FUEL PUMP FAILINGS

FUEL PUMP SERVICE: AC TYPE ‘T’

Our Ruby had not been run for several weeks during the Civid 19 virus lock-down, refusing to start fuel starvation was diagnosed.  Suspecting an air leak in the fuel pump I took it off for investigation.  The diaphragm looked suspect so was replaced, both non return valves were cleaned and serviced. 

Working on the pump I noticed the cam follower (rocker arm) looked worn.  I replaced it with one that is noted as the correct one with part number number 856955 on it. I had two levers with this number, unfortunately they have different profiles! See image below. I trial fitted them to a pump and fitted them in a spare crankcase. I used the one that gave best results.

I have four spare diaphragms and they are all different!

Two diaphragms of different construction and form.

Some of the challenges working with parts for old cars, rocker arm ‘B’ was in the pump on the car, it has the wrong part number and shows severe wear.  ‘C’ and ‘D’ both have the correct part number but are not the same shape,  ‘A’ would appear to be for a different application. 

The two levers with the correct part number.  I have fitted the top one and it works fine.

The  mating surfaces were cleaned and trued up, the most deformation was round the screw holes.

Three inner levers I have, the top one is the best as the spring is longer.  With the bottom one the diaphragm shaft can slip past the spring when attempting to fit the diaphragm.

Once the diaphragm has been sorted out the non return valves may need some work. Judging by the quantity and variety of sealant I have found on my pumps air leaks have been a major problem.

I was having a problem as well, though all the joints were sealed I still had an air leak on the input line. In the end I used a pipe to test the non return valve on it’s own. It was sealing well.

Then I tried soap to look for leaks, this highlighted that the casting was cracked. This was beyond repair. The leak is between the input and output chambers.

Trying another casting I found it had this hole in the corner, this one I will mend with JB Weld, it will be OK as an emergency spare.

A third casting was good except that the thread in the top had stripped out! that was easily fixed by drilling and tapping 5/16 instead of 1/4in. This did give me a clue about the split casting, it seems most likely that the top bolt had been over tightened, this pulling the casting apart.

These are the components of the non return valves.

Valves plates in situ, one with spring on top one with spring under. Held in place by the plate.

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