Here's a quick 'How To' repair when your nylon catch decides to seize.

The spring inside the mechanism basically corrodes and falls apart, then one day you'll shut the cap and it'll spring back open because the latch hasn't got anything to lock against. So remove the complete filler cap, 4x counter sunk retaining screws and wiggle the cap from the sealant, carefully.



Centre dot and drill off the heads of the domed rivets with a 4mm drill, just the heads to release the plate so don't go any further once the dome has been drilled.
Remove the spring plate, corroded spring and nylon catch and clean any debris.




Drill out the rivet pegs with a 2.5mm clearance drill and tap the holes to a 3mm x 0.5mm thread, be careful while drilling otherwise you'll drill all the way through so no more then 4mm if you can judge it right.



Find a new spring, I used a spring from an old pen ball point pen which was cut slightly shorter, fit into place with the nylon catch and test it'll compress enough and return fully, there's a peg stop for the nylon catch on the underside of the plate. If all is OK refit the plate with new screws cut to the correct length, domed or counter sunk, either will work as there's plenty of clearance underneath once refitted.

Nice work Joe,

I changed a fuel cap last week because of this problem. I will now go and rebuild the old one as its in better condition than the replacement.

Cheers.

Frazer

Alternatively, in the "how to do" section:

Repairing the petrol cap spring.

Bic or Biro spring?

Well done Joe
Keep up,the good work

Thanks for this, I didn't realise there was supposed to be a spring in there, I assumed the nylon had worn away. Will have to take mine apart some time to save standing at filling stations using my penknife to pull the nylon back out when it had slid back.

Nice work Joe, you have Pm also =)

Tom.