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Re: Mechanical Fuel Pump Observations...
Posted by: JimBrandberg ()
Date: April 16, 2018 05:10AM

Good information, thanks. I had a new one a year or so ago that would not draw fuel so I just returned it. It makes sense that there can be other problems with valves besides coming out.

Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: Mechanical Fuel Pump Observations...
Posted by: JimBrandberg ()
Date: May 06, 2018 02:51PM

My local O'Reillys has been keeping a mechanical fuel pump in stock for a few years now for about $45. I went to get one today and it was $97. I couldn't pay that much figuring I would have to bring it home and cut the spring at the least.
I don't know if it's still the same or if anything has changed, like the supplier.
Until recently, I believe the Precision was a reboxed Airtex although I don't know for sure.
Someone reported recently that a pump from Clarks was sporting about 5#s, I can usually live with that. $65 isn't so bad if I don't have to take it apart before putting in service.

Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: Mechanical Fuel Pump Observations...
Posted by: kenzen ()
Date: May 06, 2018 03:51PM

I can verify that the Clark's gave me 5.5# out of the box.

Also, sorry I slipped behind on this study. My dad had been very ill, and he passed away last week at a wonderful age of 93. We're still working through things from our loss.

Lane66m just sent me a set of springs to add some data points to the study. (Thanks Al!)

Ken

kenzen
66 Monza Coupe 110/PG
Bel Air, MD

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Re: Mechanical Fuel Pump Observations...
Posted by: MonzaJPD61 ()
Date: May 07, 2018 04:58PM

kenzen, Sorry for your loss.

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Re: Mechanical Fuel Pump Observations...
Posted by: kenzen ()
Date: May 09, 2018 06:47PM

Thank you smiling smiley

kenzen
66 Monza Coupe 110/PG
Bel Air, MD

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Re: Mechanical Fuel Pump Observations...
Posted by: kenzen ()
Date: June 08, 2018 05:27PM

I finally got to profile all the springs that Lane66m sent me, plus the one from the pump St. Hubbins sent me from this thread Pump Spitting,plus some I had including a NOS type B (probably from the 70's) and the new one from Clarks I've been driving on.

I'm still working more analysis on this, especially to run some of these springs and measure real discharge pressure, but I figured I'd get some data out to the masses.

When looking at this graph, consider that the static compressed length (i.e. the pump not operating) is 13/16", so the tensions between 1.0 and .75 inches of compression on the graph are what we're interested in.

The "Clarks" spring discharges 5.5# of pressure once warmed up, and reflects about 250oz of tension at 13/16".

The "compressed" spring is one I smashed down to a smaller height just as an experiment.

I'm very interested in the cluster of spring curves that all end at and just below 300oz of tension at 0.5in: I think these might be the right springs for the intended 3-5# discharge pressure.

Thanks again to Lane66m and St. Hubbins for providing stuff to measure!

Ken

kenzen
66 Monza Coupe 110/PG
Bel Air, MD



Edited 1 time(s). Last edit at 06/08/2018 05:28PM by kenzen.

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Re: Mechanical Fuel Pump Observations...
Posted by: kenzen ()
Date: June 08, 2018 05:46PM

Also, I captured the at-rest spring length, # turns in the spring, and coil wire thickness data. If anybody is interested in the raw data in a spreadsheet, PM me. Intent is to have the specs on the "perfect spring".

Also #2: If anyone is interested on the specs for a particular output pressure, I can work that into the analysis if requested.

Ken

kenzen
66 Monza Coupe 110/PG
Bel Air, MD

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Re: Mechanical Fuel Pump Observations...
Posted by: JimBrandberg ()
Date: June 09, 2018 05:27AM

How did you compress the one, bend it a little all through the length or...?
The lower cluster of colored lines includes the Clarks? Are the rest of the springs in that lower cluster original ACs?

I had a pump this week putting out 9#s. I couldn't get it below 7#s even when cutting more than a coil and reforming to a height where it barely went down when putting the cover on. One of the carburetors can't handle this pressure, even with a new needle and seat.

I had another pump this week putting out 9#s. I ground the pushrod down a little and the pressure went up to 11#s. I think the pressure on the other spring below came into play.

Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: Mechanical Fuel Pump Observations...
Posted by: kenzen ()
Date: June 09, 2018 05:38AM

See attached pic for the test rig. It's a digital scale (25# capacity). The machinists ruler "floated" with the scale platform, and I could measure the height against the grinding stone edge I used as a flat surface to compress the spring with the drill press. (Obviously, I didn't turn the drill on...)

kenzen
66 Monza Coupe 110/PG
Bel Air, MD

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Re: Mechanical Fuel Pump Observations...
Posted by: kenzen ()
Date: June 09, 2018 05:43AM

The Clark's spring is the one that has the maximum tension of 350oz, which is with the upper cluster. Again, it delivers 5.5# once warmed up (it's a little over 6# cold). This is why I made my earlier comment that the middle cluster of springs might be the right design for in-spec pressure. I don't know the pedigree of all the springs that are numbered - these are the ones lane66m sent me in a bag. I have all the measurements in a spreadsheet if you want them.

Ken

kenzen
66 Monza Coupe 110/PG
Bel Air, MD

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Re: Mechanical Fuel Pump Observations...
Posted by: kenzen ()
Date: June 28, 2018 01:22AM

I wanted to chime in with a new observation I've made on the pump analysis.

Based on my ongoing research, I'm noting the base of the pump (i.e. the part that inserts into the block) is warping on the modern pumps. This is causing an internal leak of fuel into the block, and tightening the screws is not fixing it after it has warped.

As I was handling the pumps on my workbench, I noted that the newer pumps weighed significantly more than older ones I have. I weighed them and determined the older ones were about 13oz vs 26oz for the new ones. The base of the pump also became thicker in the newer models, but not thick enough to double the weight of the pump.

I then considered this finding with the warped lower bases I'm observing, and now I'll propose that the warping is thermally driven: If you consider that one side of the pump base is heated by the engine block, and the other side is exposed to the cooler flow of fuel (not in direct contact with the fuel but through the lower gasket), there's a significant temperature difference across this part.

For this weight increase to have happened, there must be a change in the metal away from a lighter aluminium alloy to a cheaper but heavier/denser metal that is causing a larger temperature gradient across the part and promoting the warping. I state this since my new pumps on hand have perfectly flat bases "as cast" (not machined flat), but he ones I've acquired with leaks all have warped bases.

One other thought is improperly cooled engines (i.e. missing engine seals, cylinders not deflashed, etc.) may be running hotter and aggravating this condition.

My jury is still out on this finding, but if this hypothesis is true, there are no good modern pumps to be had unless they go back to a lighter alloy. This is kind of a damning statement, but it could very well be valid. I'm thinking of a way I can test this...

Ken

kenzen
66 Monza Coupe 110/PG
Bel Air, MD

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Re: Mechanical Fuel Pump Observations...
Posted by: Lane66m ()
Date: June 28, 2018 02:18AM

How about a survey of forum members who have new pumps with no problems and forum members with pumps that leaked? Then ask questions of each group.

You might find some common denminators in the answers. Just ask them to PM you with their answers.

Al Lane
Ellabell GA

1966 Monza Coupe, 110 hp, 4 Spd
1968 Camaro SS Coupe 350 CI 295+ HP PG
1964 Greenbrier Deluxe, 6 dr, 80 hp car engine, PG
2015 Chevrolet Malibu 2LT
2018 Chevrolet Silverado LTZ Z71 Centennial Edition
1947 Farmall A tractor 15 hp


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Re: Mechanical Fuel Pump Observations...
Posted by: kenzen ()
Date: June 28, 2018 03:06PM

Lane66m Wrote:
-------------------------------------------------------
> How about a survey of forum members who have new
> pumps with no problems and forum members with
> pumps that leaked? Then ask questions of each
> group.
>
> You might find some common denminators in the
> answers. Just ask them to PM you with their
> answers.

I'd be pleasantly surprised if people did anything beyond throwing the pump out, or leaving it with the mechanic who did the repair.

If there's anyone out there that happens to have input on pump failures related to the base plate warping, please chime in. Thx!
Ken

kenzen
66 Monza Coupe 110/PG
Bel Air, MD

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Re: Mechanical Fuel Pump Observations...
Posted by: MattNall ()
Date: June 28, 2018 04:37PM

Sorry... I'm a recycler /fixer....but all my work stopped after Summer of 99..when Vairchet sold me one of Lon's pumps

'60-80s it was mainly Staked Poppet valve that still came loose! or debris...never bought a pump until '99





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Mechanical Fuel Pump Observations...
Posted by: Brizo ()
Date: June 28, 2018 09:06PM

Kenzen, Refer back to my post on April 12 on page 4 of this topic

Dan Brizendine,
'64 8door Greenbrier 140 PG. "In beautiful Wanamaker Indiana...with one stop light and 5 pizza shops"

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Re: Mechanical Fuel Pump Observations...
Posted by: kenzen ()
Date: June 29, 2018 12:10PM

Brizo Wrote:
-------------------------------------------------------
> Kenzen, Refer back to my post on April 12 on page
> 4 of this topic

You already had the warping problem figured out...sorry I didn't read this more carefully.

