Reading Tim Stockdale’s article on tank sealing got me thinking about my bikes, although not regarding sealing. I have 2 slimline tanks for my 88 and Atlas “projects” (ie crates of bits): both are bare, and the cage nuts in the bottom are absent. I have in the past rummaged about the interweb for these with no luck, and the usual suspects do not list them. Tim mentioned that at 5/16”BSW 18tpi this is close to 5/16” UNC (different pitch angle?), so I have briefly trawled about and these captive nuts seem to be fairly easy to get, but there seem to be different styles of cage.
Has anybody got some good pictures of a SL tank base to show the right nut form?
It then gets more confusing trying to sort out the waisted bolts. Andover Norton show 2, but provide no further details, their # 06.7895 and 06.7798, with the latter appearing from the photo to have a shorter shank.
Norvil list both, again without a spec, but with the option of the first in Stainless.
RGM only list 24979 as an equivalent to 067895. The spec is a shank length of 13/16”, and with an extended head for ease.
NOC shop drew a blank.
Can anybody shed any light on any of this? (and that’s before I start on the rubbers and washers!)
My tanks are all threaded. …
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Interesting, Phil. Now I…
Interesting, Phil. Now I know they exist, I also need to find one to sort out a stripped thread.
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Are you sure...
... they're UNC Philip? I didn't think American threads were used on Nortons until the Commando. The corrsponding part for my ES2 is Whitworth. I accept both are 18 tpi but of course thread forms and angles are different.
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From the RGM website
PETROL TANK MOUNTING BOLT, Part No 24979
THESE FIT MANY PRE COMMANDO PETROL TANKS, SLIMLINE AND EARLIER. THE HEAD IS EXTENDED TO GIVE IMPROVED ACCESS.
MATERIAL: STAINLESS STEEL
COUNTRY OF ORIGIN: UK
THREAD: 18TPI, 5/16" BSW X 7/16" (11.5MM)
PLAIN PORTION: 3/8" (9.5MM) DIAMETER AND 13/16" (20.5MM) LONG
THE HEX IS: 1/4" BSW. .650" (16.5MM) AND NICELY DOMED
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Fred's Threads
Ian....I agree .........but apparently some early post-WW2 Nortons had a whole bundle of mixed threads holding them together. Also a few parts after 1960 either had an AF/UNF/UNC threads or were converted during the Commando era. The Atlas engine breather elbow and rocker cover bolts being a few such examples.
My guess being that this tank bolt started life with a 5/16" x 18 BSW thread which has now been converted to 5/16" x 18 UNC. Adding to the fun, the tank bolts I purchased have over-size 3/8" hex heads.
Michael - attached photos show captive nut.
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Phil, thanks for your photos…
Phil, thanks for your photos- wow, that's certainly a mess under your tank. Ethanol- as if we haven't enough to worry about.......
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My tanks are all threaded. No nuts.
The bolts (screws) are the same from 1930's to end of featherbed.
They should be tightened hard with their shoulder against the plates under the tank. The gap contains a steel cup washer under (above) the head, then a rubber disc, folled by the frame mounting bracket, a top hat rubber washer above and then the tank. The length of bolt just squeezes the rubbers each side of the frame brackets.