I need help again

Any topics pertaining to the BMC A-Series engine.

I need help again

Postby johnmcguire » Fri Dec 06, 2013 9:19 pm

The engine is now back in the car and I am ready to install the carbs. However I get no fuel from the mechanical fuel pump that I rebuilt. It produces suction on the input side but no fuel on the output fitting. I could not figure what I might have done wrong so I bought a new one from Moss. The same thing now. Could this be a cam problem? With my finger in the hole I cam feel the cam lobe but when I install the pump it does not pump. Any ideas as to what I am doing wrong?
Thanks, John
johnmcguire
948cc
 
Posts: 59
Joined: Tue May 14, 2013 9:35 pm

Re: I need help again

Postby perdido » Sat Dec 07, 2013 12:18 am

John, what engine do you have? I've forgotten which one, Ford maybe, that matches the original and is pretty cheap. If you were getting suction on the original pump it should be working and you could have a blocked fuel line between the pump and tank. A good test would to take a container of fuel and see if it pumps from that...if it does you have a blockage. It could be in the line or in the tank such as rust or debris that needs to be cleaned out.
Rut
perdido
Pit Crew
 
Posts: 17
Joined: Mon Mar 14, 2011 3:49 pm
Location: Tuscaloosa, AL

Re: I need help again

Postby johnmcguire » Sat Dec 07, 2013 9:34 am

Thanks, but I doubt it is an obstruction. I can easily suck gas thru the line and pump all the way to the pipe supplying the carbs. But it does not pump it forward after I get the gas to this point.
I hate to do it but am considering dropping the pan with the engine still in the car to be sure the pump arm is being pushed by the cam. Alternatively I could take the pump apart where it is installed and be sure the diaphragm goes up and down.
I was kind of hoping I had done something wrong that would be simply fixed.
John
johnmcguire
948cc
 
Posts: 59
Joined: Tue May 14, 2013 9:35 pm

Re: I need help again

Postby johnmcguire » Sat Dec 07, 2013 10:09 pm

So I pulled the pan and found that the arm of the pump was not close enough to the cam so that if it were 3/8 inch further in it would work fine. It pumps if I use a screwdriver to push the arm further than the cam does. The cam lobe is not worn so it must be that the pump arm is not correct. This is the problem for both the original one and the new replacement.
Charlie, what am I missing here?
John
johnmcguire
948cc
 
Posts: 59
Joined: Tue May 14, 2013 9:35 pm

Re: I need help again

Postby perdido » Sat Dec 07, 2013 11:53 pm

Do you have the pump spacer in place? The 2 most common pumps differ in that one uses a spacer of about 3/8" and the other does not. Check the depth of the pump arm and see how if matches up with the available options.
Rut
perdido
Pit Crew
 
Posts: 17
Joined: Mon Mar 14, 2011 3:49 pm
Location: Tuscaloosa, AL

Re: I need help again

Postby johnmcguire » Sun Dec 08, 2013 9:51 pm

No spacer in place. How can I find "the available options" as both my original pump and the replacement are not close enough to the cam. Does anyone have the cam lobe dimensions for the fuel pump lobe? The cam does not appear to be worn to me.
I really do not want to resort to an electric pump .
John
johnmcguire
948cc
 
Posts: 59
Joined: Tue May 14, 2013 9:35 pm

Re: I need help again

Postby Charlie Tolman » Mon Dec 09, 2013 1:01 am

An old pin-drive cam:
The fuel pump "lobe" measured close to 1.32" in diameter.

Charlie T.
Charlie Tolman
Judson Supercharged
 
Posts: 1197
Joined: Wed Mar 01, 2006 10:36 am
Location: Minnesota

Re: I need help again

Postby Charlie Tolman » Mon Dec 09, 2013 2:14 pm

I have two other old cams, which were re-ground many years ago.
One is a pin drive, and the other is a star drive.
Neither cam has a fuel pump "lobe". ???
Both cams have wide lobes for the lifters.
The star drive cam has numbers AEG 596.

The cam mentioned in my previous note, with the fuel pump "lobe",
has narrow lobes for the lifters.

Charlie T.
Charlie Tolman
Judson Supercharged
 
Posts: 1197
Joined: Wed Mar 01, 2006 10:36 am
Location: Minnesota

Re: I need help again

Postby Charlie Tolman » Mon Dec 09, 2013 4:38 pm

If I remember correctly, the 1098 cc block (1275 cc too ?) did not have a provision for a mechanical fuel pump. The mounting casting in the block is there, but there is not a hole in the block for a fuel pump arm. Hence, a fuel pump "lobe" on a camshaft is not needed. This might explain the "lobe" absence on two of the cams that I have.

