Mechanical fuel pump

[Deleted member 8987]

I don't know, Bill. He says it's a "new" problem in post number one.
He didn't mention massive oil leaks, so we can guess he doesn't have massive blowby and plugged vents.
I used to do a lot on Onan opposed twins (Cushman), and every once in a while you'd get one in, freshly rebuilt, and no fuel pressure. There was a way to set up the shaft to actuate the pump, and if you had it 180 out, the pressure of the twin slugs coming in towards the crank at the same time held the diaphragm away from the spring from the engine side....worked great cranking, but rev it up a bit and it would fall on it's face.
You just never know...and first step is to bench test the pump by hand.

 

[markberry]

I don't know, Bill. He says it's a "new" problem in post number one.
He didn't mention massive oil leaks, so we can guess he doesn't have massive blowby and plugged vents.
I used to do a lot on Onan opposed twins (Cushman), and every once in a while you'd get one in, freshly rebuilt, and no fuel pressure. There was a way to set up the shaft to actuate the pump, and if you had it 180 out, the pressure of the twin slugs coming in towards the crank at the same time held the diaphragm away from the spring from the engine side....worked great cranking, but rev it up a bit and it would fall on it's face.
You just never know...and first step is to bench test the pump by hand.

thanks for the replies Dave and Bill,
I took the fuel pump off the car this weekend and rigged up a quick bench test per Dave's suggestion. basically with the pump clamped in the vise I could easily manipulate the pump lever through it's full travel. so with a spare inlet line hooked up and inserted in a bucket of water, I could pump a large amount of water through the pump in a short period of time. I didn't bother measuring it, but suffice it to say...it was enough fluid to keep a big block V8 running. obviously there was no back pressure operating on the diaphragm from the carb floats and I didn't hook up a pressure or vacuum gauge either, so it was a simple test. I disassembled the new (Powertune) made in Taiwan fuel pump and noted that the lower chamber had a considerable amount of engine oil in it. there was no seal around the diaphragm shaft as the workshop manual describes either. I'm wondering if the lower chamber is filling up with engine oil at higher engine RPMs and the oil is either heating up the diaphragm and causing it to loose efficiency or if the oil could be causing some kind of hydraulic lock in the lower chamber. I'm going to see if I can find a seal that would work in the area the diaphragm shaft goes through the pump body. I may put it all back together, hook up a pressure gauge and repeat the test.
more to follow! thanks for the ideas.
mark

 

[markberry]

Ok I did a little modifying to the Powertune pump in an effort to get it to work and only made things worse; but it ruled out one thought I had about the problem. I found and installed a grommet that fit in the hole the pump diaphragm shaft goes through into the cam lever chamber below the lower diaphragm chamber

I then measured the levers' reach on both pumps and found the original one had about 1/4" longer reach than the new Powertune pump had.

so I swapped the arms and put the pump back together thinking I had solved the problem for sure; not so much as it turned out. I went ahead and installed the pump to just go straight to a full functional test, and found the newly modified fuel pump doesn't pump any fuel at all. my guess is the grommet seal I put in is causing a vacuum in the lower chamber and preventing the diaphragm from working. I need to take the thing off and go back to the bench test to see if I get similar results. maybe something just didn't get reassembled correctly, or maybe one of the check valves finally gave up and stuck open, but I'm betting the grommet test failed. it was interesting to see the difference in the design of the levers on the two pumps and finding out that the new one has a shorter throw. I was digging around on the interweb and saw a post from a triumph forum where someone says those levers barely touch the cam eccentric and thus cause such low fuel flow at idle that they vapor lock (or cause a vapor lock).
more to follow. thanks for reading!
mark

 

[markberry]

OK I've got an update for anyone still following this thread:
I pulled the pump back off of the car and did the same bench test I performed earlier; the fuel pump pumped fuel on the bench after not pumping fuel on the car. so...I removed the grommet seal anyway and tried again on the car and it still doesn't work. now one of our great members here at BCF sent me a couple of old, unrestored, original fuel pumps to work with that he didn't need anymore. there were some interesting differences between these old original pumps and the new Reproduction pump:
the original pumps did in fact have a fabric seal and washer at the base of the diaphragm spring. the new one doesn't.

also, there is a small hole drilled through the lower diaphragm chamber of both of the original pumps, which I suspect is to allow oil that may have made it past the seal to drain out, and/or allow air in and out to prevent a vacuum or pressure lock.

