TAB II Alloy Tank #3

City Garage · Sep 12, 2023

Stephen_Spencer said:
Yep, remember you asking the question CG. Don’t doubt what you’re saying, although others with the same tank on the site have no such leaking. The fact that TAB warn about it suggests others may have experienced it though, so venting might not be quite right. I’m just lucky I suppose !

I’ll try the adjustment first and switch the vent to 9 O’clock.

More volume/more pressure against spring. Look how oem's vent typically has two hoses.

And as you have found, placement can be an issue because its not the "highest point"

Voodooo · Sep 12, 2023

Stephen_Spencer said:
Short tank first test ride today. Bike was faultless - tank not quite so!

I filled up prior to setting off, making sure not to overfill as TAB recommend. 50km in I stopped for a coffee and noticed fuel dripping down the RHS of the tank. Cleaned it off and made the return journey. 100+Km total and still losing fuel from the cap at the end of the ride - so definitely not an overfill situation.

Pretty sure it’s coming via the cap itself, so maybe vapourising and forcing past the diaphragm because the vent hole is blocked? Or the diaphragm nut needs to be adjusted (tightened) slightly to increase the spring pressure between diaphragm and tank closing face?

TAB warn of slight leakage because of the Monza style of cap as its requirement to ‘breathe’, especially when topped off. Hoping this is not the norm for anyone who wishes to fit decals or paint the tank.

I’m a Monza virgin - anybody experienced this with their TAB tank, or other - Ideas?

Should’ve fitted the decals after the test ride - right one is ruined! DOH!

Rhymes with ‘clucking bell’!

View attachment 109747
View attachment 109748

Is that cap welded to the tank or is it a threaded on cap?
My Norton aluminum tank monza cap is threaded on. I used a same sized flat o-ring between the cap ( think of a o-ring from a spin on oil filter).

This stopping my fuel seeping and also allowed me to tighten the cap and align it to my liking.

Stephen_Spencer · Sep 13, 2023

Voodooo said:
Is that cap welded to the tank or is it a threaded on cap?
My Norton aluminum tank monza cap is threaded on. I used a same sized flat o-ring between the cap ( think of a o-ring from a spin on oil filter).

This stopping my fuel seeping and also allowed me to tighten the cap and align it to my liking.

His terminology is a bit vague Voodooo, but my understanding is that no it’s not threaded. The cap ring (which he manufacturers) is welded to the tank. The cap itself is positioned, by interference fit. over the cap ring and secured/sealed with a chemical metal two part epoxy.

I don’t believe it is leaking via interface between tank/ring or ring/cap. Pretty sure it’s breaching the seal or slopping straight out of the vent.

Voodooo · Sep 13, 2023

Stephen_Spencer said:
His terminology is a bit vague Voodooo, but my understanding is that no it’s not threaded. The cap ring (which he manufacturers) is welded to the tank. The cap itself is positioned, by interference fit. over the cap ring and secured/sealed with a chemical metal two part epoxy.

I don’t believe it is leaking via interface between tank/ring or ring/cap. Pretty sure it’s breaching the seal or slopping straight out of the vent.

Sounds like you need less fuel in the tank. Or, another / better tighter seal.

Too tight, and the cap will be hard to close, and it’ll put more pressure and wear on the latch and hinge pin.

Stephen_Spencer · Sep 13, 2023

Voodooo said:
Sounds like you need less fuel in the tank. Or, another / better tighter seal.

Too tight, and the cap will be hard to close, and it’ll put more pressure and wear on the latch and hinge pin.

Agreed Voodoo, but less fuel doesn’t work - it was still leaking at about 60-70% full and let’s face it, the 961 doesn’t have the best range to start with.

I’m getting advice from the cap manufacturer (via TAB) about adjustment of the cap: how much to apply; line up of vent holes between pressure plate, rubber washer and backing plate; and whether the adjustment nut is loctited - don’t want the whole assembly landing inside the tank. It’ll definitely leak then

!

Stephen_Spencer · Sep 18, 2023

No luck with the cap - it leaks quite badly regardless of how it’s adjusted. It is breaching the sealing face when fuel washes/tumbles over that area.

I can actually reproduce the leak by pulling the bike firmly to the right with the bars, whilst stood to the RHS of the machine.

Difficult to see why this is occurring. Most likely:

- Insufficient spring pressure, regardless of setting - incorrect spring length (17 mm)/weight?

- Cap-ring mating surface is ridged from the machining process, providing a poor sealing surface?

- Sealing washer is inadequate in some way?

- Cap to ring interface is misaligned for some reason - unlikely.

The individual components look OK.

Awaiting a response from TAB - they suggested sending a new cap lid so I’m guessing that’s the next step.

Gives me time to get the seat recovered while I wait I suppose! Also answers the wife’s usual question “why‘d‘ya need multiple bikes when you only have one ass!?

Voodooo · Sep 18, 2023

Stephen_Spencer said:
No luck with the cap - it leaks quite badly regardless of how it’s adjusted. It is breaching the sealing face when fuel washes/tumbles over that area.

