MGTA Petcock cork insert replacement

2 Jun

I have just made a replacement for the cork insert in my MG TA petcock.  I believe the MG TB uses the same petrol line switch – probably more accurately described as a valve.  The previous cork had dried out over the hot summer of 2018 while the car was laid up having the clutch replaced (more cork issues!).

Items required (see photo):

  • Sharp kitchen knife
  • Cork from Champagne bottle, Asti or similar (the finer grain the better in my experience), dry condition.  I have a sack of them in the garage saved up over the years – never throw one away.
  • Small square rough file
  • 4.5 mm drill
  • 4 washers, the same size as the loose brass collar, or slightly less.

This is the method I used, and it was easy to make a small batch while everything necessary was laid out.  Total time about two hours start to finish for three new cork inserts.

  1. Cut off the head of the cork just above where it widens.
  2. Take the compressed part of the cork and drill a 4.5 mm hole through the centre.  This does not have to be exact.  I use the compressed end on the theory that once installed it will expand for a tighter fit, rather than shrink and let air or petrol pass through.
  3. Push the square file through the hole a couple of times to produce a tight(ish) fit for the square brass insert.
  4. Using the kitchen knife, cut off about half of the excess cork using the insert and the hole at the other end as a guide, but not too much at this stage.
  5. Using the insert cut the angled face parallel.  Just a guide cut first, then remove the insert and complete the cut.  It is unlikely you will get the angle correct first time so trim/sand as necessary.  Any slight misalignment will be pulled up when the locking nut is finally tightened.
  6. Put the square insert back in, add 4 washers, the circular collar and tighten loosely with the circular nut.
  7. Take the knife and using the collar and angled end of the insert cut off further excess cork.
  8. Finish off trimming cork with sandpaper laid on a flat surface.  Leave cork a little proud for a tight fit.
  9. Now test length of cork so that there is sufficient length of thread on the insert to tighten up the circular nut.  Sand the end square if necessary.
  10. Trial offering up the whole assembly including the actuating lever to ensure everything is in the correct orientation.  Note that the large washer has the tab at the opposite side to the sloped surface of the valve and therefore opposite to the fuel line in use.
  11. Remove the cork and soak in engine oil for 24 hours, or at least overnight.
  12. Reassemble Petcock.  Test that it works reasonably freely.
  13. Test for air leakage by disconnecting the fuel pump line to the first carburettor at the float bowl and insert into a clear dry pop bottle.  Run the pump until the free end is submerged and look for absence of air bubbles as the fuel flow settles down.
  14. Reassemble fuel line.
  15. Treat yourself to the Champagne or Asti – it should not have gone flat yet!

For reference there is an excellent drawing at http://www.mg-tabc.org/library/TA-TB-fuel-switch.htm

Ian Linton
25th February 2019

Ed’s note: Ian surmises that the TB also uses the same petrol line switch – he is quite correct.

My copy of the Service Parts List for the TA and TB lists the following:

MG476/2 Petrol tap (less control) Ceased Ch. No.  TA0823
MG695/1 Petrol tap (less control)  Comm. Ch. No. TA0824

This Service Parts List is shown as Revised September, 1946, so the later part number must be the one fitted to the TB.


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One Response to “MGTA Petcock cork insert replacement”

  1. Gordon Norman 05. Jun, 2019 at 11:50 am #

    I had the same problem as Ian and after making a couple of cork seals like Ian and the petrol still leaking after a time I made a seal from PTFE.
    It has been on the car now for 2 years with out a leak and it works fine when I switch over to reserve. I have also replaced all the cork seals on my old bikes with PTFE and now no more leaks from modern petrol like I had before.

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