Quick fuel pump question

[Jake]

I'm getting a new rebuilt pump from a very reputable parts guy I know next week and plan on replacing my pump then.

Just about every Corvair owner I've spoken to has told me stories about fixing a leaking pump.
So you're telling me you should never use a pump that leaked but stopped after being tightened?

[Dennis66]

Two leaks we're talking about here: External leak, that can come from loose fittings or possibly loose housing screws. Not a problem, but I would be cautious about the loose screw issue. ANY fuel leak in the engine compartment, keep checking to make sure leak doesn't come back.
Then INTERNAL leak. This could be a leaking diaphragm, very likely with ethanol gas, older fuel pumps, and cheap, non quality repros. This leak can kill your engine by diluting your oil with gasoline. GOOD oil is very critical to a Corvair (or any air cooled engine) as the oil helps carry engine heat to the areas where it is dissipated (fins, cooler, etc.) This is the main reason I, and many others, are going ot an electric pump.
The stock, original Corvair fuel system trips up many "modern" mechanics. Today's systems are fuel pressurized from the tank. Mechanics look for failed pumps (in the tank) or pressurized leaks (outside the tank). The Corvair system had an external pump that sucked from the tank and fuel problems can come from a tiny crack or pinhole in an aged rubber line. Dennis

[66vairguy]

Many years ago when you still get new fuel pump diaphragms, a fellow posted that most folks end up with a new diaphragm failures because they don't assemble the fuel pump correctly. He said you have to push the rod up into the fuel pump BEFORE you tighten the screws. This allows the diaphragm to move up and down without it tearing from being too tight. I DO NOT KNOW IF THIS IS CORRECT - just passing it along.

[Jake]

thanks for the info !

always appreciated.

[bbodie52]

The Corvair mechanical fuel pumps have been generally very tough and reliable for many years — but old age is catching up with them, and rebuild kits with replacement internal components have not been available for decades. Ethanol fuel has likely made for a somewhat hostile operating environment too. Clark's Corvair Parts is the largest Corvair parts supplier in the world and has a lot of experience with having reproduction parts manufactured — yet even Clark's is now having difficulty obtaining this critical 'Corvair component.

If you say that the writing is on the wall, you mean that there are clear signs that a situation is going to become very difficult or unpleasant.

RIP = Retired 1 Pump

[gbullman]

I have to continue my fuel pump story because every victory must be celebrated....

I got 2 used, very suspect fuel pumps from a pal of mine, he just had them sitting on the shelf and said I could have them.
"Just give them a try, hopefully they'll fix you up"
I installed the first one and it leaked far worse than my original one. The second one didnt leak, which is a big positive, but it didn't pump either.
While I was looking at my now 3 rotten pumps I decided to back off the screws on my original pump that worked great but wept fuel.
After loosening everything and retightening them I reinstalled the original pump and it works like a champ. Pumps beautifully and doesnt leak at all. I'm still doing an electric pump buts its nice to have it running while I'm planning that job.

I'm just psyched that my new Corvair is not actively leaking fuel for the first time.

Glad you had that success! I also managed to stop my leaking fuel pump by tightening the screws, even getting longer screws and adding nuts and lock washers. That “fix” worked for a couple of months then it started leaking again and I couldn’t get it to stop. That is when I put the electric fuel pump and bypass in. In September 2021 I bought pump C5606 from Clark’s and I’m very happy with it. Unfortunately it sounds like manufacturers have changed hands and it isn’t clear to me they are still selling that same pump. I also installed Inertial Safety Switch C9848. I feel that gives me the safety I feel comfortable with without making things too complicated.

[emceebrooks]

Guys, I thought I'd jump on this thread....I've had constant fuel pump issues with my 64 for as long as I've owned it.....(5 years)

Original lasted 1 year
2nd lasted 2 months
3rd lasted 1 year
4th lasted 1 hour (today)

Two weeks ago the 3rd mechanical pump failed and leaked gas into the oil....I ordered the only pump I could find online (since Clark's doesn't have them as you mentioned) from Amazon (Carters), cut the shaft down to the correct length, and got it installed; (and changed the oil/filter). It worked beautifully for an hour.....then I let the car rest, came back to start it and it was pouring out gas out of the seals on the pump. Tightened the screws on top of the pump as much as I could and it started right up-- ran for a minute and the engine died. Now I can't stop the leaking. Tightened pump some more and broke off one of the screws.....so I'm ordering another....

Why am I having so many fuel pump issues?

