Tight fuel cap

VanguardontheLav

VanguardontheLav

Hero member
Location
Cambridge, UK
Lee (dobbinuk) just posted this on the ILOC site...

After standing at the pumps for 10 minutes, trying to remove the fuel cap on my 750, I had to use the allen key to beat the cap round.  The cap will screw on, albeit feeling tighter than normal, but is extremely difficult to remove.

I took the bike down to Moto Corsa, who tested my cap on another 750, which was fine (but no alternative cap available to test on mine). So that leaves the tank itself as the suspect.

I cannot see any obvious signs, although the threads on the tank do feel a little sharp underneath. I can't understand what the problem is or how it has happened. How can two large plastic threads go wrong? Grease/lubricant does not help.

Has anyone else experienced this?  Any advice much appreciated.
Click to expand...

I have the same frustrating problem.

Anyone any ideas?

--
Dick

 
Dick,

Same, just never did it up tight,told this to Spider when he bought the bike.

Shaun
 
Had perhaps a similar thing on my Bimota, plastic tanks expand a lot when hot. Although the cap is a long way from the heat source on a Zane Lav it might be the same thing.  Take cap off and cap cools quickly but tank is still hot, so when reinstalling the thread clearance is gone.  Once this happens a few times, the thread can start to become damaged.
My first Bimota had a plastic tank atop the engine and an aluminium cap - that was all but impossible to reinstall when the tank was hot (typical bit of Bimota "character", nobody thought to test whether you could put fuel in).
Cheers
Steve B
 
Thanks for the idea Steve. I doubt this is the reason - as you say it's a long way from the heat, but maybe it gets hot under the little black seatperch flap...

And damage to the threads - however caused - is possibly the problem. How did you (did you?) fix the threads - a bit big for a die!

--
Dick
 
They all do that, Sir.....

OCT has 4 bikes in the yard with tight gas caps, all but impossible to budge by hand.  We've thought of making caps from alloy with a bit of built-in play..... something to do in winter, I guess.

I assume it has more to do with fuel reacting with the various plastic bits.  There is no visible damage on any of the tanks or caps, either the tanks have expanded or the caps have shrunk.  New caps (still made by Acerbis, OCT can supply) are quite tight but can be fully screwed down, so it seems to be a bit of both.

piet
 
Pleased to report that my cap seems back to normal now.  Have been reading various posts about ethanol being added to UK fuel these days and wondering if that might have been the culprit in my case.  Just thought I'd post for consideration in case people are still having this problem.
 
Possibly due to the gradual formation of small ridges in the plastic thread, similar to the formation of corrugations on gravel roads, due to the tension when tightening. It will become slightly tighter when fitting but on attempting to loosen it will be like turning against a ratchet. Maybe try gentle sanding the upper surface of the cap threads and under-surface of the tank threads and then lubrication. 
 
Having worked with plastics for years (pipe lines ) it does not wear smooth unlike cast iron or steel,if you look closely at any plastic pipe (inside) you will see that it wears to a semi rough surface a bit like the cloth suede,Clem will know more about this than me,although the amount of times a petrol cap is removed /replaced ? a touch of Vass now and again wont do any harm.not so sure about sanding the threads might make it worst.
 
I did consider using grinding paste but glad I didn't; as I said, the problem has gone away by itself.  I still don't know root cause which is why I posted the comment about ethanol in fuels as a possible contributor/cause.

I suspect many people are already aware of the proposal to increase ethanol in UK fuel to 10% in 2013 but if not, here is some further reading including recommended/non-recommended materials for use with bio-fuels.  You'll need to go down the page a way to reach the petrol section.

My next step is to establish what type of plastic my tank and petrol cap are.
 
I experienced a similar problem with a flow meter in a marine application. The material used was Nylon 66, one of the properties of this material was that it abssorbed water causing an expansion of the material and it ultimately jamming. Dont know what your fuel caps threads are made from but worth a thought.

Scrumpy
 
My guess would be Nylon 6,6 or a coextrusion with HDPE.
The HDPE would offer superior water barrier and is what the plastic jerrycans are made from. The Nylon will give better chemical barrier, but is  more susceptible to water.
 
Yup!, thats the way to go Ray, Grinding paste in the petrol should help accelerate the self destruction mode built into them litlle Zanes . When all the engines have prematurely worn themselves into oblivion, we can concentrate on stretching the tubey bits and grafting the front ends on to Triples.  ;) ;) ;)

Dear Marge, why am I frightened My little Zane is going to blow up soon.
                It's coz you have been listening to Piet again havent you!.
                Yes, ------ but it's true isn't it.
                Fraid so sucker!.
                  :( :( :( ;) 
 
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