O-Ring Problem

[EasyGoingPat]

Hi,

I have just removed the fuel tank from my BMW R1100S. Around the fuel-filler is a circular recess in which there is an O-ring. A thin metal plate then goes on top of this, followed by the plastic-and-metal panel that forms the visible centre-section of the tank. The whole thing is held in place by 6 Allen bolts that pass through the exterior, visible rim of the fuel filler, then through the concealed plate, and finally tighten into screw holes in the the tank itself.

I am having a huge amount of trouble reassembling this. The problem is that the O-ring seems to have been deliberately engineered to be slightly too large for the recess in which it sits. I presume this is so that, as the steel plate above is tightened down, the ring compresses, forming an air-tight seal. The problem is that, while putting in the Allen bolts that hold the whole thing together, it is impossible to get fingers or anything else close to the O-ring, to nudge it into the recess. The result, after many attempts, is that the ring is always bulging somewhere, and I doubt it is forming a good seal.

Can anyone think how to tackle this? I was thinking of some kind of glue, to hold the ring in place while I tighten it down. Any suggestions? It doesn't need necessarily to be petrol resistant, because, once the plate is tightened, this will hold the O-ring firmly in place (though obviously I don't want a glue that will dissolve and contaminate the petrol).

Any suggestions would be very much appreciated.

Kind wishes ~ Patrick


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[stinkwheel]

I'm not clear exactly what you have there from your description. Post pics?

Might be the o-ring has stretched/deformed and you need a new one.

In terms of adhesive. A little smear of RTV gasket sealant woudl seem the logical thing to seal a gasket.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Pete.]

Did you clean everything? O-rings expand with certain solvents.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[EasyGoingPat]

Might be difficult to get useful pictures, but I'll give it a go if the gasket sealant doesn't work out.

I haven't cleaned the O-ring in anything. It appears to be in very good condition, and - though I accept the point about O-rings deforming - it looks to me like it had been deliberately over-sized. Guess it wouldn't hurt to order a new one though. It's good practise anyway.

- Patrick
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[Pete.]

It's a common occurrence. You'll find that a new o-ring will fit perfectly.
Do you not have any bearing/seal/o-ring shops nearby? If not you might find one online. O-rings are sized by internal diameter (ID) and cross-sectional diameter (CS), so measure the ID and width of the groove and that's your size.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[raesewell]

you need some red rubber grease to hold it in place, assuming the O ring is in good shape
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Yamaha FJR 1300 Normanton West Yorkshire

[EasyGoingPat]

Thank you all very much for the advice. Lots for me to try there. I will try to remember to pop back and report what worked out.

- Patrick
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Thank you to anyone taking the time to read my posts.

[Pete.]

I stumbled across this advice when doing a search for something else - boil the o-ring to shrink it back to (near) it's normal size:

https://forums.pelicanparts.com/bmw-r1100s-r1200s-tech-forum/568177-black-kadork-thing-fuel-tank-2.html
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[EasyGoingPat]

Maybe worth a go. Though, if I do have a real problem with it, I am inclined to take the advice of my Haynes manual and fit a new one. Being a motorbike part, it can't be more than £100 for an O-ring.

Thanks.

- Patrick
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[temeluchus]

https://www.motorworks.co.uk/vlive/Shop/Parts.php?T=5&NU=15&M=30&Ct=GA&SbCt=BA_15_30_GA_25

Last item in the list. Cripplingly expensive!
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Some shite cruiser. Now with guns and FREEDOM!

[EasyGoingPat]

Just ordered. Thank you. (Now I feel like such a lazy arse, for not looking it up myself.)


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Thank you to anyone taking the time to read my posts.