8ba fuel pump rod getting stuck

[Terry,OH]

If when you loosen the pump mounting bolts the pump becomes free there must be some distortion when the bolts are tight. DO check both the face of the pump mount surface and the pump riser to see they are flat. Make sure the gasket is flat when installed and the fuel pump operating arm has it's spring installed and the arm has slight clearance to the sides of the pump casting. Do lube the pump arm pivot with some oil.

[jetmek]

FYI. I just used one of the current pump rebuild kits. The eye in the diaphragm rod was binding on the back side of the arm hook that goes in it on full extension. I found it because it would rack the diaphragm rod enough to cause it to leak fuel. I ground a tiny bit off the backside of the arm hook so it would fully articulate. Mite be worth looking into

[bill41ford]

That sounds like a possibility, I will look at that - The holes in the diaphram do not exactly line up and I have to move diphram around when I put screws in top - doesn't seem right and it forces me to slightly turn diaphram and therefore puting slight twist possibly on that eye - I am checking it out

[bill41ford]

I was looking hard at all parts involved and noticed that the fuel pump rod moves up and down smoothly on its own or when I move it up and down in the bushing, but any position of rod in bushing other than perfectly straight up and down and it does get "stuck" . This is with engine cold - when I seat the fuel pump on the rod I am not sure of the vertical alignment in the bushing - but I can't believe it is perfectly vertical as it seems to need? Considering how much bigger the newer rods are compared to the older ones, why isn't the cup from the fuel pump linkage bigger to allow for some self centering? What I should I be feeling for clearance in the bushing, I asked my engine guy about putting and sizing the bushing , and he said he did it and it does have an easy movement when straight, but with any pressure off the center of the bushing I could see how it could hang up - especially with some heat expansion involved - does any one have the inside finished size of the bushing for the 8ba pump - how much play should I feel when I insert the rod? The straightness of the pump stand and pump mounting face seem to be much more critical with this bigger rod - any body else have an issue with any of this rod bushing clearence?

[jetmek]

Quick measurement on a NOS bushing is .439. A used pushrod measures.430. New one .431

[Bill OH]

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Cadillac512 - you are correct 0.20” - my mistake- my apology.

[bill41ford]

After what I have seen on how easy it is to stop the rod movement I can now believe that is what is happening - now I need to figure out what to do about it - could I possibly polish the bushing somehow - I know the easy out is an electric fuel pump, trying to avoid that until a couple more tries at fixing this .

[Bill OH]

I would try a different fuel pump stand (that has not been modified?) and use a set of mics on the end of the push rod that passes thru the bushing. A previous post gave the size. I still think heat is causing a change in the size of the bushing and push rod. Do you have a used push rod - try it and see what happens. Also, does the spring on the fuel pump arm have enough tension. As hard as those fuel pump are to manually operate, I am surprised that the push rod is hanging up. Just some thoughts.

[cadillac512]

Originally Posted by bill41ford

After what I have seen on how easy it is to stop the rod movement I can now believe that is what is happening - now I need to figure out what to do about it - could I possibly polish the bushing somehow - I know the easy out is an electric fuel pump, trying to avoid that until a couple more tries at fixing this .

It'd be easier to polish a thou or two off the pushrod than the bushing. Chuck it in a drill and use emery cloth followed by fine sandpaper to finish it. You're going to fix this thing!


Terry

[bill41ford]

Checked trueness and size of rod and both are good - rod fit in bushing is more loose than tight but hard to measure in engine, if it is suppose to be a slip fit , it is definitely looser than that and has some side to side play and seems easy to bind with very little lateral movement. I have sacrificed a pump stand and cut the back off to see exactly what is going on inside. I will try that tomorrow and see what I see. If bushing fit (too loose) is the issue , I will talk to the engine guy, but without taking it all apart I can't see a fix for that. Appreciate you guys talking me through this.

