VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 1929 Chevrolet Test Fire ONE...

well spent most of the day doing final checks and then trying to test fire the 1929...

went down my list and validated everything, got everything cheeked off, and put fuel in the car. spun it over a few times, only for a few seconds at a time, then a minute rest to pump fuel to bowl. after several cycles still no fuel. so we started to diagnose the problem. tried to put fuel in pump and then go from there, nothing. so we double checked everything was sealed at the connections, still no go. pulled fuel line from pump and was able to siphon gas from tank easily. so that is a check. did a vacuum test on pump and got no reading ?!? needle did not even really move. so tried the pressure (outlet) and basically the same thing. we pull the pump double checked and on the bench we were getting 5-6 Hg on the vacuum and about 2-2.5 psi on the outlet for pressure. we could tell the cam lobe and the fuel pump arm are worn some. we did a test and put the pump back on the car with NO gasket bt the pump and the block. and did a test we got about 2-2.5 Hg and on outlet about 1.0 psi, but not enough to actually siphon fuel from the tank to the pump.

figured we were going to need to weld and build up the fuel pump arm, so we called it a day and went to get some dinner. i spent last night searching and reading post on here about this issue, and seems the general answer is to TIG weld and build up the fuel pump arm and try that, if that does not work then have to build up and grind the lobe on the cam for the fuel pump which sounds like it is EXPENSIVE !!. Now the fun begins trying to 1 find a local shop that can do a quality TIG weld and 2 one that is actually willing to do a small job of this nature. seems NO ONE around here wants to do anything unless it is a large government contract and they an make money. not many people that are willing to help out a fellow car guy on the side. its a shame...

question, i assume the arm that needs to be TIG welded is simple steel ?? nothing fancy or exotic. and based on the numbers posted here on VCCA the arm should be around .400 measuring from arm face (that rides cam) to opposite side of arm at rivet.

From what i read the proper numbers for the pump should be:
output pressure 1.50 - 2.00 PSI
inlet vacuum 8-10 Hg

though it was a failure we learned a lot, and more projects coming up...

If you need your cam done look up Oregon Cam Grinding. Not too expensive! Was recommended to me by members here and I've had them do two so far (complete regrind). I've misplaced the information and would have posted it. If I find I'll post but I'm sure someone will beat me to it.

In your pictures do you have one of the fp arm? I may have a better one. It took forever to get fuel up to my 31, I should have forced it from the tank to the pump and primed everything.

Dave

Before you go to the trouble of adding metal to the arm, put a drop of oil on each of the wafer valves in the pump. That will help them seal. Adding a little oil is even in the pump rebuild instructions. Once the wafers are wet with gas they don't need any oil.

yeah we tried that, nothing...

even filled the fuel pump with gas via the removing the wafers then putting them back in, springs, then caps. hoping to get them to seal. nothing :( wafers were nice n wet !

strange thing is it worked fine on car before tear down and rebuild, BUT not sure what kid of pressure or vacuum i was getting on it. and that was with the old diaphragm and all

thanks for the info, i will keep that in mind IF i have to go that route :)

sure do

If the pump worked prior to rebuild I would think the cam is ok but you might want to dial indicate it to check. Could be as simple as a stiff diaphragm in the pump.

Yes that pump arm looks worn a fair amount. If Dave can't help you let me know.

reading on here in previous postings the stock is around .400 mine is around .315 spare one i have is .325

diaphragm is pretty soft and pliable, easily moved, and pumped by hand.

If that's the lobe for the pump probably you'll need it ground to spec. A new or good lever for the pump may be in order as well. Might as well have the whole cam reground as I thought it was around $120?. They also reface the lifters for $5 each.

I would think that an almost 25% reduction in the arm would be enough to cause your issue. If it were mine I would much prefer replacing the arm or pump rather than building up with weld.

