Fuel Cap Tight

paul.darnell
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Fuel Cap Tight

Post by paul.darnell »

Hi everybody, new member here. I have just bought a 1961 Arrow, in very good overall condition but there are a few issues that I need to resolve before enjoying it properly. The fuel cap is a very tight fit in the tank and I cannot get it past the O-rings. Even without the O-rings it was very tight so I wrapped abrasive round to try and reduce the circumference a bit, which helped, but I cannot get the cap down fully when the O-rings are there. The O-rings do feel a bit hard so maybe there are softer versions available. I will not be using the cap as an oil measure so is there an alternative cap that will fit? A second slight issue is that oil is running slowly down the exhaust where they connect to the cylinders when the engine is running. I presume this can be cured with new sealing rings, or is this a "feature"? Any words of wisdom gratefully received. I have just got the Arrow after selling my 1966 Triumph Tiger Cub, which I got very familiar with over the 6 years I owned it. I feel as if I am starting school again and everything is strange!
JohnnyBeckett
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Re: Fuel Cap Tight

Post by JohnnyBeckett »

hi you have gone form a 4 stroke to a 2 stroke witch will be a different learning curve , but you have got a lot of good members on this forum that will give advice on what you need to know and help you out :D
ian williams
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Re: Fuel Cap Tight

Post by ian williams »

hi Paul ;
we had a discussion on this at the swindon branch meeting only just the other month .

seems after leaving cap in tank for a short time when bike parked up that the caps have gotten tight in the filler necks and general concensus is that the ethanol based fuel at the pumps is responsible for this , affecting either the plastic cap or the o ring .

what i do with mine is to find suitable o-ring that fits but allows cap to go in without too much pressure applied, i also put a wipe of copper slip around o-ring and cap and around inner of filler neck , it will of course wash off after a bit but allows a bit of confidence that the cap will come out next time you need to fill up , you could also use some silicone grease on the o ring and filler cap groove .

al though it can be a controversial subject i do also have a fuel catalyst "fuel diamond " dropped into the tank , not for any particular reason except only IF it has any effect on things like corrosion or to keep the fuel from going stale .

i have also chucked one of those magnets with a hook on down into the bottom of tank just below filler neck , to pick up any rusty bits , with a short bit of wire attached so i can get pliers in and pull it out .

there are different section of o-rings you can buy , so perhaps try a few different thickness ones from 2mm to 3mm i guess , the hardness of them is rated as a SHORE hardness , with harder ones being SHORE 90 and softer at lower value ie SHORE 70 .

you can get silicone, neoprene, rubber, and polyurethane o-rings , they are different colours , ie white , red oxide,black, i think white are food grade versions but i use white o-rings on my pcp airgun bottle neck and they seal much better .

if cap is well stuck try putting a jubilee clip round it and you can pry it out without damaging the plastic .

cheers
ian
paul.darnell
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Re: Fuel Cap Tight

Post by paul.darnell »

Thank you for your suggestions, I will persevere until I resolve the problem but it is comforting to know that it is not unique to my bike. I intend to use Esso Synergy+, which in our area has no ethanol in it, even though, by law, it has to say E5 on the pump, so the problem shouldn't get worse.
JohnnyBeckett
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Re: Fuel Cap Tight

Post by JohnnyBeckett »

hi i was wondering if a 3D printed cap would be affected by Ethanol :?: i know now there's a lot of diffident types of materials they use i have had metal parts 3D printed :D
Ivor Collins
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Re: Fuel Cap Tight

Post by Ivor Collins »

It’s surely not the size of the cap but the size of the o ring material or the dept of the o ring grove. There will be a big difference in the fit depending on the section of o ring material used, for example, if it’s 2.4mmm and too tight a fit surely a 2mm section would be worth a try.
will_curry
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Re: Fuel Cap Tight

Post by will_curry »

Here are the measurements of the cap and tank orifice from a late Arrow:

The tank hole is 1.83".
The body of the cap is 1.79"
The 'O' ring appears to be 0.11" diameter
The 'O' ring gap is 1.63" in diameter and 0.16" wide

This gives a compression of 0.02" on the 'O' ring.

The cap is not that difficult to insert or pull out and doesn't leak.
paul.darnell
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Re: Fuel Cap Tight

Post by paul.darnell »

My cap with no 0-rings was extremely hard to put in and pull out, so I am in agreement with Ian Williams above that the plastic must have swollen, possibly due to ethanol. So I had to remove material from the cap first to make that a loose fit and then I will fit new O-rings. I have ordered both 3mm and 2.5mm diameter O-rings so hopefully one or the other will be a good fit.
Trev Sellars
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Re: Fuel Cap Tight

Post by Trev Sellars »

I use narrower section O rings and use a drop of rubber conditioner on the O rings. The rings do swell after a while. Make sure the little bearing in the breather built into the cap, rattles and that any pressure build up can escape.
The dribbles and stains on the joint on the exhaust headers is quite normal. You can reduce these if you use slightly less oil in the mix but not too low.
It might be worth checking that the air filter is clean. A dirty one can cause the fuel/air mix to be rich, almost like being on choke.
paul.darnell
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Re: Fuel Cap Tight

Post by paul.darnell »

I have now fitted my new 3mm O-rings on my slightly reduced diameter fuel cap and it now all fits well - tight but removable. The new O-rings were significantly more pliable than the old ones, with a Shore hardness of 70.
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