FRACTURED STEEL ROADSTER TANK

Jason Curtiss · Aug 10, 2007

My '75 Commando roadster gast tank developed two hair-line fractures. These fractures are in the "floor" of the tank and they partially surround the right-front mounting stud.

Has anyone else ever experienced such fractures in a steel tank? And if so, did you repair it and how?

Thanks,

Jason

L.A.B. · Aug 10, 2007

That is quite a common problem on the Roadster and Interstate tanks and is generally caused by the tank not being supported properly by the correct foam pads under the tank.

After I bought my Roadster I discovered the tank was quite badly cracked around both front mounting studs as it had been repaired by somebody covering both the areas with a thick layer of epoxy adhesive, but it started to leak so I had to clean it off and then I brazed it up.
I emptied the tank and left it open for two weeks before I did it though.

hewhoistoolazytologin · Aug 11, 2007

L.A.B. said:
I emptied the tank and left it open for two weeks before I did it though.

Might not be long enough...Petrol fumes will hang around for a long time...I flushed mine with water, and in the end, submerged all but the area to be repaired, in a big tub of water, leaving a bubble of air in the end of the tank I had to work on. I used silver solder, but as above said, brazing is perhaps stronger, and in that area of the tank, you will need strength as well as a good seal.

Main point...do it so.......darned safely, that you make sure nothing can happen. A tank full of fumes, is a bomb, literally.... :wink:

cash · Aug 11, 2007

I'll make this very clear I do not recommend this method.

Our local Engineering firm had an old welder based down on the docks and for a packet of fags he'd gas weld anything, he was bloody good too. He'd just shake out any fuel left in the tank, blow compressed air through it and put the flame into the filler neck. There'd be a loud pop and the flash would blow out the flame, he'd casually relight the gas and start welding. The pop had been know to remove the odd dent.

The first time I stayed and watched him, never did again, I'd go and buy him his cigarettes while he did the job.

Cash

james · Aug 11, 2007

repairing gas tank

My brothers, both welders have repaired gas tanks by running a rubber tube into the gas tank connected to the exhaust pipe of a car / bike,fills the tank with carbon monoxide -- displacing the flammable / explosive gases, you don't need to run the exhaust continuously -- thereby gassing yourself!, just long enough to fill the tank to be repaired. Treat it cautiously.
Good luck. James

L.A.B. · Aug 11, 2007

hewhoistoolazytologin said:
Might not be long enough...Petrol fumes will hang around for a long time...

It didn't explode...therefore it was long enough!!

I would of course urge anyone to take all due care when doing anything like that.

fastback · Aug 11, 2007

A couple of panel beaters I know use the exhaust-pipe technique to weld automotive gas tanks. Not my cup of tea but they're still alive.

Ron L · Aug 13, 2007

I would take the tank to a chemical stripper and have the entire tank stripped. Then whoever does the repair will not only have a tank with clean metal to make a good bond, he will be able to clearly see where the crack leads and any other cracks that paint might be obscuring. Get it repaired once rather than put it back on only to find another crack you missed because of the paint.

Of course this means the tank will need to be repainted, but if it is leaking, the paint is probably not looking too good anyway. I would also suggest lining the tank after the repair to give a little more security against future leaks.

Most important. LAB is correct in that the cause was improper support, but the foam pads are only part of the answer. With the proper foam padding in place in the tunnel of the tank, add enough rubber spacers to the front studs to lift the tank slightly off the mounts. Adding one rubber spacer below the mount and a large fender washer, the nyloc mounting nuts should pull the tank down enough to compress the rubber and create a stress free mounting on the studs and the rubber pads.

Jason Curtiss · Aug 13, 2007

Thank you for all the excellent responses to my cracked gas tank problem. My biggest concern is making sure the crack does not recur and I'm not quite sure what I need to do in this regard. Perhaps my tank does not fit the frame properly. It seems that the center of the tunnel tends to contact the frame unless I stack a bunch of those rubber washers on the front mounting studs. Anyone else have this problem?

Also, has anyone purchased a reproduction Norton gas tank?

Thank you.

Jason

L.A.B. · Aug 13, 2007

Ron L said:
Most important. LAB is correct in that the cause was improper support, but the foam pads are only part of the answer. With the proper foam padding in place in the tunnel of the tank, add enough rubber spacers to the front studs to lift the tank slightly off the mounts. Adding one rubber spacer below the mount and a large fender washer, the nyloc mounting nuts should pull the tank down enough to compress the rubber and create a stress free mounting on the studs and the rubber pads.