I can actually reproduce the leak by pulling the bike firmly to the right with the bars, whilst stood to the RHS of the machine.

View attachment 109928

View attachment 109929

The individual components look OK.

Awaiting a response from TAB - they suggested sending a new cap lid so I’m guessing that’s the next step.

Gives me time to get the seat recovered while I wait I suppose! Also answers the wife’s usual question “why‘d‘ya need multiple bikes when you only have one ass!?

View attachment 109930

Is the rubber seal going inside the filler neck instead of sealing on the top of the lip?

Also is it possible to be leaking here where the seal wouldn’t make much contact?

Stephen_Spencer · Sep 19, 2023

Voodooo said:
Is the rubber seal going inside the filler neck instead of sealing on the top of the lip?

Also is it possible to be leaking here where the seal wouldn’t make much contact?

The rubber washer was rather hard, so I swapped it out for a silicon washer - both are toilet cistern washers by the way. This is sealing much better although the silicon is not likely to survive very well in contact with fuel.

Haven’t road tested it yet as it is now apparent that it is also leaking from the weld between Cap-Ring and tank. Awaiting guidance on a decent sealant. Just got unlucky it seems.

cliffa · Sep 19, 2023

Bummer about the weld Steve, but coincidentally there was a thread about a similar issue on the classic forum a few weeks ago...

Aluminum gas tank filler neck repair

I have an aluminum fastback tank I got from walridge over 10 years ago.The fuel has been leaking from under the quick fill filler cap were it is fastened to the tank.There was some kind of brown filler they used to seal it when made .It has been flaking off now when I fill it anywere near the...

www.accessnorton.com

Regarding the leaking top seal, I reckon you could limit the amount of fuel sloshing up there by fitting an inner cap (think bathplug). The ring of weld would stop it dropping into the tank.

Stephen_Spencer · Sep 19, 2023

cliffa said:
Bummer about the weld Steve, but coincidentally there was a thread about a similar issue on the classic forum a few weeks ago...

Aluminum gas tank filler neck repair

I have an aluminum fastback tank I got from walridge over 10 years ago.The fuel has been leaking from under the quick fill filler cap were it is fastened to the tank.There was some kind of brown filler they used to seal it when made .It has been flaking off now when I fill it anywere near the...

www.accessnorton.com

Regarding the leaking top seal, I reckon you could limit the amount of fuel sloshing up there by fitting an inner cap (think bathplug). The ring of weld would stop it dropping into the tank.

Thanks Cliff.

Thats very useful - JB weld it is. Don’t use ethanol fuel options anyway.

I can create a leak through the weld, by surging the fuel (moving the bike sideways) and then blow fuel down the outside of the tank from the inside of the filler neck, using a puffer bottle! So there’s definitely a hole or holes in the Ring-Cap to tank weld. Unfortunate but no big deal!

I’ll take a look for an inner cap - that may be pretty useful

!

cliffa · Sep 19, 2023

Stephen_Spencer said:
Thanks Cliff.

Thats very useful - JB weld it is. Don’t use ethanol fuel options anyway.

I can create a leak through the weld, by surging the fuel (moving the bike sideways) and then blow fuel down the outside of the tank from the inside of the filler neck, using a puffer bottle! So there’s definitely a hole or holes in the Ring-Cap to tank weld. Unfortunate but no big deal!

I’ll take a look for an inner cap - that may be pretty useful !

If you get stuck, let me know the diameter of the inside of the neck and I could knock something on the lathe.

Stephen_Spencer · Sep 19, 2023

cliffa said:
If you get stuck, let me know the diameter of the inside of the neck and I could knock something on the lathe.

Thanks Cliff, really appreciate that. I’ll get back to you

.

TonyA · Sep 19, 2023

Stephen_Spencer said:
No luck with the cap - it leaks quite badly regardless of how it’s adjusted. It is breaching the sealing face when fuel washes/tumbles over that area.

I can actually reproduce the leak by pulling the bike firmly to the right with the bars, whilst stood to the RHS of the machine.

View attachment 109928

View attachment 109929

The individual components look OK.

Awaiting a response from TAB - they suggested sending a new cap lid so I’m guessing that’s the next step.

Gives me time to get the seat recovered while I wait I suppose! Also answers the wife’s usual question “why‘d‘ya need multiple bikes when you only have one ass!?

View attachment 109930

With the weld leaking , you may want to send it back to TAB II and get it repaired /tested this time ?? Now , is it the weld or the JB weld joint leaking ?

Stephen_Spencer · Sep 19, 2023

TonyA said:
With the weld leaking , you may want to send it back to TAB II and get it repaired /tested this time ?? Now , is it the weld or the JB weld joint leaking ?

JB Weld Original is the recommendation Tony.

Thought about sending the tank back for a nano-second. Really don’t want to be screwing around swapping fuel pumps back over and shipping it back across the globe, for what might be a simple repair. If I can’t fix it easily and it keeps leaking I’ll ship it.

TAB II Alloy Tank #3

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