[Bill OH]

. I have another thought: Does the bushing for the fuel pump push rod have an oil hole that is fed by a corresponding hole in the engine block and is the hole in the bushing lined up with the hole in the engine block. I am not informed as to existence of the two holes. You may have to put an inspection probe in the bushing. I would think the bushing and rod need oil, which you can supply with an oil can, put every thing together, fire it up and see what happens. Temporary fix.

[Ol' Ron]

I've always eliminated the stock fuel pump pushrod. It's a major source of problems with these engines, and the Auto industry has eliminated them almost 20 years ago.. On the 8ba blocks I push out the bushing and tap the hole for a pipe plug, them rotate the rear cam baring to block the hole. Then use an electric Fuel pump. I like to use an in tank pump Gramps

[Bill OH]

I have used an electric pump at the tank on an 8ba without plugging the pump rod bushing and did not have any problems - oil pressure okay. I wonder if bill41ford has a blocked oil passage - if that is the problem - I would put a electric pump (Fascet) on at the tank and be done with it. Would not have to block the pushrod bushing -already blocked.

[bill41ford]

Worked on problem all day - I did cut the back off of the fuel pump stand and put a small mirror taped to the firewall so I could see everything inside pump stand. Tried a couple different things - put stand with fuel pump bolted on without diaphram - turned engine over and pump rod only moved up and down a couple times - loosened pump bolts slightly and rod movement looked better - removed pump and stand and looked at pump arm closely and found it to be hanging up - this was the arm supplied with the rebuild kit - I had an older fuel pump from my original motor and the arm movement seemed much better, after taking apart I see this older mechanism had a bushing where the pin goes through - I swapped this older and better set up for the kit arm and the basic movement now seemed much better - I installed this pump on stand with an extra gasket between the pump and the stand - turned over motor and rod movement did not hang up as before - installed diaphram and turned motor over and things looked ok - installed top of pump , bowl and fuel line - choked and started motor - now I was able to see rod movement with the cut away stand - had good steady fuel pressure , ran for a few minutes and all looked good so far, then it stopped - no fuel pressure - I RAN OUT OF GAS in my little tank setup... Put in gas and started right up and good fuel pressure. So far so good - I worked last night so it has been a long day but I am hoping what I have changed and done will continue to work when engine gets hotter - will continue with a longer run time tomorrow - thanks for all the suggestions - still having idling issues - will address these problems after running this motor through some heat, tomorrow.

[Bill OH]

Thanks for the report - hope your success continues!!!

[Ol' Ron]

This is why I eliminate the pump in the first place!!
Gramps

[bill41ford]

Ran engine this morning to running temp 2x and no fuel issues - guage steady at 2psi, even at really slow speed, never looked that good before - bottom line to this point - found binding in the pump arm from the rebuild kit that was hanging the pump rod up - replaced it with a million year old arm from an old pump that I had - but it had a small bushing where the pin goes through pump to hold arm. I am inserting some pictures showing my cutout pump stand with a mirror on the firewall to see inside stand when running. I have a couple more issues that I mentioned early in this thread ,but will end things here and fix some small oil leaks, change oil etc. I checked and adjusted the static timing first thing this morning and I was slightly retarded - that adjustment helped with response and rpm - appreciate all the suggestions and help.

[petehoovie]

Originally Posted by bill41ford

Ran engine this morning to running temp 2x and no fuel issues - guage steady at 2psi, even at really slow speed, never looked that good before - bottom line to this point - found binding in the pump arm from the rebuild kit that was hanging the pump rod up - replaced it with a million year old arm from an old pump that I had - but it had a small bushing where the pin goes through pump to hold arm. I am inserting some pictures showing my cutout pump stand with a mirror on the firewall to see inside stand when running. I have a couple more issues that I mentioned early in this thread ,but will end things here and fix some small oil leaks, change oil etc. I checked and adjusted the static timing first thing this morning and I was slightly retarded - that adjustment helped with response and rpm - appreciate all the suggestions and help.