere are a ticket to very early failure. I can further attest to this experience. Had a fresh GMB make it about 10 km before leaving a customer/friend stranded.

So after much investigation of the issue, I have good news. 

1. The GMB and more expensive Spectra are identical inside. The diaphragm and check valves are visually and texturally identical. Might as well buy the GMB ($18.72 CAD on Rock Auto)

2. The problem is with the check valves. The design of the flapper is weak and shitty. The OEM diaphragms are thick and strong and seem fine. The failure is that they stop (or barely start ) being able to pull fuel from the tank. Any air gets in there and they loose prime. If you actuate the pump by hand on the bench in a vise with your finger over the intake, you can barely feel any suction. Do that with OEM pump and it will suck the skin off your finger tip. (Air intake only, no liquid). 

Now the really good news happens when you want to rebuild your old OEM Pump. Up till now it's been tough to find rebuild parts.

I took apart about 20 OEM pumps (all three brands, 14 Z and 6 510 ) and noticed the following.

1. Diaphragms; Depending on age and use, some were fine, some were hard and/or cracked. No surprise. About 40/60 good/bad.

2. Upper diaphragm. Not even sure what the function is of the upper rubber diaphragm, but 100% were soft and reusable. Don't think they endure much hardship. Maybe one was a little stiffer than the others. I'm sure we could fill an long thread discussing what its for.... Please don't here.

3. Check Valves. The real surprise. 100% of them were 100% perfect and appeared nearly brand new. All were clean, no sign of crud buildup or damage or erosion/corrosion. These things are indestructible apparently and totally un-affected by fuel or time.

4. Lower seals. Where the rod passes through to the actuator. About 4 out of the 20 were still soft and usable. Lots of splits and hardness.

Ok, knowing what we know about the new copies (GMB and Spectra) and the old faithfuls, and what's wrong and right about both species, is anyone seeing the possibilities here?

 

IMG_6315.JPG

OEM Body, check valves removed

IMG_6308.JPG

OEM check valves, front and back. Thick solid valve body. 

IMG_6309.JPG

GMB check valves, front and back. Thin rubbery floppy material.

IMG_6310.JPG

GMB check valves are held in place with punched nibbins. Very hard to replace the valves. Well, easy to get out, but how do you keep new ones in?

You'd have to drill and tap a pair of center holes to use the stock center hold down bracket thingy. Do-able, but....

Are these held in tightly against the gasket? Is there a gasket? Do they come loose with use and abuse? Inquiring minds need to know!

IMG_6311.JPG

GMB mid case with their check valves in place, top view

IMG_6312.JPG

back side of GMB upper hosing. Note different shape of center beam.

IMG_6313.JPG

Top of GMB pump housing. Fuzzy picture like the whole situation.

 
Edited by zKars
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What you do, is go buy the $19 GMB, replace its check valves with your old perfectly good OEM ones, and put that hybrid baby back in the car for millions of additional miles and smiles.

(Please put the GMB check valves on the cement floor and crush them into dust with a large hammer, lest you get tempted to use them at a later date. Don't)

You get a new diaphragm, new lower seal, your perfectly good check valves, and the new GMB upper diaphragm that all make up a nearly new unit, and should run for a few years pump.

Ok, all is not perfect here, there are a couple of details you need to deal with, but its all manageable. I'll explain in a but once I take some pictures. 

I guess the risk is that the GMB diaphragm material will fail faster than the OEM (or the new Nikki ones you get with Nikki pumps for non Z's to steal their internals from, remember that thread?) that is still to be seen, but all in all, maybe we have a cheaper route to rebuilt pumps here.

 

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Posted (edited)

First thing to say about the "details" is that all the OEM pumps I took apart and scavenged parts from are identical as far as the location and size of the bolt circle that bolts the main body halves together and the top cap in place. So you can interchange just about any part with any part from any brand.  

The GMB and Spectra ALSO use the same bolt patterns. So you can interchange their bits with the OEM bits. 

There are small gotcha's here. Some of the upper caps are not interchangeable across all brands as the divider wall in the center is not in the same clocking with the bolt pattern. All you have to do is use a matching cover and middle housing from any one brand.

Next is a small annoyance that the way the check valves are held into the middle housings is VERY different with the GMB/Spectra. Cheaper and crappier of course. They use a 4 point punch around the perimiter to trap the check valves into the housing. Hard to get them out, and if you did, you couldn't get your OEM check valves to stay in as you'd have a heck of a time re-punching around the edge to keep them tight and in place. Pictures coming.

SO,. It actually makes sense to use the check valve housing and its matching cap from your old OEM pump and bolt it to the GMB/Spectra base housing. Keep all the good bits together. It does mean you have to do so sort of clean up of your OEM castings to match the new GMB castings if you care about that stuff

Edited by zKars
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Posted (edited)

The last "gotcha" is the tiny thin seal washer between the check valve and its seat in the housing. I was able to remove virtually NONE of the OEM ones. They were hard and stiff and stuck in real well. They were easy to scrap out, but were always destroyed in the process.

