Leaking fuel cap

[Mike Killay]

My fuel cap is black plastic.
When I bought the engine, fuel leaked out so I fitted an new cork washer and the composition washer under the air inlet.
It still leaks!
Any suggestions?

[phil]

So it leaks at the fuel tank to cap joint as well as under the air inlet?
This after the old gaskets were replaced with new gaskets?
When you run your finger over the surfaces the gaskets bear against are the surfaces both smooth, any roughness anywhere in those areas? If there is roughness remove away from tank and smooth with suitable 220 and 320 grit body shop sandpaper, then clean off with compressed air, solvent and wipe down.

[chris]

good advice phil, should have thought of it myself as I have a leaky cap as well

[headdownarseup]

another suggestion
dont fill it up so far.
have you tried the boiling trick yet? not only does it work on the fuel plunger cork, but try it on the cap gaskets as well.
does your breather/vent have a rubber or nylon washer? (sometimes they were cork as well)

jon

[Mike Killay]

I boiled the cork in the tap and that worked very well. I did not think to boil a brand new cork washer for the cap. The smaller washer under the air valve is some sort of cardboard looking thing (also new).
I will try smoothing the top of the tank inlet, but my friend who also has a seagull says both his leak slightly.
I have got plastic bottles with various fluids in them and they don't leak, so why do Seagulls?

[chris]

they leak because they are old and british, everything old and british seems to leak

[phil]

The car parts places here carry a variety of gasket materials. Yours probably do as well. I like to use Victor Reinz brand JV 121 gasket material in the 1/32" thickness ( not sure what that would be in mm) for under fuel caps etc. very happy with it.

It looks similar to ground cork but is synthetic. If you do any gaskets for other portable fuel tanks good there as well. I also use same brand JV 127, same thickness for most other things including low compression head gaskets. It is black, I only mention it because sometimes I get the JV numbers mixed up.
The rest I can buy or get from heavy paper.

[Mike Killay]

Well, I found out what the trouble is.
When the air screw is tight down without a washer, it remains 1.3mm above the top of the cap.
The washer is also 1.3 mm thick, so when you tighten the screw down, you think that it is tightened by the washer, but it is actually at the end of the thread.
I got a rubber cold water tap washer, enlarged the hole and fitted it. It is 2mm thick and has done the job a treat!
I don't know whether they are all like this or just mine, but if your engine drips, try checking the air screw.

[phil]

If folks are going to use your neat trick, we hope they will soak the washer in fuel mix for 24 hrs, to make sure it does not start to go mushy. Do they use ethanol in motor fuel in the U.K.?

[Mike Killay]

Phil,
I am testing this rubber washer, so far, so good but I suspect that it will not hold up long term.
Plan B is to make a sheet of 2mm thick Sikoflex between two oiled sheets of glass and use that!

[phil]

So Sikoflex as in boatbuilding material? For no gasoline problems you need Buna N rubber or Neoprene.
I keep a small box of leather scraps for just that kind of emergency. When it's time to throw away an old pair of boots or other stuff with good leather in it, I just throw it in the box, mostly nice flat pieces of differing thicknesses.

PM me your address and I will tuck some pieces of the proper gasket material in a letter for you, no charge, I have more than I will ever use.

[Mike Killay]

Phil,
That is very kind of you but no need.
The rubber washer is still steeping in petrol with no ill effect so far.
As for Sikaflex, it is a polyurethane mastic and is so effective that they say 'It will stick ice to water!'
It does not dissolve in anything, so when building campervans etc. if you make a mistake, the only way to remove it is to use a red hot knife and cut through it.

[Charles uk]

I don't know why your putting all this effort in to refurbishing a fuel tank cap washer, if you cantact John about Seagull part number 238 you will find he probably has them in stock & they cost less than £1 inc. VAT or they did last time I bought some 18 months ago!

He also has fuel tap corks though they cost circa £3.00 but they do last 25 years, & just about all the bits you'd need to build yourself a completely new Silver Century!

[Mike Killay]

Charles , I did, as explained above, the new washer etc. could not work satisfactorily

[Charles uk]

I use new standard Seagull ones around the base of the fuel cap on a regular basis & I'm not seeing any signs of ethanol damage even though we now seem to have 10%ish in our fuel.
Sorry I was talking about the bottom ones.

Most of the top ones seem to be of the fibre type.