Fuel tank mount questions...

Vincenthdfan

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Hey all....I have a couple questions regarding the interchangeability of fuel tanks on a Special frame.

The 81 Special II that I am going to Street Track has all its original tank mounting points, but I'm contemplating mounting an old style Standard fuel tank from a 70-72 "Badge Bike" as I have a spare tank or two that I've purchased over the years sitting in my stash.

When I compare forward mounting points (cups) on the frame, they are mounted higher on the frame of the Special and makes the Standard tank rub on the triple tree when turning. I have an extra 72 XS-2 project bike sitting right next to the 81 Special that I've been doing a direct comparison fit on and they are indeed different.

Has anyone removed said cups by drilling out the spot welds, yet made a readily changeable location for these cups?

I have a welder, but dont really want to locate them in permanent lower location because I may swap tanks back n forth when I get bored with the looks of one tank or the other (which happens quite regularly, lol).

I keep thinking of a strap over the backbone, or maybe some countersunk fasteners of some sort, drilled through the cups to screw into the frame, etc...

Anyone done this or seen anything like this done in the past?
 
One solution would be to install rivnuts in both locations on the frame. If need be, weld the holes closed on the cups (from drilling 'em off) then re-drill them so there's two screw holes that match both rivnutted locations.
I'd think that two 5/16 or 1/4" screws in each cup would be more than enough.



Pull the tank, 4 screws to change cup locations, install the other style tank, go ride... easy peasy.
 
They make countersunk rivnuts... so they'd be flush with the frame. You could then go with 3 (per side) M5 or 3/32" rivnuts and countersunk screws... just countersink the cup holes.


1679768171592.png
 
One solution would be to install rivnuts in both locations on the frame. If need be, weld the holes closed on the cups (from drilling 'em off) then re-drill them so there's two screw holes that match both rivnutted locations.
I'd think that two 5/16 or 1/4" screws in each cup would be more than enough.



Pull the tank, 4 screws to change cup locations, install the other style tank, go ride... easy peasy.

I wonder if I could make the fasteners flush enough (in the cups) so as to not interfere with the rubber pucks/grommets??

Maybe shave the rubber down in strategic spots?

Just one of those things (out of many!) I've been mulling over in my head. 🤔
 
So I had an epiphany of sorts after posting this.

One wouldn't need to re-fasten the cups on the inside...it would be easy enough to weld a tab or two on the outside of the cups that you could drill through and bolt to the frame.

I went out and looked at them again and theres not a lot of flush real estate to work with on the frame gusset either. They sit on a raised rib style area.


1972 XS-2 Frame: 1679780013435.png

1981 Special II Frame: 1679780095554.png
 
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