So you may need to source or make some new ones. 3/4 OD (19mm) and about 18mm ID. Only about 0.05 thickness. 

A tiny ring of RTV would do as well.... You want that check valve sealed to the housings. NO LEAKS ALLOWED around the check valves.

 

Edited by zKars
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On 6/4/2020 at 10:18 PM, zKars said:

I've recently been through the wringer on mechanical fuel pumps. I LOVE the stock mechanical pumps and dearly wish to be able to use them more. Silent, plenty of volume to run triples etc up to 250 hp (my educated guess). Stock new pumps put out a CRAP load of volume even at cranking speeds. 

The cheap "offshore" GMB and Spectra fuel pumps that are out there that look like the stock Nikki/Ampco/Kyosan Densi  pumps have been reported here and elsewhere are a ticket to very early failure. I can further attest to this experience. Had a fresh GMB make it about 10 km before leaving a customer/friend stranded.

So after much investigation of the issue, I have good news. 

1. The GMB and more expensive Spectra are identical inside. The diaphragm and check valves are visually and texturally identical. Might as well buy the GMB ($18.72 CAD on Rock Auto)

2. The problem is with the check valves. The design of the flapper is weak and shitty. The diaphragms are thick and strong and seem fine. The failure is that they stop (or barely start ) being able to pull fuel from the tank. Any air gets in there and they loose prime. If you actuate the pump by hand on the bench in a vise with your finger over the intake, you can barely feel any suction. Do that with OEM pump and it will suck the skin off your finger tip. (Air intake only, no liquid). 

Now the really good news happens when you want to rebuild your old OEM Pump. Up till now it's been tough to find rebuild parts.

I took apart about 20 OEM pumps (all three brands, 14 Z and 6 510 ) and noticed the following.

1. Diaphragms; Depending on age and use, some were fine, some were hard and/or cracked. No surprise. About 40/60 good/bad.

2. Upper diaphragm. Not even sure what the function is of the upper rubber diaphragm, but 100% were soft and reusable. Don't think they endure much hardship. Maybe one was a little stiffer than the others. I'm sure we could fill an long thread discussing what its for.... Please don't here.

3. Check Valves. The real surprise. 100% of them were 100% perfect and appeared nearly brand new. All were clean, no sign of crud buildup or damage or erosion/corrosion. These things are indestructible apparently and totally un-affected by fuel or time.

4. Lower seals. Where the rod passes through to the actuator. About 4 out of the 20 were still soft and usable. Lots of splits and hardness.

 

Ok, knowing what we know about the new copies (GMB and Spectra) and the old faithfuls, and what's wrong and right about both species, is anyone seeing the possibilities here?

 


 

 

 
 
 
 
 

What happened to the Pictures/Images that were Posted here?

thanks,

Carl

 

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Not sure what is up with the pictures. I uploaded to the site, they were not on some other service or web site. 

@Mikecan you have a look and see what might be up?

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Today I rebuilt 3 Kyson Denki pumps using the Delphi/GMB internals. I used the original housing and swapped out all the rubber diaphragms. The check valves were removed, cleaned, and reinstalled. My o'rings were is great shape but I did install some Permatex fuel resistant gasket dressing to make sure there was a good seal. Next, I tested each pump manually by pumping fuel. Installed one and she runs great. I did notice while disassembling the Delphi/GMB pumps that the screws were a little loose which could be the reason some of them fail. I had another Delphi/GMB pump with a bad check valve. As mentioned, the Ampco and Atsugi have different internals and the top diaphragm holes do not line up. 

 

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I think I'll be doing that soon for Bill's car, @David Downs. I have the carbs tuned nice, but it is starving for fuel.

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I have another case reported today from a local customer with a <100 km use new Spectra pump that failed. 

Fortunately it was initial warm up in his garage, not on the road, but that was just pure luck. He was on his way to a wedding (not his at least) but was anxious to show it off to family members. Very disappointing.

I'll have that rotten pump and the Z in my shop tomorrow. I will thoroughly diagnose the issue with the pump and let you know what I find.

 

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Weren't the fuel pump companies looking in to this?  Whatever happened with that?

And how about those pictures?  Probably got disappeared when Mike went back to the old format, whenever that was.  They gotta be on a server somewhere.  @Mike

There's a lot of value in this thread, stopping Z cars from dying dead.  

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The pictures are on my phone somewhere. I'll do more to spruce up the thread when I find out details on this pump tomorrow 

I was doing a bit of research again on what's out there, and wanted to share the current status of what RockAuto sells.

The GMB, US Motor Works and Delphi are shown as having the OEM look, but look at that price difference! 

