LEAKING PETROL TAP

1930-1932 scuttle tank models with Ewarts tap

Tattybogle, my RN box saloon, had been plagued by a leaking petrol tap for several months.  No matter how many times I dismantled, cleaned and adjusted it, it persisted in leaking. I even tried wrapping the cork seals in PTFE tape, as I had read somewhere this was a sure-fire way of sorting it out. This worked for a bit but, after a while, the tape turned slimy and the leaks re-started.

It was frustrating.  I would think I had fixed the problem when the tap held back a tankful of petrol overnight. Then, when I operated the tap in the morning, it would not close off and there was a steady drip-drip of petrol from it.

The construction of the tap can easily be seen in the ‘exploded photo’.  The tap is double-ended with main and reserve supply.  The main is fed from the tank by the short standpipe and the reserve by a drilling in the brass body at the base of the main standpipe. There are main and reserve tap plungers with cork seals which close off the appropriate drilling in the tap body. These plungers are retained in the body by small set screws, locating in slots along the plungers, which also act as limit stops.  The effective diameter of the corks can be adjusted by screwing the seal shafts in or out. Theoretically, one could go on almost indefinitely increasing the diameter by small amounts to compensate for wear.

Removing the tap from the car is a bit of a fiddle; first the fuel has to be drained off, and then the tank mounting bolts removed to allow the tank to be jiggled on the scuttle to give clearance to withdraw the tap from the hole in the bulkhead.  In desperation, I removed the tap for a final Kill-Or-Cure Attempt. Yet again I dismantled the tap on the bench, cleaned it with brake cleaner and blew it out with compressed air. This time, however, I inspected the body more thoroughly than before – for some reason, I had not previously paid much attention to the bores in which the plungers operate, beyond ensuring they were clean, and had addressed myself more to the state of the cork seals.

Now, under strong light, I could see slight ridges in the bore of the main tap worn by the cork seals over the past 75 years.  It now became clear to me that if the seal rested on a ridge in the closed position, petrol could leak past it.  My previous attempts to adjust the tap would have resulted in the seal being in a different position and probably resting on one of the ridges.  Fellow member, George Mooney, came up with the suggestion of truing the bore and removing the ridges with an adjustable reamer. The danger with this is, if one were too gung-ho, the diameter of the bore could be increased beyond the limit of adjustment for the cork seals.  I measured the bore and concluded that it was originally about 9mm diameter (so much easier to think in metric!) but now was worn slightly oval and, of course, ridged.

I was then alarmed to discover that new corks for this tap are not made.  There are some readily available for vintage motorcycles, which initially appear the same, but are too large at 10.7 mm diameter.  I checked with the Seven Workshop and other suppliers who confirmed that the correct corks are not available at present.  Then I discovered some Viton seals that look like small rubber O-rings sold specifically to replace the corks on Austin Sevens.  These are available from Nigel Mills of Functional Products on 01455 845512, and I wasted no time in ordering a set.  These are fitted and adjusted in exactly the same way as the original cork seals.

I obtained a reamer that adjusted between 8.7 and 9.5 mm and carefully reamed out the bore in the tap body with a series of very shallow cuts until all traces of the ridges were removed and the bores were smooth and shiny. Then I reassembled the tap and fitted it back in the car.  Unbelievably, despite checking I had ensured an air tight seal by blowing down the tap with my mouth, it still leaked!  Once more I removed the tap and adjusted the seal shafts, and hallelujah, it stopped leaking!

And, two weeks later, it is still not leaking!

Roger Bateman DA7C

ADDENDUM - Ewart Petrol Tap Screws.

When refirtting the petrol tap, I noticed neither retaining screws for the plungers were original and I had great difficulty in getting them out. Finally, I put the petrol tap in the deep freeze for 20 minutes and the final screw came out as easy as you please. Then came the job of trying to find replacement screws.  After a long and tedious search I found GWR Fasteners website, and a wonderful selection of machine screws with a very helpful helpdesk. So I ordered 10 x 5BA brass, round headed, slotted machine screws for £4.44 inc postage. The smallest length they do is 3/8” so the screws needed cutting down. However, I am pleased to say they fit perfectly and I can’t wait to give everything a test run! Andrew Gossage DA7C