55 SR1 Magneto Threads

[59G3LS]

My 56 16MS has had a rough life by all accounts, it came to me via Malaysia/Singapore where I believe it was kept running far beyond it's retirement date using farmyard technology.
Basically every screw/bolt head is mashed/rounded, hammer marks on crankcases etc. Too much to digest in one go, so I decided to compartmentalize and took the mag aside, locking the rest in the shed.

My question is, does anyone know the thread type for the shaft that the A/R unit mounts on and also the two coil retaining screws on top? One is missing the other sheared off and I can see a re-tap coming on.

HT coil is o/c and end cover damaged, apart from that, not too bad! Bearings seem good and magnets feel nice and 'magnety'.

Regards - Mark, Perth Australia

[Rob Harknett]

I would had thought armature shaft 26tpi cycle and smaller fittings BA, try a 5/16 cycle nut on the shaft if there's still one on the bike

[aobp11]

It's 3/8" BSF, 20TPI.
The coil set screws are 3/4" x 1/4", 20TPI, so probably BSW.
Albert

[59G3LS]

Thanks for the replies Guys.
I got the vernier out today and did some historic thread research also. I think the main shaft is 3/8" BSF 20 TPI and the coil set screws seem to be 0BA 25.4 TPI, the drilled holes are less than 1/4" and I counted the threads over the available depth in my one good fixing using a pin, crude but I think it all adds up to 0BA.

What else is there to do on winter evenings?

Thanks again.

[Rob Harknett]

I had loads of the CSK BA screws for the Bakelite cover plate. I disposed of many bags of 20 at Jampot rallies. Not sure if the club stock these. If I've any left they are probably no longer bright plated.

[aobp11]

That's strange Mark. The set screw size I gave came from a measurement. Today I measured a set screw from another SR1 body. Again 1/4" 20 TPI, but slightly shorter, about 17 mm. In hindsight I think the screws in the first body are replacements since they were not blocked to come out upward (even were not fully in when tightened). In the second body I had to turn the screw inward (coil removed) to get it out. Because of the blockage (hole wall tapped in), when viewed from the outside the hole diameter looks less than 1/4". The screws in a third body look identical to those of the second body.

My main shaft data comes from a Lucas document.

Albert

[Rob Harknett]

The SR1 mags were also used on stationary engines, maybe your bike got hold of one of those.

[Groily]

Strange, as Albert says. Out of curiosity I went and measured one too - and for what it's worth the example I have is also 1/4" x 20 tpi for the coil retaining screws.

[59G3LS]

Now you've got me thinking guys! I'll re visit this tonight and post my measurements. I'm using a cheap digital vernier but it can't be that cheap!

Thanks for your interest!

[Rob Harknett]

http://archives.jampot.dk/technical/Ele ... tions_.pdf