So I guess the take-aways here are that 1) the new pumps fail quickly because they warp quickly, 2) this has nothing to do with modern fuel or the quality of the gasket material, and 3) to reliably run a mechanical pump, it is necessary (but probably not sufficient) to swap in an an older base.

I'm going to finish out the spring analysis, to provide the community with the spec's on a proper spring...and then I'm going to convert my car to an electric pump since we've now determined a quality flaw that can't be overcome by re-working the newer pumps.

Maybe some of our vendors can communicate back to the suppliers on this to address the problem, but I doubt the manufacturers will make the necessary changes (or the pumps will become $125 each or something like that).

Bummer...

Ken

kenzen
66 Monza Coupe 110/PG
Bel Air, MD

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Re: Mechanical Fuel Pump Observations...
Posted by: MattNall ()
Date: June 29, 2018 01:06PM

You need to machine the surface flat again and then run it and after 1,000 miles re-measure...





MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: Mechanical Fuel Pump Observations...
Posted by: kenzen ()
Date: June 29, 2018 04:01PM

It takes me quite a while to put 1000mi on my corvair... smiling smiley

There may be a point where it doesn't warp any more and machining the surface flat will endure, but that doesn't give me the "warm fuzzy feeling" I'm looking for with a reliable pump. It'd be one thing if this flaw was about being left on the side of the road changing to another pump (e.g. loose check valve). However, this flaw is about dumping (actually pumping) fuel into oil pan.

Maybe if our community here that are sitting on a lot of parts would be able to provide a volume of the old style pump bases (or the whole pump), there might be a critical mass to keeping reliable mechanical pumps available. But not everyone is tracking this thread, so unfortunately there will be people going to the FLAPS (or our vendors) and bolting in a new pump that it seems is guaranteed to fail in short order, in a bad way.

kenzen
66 Monza Coupe 110/PG
Bel Air, MD

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Re: Mechanical Fuel Pump Observations...
Posted by: Lane66m ()
Date: June 29, 2018 04:59PM

Well, I have several bases from 1960/70s pumps sitting around in a box not doing anything. Anyone interested in mounting one on a leaking pump to see if it fixes their issue?

Hate to throw them in the recycle bin, if 8 or 9 newer pumps could remain in service by using them.

Al Lane
Ellabell GA

1966 Monza Coupe, 110 hp, 4 Spd
1968 Camaro SS Coupe 350 CI 295+ HP PG
1964 Greenbrier Deluxe, 6 dr, 80 hp car engine, PG
2015 Chevrolet Malibu 2LT
2018 Chevrolet Silverado LTZ Z71 Centennial Edition
1947 Farmall A tractor 15 hp


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Re: Mechanical Fuel Pump Observations...
Posted by: Brizo ()
Date: July 01, 2018 07:16PM

kenzen Wrote:
-------------------------------------------------------
> It takes me quite a while to put 1000mi on my
> corvair... smiling smiley
>
> There may be a point where it doesn't warp any
> more and machining the surface flat will endure,
> but that doesn't give me the "warm fuzzy feeling"
> I'm looking for with a reliable pump. It'd be one
> thing if this flaw was about being left on the
> side of the road changing to another pump (e.g.
> loose check valve). However, this flaw is about
> dumping (actually pumping) fuel into oil pan.
>
> Maybe if our community here that are sitting on a
> lot of parts would be able to provide a volume of
> the old style pump bases (or the whole pump),
> there might be a critical mass to keeping reliable
> mechanical pumps available. But not everyone is
> tracking this thread, so unfortunately there will
> be people going to the FLAPS (or our vendors) and
> bolting in a new pump that it seems is guaranteed
> to fail in short order, in a bad way.

If you machine the base flat again, then the part will be thinner than it was, and I'm afraid it will just warp again even sooner.

Dan Brizendine,
'64 8door Greenbrier 140 PG. "In beautiful Wanamaker Indiana...with one stop light and 5 pizza shops"

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