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December 2, 2013

Fuel Pump

The TR6 used a pretty standard mechanical  diaphragm fuel pump driven from an eccentric on the camshaft.

As the diaphragm moves down, it pulls fuel through a check valve from the fuel supply line into a sediment chamber, through a fine screen, and into the cavity above the diaphragm, while on the upstroke, it forces fuel through the other check valve to the pump outlet.  The two opposing check valves are held in place with a retainer.  After over 30 years of storage, this pump chamber still had liquid fuel residue in it.

Here are all the parts of the fuel pump.  Rebuild kits are available that include mostly "soft" parts, but they seem to be pretty generic, so there are extra parts in the kits, and in the case of this pump, a couple missing.

This pump has a spring loaded lever on the underside so that the diaphram can be moved manually.  I guess this could be used to "prime" a carb by filling its float bowl, but I'm not sure what the real intent was.  At any rate, the kit didn't include the O rings for the lever shaft, and made no mention of it in the instructions.  The lever is fixed to a little cam shaft by hexagonal protrusions on the ends of the shaft that are peened over slightly to lock the lever in place.  There is an O ring on either side of the cam shaft where it passes through the pump body,  When the lever is raised, the cam presses on an internal link that moves the diaphragm.  The O rings were not in the rebuild kit, and had to be bought locally.  The second picture shows the lever after zinc plating.  

Before I started to put everything back together, I linished all the mating surfaces to see that they were flat.

There are several interconnected linkage parts deep within the bottom part of the body.  The instructions suggest using an "assembly pin" to help get everything together.  It is just a pin that goes place of the pivot pin, but has one end a smaller diameter than the pivot pin.  This end holds all the parts in place, but allows extra movement  to get the rocker arm spring and diaphragm installed.  The assembly pin is then shifted to the thicker end so that it locates everything, and so that the real pivot pin can be driven in.

There is an oil seal staked in the bottom body casting, which  rides on the diaphragm shaft and seals off the part of the pump that opens to the engine crank case.  Though I wouldn't have a problem unstaking it, the seal is not part of the rebuild kit.  Instead, the kit contains a new seal "cap" that  fits over the old seal housing, and under the diaphragm spring.  

Next, the diaphragm itself.  It's a little tricky trying to get the end of the diaphragm shaft to engage properly with the actuating linkage without being able to see it.

These little devices are someone's idea of a cruel joke.  They go into little grooves in the ends of the rocker arm pivot shaft.  I put my odds at about even for having at least one of them launch itself to some unknown hidden place in the shop.  Surprizingly, I finally got both of them in place with only a little swearing.

The new check valves.  Literal interpretation of the instructions would have had me install them backwards.  The text must have been written for a different valve design.  This is a case of reading between the lines to determine what the instructions intend, not what they say.  A little Locktite buys some insurance.  

The top part of the body gets a screen and gasket under the domed cap.  The cap was pretty rusty, so I zinc plated it and its fastening nut.

Finished pump on the shelf until it's needed.

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