BSA A65 Crankcase bolts

[Hook]

Good Morning, I am readying the bottom end for it's final bolting up, I have all the bolts from the A65 spare parts book and....drum roll...two of them are wrong!.
Spare part book 1969 & 1970 (I have the 1970 case with the oil pressure switch) give page number 18 & 19, part number 6 as 14-0221 5/16" Unified thread 2" long x 2!
These are the two bolts that are inserted from the primary side and screw into the aluminium of the timing side case. Good job I tried all the bolts finger tight first!! the thread is NOT UNF it is BSW..GRRR yet another replacement to buy. Checke the tread on an odd 5/16 BSW bolt and found a perfect fit..pity it is only one and an inch too short.

[limeyrob]

I'm not sure when BSA swapped over from BSW / BSF to UNC / UNF. My 1971 A65 was UNC / UNF.
5/16" UNC and 5/16 BSW are both 18 TPI so they will interchange, not perfectly as Unified is 60 deg and Whit is 55 but its possible your thread should be UNC.  What are the other threads on the engine?

[Hook]

The long studs  are BSW on the casing and AF on the nuts, I havent removed the cylinder studs so I don't know. All I can think that this may have originally been on an American Thunderbolt and the studs were changed for customising.

[limeyrob]

The studs won't be BSW one end and Unified the other. Its most likely the coarse threads are UNC.  If the engine is AF inch sizes on the spanners it will be all Unified - UNF and UNC

[Hook]

Oh well, yet another dodgy flea bay seller who doesn't quite understand his nuts anfd bolts I bought brand new UNF and UNC from him and none of them are any good.
Thanks for your help.

[limeyrob]

Its worth downloading some thread charts so you can measure the TPI and check what you have.  Also a set of imperial thread gauges, they don't cost much and yes, a lot of stuff is miss sold or mis-described.
I also have a 1970 Land Rover and the early 70's are the absolute worst period for threads, the UK industry was swapping out of BSF and BSW to UNF and UNC, mostly, but they didn't want to spend the money so there was a lot of old stock getting used up. Some such as Lucas went straight to metric but never told anyone and some stuck with BA for small threads. Land Rover changed to Unified in 1972 but not for the axles and gearbox, or some brake parts and now the spares are simply random. "Unified" means anything but. I needed some high tensile BSF bolts and was being offered HT UNF with the threads cut so they had AF heads.  Rant over but the thread thing is a mess.
My best purchase has been sets of "workshop" (ie cheap) grade taps and dies for UNF, UNC, BSF, BSW and Cycle. Paid for themselves many times over as often you are recovering a thread butchered by a previous owner with the wrong nut or bolt.

[Allan G]

69 was the first introduction of Unified threads on the twins. Excluding carb mounting studs and cylinder head bolts/nuts. These stayed as BSF/CEI

ANYTHING in that threads into the crankcase, whether it be a stud or a bolt has a UNC thread. Any nuts onto such studs are UNF.

The beauty of the 69-on parts books is that dimensions of MOST studs, bolts and setscrews are give along with thread form.