I agree with Ron L about the foam pads being only part of the answer, as a front pad will help to limit the amount that the tank rocks from side to side which can stress the areas around the studs, as the weight of the tank (+fuel) should be supported by the rubber washers, the rear of the tank is supported by the rear foam pad, which is partly compressed by the rear tank strap (steel tanks) being tightened against the rubber 'cotton reels'.
One thing worth noting is that the cotton reels do not actually support any of the tank's weight when the strap nuts are tightened the cotton reels are actually under tension and not compressed.

It is also important to use pads made of the correct density foam and correct number of washers for the particular tank type

I use four rubber washers between my Roadster tank and the frame bracket and one below (which is an extra one) with the large diameter metal washer on each side, and a thick foam pad front and rear.

79x100 · Aug 13, 2007

I think that another potential cause of fractures here can simply be overtightening the front nuts at some stage. They only need to pinch the rubbers.

The tank tunnel should easily clear the top tube but there are two factors here - The metric tubes and the later "seamless" tanks. I have discussed these tanks with L.A.B. in the past. His seems OK but mine is a dreadful fit. If you do go for a repair, I would ask a panel-beater to ease it a bit where it contacts.

Unity Equipe had alloy Roadster tanks at Stafford a couple of years back. They were expensive but looked gorgeous and were feather-light.

L.A.B. · Aug 13, 2007

79x100 said:
I think that another potential cause of fractures here can simply be overtightening the front nuts at some stage. They only need to pinch the rubbers.

I only tighten the (Nyloc) nuts until the studs draw level with the underside of the nuts.

79x100 said:
The tank tunnel should easily clear the top tube but there are two factors here - The metric tubes and the later "seamless" tanks.

Well, I'm not sure the couple of extra millimetres on the diameter of a metric top tube would really make all that much difference?

79x100 said:
I have discussed these tanks with L.A.B. in the past. His seems OK but mine is a dreadful fit.

I seem to remember thinking at the time from what you said and seeing the photos that your bad tank may have had a repair done to it? As you remarked that the knee indentations were in slightly different positions, and I seem to remember seeing a welded patch on the underside of the tank that could have been an opening made to insert a panel beater's dolly?
I don't know why but I didn't say anything about that at the time.

Possibly the patch repair was there for another reason?

Ron L · Aug 13, 2007

It seems that the center of the tunnel tends to contact the frame unless I stack a bunch of those rubber washers on the front mounting studs

It typically takes 4 rubber washers above the mount, but if the tank still rests on the foam pad, add another one. When there is no space between the last washer and the mount, you have the correct number.

There should be a thin pad in the tunnel about 4-6 inches from the steering head and a thick pad about 4 inches from the rear of the tank.

LAB brings up a good point about overtightening the nuts. You can bottom out the threads on the stud and turn it into the tank and cause leaks that way too!

79x100 · Aug 13, 2007

I don't actually use nylocs due to their habit of bringing the stud with them. plain nuts lightly pinching the rubber have never come loose on me.

My brother in law has a metric frame on a '73 750 and one tank that I lent him wouldn't clear. I can't remember now which tank it was. I suspect that if the frame is a bit oversize and the tunnel a bit under then it can become a squeeze.

You have a good memory L.A.B. The black tank with the repair though was just one that I had lying around and used as an example (wouldn't want you to think that I collect Commando tanks !)

My "problem tank" is actually this white one. I have had it back to metal and it has no repairs and had no filler under the original white / red / blue (could've done with it though !)

Apologies for the poor photo angle. I was a bit worried that the helper was going to drop it (it was full at the time) and wanted to get it over with quickly. The oil underneath resulted from the top of the tacho cable leaking incident.

On the underside, you can see a mark where one of my twin pull throttle cables which ran over the top tube had caught and rubbed when fitted with four or five rubbers at the front (I now have six) and a rubber above the rear bush as well. I have never had any of these problems with the "seamed" Roadster tanks.

Jason Curtiss · Aug 13, 2007

The attached photo shows the spot where the tank tunnel was contacting the frame. It took six (6) washers to prevent this metal-to-metal frame contact. You can see the glue-marks from the foam pads that I installed to the underside of the tank. The frame is 1975 I assume the tank is the same vintage. The upper left-hand stud is the one with cracks around it.

I have a spare fiberglass tank that seems to fit the frame much better. So, I think I'll paint it yellow and mount it on the bike instead of trying to repair and re-form my steel tank.

