Petrol leaking from filler cap

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TobyC
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Petrol leaking from filler cap

#1 Post by TobyC » Sat Feb 27, 2021 9:45 pm

Could be a simple one this ... out on a run today and noticed on return that fuel had been leaking from the cap. Tank is half full. An aftermarket filler/cap has been fitted by previous owner as per photo with a less than perfect seal - should the cap be vented or am I just not tightening the cap enough?
First time I filled her up it was a devil of a job to undo the cap so I suspect the previous owner just tightened the cap as much as he could to minimise/prevent leaks.
Just surprised with a tank half full that fuel was forced from the cap! I wasn't rallying or going up on two wheels or anything!
Anyone had this and do I just need to put an extra half turn on the cap?!
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Re: Petrol leaking from filler cap

#2 Post by TobyC » Sat Feb 27, 2021 9:46 pm

second photo
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fuelcap2.jpg
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Re: Petrol leaking from filler cap

#3 Post by johnnydog » Sun Feb 28, 2021 12:24 am

Our Triumphs are notorious for leaking fuel from the filler neck usually on anything above half a tank. That is why some Police Forces (Lancashire being one of them) omitted spray painting the rear nearside wing in the orange Dayglo paint when commissioning their fleets in the 70's, as leaking fuel quickly stripped the fresh cellulose paint, which looked unsightly.
Locking petrol caps are no better in my experience.
I have gone back to the original chromed AC twist non locking fuel cap on all my Triumphs. As long as the seal on the rear is still flexible, they seem to seal better than any other I've tried.
I never leave them anywhere that there is a remote possibility of fuel theft, so that isn't a concern.
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Re: Petrol leaking from filler cap

#4 Post by Charles H » Sun Feb 28, 2021 11:27 am

Toby
That aftermarket cap appears to firstly have a broken rubber seal on the cap, and secondly the attachment ring on the filler neck will also have a seal. Therefore there are two potential seals to leak. I do the same as John, revert to the bayonet original cap. They are available from CW. I carefully rub off the painted section to look better. https://www.chriswitor.com/proddetail.php?prod=618389RM
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Re: Petrol leaking from filler cap

#5 Post by agtreves » Sun Feb 28, 2021 11:37 am

After fitting a 'proper' cap check out the breather pipe that should come out under the wheel arch (I think it is the same on the MkI). In the early days I had petrol starvation when the wheel arch got covered with mud and I have heard of people collapsing the fuel tank. I did manage to get an early Unipart locking cap but it was very tricky to fit the locking collar around the pipe flange.

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Re: Petrol leaking from filler cap

#6 Post by TobyC » Sun Feb 28, 2021 7:17 pm

Thanks All

Petrol Cap ordered from CW (although it says not for early Mk1's on the web site and mines a pre face lift Mk1 so fingers crossed it fits!)

I'll try to remove the aftermarket filler neck and revert to the original. I tried giving it a good tug but it wasn't shifting so I'll have to see how its fixed and see if I can remove it.

Thanks for the advice - I'll let you know how I get on!
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Re: Petrol leaking from filler cap

#7 Post by johnnydog » Mon Mar 01, 2021 7:22 pm

I think it is only the extremely early Mk1 that the filler neck (where the cap fits) is different - you should be ok with the age of your car.
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Re: Petrol leaking from filler cap

#8 Post by TobyC » Fri Mar 05, 2021 5:16 pm

I prised off the aftermarket cap but the replacement from CW doesn't fit unfortunately - way too big and only 2 prong - my filler neck is smaller at 1.5" across and 3 prong. Guess someone has replaced the tank at some stage. Now on the hunt for a 1.5" 3 prong cap!

I've put the old filler cap back on and wrapped a rag around the filler neck to catch the leaking fuel and so I can have that mobile Molotov cocktail look and feel ...

Worst case I'll look at another cap/neck that can fit over the top or buy some sealant and try to fit the brass one back on with a decent seal.

I'll let you know how it goes ...!
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Re: Petrol leaking from filler cap

#9 Post by Charles H » Sat Mar 06, 2021 1:56 pm

Thats a bugger!
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Re: Petrol leaking from filler cap

#10 Post by johnnydog » Sat Mar 06, 2021 3:42 pm

This is what the filler neck should look like with the two cut outs for the twist AC style non locking cap which I have in all my cars.
20210306_153404.jpg
I'll check when I can, but I believe earlier cars had a different flared end on the filler neck for the cap.
This is the the front and back of the AC cap showing the fixing tabs. Should be self explanatory.
20210306_153353.jpg
20210306_153502.jpg
20210306_153509.jpg
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1967 Mk1 2000 in Gunmetal Grey
1969 Mk1 2000 in Royal Blue
1970 Mk2 2000 in Valencia Blue
1972 Mk2 2.5 PI in Triumph White
1973 Mk2 2.5 PI in Sienna Brown
1976 Mk2 2500S in Carmine Red

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