[bbodie52]

It appears that the time for the old mechanical pumps has expired. Aftermarket pumps seem to be poorly designed or made of poor materials that won't last.

The potential for a gasoline fire or fuel leaking into the crankcase oil is a risk I won't take. That is why I reluctantly abandoned the no-longer reliable (or available) mechanical pumps, and switched to a carefully selected electrical fuel pump system. Note that a good fuel pump system design will include a quality electric pump with the correct pressure and volume capability, a good fuel filter to protect both the electric pump and the engine components, safe plumbing to avoid fire hazards, and safety cutoff systems to kill the pump in the event of a vehicle accident.

ELECTRIC FUEL PUMP CONVERSION IDEAS & SUGGESTIONS

viewtopic.php?t=17257



UNFORTUNATELY THIS PUMP WAS IDEAL, BUT IS NO LONGER AVAILABLE! I'm sure there are alternatives, but non I have ny experience with.

[emceebrooks]

Brad, thank you for your detailed reply. I'm moving rapidly toward your electric fuel pump solution. It seems Clarks has all of the supplies needed in stock to do this-- they suggest two types of shutoff switches in the install here: https://ssl.corvair.com/user-cgi/catalo ... ow_page=66. Is that similar to what you've installed?

However, before I move to the electric pump system, I'm wondering if there's something else is going on here that I'm missing. I ordered ANOTHER pump and put it on last night, made sure the connections were correctly tightened (and the set screw not overly tightened), and then ensured the screws on the top of the pump were tightened (but not overtightened). The pump immediately started leaking from the seams where you can see the black membrane sandwiched between the metal on the pump. Other than the poor construction of the available pumps, is there anything else in my fuel system that could be causing the pumps to fail immediately-- too much pressure or something? Four pumps failing nearly immediately seems too coincidental.....

As always, thanks again for your help and advice! Marcus

[bbodie52]

The mechanical pump operation is fairly simple, as described below. Other than poorly made diaphragms internally or a bad aluminum housing/casting, I cannot think of anything in the external pump environment that would cause a leak to form immediately after installation at the proper insertion depth (controlled/determined by the set screw indexing properly with the tapered hole in the side of the pump shaft).



The pump push rod is driven by a cam lobe on the crankshaft. The repeated "upstroke" causes the pump to form a vacuum in the feed line from the fuel source (tank or gas can). As the fuel is drawn into the pump chamber, the one-way valve in the pump inlet closes at the top of the stroke, and the spring in the pump forces the diaphragm back down to push the fuel out of the pump through the other one-way valve, toward the carburetors, with a designed fixed-pressure (determined by the spring) of 4-5 psi.

The fuel delivery system that included a fuel return line to the fuel tank was added by GM for the turbocharged engine configuration. A variation of that return system (using a brass cross connector at the mechanical fuel pump) was added in later years to keep fuel flowing in the gas lines when the carburetor fuel inlets (on non-turbo cars) shut off because the carburetor float bowls were full. When this occurred, the fuel flow would normally stop when the fuel pump spring could no longer push fuel in the direction of the carburetors. Providing a thin fuel return line (Z) from the pump back to the fuel tank allowed fuel to keep moving, even when the carburetor float bowls were full. The continuous fluid motion had the effect of keeping the circulating gasoline cool, which helped to prevent vapor lock in the steel fuel line in the hot engine compartment. (Vapor lock happens when your fuel boils in your carburetor or your fuel line. Vaporized fuel creates back pressure in your fuel system and prevents gas from getting to your engine. It commonly occurs when a car has been idling or has been turned off and then back on).



In any case, the length of the mechanical crankshaft cam-driven stroke is fixed by the proper insertion of the tapered set screw, which establishes the stroke depth of the push rod. The push rod only causes an upstroke that forms a vacuum in the inlet fuel line from the fuel tank —sucking fresh fuel from the tank. The spring in the pump cover is fixed in tension. If the outlet flow was blocked by the closed needle/seat assemblies in each carburetor float bowl, the pump diaphragm and body assembly (3) would simply remain in the up position until an open needle valve in a carburetor float bowl permitted more fuel flow. When the diaphragm descended to the bottom of its travel, the next push rod stroke would raise it up again — forming a vacuum to draw more fuel from the tank.

There is nothing in this simple pump mechanism to cause any damage to the pump seals or internal diaphragms. If the pump materials used in its manufacture were faulty or damaged during factory assembly, the pump may leak upon installation.

Mechanical Corvair Fuel Pump Cross-Section

Mechanical Fuel Pump Exploded View