Fuel tank mounts.

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Time Warp

Time Warp

.......back to the 70's.
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I have to be missing the obvious.

Stock Roadster tank, the pressed front frame plate that has the large holes to suit the tanks forward mounts. (In my case someone had cut the outer side of the R/H hole and now see why)

There has to be a 3/4" difference in the frame and tank hole spacing, so much that the front studs on my tank have been bent inward (OEM baffled tank as far as I know) to get it to fit plus that one hole being bodgerated to get more room for the bent studs.
If the studs were parallel they would be beyond the edge of the frame plate holes.

That can't be done at the factory, surely.

Edit.
My Fastback tank fits its frame holes nicely but the spacing is different to the 850 tank (and maybe the frame)
If the studs on the 850 fuel tank were not bent inward they would not go through the large mounting holes in the frame pressing.
As it is they are bent inward and it has a hack job to one hole to fit.

Can someone post the stud centres/centers for a Roadster tank please... A 15 minute job turned out to be anything but.....
 
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on my 74 Mk2 roadster, the forward tank mounting studs - center to center is 5-3/8". mine appears to be factory original and parallel. BTW, the center to center dimension of the large holes in the frame plate is also 5-3/8". hope this helps....
 
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I really do appreciate you taking the time to get that measurement.

My frame is 5-3/8" centres.
The fuel tank which still has its original faded CAR paint on the underside = 6-1/4" stud centres.
 
What's CAR paint?
My EMGO tank on the bike now looks to be the 5-3/8". I have 2 more tanks - stock ones - one fiberglass and one steel I can check.
Have never heard of bending tank studs to fit. Can't be good.
 
Time Warp said:
I really do appreciate you taking the time to get that measurement.

My frame is 5-3/8" centres.
The fuel tank which still has its original faded CAR paint on the underside = 6-1/4" stud centres.
Click to expand...
something's not right - even with manufacturing tolerance stack-up, the absolute maximum, center-to-center, stud dimension would be 5-15/16". nobody would cut things that close. it's beyond normal engineering practices. any chance you can "persuade" things for a better fit? good luck....
 
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I will take a look tomorrow.
To the outside of those large holes in the frame mount is around 6-1/4" and why one hole is bodged and the tank studs @ 6-1/4" are bent inward.

I might have to modify the frame brackets, the aim is to use bobbins instead of the stacked rubber disc's and studs which must have looked pretty funky with this bodge.

Back in better days.

Fuel tank mounts.
 
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Wonder if someone tried to excessively pressure test your tank? I think that would make it splay out like that.

Have to plead Duh on the CAR paint.
 
It seems the only logical thing but shows no signs of obvious oddity on the outside so will have to get back to it.
The widest part (inside) of the lower seam is around 245 mm ( a tad over 9-5/8" ?)

Add it to the list.
Thanks for the replies.

Maybe someone will see the pic's and quickly hit the back button. :D

Fuel tank mounts.


Fuel tank mounts.
 
Red paint on the studs. Not an OEM paint job. My guess is the tank has been damaged, repaired, and leak tested with a little too much pressure.
 
Time Warp said:
It seems the only logical thing but shows no signs of obvious oddity on the outside so will have to get back to it.
The widest part (inside) of the lower seam is around 245 mm ( a tad over 9-5/8" ?)

Add it to the list.
Thanks for the replies.

Maybe someone will see the pic's and quickly hit the back button. :D

View attachment 12169

View attachment 12168
Click to expand...
if i'm measuring the same place as you, which I think I am, I measure 9 inches - seam to seam (inside), widest part of the tank.

edit - pic 74 Mk2 roadster - almost 100% sure original tank, original paint

Fuel tank mounts.
 
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Ron L said:
Red paint on the studs. Not an OEM paint job. My guess is the tank has been damaged, repaired, and leak tested with a little too much pressure.
Click to expand...

The story goes it was painted in 2005 by someone named the 'pinstripe r in New York for his wife.
There was a Commando listed on FB a while back and it mentioned a pinstripe company in New York, which I googled and it went to a long running family company (but forgot to save the link).. the same pinstripe r who knows.
 
it sure looks like the thing has a bit of a spread. THIS IS JUST ONE OF MY BRAIN FARTS, but if it was caused by over pressure, and depending on how gutsy you are, you might try some sort of a clamp, maybe a woodworker's type, on the upper parts of the studs, and try to pull the tank back into a more normal configuration. it may not take much, and you can control the pressure. it may be a dumb idea, and it may not work - just food for thought....

EDIT: MOST LIKELY THIS IS A BAD IDEA --

Fuel tank mounts.
 
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Reverse the process... apply vacuum while measuring the distance between studs. Stop when you reach 5-3/8".
 
joe czech said:
if i'm measuring the same place as you, which I think I am, I measure 9 inches - seam to seam (inside), widest part of the tank.

edit - pic 74 Mk2 roadster - almost 100% sure original tank, original paint
Click to expand...

Thanks Joe.
I do not think this is a OEM tank now, the welds are on the inside and look to be machine produced, the bottoms of the tank for the fuel taps do not look flat to each other like your pic either.
Maybe it is an EMGO that indeed has been pumped up.

It only came up as I was machining some other bits yesterday and did a couple of stepped alloy inserts for those frame mount holes at the same time.
The intention being to drill holes in those for rubber bobbins but its a little more complicated it seems......... Its a nice paint job so probably won't touch the tank to fix things.

About 9-1/2" with a second check.

Fuel tank mounts.


Fuel tank mounts.


Fuel tank mounts.


It could be worse, I guess it might hold an extra half litre that might get me home one day.
 
joe czech said:
it sure looks like the thing has a bit of a spread. THIS IS JUST ONE OF MY BRAIN FARTS, but if it was caused by over pressure, and depending on how gutsy you are, you might try some sort of a clamp, maybe a woodworker's type, on the upper parts of the studs, and try to pull the tank back into a more normal configuration. it may not take much, and you can control the pressure. it may be a dumb idea, and it may not work - just food for thought....
Click to expand...

I could probably machine something that attached over the studs and attempt to pull the tank in enough to fit neater to the mount holes then use the machined inserts with offset holes to suit.
I will save that for a brave day, candy paint might not be to flexible but a 1/2" would do it.
 
Maybe something like ratchet straps or turnbuckles or some contraption with threaded rods.
 
I could machine two heavy tubes to go over the studs with nuts to hold them down and some form of turn buckle between them as close to the base of the studs as possible.
Maybe give them a half turn a day over a week or some such thing.

Can someone tell if it is a Norton OEM or EMGO tank off the pictures up the thread please.
I would have thought based on the LR Fastback tank I sold earlier in the year that any welding would have been by oxy/acetylene torch.
That rear portion looks machine welded.
 
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