Author Topic: Replacement lockable flip-up fuel filler cap  (Read 1871 times)

Rob B

  • Full Member
  • ***
  • Posts: 195
  • L-Twins and Tripples Fan
Replacement lockable flip-up fuel filler cap
« on: December 30, 2012, 07:51:02 PM »

In looking for a new filler cap I found that Burton Bike Bits sell the same one as fitted to the HESKETH, as do a number of other people such as MOSS and TR Supply etc. However, I noted that all the suppliers for these Petrol Caps make it very clear that the Petrol Cap is NOT VENTED. Any ideas? Could this be the answer to some of the historical fuelling problems with the H? My existing filler cap lets in loads of rain water so I don't think it has a problem with venting!


FUEL TANK CAP - BSA, Norton, Triumph

 Flip-up chrome cap. Cap Locking, complete with 2 keys (UK Made)

 Chrome Plated: Yes
 Polished Alloy: No
 Vented: No
 Lockable: Yes
Hesketh V1000 Black/Gold/Gold EN10++
Hesketh V1000 Red/Black/Black EN10++
Hesketh V1000 Black/Red/Black EN0
Laverda 180 Jota  Orange!
Triumph 900 Sprint

Will F

  • Jr. Member
  • **
  • Posts: 39
  • Brit V-Twin Fan
Re: Replacement lockable flip-up fuel filler cap
« Reply #1 on: December 31, 2012, 12:21:53 PM »
My v1000 had a new filler fitted by hesketh motorcycles and was not vented,i just swapped the internal bits from the old filler,sorted in 20 mins


  • HOC Committee
  • Full Member
  • *
  • Posts: 398
  • Brit V-Twin Fan
    • Hesketh Owners Club
Re: Replacement lockable flip-up fuel filler cap
« Reply #2 on: January 02, 2013, 06:16:10 PM »
My own V1000 had a new cap when I bought it.  It was the unvented one...

As Rob B noted, they're available as Pt No 06-0681L from vendors such as Burton Bike Bits.  Looks like this:

The unvented version DEFINITELY causes problems with the tank "vacuuming".  Without a proper vent, the air can't get in anywhere near as fast as those big Dellortos can suck it out...  I found out about my unvented cap when riding the bike in between local villages.  After about 10 miles, the bike simply faded and cut out... I stopped, checked for loose connections leaks, etc... Found nothing and tried to restart the bike... It just started...  Another 7 miles, or so, it stopped again...  I suspected "vacuuming" and tried listening for a "hiss" of air rushing in when I opened the tank... Very difficult in a full face helmet... Concerned that the bike may have a fault, I turned around and headed home... 5 miles later I'm at the side of the road again...  I opened the tank and, as it was only half full, left it open.  After that the bike never missed a beat all the way home...

So... I examined the tank cap and dismantled it in-situ. (sorry, no photos just now).  The assembly is secured by a roll-pin and there is an o-ring at the bottom of the shaft (to stop water getting in via the keyhole) so no air gets in that way.  The tank seal is a rubber disc with a metal centre formed like a sort of hollow eyelet.  It's a close fit around the lock casting, so not enough air gets in there.  The metal eyelet part is formed such that it has a toroidal (doughnut-shaped) swelling concentric to the centre hole.  On vented examples, this swelling has two holes drilled ino it.  One from the bottom of the seal, into the inner chamber of the swelling and another from the top, 180 deg away from the first hole.  (The hole positioning is intended to stop fuel splashing out of the holes as the bike is ridden).

I drilled 2 x 2.5mm holes into the metal part of the seal (as described above).  The size was a guesstimate, but owners with genuine/original items would be able to confirm what size these holes should be...

On reassembly, the cap gave no problems and has continued to work perfectly over the past year.


1974 Triumph T160 Trident (New Project)
1981 Yamaha XS1100 Sport (Trike Project)
1981 Yamaha XS1100 Sport (Red Sport)
1982 Hesketh V1000 (Production/Development Engine)