also the check valves are a completely different design; the old ones being brass and spring loaded, the new ones are metal and plastic.


neither of these old pumps will work right now as the diaphragms are dried up and stiff, but i'll update this thread when I get one rebuilt!
bottom line moral to this story is.....don't throw any original parts away! somebody out there is probably able to repair them to an operating level that exceeds what is available off the shelf today. not trying to bag on our suppliers; god bless them! I don't know where this sport would be without them. just beware of "suitable substitutes", that have made it into the supply system. they may possess hidden weaknesses. in fact, I wonder how our suppliers would embrace a dialog like this? I may ask.
regards
mark

 

[HealeyRick]

Unless you're going for concours, I'd seriously consider a fuel pump blanking plate for the block and an electric fuel pump.

 

[catfood]

Sounds like a problem I had when I had a frogeye. The car would run fine for half an hour or so then splutter to a halt. It happened once when I was moving house and I had to drive the car around 150 miles. I guessed it was fuel vapourisation so I removed the steering column blanking panel from the passenger side to get more airflow and once I got the car going again it ran faultlessly. I eventually tracked the fault down to the rubber diafram in the fuel pump presumably going slack with heat. With the extra airflow from the removed panel it stayed cool enough to work. Replacing the rubber diafram cured the problem permanently and I could replace the blanking panel (fumes in the cockpit is never a good idea anyway)

 

[markberry]

Unless you're going for concours, I'd seriously consider a fuel pump blanking plate for the block and an electric fuel pump.

thanks for the input Rick but I can't help but think that at some point a mechanical engineer designed that engine to run with that mechanical pump. almost all cars had mechanical pumps until (I assume) the introduction of fuel injection. plus I hate the thought of finding a pump, then finding a way of mounting it, then modifying the fuel lines, then running wires to it:mad-new:....blah, blah, rant, rant!
thanks though.

 

[markberry]

Sounds like a problem I had when I had a frogeye. The car would run fine for half an hour or so then splutter to a halt. It happened once when I was moving house and I had to drive the car around 150 miles. I guessed it was fuel vapourisation so I removed the steering column blanking panel from the passenger side to get more airflow and once I got the car going again it ran faultlessly. I eventually tracked the fault down to the rubber diafram in the fuel pump presumably going slack with heat. With the extra airflow from the removed panel it stayed cool enough to work. Replacing the rubber diafram cured the problem permanently and I could replace the blanking panel (fumes in the cockpit is never a good idea anyway)

I'm guessing that's what's going on here. I'm guessing that mine is filling up with hot oil that was accumulating because the manufacturer failed to include the oil seal and the drain hole that the original AC pumps had. right now mine isn't working at all and I'm now thinking that I may have inadvertently allowed the pump lever to get behind the cam eccentric when installing it. I found a thread on a Triumph forum where someone said you can do that if you aren't careful reinstalling the pump.
thanks for replying.
mark

 

[markberry]

Ok, I have an update for anybody still interested in this goofy thread. I'm sure most of you are wondering why I don't just throw an electric fuel pump in the car and be done with it. At any rate, I finally received the fuel pump repair kit and installed it in one of the original AC fuel pumps that Bill M sent me. the kit contained a new diaphragm, new check valves, and seals.
I rebuilt the fuel pump and installed it on the engine. while I was waiting for the fuel pump kit I made a new steel fuel line and added an NOS flexible braided section of hose that apparently was a factory change around car #40000; replacing the coil of tubing just prior to the fuel pump. I have never seen a picture of this installation so I just guessed and routed it in a
fashion that would not be vulnerable to heat soaking from the exhaust pipe.