Keith1069 · Aug 14, 2007

Interesting thread. I have the same problem on my welded (non flanged) Roadster tank as Jason and 79x100 with almost identical marks and positioning on the tank tunnel. Even a 1/4" cable tie holding the harness would contact the tank and I eventually lost the front foam. One stud mount had cracked many years ago and my temp repair was 1.5" dia. fibreglass tissue patches (3 layers) which are still holding up 20,000 miles on (surprisingly). I'd like to get another rubber washer under each side (5 at present) but have run out of stud length. With this arrangement I have no room for the single rubber washer under the bracket, only the penny washer and nyloc. Frame is an early 850 but unsure if it's Italian or UK.
I will rethink the missing front foam now I have raised the tank by one rubber washer thickness.

Ron L · Aug 14, 2007

Jason,

If you have a thick foam pad at the rear and a thinner one at the front, as the glue marks indicate, I would take a look at your frame. All Commando frames have a slight hump in the backbone. If you put a straight edge on the main tube you will see this. However, in order to make the mark I see in yours, I have to wonder how extreme it is. Could the frame have been damaged and straightened at some time?

79x100 · Aug 14, 2007

Keith,

Thanks for confirming that and good luck with your repair. Three cases in a row can't be coincidence. Does yours also come close to the small diameter cradle tubes at the rear due to a lack of properly formed cut-outs ?

I think these seamless tanks are dreadful !

It's not the first time that Nortons sent bikes out with ill fitting tanks. Some way during the production of the Long Range Fastbacks they changed from the single-sided coil brackets with spacer tubes to the later double brackets. No problem on the tanks with a cut-away but the LR tank sits hard on the bracket.

I have spoken to an original owner about this. Rather puzzlingly, he had put a piece of rubber in between rather than simply grinding the coil bracket which is what I've done on my 750.

L.A.B. · Aug 14, 2007

Keith1069 said:
I'd like to get another rubber washer under each side (5 at present) but have run out of stud length. With this arrangement I have no room for the single rubber washer under the bracket, only the penny washer and nyloc.

I'm wondering if those experiencing problems are using the correct thickness (and density) foam pad at the rear of the tank? As adding extra rubbers at the front may not be the complete answer, the thickness of the rear pad and the amount it is compressed will also affect the tank to frame clearance.
I would also position the pad above the strap and not forward of it as the glue marks in Jason's photo shows. So raising the rear of the tank should also be tried as well as raising the front if there is a clearance problem fit a new pad and maybe re-profile the strap (make the curved part deeper) so that it doesn't pull the tank down as far at the rear?

This is the rear pad, supplied by Norvil that I fitted to my Mk III Roadster tank:

Keith1069 said:
Frame is an early 850 but unsure if it's Italian or UK.

If you measure the spine tube accurately then a British frame will (supposedly?) have an Imperial 2-1/4" diameter tube (just under 58mm -allowing a little extra for paint thickness) and an Italian frame tube is likely to be 60mm (+ paint) diameter.

79x100 · Aug 14, 2007

I've got one of those thick pads at the rear, now combined with a thin one and extra (front type) rubber washers above the metalastic to raise the tank rear and stop the underside of the tank sitting on the convergence of the cradle tubes with the main spine and to keep the rear of the tank off the spine.

I really think that the problem with these tanks is that they are hand made or finished and the quality control was abominable. Some of them fit and some simply don't have enough clearance. The earlier tanks with a seam are a beautiful crisp pressing that clear where they're supposed to.

My frame is a 1997 Andover replacement and has Imperial tube.

I could go to the garage now and put on one of my seamed tanks and it will fit perfectly with one standard thick foam pad at the rear and four rubber washers at the front. The measures that I have taken to make the seamless tank fit do not lie with my frame or my knowledge of how Roadster tanks need to be mounted.

Unfortunately, I spent a lot of dosh on a white / blue / red paint job so it's going to have to stay on for a while yet (unless L.A.B. decides he wants a quality white two pack painted tank & panels and makes me an offer I can't refuse

)

FRACTURED STEEL ROADSTER TANK

Jason Curtiss

L.A.B.

Moderator

hewhoistoolazytologin

cash

james

L.A.B.

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fastback

Ron L

Jason Curtiss

L.A.B.

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79x100

L.A.B.

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Ron L

79x100

Jason Curtiss

Keith1069

Ron L

79x100

L.A.B.

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79x100