Author Topic: Mk5 Tank Cap Fix  (Read 271 times)

0 Members and 1 Guest are viewing this topic.

Offline Hamwic

  • Full Member
  • **
  • Join Date: Feb 2020
  • Posts: 86
  • Location: Hampshire, UK
Mk5 Tank Cap Fix
« on: 24 Jun 2023 at 09:48 »
Hi All,

My MK5 has had issues with the petrol tank cap fixing ever since I've had it. Probably due to bad storage the top of the tank mouth, has always leaked, and once or twice the cap seemed to come loose by itself. In the end, I lost the cap, and have struggled to find a replacement. The cause of the loss was a loose spigot pin in the tank mouth, which accounted for the dribble of fuel that had been occasionally seen running down the tank after a ride.

So, what to do? The suggested Harley Sportster cap needs serious modification to fit as the spring steel ears don't reach the spigots. The lack of a return on the ends, means making a new spring steel retainer of the more complicated kind detailed elsewhere in these pages, and wouldn't help with my loose spigot.

The answer, at least in my case, is the fuel cap fitted to P11 Nortons. Purists and rivet counters please look away now.

As supplied they only have two bayonet slots - see picture - and the rotating bayonet section is slightly over size.

Simply put, the fix was as follows.

Grind back the rotating portion of the P11 cap to 52mm OD approx. or a bit less.
Fill drained tank with water - most important!
Grind off and tap out two opposing spigot pins.
Weld up the two resulting holes - the material is very thin and probably a bit rusty, so great care is needed.
Dress gasket face flat.
Try the cap. I my case I needed an extra 1mm synthetic thick cork gasket on top of the red fibre one supplied with the cap. This red fibre gasket is solidly fitted to the cap so not easy to swap out. Tweak as necessary.

Drain and dry tank, refit, etc.

I shall now concoct a hinge support strap, but the cap is now a good fit, so we are back on the road.

Cheers for now

Offline DJS

  • Full Member
  • **
  • Join Date: Aug 2019
  • Posts: 83
  • Location: Cornwall
Re: Mk5 Tank Cap Fix
« Reply #1 on: 24 Jun 2023 at 13:12 »
Hi Doug,

I donít know if it helps but LDMCC are currently in advanced discussions regarding the remanufacture of a batch of Mark series petrol caps.
I would anticipate these being available in the next 6 - 8 weeks.

All the best,


Offline yosemite

  • Full Member
  • **
  • Join Date: Aug 2017
  • Posts: 54
  • Location: kelso united kingdom
Re: Mk5 Tank Cap Fix
« Reply #2 on: 25 Jun 2023 at 10:11 »
Lost one off my mk 4 , in a box found one from a harley, still in it wrapper, no idea where itcame from as I wanted to use the bike tried it , ended up removing the harley clip, making a new clip from spring steel and screwing it to the two holes in the cap left from where the rivets were removed,  fits ok looks reasonable. Keeps petrol in rain out.
Only problems I had were that I forgot to temper the spring steel after hardening the first one, snapped the lugs on the clip so had to make a second, , bent the second one the wrong way so locks be turning opposite way to normal still working after 6 months. Will be getting one from the club when available and keep this as a spare
« Last Edit: 25 Jun 2023 at 10:29 by yosemite »