GMB is free is $18 buck, where as the USMP is $72!! Maybe it has quality innards.   yeah, right.....

RockAuto_today_FuelPumpDifferent_Options.png

Edited by zKars

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Interesting that Delphi and Spectra are out of stock.  Sometimes that means discontinued.

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Ok, I have a clue! Highly unexpected, but true.

What I need is someone with a failed Spectra or GMB mechanical pump that is willing to take the top cap off and tell me what they see. 

Don’t take it off without marking it’s position relative to the body first!! Very Important!!!!

Anybody?

 

 

Edited by zKars

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48 minutes ago, zKars said:

Ok, I have a clue! Highly unexpected, but true.

What I need is someone with a failed Spectra or GMB mechanical pump that is willing to take the top cap off and tell me what they see. 

Don’t take it off without marking it’s position relative to the body first!! Very Important!!!!

Anybody?

 

 

I have taken a few apart to rebuild some Kyson Denki pumps. Enlighten us on what you expect us to see. I can tell you when I removed one of the caps on a GMB or Delphi the top of the rubber gasket was wet (one side only). I believe this pump failed because the gasket didn't seal properly around the cap screw. One of the other pumps had a bad check valve and you could see the seal damage.

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Following, I’m new to this game so excuse me if I sound uneducated. I cannibalized a GMB pump for the diaphragm and check valves to install on my Kyosan Denki as a preventative maintenance measure. Drove about 25 miles with no issues on the test drive yesterday. Cranked the car today, fired right up, ran about one minute and died. Tried to start it a few more times to no avail, took the outlet line loose and no fuel came out while cranking. Was running late for a tee time so that’s as far as I got. I will say the GMB parts did not feel of the same quality as the originals I pulled out. Thankfully I saved them and will be reinstalling them tomorrow. 
 

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Ok, what I think the issue is that the top cap is installed at the factory 90 degrees wrong, The internal center rib on the cap MUST be aligned with the mating center rib between the two check valves. Having the cap on with the ribs crossed allows flow to sneak through that upper diaphragm. This was the case with the one I looked at today. Turned the cap 90 and put it back on, and boom. Perfectly functioning pump. 

I wanted others with failed pumps to take the top off and see if the factory has the ribs aligned or crossed.

My guess is that from the factory, the diaphragm is sticky enough in some way to limit the leak, but eventually and quickly the dam bursts and that’s it  No more suction. At least that’s today’s theory. I need someone else to find the same flaw.  

Secretly I ordered three more GMB pumps from RockAuto today (can’t beat $17.83 CAD each!) to see if any or all have the flaw. Is it random or is the assembly line guy/robot slapping them together. however they like?

Edited by zKars
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49 minutes ago, zKars said:

Is it random or is the assembly line guy/robot slapping them together. however they like?

You know it's rural people, who probably don't know 90 from 180, in a warehouse in Asia.  Certainly no robots.

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On 8/16/2020 at 2:03 PM, Zed Head said:

Weren't the fuel pump companies looking in to this?  Whatever happened with that?

Here is what I remembered.  It was Carl Beck.  @Carl Beck

 

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7 hours ago, zKars said:

Ok, what I think the issue is that the top cap is installed at the factory 90 degrees wrong, The internal center rib on the cap MUST be aligned with the mating center rib between the two check valves. Having the cap on with the ribs crossed allows flow to sneak through that upper diaphragm. This was the case with the one I looked at today. Turned the cap 90 and put it back on, and boom. Perfectly functioning pump. 

I wanted others with failed pumps to take the top off and see if the factory has the ribs aligned or crossed.

My guess is that from the factory, the diaphragm is sticky enough in some way to limit the leak, but eventually and quickly the dam bursts and that’s it  No more suction. At least that’s today’s theory. I need someone else to find the same flaw.  

Secretly I ordered three more GMB pumps from RockAuto today (can’t beat $17.83 CAD each!) to see if any or all have the flaw. Is it random or is the assembly line guy/robot slapping them together. however they like?

Could you take a photo or two and post here? I have one I can take apart.

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Here are a couple of pics “under the hood” so to speak on the Spectra pump I’m testing.

859A859C-23EB-44ED-AB95-D7753D61BBC8.jpeg

BE578A0F-CA2A-4864-B568-1B96BB3E04E8.jpeg

Here is the internal divider wall between the intake and output check

18D497C7-F55B-4AFA-B47F-92E2EE1BB0ED.jpeg

and here is the cap showing its internal divider wall in line with the lower one. When I first opened it the cap was 90 deg out.

I tried putting the cap back on “wrong” this morning to see if I could get it to run for a while then quit, but no such luck. Pump output, as seen by taking a hose off the carb, was 0, nadda, szilch. Switch it back and boom, perfect working pump.

 

Edited by zKars

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