Charlie T.
Charlie Tolman
Judson Supercharged
 
Posts: 1197
Joined: Wed Mar 01, 2006 10:36 am
Location: Minnesota

Re: I need help again

Postby Sprite33 » Tue Dec 10, 2013 1:21 pm

You are right Charlie. The 1098 does not have a provision for a mechanical fuel pump. At least the big main 1098 didn't. They came with the Lucas electric fuel pump. All of my after market cams have the lobe for the fuel pump but that is probably because they are universal and could be used with a 948 also. I don't remember if any of the stock cams that I removed had the lobes, probably not.
61 Sprite 1098
Set up for full prep racing in SCCA
2004, 2005 & 2006 Southern Pacific Divisional GP Champion
2008 & 2009 Southern Pacific Divisional HP Champion
User avatar
Sprite33
948cc
 
Posts: 140
Joined: Wed Oct 06, 2004 6:03 pm
Location: Costa Mesa, CA

Re: I need help again

Postby johnmcguire » Tue Dec 10, 2013 10:09 pm

Charlie,
The fuel pump lobe that you mention being 1.32 " in dia. is of course eccentric. Any idea of dimension of short versus long radius?
I think my cam is stock. The lobes for the tappets are as wide as the tappets and none of the lobes appears to be worn.
I am at a loss to explain why the pump arm rests on the lobe and goes back and forth but not far enough to push the plunger up and down. There is a built in gap between the arm on the cam lobe and it's connection to the arm attached to the plunger. Same thing for both the original and the replacement from Moss.
Easiest explanation is that the cam is worn but surely 3/8 " would be obvious.
Has anyone replacing a mechanical pump run into this?
Thanks, John
johnmcguire
948cc
 
Posts: 59
Joined: Tue May 14, 2013 9:35 pm

Re: I need help again

Postby Sprite33 » Wed Dec 11, 2013 2:02 pm

I don't know anything about the Sprite mechanical fuel pump but here is something to consider. Could the pump have a built in spacer that is not easily seen. Check it out closely.
61 Sprite 1098
Set up for full prep racing in SCCA
2004, 2005 & 2006 Southern Pacific Divisional GP Champion
2008 & 2009 Southern Pacific Divisional HP Champion
User avatar
Sprite33
948cc
 
Posts: 140
Joined: Wed Oct 06, 2004 6:03 pm
Location: Costa Mesa, CA

Re: I need help again

Postby johnmcguire » Wed Dec 11, 2013 3:26 pm

Charlie, et. al.,
The cam lobe measures 1.29 in greatest diameter so that does not appear to be the problem.
Could there be two different pumps for the 948 engine?
But even the original one rebuilt now does not pump
I am frankly stumped!
John
johnmcguire
948cc
 
Posts: 59
Joined: Tue May 14, 2013 9:35 pm

Re: I need help again

Postby Charlie Tolman » Thu Dec 12, 2013 1:48 am

The diameter of the shaft of the cam is near 0.820", the minimum distance from the shaft surface to the low side of the fuel pump lobe is near 0.120', and the distance to the high side is near 0.360'.

Therefore, the low and high regions of the fuel pump lobe are about 0.53" and 0.77", respectively, from the center-line of the cam; (radii).
The surface of the fuel pump lobe moves by 0.24", total, approx.

A cross-sectional diagram in a shop manual does not show a gap between the rocker arm and the connecting link to the diaphragm pullrod. Is the diaphragm return spring in place ?

Charlie T.

P.S.: I have never seen a Sprite camshaft where the valve lobe width is about the same dimension as the diameter of a lifter.
Charlie Tolman
Judson Supercharged
 
Posts: 1197
Joined: Wed Mar 01, 2006 10:36 am
Location: Minnesota

Re: I need help again

Postby johnmcguire » Thu Dec 12, 2013 11:24 am

Charlie, Thanks once again,
I'll take a closer look at the cam lobes next time I speak up.
The return spring is in place. There is a "break" in between the arm riding on the cam lobe and the arm that attaches to the connecting link to the diaphragm pull rod. This disconnect needs to be there so that when the float chamber in the carb is full and flow is shut off the diaphragm no longer goes up and down as it is held in the fully down position by fuel in the pump. At that position the rocker arm maintains contact with the cam and goes back and forth but but the connecting link no longer activates the pull rod as it is fully depressed.
My problem is that the rocker arm goes back and forth but is not pushed over far enough to move the connecting link. The first 60% of the arc is where the arm does not move the link and the arm does not get pushed over to the last 40% of it's arc where the link is activated.
I can only assume that the pump was working before I took it apart.
Does anyone have an old pump with a priming arm that I can buy or even just look at?
This is a genuine conundrum.
John
johnmcguire
948cc
 
Posts: 59
Joined: Tue May 14, 2013 9:35 pm

Next

Return to A-Series (948cc, 1098cc, 1275cc)

Who is online

Users browsing this forum: No registered users and 1 guest