Fuel Pump

[Guest Lincoln]

Does any one know what the specifications on how far the fuel pump push rod protrudes from the side of the block at it's minimum and it's maximum extension on a 1930 Franklin? Also what is the specifications given for the free play and the maximum stroke of the push lever inside of the fuel pump?

[odyssey]

This was written up for Air Cooled News a few years back. Maybe more than you wanted to know, but...

HOW TO CHECK THE LENGTH OF THE FUEL PUMP PUSHROD

Another common question arises as to the proper length of the fuel pump actuating pushrod as used on 1929 and later engines. This seemingly simple item is frequently the source of trouble on the road, causing fuel starvation in extreme examples.

The problem begins with the fact that the fuel pump pushrod, actuated by an eccentric lobe on the camshaft, has a very short stroke. The AC fuel pump, by comparison, has a longer stroke capability. It also has a very long free-play stroke before the pump linkage actually begins to pump. Over time, the pump linkage wears, free play increases and the actual pump stroke, the part where the pumping happens, lessens.

It is quite common that the wear will progress to the point where the pump will have just enough stroke to run the car under normal conditions, but when the crankcase gets hot enough, thermal expansion causes the engine crankcase to grow until the fuel pump pushrod effectively becomes too short to operate the pump. The car shows signs of vapor lock and then stalls. This can be a difficult problem to trace (believe me, I know).

A fuel pump pushrod that is long enough to deliver full stroke of the pump is critical. Here is how to check it using a caliper:

1 Remove the fuel pump and gasket

2 Hand crank the engine over until the fuel pump pushrod is determined to be in as far as it will go, on the ‘bottom’ of its stroke.

3 Using the caliper, record how far the pushrod protrudes from the crankcase.

4 Find a suitable means to hold the fuel pump securely (an extra pair of hands helps). Depress the fuel pump pushrod (a screwdriver works well here) to the point where the free play has just been take up. It’s easy to feel, as the resistance will be much greater at the point where the linkage begins to actuate the pump diaphragm.

5 With the linkage at this point, measure the distance from the mounting flange of the fuel pump, down to the tip of the fuel pump linkage arm. This can be a tricky measurement. Try laying a machined piece of steel across the flange and measure from the center of the steel piece, down to the linkage tip. Subtract the thickness of the steel and record the measurement.

6 Measure the thickness of the gasket under the fuel pump, and add to the fuel pump linkage measurement.

7 Compare the linkage measurement, with gasket, to the pushrod protrusion measurement. If you find the pushrod measurement is equal or greater than the fuel pump linkage measurement, then you’re pre-loading the pump to some degree, which insures a good, full stroke out of your pump. You can now pat yourself on the back and be happy and go for a drive. If, however, you find the pushrod measurement is less than the fuel pump linkage measurement (with gasket), then the pushrod is not actuating the pump until part-way through its stroke. This must be corrected, or fuel starvation can result.

To correct this situation, we must either lengthen the pushrod, or bring the fuel pump in closer to the crankcase. Installing a thinner gasket will bring the fuel pump in. Measure the old and new gaskets, or run without a gasket (but use some sealer).

In cases where the pump cannot be brought in closer by changing or eliminating the gasket, a new pushrod will be required. New pushrods are not too difficult to fabricate. We make them from letter ‘U’ (0.368”) oil hardening (O-1) drill rod, rough cut to length, ends squared in a valve grinding machine. The pushrod is placed in position in the crankcase, on the bottom of its stroke and measured. One end should be precision ground to achieve a pushrod protrusion that is approximately 1/16” greater than the fuel pump linkage measurement, with gasket. The final task is to harden the ends of the new pushrod by heating the ends to a dull red and quenching in oil. (Note that the 0.368” letter ‘U’ stock is a couple thousandths smaller than the original pushrod. Using the letter ‘U’ stock makes the job possible without centerless grinding and the extra clearance does no harm on this part.) Pushrod length was 8.0" for 1929 - 1931 engines, and roughly 8-1/8" for 1933-34 engines. But bear in mind that the stock length may be too short due to pump wear!

Jeff Hasslen’s roadside fuel pump pushrod repair trick is legendary in the Midwest region as it has brought more than one ailing Franklin home. It involves fabricating a shim from a tin can, or soda can. Fashioning the shim into a cup shape, it can be placed over the protruding end of the pushrod, thus giving a bit of extra stroke to the fuel pump. This is frequently all that is needed to ‘get home’, but is certainly a very short-lived repair.

Tom Rasmussen 2001

[Franklin31]

I measured the stroke at the end of the pushrod at 0.119" and the pushrod length @ 7.953" and pump wouldn't pump. Assumed it was camshaft wear and installed a 6v pump after tinkering with it a week or so. Is there still hope for this one somehow, Tom?

Tks~~

Richard-- Greensboro NC

[Guest Lincoln]

Does any one know what the specifications on how far the fuel pump push rod protrudes from the side of the block at it's minimum and it's maximum extension on a 1930 Franklin? Also what is the specifications given for the free play and the maximum stroke of the push lever inside of the fuel pump?

The answer to my question still has not been answered--How far does the rod suppose to protrude , max. & min., to begin with? What are the engines specifications on this?

[odat]

Just a note on the heat treat of the pushrod. After you bring the tip to red and quench in oil you should polish it to a shinny finish then reheat it until it turn a light straw color, this will temper the end and have a better chance of not chipping.

[odyssey]

There is no spec for pump rod protrusion. We could come up with a 'new' spec but it would steer us the wrong way. Because:

The gasket thickness varies,

the pump linkage wear varies,

the cam lobe condition may vary,

the pump base thickness can vary on the later cars.

A very small variation can be the difference.

Measure the protrusion with the rod fully retracted

Measure the distance from the pump flange to the pump arm after taking up all play- when the diaphragm is just beginning to move

Make sure, with gasket, that the rod is long enough.

Richard- your numbers are good, but the pump is not pumping. What if you remove the pump gasket? It may be that you need a longer rod. Can you try a pump with less wear?

Tom

[odyssey]

Just a note on the heat treat of the pushrod. After you bring the tip to red and quench in oil you should polish it to a shinny finish then reheat it until it turn a light straw color, this will temper the end and have a better chance of not chipping.

Thanks Dick- good point

Tom

[f147pu]

Richard, What electric pump did you use?

Gordon Howard

[Franklin31]

JC Whitney #2404-29 Cat # 730906 Walbro electric fuel pump 6 V

seems to work ok--no regulator 3.5# at carb; mounted adjacent to sector in order to stay below tank bottom even tho it should have been closer to tank.

Am pumping thru orig pump(pump pushrod removed); but want to get orig pump going and just use 6v for backup, etc.

Edited December 18, 2012 by Franklin31
addition (see edit history)

[Steve Braverman]

I would just like to add, that my '32 runs on a stock mechanical fuel pump, and I've NEVER had any fuel delivery problems. I've driven it from sea level through the mountains, and from below freezing temps to triple digit temps. If your pump is working right, there is no reason for an electric pump.