Fuel pump oddity

Steve_S

Steve_S

Member
When mounting the fuel pump to my 8CM, the rod seems to be about 1/2" too long because when the cam is as full rise, the pump sits about 1/4'1/2" off the intake manifold. The rod is seated in the receptacle of the pump. Is there something I'm missing here?

I got the engine disassembled but this is definitely the rod and pump that were on it before. The photo does not show the pump raised up but maybe there's something else obvious?
 

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Hello Steve Is that with or without a gasket. One or two. It does seem odd that there is that much space. My dad use to use the gaskets (adding more for less fuel pressure) removing them for more pressure. Some of the old carburetors were pressure sensitive.I do not have a fuel pump rod pulled on my 53 8CM so I cannot give you a measurement. Lyle
 
The correct pushrod is 10-1/16 inches long. When the lever cup is positioned on the rod you have to push the pump down into position to bolt it. (this is to overcome the the spring preload) Doesn't sound odd to me.
 
Steve,
Do not be surprised if when you remove the FP the cup that
traps the push rod is smaller than the pushrod. The small cup accomodates
the '48 back push rod which is smaller in dia than the 8ba.
The other thought is...are you just feeling the resistance of the
spring and diaphram? I like to get the push rod at full height then install
the pump and stand pushing it down with the heel of my hand until
the stand smacks solid on the intake....with a fresh pump there is some
resistance before the smack.
Charlie ny
 
Charlie ny said:
Steve,
Do not be surprised if when you remove the FP the cup that
traps the push rod is smaller than the pushrod. The small cup accomodates
the '48 back push rod which is smaller in dia than the 8ba.
The other thought is...are you just feeling the resistance of the
spring and diaphram? I like to get the push rod at full height then install
the pump and stand pushing it down with the heel of my hand until
the stand smacks solid on the intake....with a fresh pump there is some
resistance before the smack.

Charlie ny
Click to expand...

Same goes for children.:D
 
There is also a rod length difference between the aluminum and cast iron intake manifolds. I believe it is a full inch though if memory serves me. Joe
 
Joe that only applys to 48 and older engines.Some one could have mistakenly installed the wrong cup arm on the pump as Charlie said. 49 up has a fatter rod and only 1 length 10+" ken ct.
 
Thanks guys, first please note that in the photo above the pump is sitting flush because the camshaft lobe is down. When up, the fuel pump comes WAY up, probably 1/2". I just didn't take a photo of that when i had a chance.

- The engine is back together and nearly ready to run, so the camshaft is in position.
- The rod is a shade over 10" long.
- The fuel pump has not been rebuilt yet.

Also, I did make sure the rod would fit into the cup in the fuel pump, and the spring is not terribly strong so no problems overcoming it.
 
ken ct said:
Joe that only applys to 48 and older engines.Some one could have mistakenly installed the wrong cup arm on the pump as Charlie said. 49 up has a fatter rod and only 1 length 10+" ken ct.
Click to expand...

Ken, Thanks for the correction. Keep forgetting about those NEW flatmotors. By the way, that carb is working great on our 59AB that I put in the 40. Thanks again. Joe
 
Steve,
I am having the same problem with my 1950 8CM and an after market 2x2 intake. My pump with stand won't sit flat even with the push rod in it's lowest position.
The rod is fitting well into the FP cup. I don't know what the problem is. I hope we can find out here.
 
koolman said:
Steve,
I am having the same problem with my 1950 8CM and an after market 2x2 intake. My pump with stand won't sit flat even with the push rod in it's lowest position.
The rod is fitting well into the FP cup. I don't know what the problem is. I hope we can find out here.
Click to expand...
The aftermarket 2x2 manifold you say you are using. Is it designed for the 8BA style block or for the earlier 59AB block?
 
My intake is labeled 8CM, same as the block, so I know that isn't my problem. But darned if I know what IS my problem! I'm not comfortable just cutting down the rod to fit. It came with this engine so it should work!
 
with a straight edge across the stand mounting behind the push rod You turn the moter over,The rod should move up just over 1/4 I think 2 tenths of a inch which reflects the pump cam size on the cam shaft .You can mark it with a marker,The amount the rod is sitting above the manifold ,at its lowest point should be the same length as the mounting flange to your pump cup , you can check this by putting something like a screw driver in the cup of your pump and push it to take the slack out from the light spring.Then mark it with a marker .
 
Steve_S said:
My intake is labeled 8CM, same as the block, so I know that isn't my problem. But darned if I know what IS my problem! I'm not comfortable just cutting down the rod to fit. It came with this engine so it should work!
Click to expand...
'STEVE S' - Take note. My response is to 'KOOLMAN' See the quote in my response to him.
You don't have a problem if all the parts are the same as you removed them.
 
51-MERC-CT,

It is an Offenhauser for the latter block. The engine was rebuilt before I bought it. The push rod is new, pump and stand are old. Are the 8CM and 8BA pumps interchangeable?
DK
 
Steve,
I've been following this thread and wonder.....have you tried
another pump?
I'm guessing from afar that cutting the push rod ain't such a good
idea.
Charlie ny
 
koolman said:
51-MERC-CT,

It is an Offenhauser for the latter block. The engine was rebuilt before I bought it. The push rod is new, pump and stand are old. Are the 8CM and 8BA pumps interchangeable?
DK
Click to expand...



The 8BA pump will work in place of the 8CM double pumper. ( that's what I use)
Something to try- Turn the engine to #6 cylinder TDC. Lining up the rotor to the cap is close enough (this puts the fuel pump pushrod at it's lowest point making it easier to install the pump)
 

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