So...did it work?.... yes and no. the pump is working so well that it's forcing fuel out of the float chamber overboard vents. now I'm going to replace the float needle valves and go from there. More to follow!
Thanks for reading
Mark

 

[markberry]

Hi All,
i'm going to say this problem has been solved. It's apparent to me that the reproduction pump was barely (if at all) pumping fuel. Upon inspection I couldn't find anything wrong with the pump, but when it was on the engine it just wouldn't work. The rebuilt, original pump pushed fuel right past the float needle valves requiring them to be changed and the float height to be tweaked. Then once that was fixed I noted the car was running extremely rich; a result of me having enriched the mixture over time to get the car to run on the little fuel that was making it up to the carbs. I've taken it on a few long drives and haven't had any problems yet but I'll keep at it.
Anyway that's my story. Thanks for reading!
mark

 

[Billm]

Mark
You may want to investigate what spring you have in the "old" pump (the one that produces too much pressure). The coil spring that pushes against the diaphram is what determines the fuel pump pressure. If the spring is too strong you will have too much pressure.
You may want to get a cheapo gauge to see what your pressure is.
BillM

 

[markberry]

Mark
You may want to investigate what spring you have in the "old" pump (the one that produces too much pressure). The coil spring that pushes against the diaphram is what determines the fuel pump pressure. If the spring is too strong you will have too much pressure.
You may want to get a cheapo gauge to see what your pressure is.
BillM

thanks Bill, good idea! I have a fuel pressure gauge. when gas started running out of the vents I went straight to the needle valves and sure enough they were both badly scored . I put new Viton tipped replacements in and the venting stopped. the floats were set a little high as well so I adjusted them while I was in there. of all the diaphragm springs I have, the one installed is the lightest and still pumps like there's gonna be no tomorrow . I can't say enough good things about that Goss pump repair kit coupled with the original AC pump!
Mark

 

[wildtr3a]

I have a Triumph TR3A and had a similar problem where the car would run fine, and once warmed up would cut out. Once it cooled down, it would start up and run again like nothing was wrong. I, too, went through multiple scenarios and finally found that when the engine was hot and stalled out, I pulled the fuel line off from the carburetor and found that the fuel was just barely coming out during cranking. I let it cool off, cranked it again, and a full-flow of fuel came out of the end of the fuel line. I got it back in the garage, took off the fuel pump, which is only about a year to two years old, and upon close inspection, I found that the arm that rides on the cam shaft and pumps the fuel, that one side of the pin which holds the arm in place was slightly offset and when the engine heated up, the pin was free to move and not make good contact with the cam itself, thus not pumping any fuel. when the engine and the fuel pump cooled down, the pin went back into place and rode the camshaft the way it was supposed to and the cycle would continue during the heat up and cool down. In checking with Moss Motors where I purchased the after-market fuel pump, they stated that they were not having any issues or other complaints. So, I wrote it off as a design malfunction and rebuilt my original AC fuel pump and have not had a problem since. Not sure if this is your problem. I thought I would give you my experience that I had. Hope it helps.

 

[markberry]

I have a Triumph TR3A and had a similar problem where the car would run fine, and once warmed up would cut out. Once it cooled down, it would start up and run again like nothing was wrong. I, too, went through multiple scenarios and finally found that when the engine was hot and stalled out, I pulled the fuel line off from the carburetor and found that the fuel was just barely coming out during cranking. I let it cool off, cranked it again, and a full-flow of fuel came out of the end of the fuel line. I got it back in the garage, took off the fuel pump, which is only about a year to two years old, and upon close inspection, I found that the arm that rides on the cam shaft and pumps the fuel, that one side of the pin which holds the arm in place was slightly offset and when the engine heated up, the pin was free to move and not make good contact with the cam itself, thus not pumping any fuel. when the engine and the fuel pump cooled down, the pin went back into place and rode the camshaft the way it was supposed to and the cycle would continue during the heat up and cool down. In checking with Moss Motors where I purchased the after-market fuel pump, they stated that they were not having any issues or other complaints. So, I wrote it off as a design malfunction and rebuilt my original AC fuel pump and have not had a problem since. Not sure if this is your problem. I thought I would give you my experience that I had. Hope it helps.

that's interesting, thanks. I would have to look at my reproduction pump and see if I can see what you're talking about. that pump has a really thick arm made of multiple pieces of steel riveted together (the pump furthest from the camera).

so the pin that goes through the pump arm heats up and allows the lever that contacts the cam eccentric to wander laterally and fall out of contact with the cam eccentric? that would explain why the pump diaphragm didn't appear to have anything wrong with it and why the pump always worked on the bench. Hmmmm. it would be easy to shim that lever on either side. I'd still rather use the original AC with the priming lever but it would allow someone to buy one of these reproduction pumps and cannibalize the diaphragm from it to install in the AC pump. cheaper than what I paid for just the rebuild kit too. I'm going to take a look at that.
thanks
Mark