Jerry, did you have the fuel pump connected to the tank fuel line and then pump it by hand? I just went through this the other day. I found the bowl gaskets tend to leak, especially the rubber ones ( which doesn’t make sense to me) so I used good old cork. My own cam doesn’t move the arm much but my pump pumps a ton of fuel. If the lift of the cam lobe is supposed to be .400, that sounds high to me as that is close to 3/8-7/16” stroke. The .312 you get should be plenty. When you put the pump in the block, do you feel contact with the cam and pump arm? Often, depending on the where the cam stopped in rotation, the pump actually gets pushed away from the block as you loosen the pump mounting bolts as the pump is on the high side of the pump lobe.
If you can rotate the motor to the high side of the lobe, put the pump in and feel for the contact. Push the pump up to the block surface and let it come out again with the fuel line attached to the tank and see if it pumps. Again, make sure your bowl seal is good. Remove the bowl screen and try it with just the glass and gasket. I’ve also seen the screen cause issues with a too wide gasket.

I have probably rebuilt 50 of those fuel pumps over the last 50 years. Found the # 1 problem to be the diaphragms with modern gasoline. # 2 is warped housing at the glass bowl. In most cases a cork gasket will work. If not then heating with weight will return housing to flat position. Then the neoprene gasket will also work. Rarely is the wear on the cam or pump arm a problem. Remember that it is not the lift on the cam lobe that is critical. It is the movement of the pump arm transferred to the diaphragm that actually does the pumping. So if the arm is worn too much the diaphragm doesn't move much if any?

If the cam lobe is worn and the arm is also worn there would be the possibility of the arm not always touching the lobe and a possible reduction in the stroke. Maybe? Something to at least check and not scoffed at offhand. Maybe I shouldn't make suggestions.

I have used AC arms from .314-.348 measuring on the hump opposite of the cam to the wear spot on the face. I measured a brand new aftermarket 405 pump and it measures .362 and another slightly worn non AC measures .388. I don't believe a new 855377 arm would have measured .400 but my info does not give me that spec.

I don't think I can make any real difference for you but let me know.

Dave

On the 36 we bought 2 years ago it took awhile to sort out a fuel problem. Would run great with the tank all the way full, but after a little while would start sputtering, coughing, and sometimes backfire. Noticed some air in the fuel pump glass bowl. I installed a temporary piece of 3/8" clear plastic refridgerator icemaker drain hose just ahead of the pump. It showed a lot of bubbles. I moved that back to just in front of the tank. Still bubbles. The tank pickup had a hole rusted inside the tank near the top. Replaced the tank. Still sorting out the tank filler tube. Use one of those little hand pumps from Harbor Freight to make sure you don't have a different problem before you spend $$$.

thanks guys will do some diagnostics this coming week.

tore down the pump and pulled the arm, found a guy around the corner from me that owns his own welding company and does side jobs. he squeezed me in and welded up one of my arms today. just need to clean it up and grind it back to match profile.

that would be super cheap, figuring around $1000 or so to build up and grind a cam back down now a days

tried with neo gasket, cork gasket, etc... all the same. plugged the inlet and could pull and hold a vacuum on the tank. so glass is sealing with either gasket.

not sure what the lift on the cam is, need to get a gauge to see what we have, may try to borrow one from work tomorrow. one tool i do not own

we did turn the cam to high side out towards pump, when i install the pump i can feel it push up against the arm. about 1/4" out or so maybe 3/8"

we could pull fuel from the tank to pump when not installed. we tried to siphon fuel to the pump manually and then have pump pull it though, did not work.

we put 2 gallons in the tank, and can easily siphon it to the fuel pump manually NO air. used a section of clear hose to SEE what was going on

Just an FYI
there is about 1/4" of travel before you can feel the diaphragm engage/ move. basically the amount of travel before you can feel any resistance other than the springs.

borrowed a dial indicator to check travel of the cam lobe.

set it up with the point aiming at the center line of the cm shaft. sure it is NOT perfect, but pretty good results. tried several different ways and came out about the same results each time. +/- .015

found out from low to high getting about .269

took a straight edge and laid it against the cam to see how much deviation/wear was in the lobe. you can clearly see the 3 sections that match up the fuel pump arm  there is Not really that much wear from the standard lobe to the wear section.

really hard to measure the difference, not that noticeable with the fingernail drag across the face of the lobe on any side.

Jerry, I remembered and found my spare AC reman 405. The arm travels 1/4 of an inch before any resistance other than the spring is felt and the arm is .340 thick at the rivet or hump.

Dave