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classicauto

2016 ST 250 Fuel petcock leak FIX

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Good day gentlefolk from the world of Trials.

I own a 2016 Sherco ST250 and it developed a fuel leak around the petcock flange in the summer.  I tried a few different things, fitting a larger O-Ring around the factory one, replacing the O-Ring altogether with a thicker one and trying to massage the plastic to bow toward the ring instead of away from it.

Nothing worked for me in a permanent sense.

Being an auto body guy I am familiar with methods of plastic repair, specifically hot air welding, and had a light bulb moment involving using our hot air welder to build up, thicken and reinforce the flange area of the tank itself.

I performed a few rod adhesion tests (literally just throwing different rods at it until something sticks) I found our Fiber-Flex ribbon to be the best match.  Unfortunately the plastic in these tanks doesn't like a good fusion weld like typical PP plastic or even nylon.  I'm not sure what it is exactly, a type of HDPE I would guess.  Regardless, the material did seem to root in quite well and I managed to weld, file and refit the petcock.

So far so good......but another year of bumps vibration heat and my novice abuse will tell the tale.  I will update this thread if it ever becomes an issue again.

 

Materials used:

-Surface cleaner/degreaser

-Stainless wire brush

-Hot Air/Nitrogen Welder by Urethane Supply Company (Renamed "Polyvance") 

-Fiber-Flex Ribbon Part No.:R10-04-03-BK

-Flat ******* file

 

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Hi,when mine started to leak Nige Pearson at Trials UK fixed it by using a gasket made of some kind of rubber material between the tap and tank. Not sure what bike the gasket came from but I’ve never had a problem since it was fitted, Nothing wrong with the plastic weld repair but this is easier to sort for the diy types who do not have access to the equipment needed.

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classicauto, you probably know more about plastic weld repairs than I do and your repair looks good. There is another way that can most often work too! People tend to resort to a silicon type sealant, smear it on where they think it will do best and then tighten everything down...hey presto usually a leak develops after a few days. Instead if they were to apply a suitable fuel resistant sealant that sets (rather than remains tacky) leave in place; having formed a nice even 10 mm or more thick surround, without fitting the fuel tap or outlet.... for about 5-10 minutes to semi set, then refit the fuel tap/outlet but tighten the fixing screws/bolts just over finger tight...wait a few more minutes and then tighten equally a few more turns leave overnight and tighten down but not excrutiatingly overtight...comfortable tight. This method is used in the Marine Industry admittedly for skin or hull fixings but it certainly develops a watertight seal for fixings that take a hell of a beating under load and stress. Worth a try as it has been my experience that people tend to rush with sealants and don’t always follow the instructions. 

Ethanol will do its worst on whatever it contacts so I guess we are all doomed to having dodgy seals, gaskets and knackered plastic tanks....Funny thing is that I have just removed an Aprilia Futura fuel tank ( platstic ) and there appears to be no Ethanol issues at all!🤔I wait with baited breath!

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