Which thread ?

john kitchen · Post by **john kitchen** » Sat Nov 22, 2003 8:19 pm

Please can someone tell me which thread is commonly used on a G9?

lawrence · Post by **lawrence** » Sat Nov 22, 2003 8:33 pm

As far as I know, all the threads going into the frame are CYCLE and all others are BSF. It is useful to have a thread guage (TPI) and a table of threads to identify bolts. When you know what the bolts are you can tell what the holes are! If it is 1/4" you are ok cos' bsf and cycle are the same then. A few of the tiny fastenings are BA. You shouldn't find any METRIC which is a shame as they are lovely and uniform and as the syaing goes 'You know where you are with a metric thread' (Usually Japan!)

Lawrence[}:)]

Biscuit · Post by **Biscuit** » Sun Nov 23, 2003 12:00 am

Not forgetting that Burman cover screws and single mag/platform bolts are BSW, at least Burman and Lucas knew the correct thread for aluminium. 1/4 Cycle and 1/4 BSF are not the same - same TPI different thread angle.

clive · Post by **clive** » Sun Nov 23, 2003 8:33 am

anyone know what the thread on the speedo mounting stud is. (tyhe one that comes out of the bottom of the speedo) the closest I have found to fit is 8 metric if I remember correctly but i am sure it cannot be correct!!!

Rohan B. · Post by **Rohan B.** » Sun Nov 23, 2003 9:25 am

A good question. The speedo stud thread appears to measure as 3/16" 26 tpi = plain old 3/16" cycle thread.

The nut does appear to an odd size though, at least the ones I have to measure. Its just possible its a BA size - which was based on a Swiss clockmakers (metric) thread series, and is often quoted as some logarithmic based series of sizes.

Someone here in Oz can make and supply these in a more common nut size, to suit available spanners, if these prove impossible to otherwise source (which I doubt).

Cheers,
Rohan.

lawrence · Post by **lawrence** » Mon Nov 24, 2003 10:17 pm

Interesting what Alan says about the 1/4" threads. My chart says ok to interchange and I have never had a problem. I'll have to check that out further.

Lawrence[}:)]

Eric · Post by **Eric** » Sat Nov 29, 2003 12:00 am

Most but not all cycle threads have the same pitch of 26 tpi regardless of diameter. 1/4 bsf is also 26 tpi while larger diameters have less tpi in proportion. 1/4 Whitworth is 20 tpi. 1/4 bsf and 1/4 cycle will generally interchange but they are not the same because 1/4 bsf has a thread angle of 55 degrees while 1/4 cycle is 60 as are all other cycle threads. Sorry to disappoint the metric enthusiats but if you go back to the time of out bikes that system was also almost as confussing with different standards in different parts of the world.

Biscuit · Post by **Biscuit** » Tue Dec 02, 2003 11:03 pm

It may well be that worn examples of 1/4 BSF and 1/4 CEI (BSC) are interchangeable but as the core dimensions of the two threads differ by 7 thou. it would require some forcing to fit a BSF nut on to a CEI bolt/stud.

Biscuit · Post by **Biscuit** » Tue Dec 02, 2003 11:26 pm

From the 400 Four manual, it would seem that 3,4,5 and 12mm. thread pitches were altered around the early seventies, must be heaven for someone restoring a rice bowl special of this era. Didn't worry me though the majority of the crankcase bolts were 6mm., and they tap out 1/4 26 nicely (BSF not CEI), as do other sizes pro rata. There are very few mickey mouse threads left on the thing!

lawrence · Post by **lawrence** » Wed Dec 03, 2003 7:18 pm

Sacre Bleu! [:0] I always thought Alan was such a perfectionist!!

Lawrence[}:)]