Petrol Tank mounts

[Taid]

I have just bought new tank mount rubbers and sleeves for the bike .. There were no sleeves when I dismantled it ...

but I find that that the existing bolts are the same diameter (3/8" ) as the new sleeves, so the sleeves are redundant in this case and the bolts are to be tightened to the end of the thread (don't really like that .. seems bad engineering, somehow)

Just wondering is my tank from a different date when a change had been made? .. the bike is a 57ish 16MS. or is it likely that someone earlier down the line has drilled and tapped the threads in the tank to a larger size?

[dave16mct]

They should be 5/16" BSCY so someone had drilled them out and re-threaded to 3/8" (naughty!)
Dave.

[Taid]

They should be 5/16" BSCY so someone had drilled them out and re-threaded to 3/8" (naughty!)
Dave.

Thank you D ..

Not really much I can do about it, for the moment, anyway. The bolt heads are drilled for locking wire, though there was none when I bought the machine, so they won't need severely tightening provided I do a good job with the wire. I suppose in the future, I could drill out again and fit a 5/16 threaded bush, but I want to get out and ride it, so that will have to wait.

Also, thinking about it, the bolt is screwing in the same same way as a stud would do, and I wouldn't be agonising over a stud.

Thanks again for the gen ..

[56G80S]

Sure you realise, but just in case, the sleeves are there for a reason. If all is correct, bolt length, sleeve length, thickness of rubber mounts (thick one between tank and frame mounting, thin one between "penny washer" and underside of frame mounting) then you can't easily overtighten bolts and punch a hole in the tank.

Bolts don't have to be that tight, too tight and the rubber mountings become almost irrelevant. The correct bolts do have a hole for wiring on, I use the heavy duty coated garden wire!

Threads in my tank are tired and I found nice new bolts and some Loctite helped! One day I'll fix that but more important work to do.

Sure someone will contradict me.

Johnny B

[Rob Harknett]

correct, bolts are only tightened to just nip up, not compress rubbers at all. That's why they are wired on. If tight expect vibration, perhaps even tank damage.

[Taid]

Sure you realise, but just in case, the sleeves are there for a reason. If all is correct, bolt length, sleeve length, thickness of rubber mounts (thick one between tank and frame mounting, thin one between "penny washer" and underside of frame mounting) then you can't easily overtighten bolts and punch a hole in the tank.

Johnny B

I suspected there may be a chance of puncturing the tank, but, since it is pretty full of fuel, I haven't yet compared the thread length on the bolt to the depth of the piece it screws into ,,

Was wondering about trying to get some 3/8 internal clearance tube to make my own sleeves and trying to open up the rubber mounts to take them .. the holes in the lugs on the frame look large enough to take a slightly larger sleeve ..

[GOLDSTAR]

pretty sure I turned up a couple of studs in brass, ensured there was a tad clearance between them an the tank locktited 'em in, drilled the lower part and wired the nuts, certainly did for the W/ng which had already been punctured by over long bolts. kind regards

[ajscomboman]

Just to clarify a couple of points. The sleeves are in there to allow the bolt to be tightened so the sleeve is pinched between the tank mount and the washer. The rubbers should compress only slightly but still have flex to dampen vibration. They are also there to stop the bolt from punching a hole through the base of the tank.

[Duncan]

The sleeves were introduced in 1950 and work exactly as Rob S says, prior to that (from 1938 going by the part number) three "tab" and one normal bolt were used with lock wire as Rob H says.

I would be wary about using sleeves on your over size bolts as the large holes in the frame mounting points permit positioning/aligning the tank this may result in either the tank or the over size sleeve rubbing on the frame and vibrating or being unable to thread cables (control and electric) in by the headstock, a trial fit should confirm.