Stainless Fasteners

... be Cycle and BSF for fasteners, BSW when threaded into aluminium etc. Middleton are good (if a bit pricy): https://www.stainlessmiddleton.co.uk/ - another is Molnar: http://www.manx.co.uk/products/stainless.html

I have used Middletons a lot- When you ask for 1/4Whitworth, they supply 1/4Whitworth not 1/4UNC (same pitch, different thread angle) unlike some of the others. Not the cheapest, but very good. There are several other good suppliers and I'm sure others will pitch in soon with their favourites too.

For what its worth, threads on original 650's include BCY(cycle), BSW, BSF and BA, so a thread gauge, vernier caliper or micrometer and a thread chart/zeus book are incredibly useful things to have in the shed.

For  what its worth, it is probably best to leave the head and barrel nuts and bolts original, as the stainless offerings can 'stretch' and loosen off in use, unless your supplier can guarantee the correct grade of steel has been used to make them. Also get a tube/pot of  Neverseez or Copperslip to put on the threads to prevent 'galling' where the nut will cold weld itself to the bolt on tightening, very easy to do on stainless fixings.

Regards,
George

The Mercury versions of the Norton 650 used an adaptation of the 06-0380 Commando cylinder head. So it is more than likely that the rocker spindle end-plate bolts were 1/4" x 18UNC items rather than 1/4" x 20 BSW. As George mentions spotting the difference is not easy.

Try acmestainless.co.uk . I've used their nuts and bolts on my last three restorations. Very good quality and the price is good too. Machine turned, not cold formed, so as per originals.

Derek

1/4" UNC is still 20TPI, just 60 deg. instead of 55 deg. for BSW.

Martyn

I found this supplier some months ago, have not tried them yet but they do stock some Cycle, BSF, UNC, UNF, BSW and BA botlts.

https://www.custom-fasteners.co.uk/bolts-nuts-washers-screws/hexagon-head-bolts.html

They are based in Newtown, Wales, Tel; 01686 629666.

Another useful supplier of ex army and aircraft fixings is Rays-Tek Surplus Ltd.  See the link https://www.rays-teksurplus.co.uk/bsf-fixings-558-c.asp

Philip

... Yes but the hexagon will be an a/f size not Whitworth. 1/4" BSF and Cycle (CEI) are the same oitch but different thread angles again however the tolerances are usually such that in non-critical applications the difference is immaterial.

I asked Andy Molnar a couple of years ago what steel he used for HT bolts and he said he uses Grade 303.  Personally, I regard S/S as just for aesthetics and would never use it in a highly stressed location such as head or barrel fixings.  As George says, it's "too stretchy".  Generally having a greater elastic limit, but that very much depends on the grade used.

Galling is often sited as a problem with s/s but it isn't confined to it.  Galling can occur with many metals, mixed or otherwise, so Copperease or similar is useful when assembling.

As has been discussed, 1/4" Whitworth isn't the same as 1/4" UNC, even if the threads are at the same pitch.  The thread angle is different but, more importantly, the hex is a different size - as Ian says.

Out of interest, there is one area where 1/4" Whitworth thread is still universally used - and probably will be forever!

OK - many of you will know this - the camera tripod/accessory thread.

.. many years ago a very heated debate between messrs Molnar and Middleton about which grade of stainless to use for wheel spindles. If I recall correctly it was played out in the pages of Motorcycle Sport and I don't remember any definitive answer emerging.