Could anyone tell me what thread the 8 mounting bolts are for the sprocket on a Bantam/Cub hub? They are 1/4 diameter but not sure if they are BSF or cycle thread - or whether there is any difference!

Thanks

both 1/4 bsf and 1/4 bscy thread have 26 tpi/ so they are both the same , using those hubs on our sidecar outfits we found the weak points , ripping the bolts out and breaking the cast lugs apart , the solution was and still is to run a 6mm drill through the holes then use ht allen bolts with nylock nuts to bolt the sprocket on , i still use this mod today on my vintage hillclimb panther with no problems, will.

the lads right.. run a 6mm drill through and use nylock nuts the spot welds holding the brake drum on the tube can be flimsly as well so put some more on for a belt and braces job.

Although the TPI is the same at 26 the thread angle is different. BSF is 55 degrees whereas cycle is 60 degrees, therefore although you may get them to go together they joint will be weak and likely to gall or strip.

Dadof2

Thanks for the replies. I'll have a look into opening them out but they've been ok for the last 25 years of trialling so I'm not really sure if I'll change anything. I'm only changing the Allen screws because the new sprocket I'm fitting is thicker so I need slightly longer ones.

Dadof2, I take it that means they are cycle thread and not BSF? Although I've owned the bike 30 years I'm still a bit green when it comes to the British thread systems!

Thanks

Hi Guy's.

Look on "BSA Bantam hub made wider".

On the BSA "Otter" site.

Regards Charlie.

Thanks for the info on the Otter site Charlie, looks to be a lot of reading for me to do there!

He mentions that the thread size is 7/32 but mine are definitely 1/4. At least I now know they are BSCY so I can get some ordered.

the original threads are 7/32 so it seems yours have been tapped out to a 1/4 no doubt when an earlier owner had the usual trouble , the original had small heads with a strange spanner size . it is worth checking the casting round the bolt holes as i have found many cracked , on my trials outfit i have two where the casting has broken away but with ht allen bolts and nuts holding the sprocket on it has been fine ,even with a big panther motor providing the power ,. will

Thanks aawil, I'll give it a good check over for cracks and look into longer bolts and nuts as suggested. I suppose it's best to beef it up now before the problems happen! Thanks for the replies everyone!