Spanner size - alternator rotor retaining nut

This is probably a 9/16 British Standard socket, if you measure the nut it should be 0.920/0.912 across flats. If you are going to work on Commando engines, gearboxes and transmissions, sets of British Standard spanners will prove invaluable. Commandos are the wierd Nortons - for some reason Norton went to American (Unified, AF) threads and spanner sizes for cycle parts, but stuck with British threads and spanner sizes for the engine, gearbox and transmission.

I can only guess that the cycle parts were a sop to American customers but it was too expensive in re-tooling to change all the engine fasteners. I know nothing about the 961 Commando, are these put together with British, American or Metric fasteners?

Colin.

That's got to be a serious wrist breaking electric drill Chris, even with the plugs out.

JEFF what do you mean byAF bolts as AF is just the size "Across the Flats" metric andunf/unc spanners/sockets are all given an AF size.

D G

Come on John, everyone knows that AF stands for "American Fred". I think the only metric thread on a Commando is the one the oil filter screws on to. Most cycle parts are held on by U.N.F. threaded fasteners. If metric fasteners have been fitted, this is a bodge by a D.P.O.

Colin.

Previously wrote:

JEFF what do you mean byAF bolts as AF is just the size "Across the Flats" metric andunf/unc spanners/sockets are all given an AF size.

D G

Jeff,

Inch size hexagon rod is everywhere, and almost certainly has been for a long time, especially in the U.S.A. The hard stuff to find is British sized hexagon to make BSW, BSF and Cycle thread fasteners. That is very hard to source, even in the UK.

Any bolts and nuts made of the wrong size hex are an incorrect bodge. A frequently encountered use of incorrect fasteners is the use of UNC bolts to replace BSW ones. The threads fit, but the heads are the wrong hex. I notice that Custom Fasteners offer UNC instead of BSW now - not good for restorers.

Colin.

UNF and UNC are unified fine and unified coarse. These threads have a form of 60 degrees. BSF and BSW (British standard fine and Whitworth) have a thread form of 55 degrees, so whilst in a few cases the threads per inch (tpi) may be the same for similar diameter screws, the threads won't match without some mechanical abuse. British standard cycle generally have a tpi of 26 irrespective of diameter and this thread form is 60 degrees.

AF or "across the flats" refers to the size of the nut/bolt head and not the thread so you could get sockets labelled as 13mm AF and another 3/8" AF

A 3/8 BSF screw/bolt will not have the same size head as a 3/8 BSW (it will be the same as a 5/16 whitworth screw)

A bolt has only part of its shank threaded, a screw is threaded all the way to the head and is refered to as a "set screw" irrespective of it's head design (Hex, socket, cheesehead, countersunk etc)

Treat yourself to a set of quality whitworth spanners if you own a Commando, they will fit your old treader too.

The first Commando bikes were basically fitted with an Atlas engine. Thismotor sported BSF, Whitworth and Cycle threads all over it. I don't think any BA threads were around except on the carbs. The Commando frame chunks were already mostly held together byUNF threads and sales of AF spanners from Norton Bike dealers took off.

Hence the need for only a set of Whitworth/BSF spanners to service these motors for a few years. Then, suddenly, somebody at the Norton factory decided to add more USA appeal to the bikes andin 1972,lots of the engine threads changed to UNF. Owners of new bikes instantly discovered that cycle threaded nuts would go on theirnew engine studs really easily to start with, then get a bit tighter andfinally magically change to becomeUNF orUsually NormallyF****d!!!

To add to the fun and games, we now had a mix of old and new threads on the same engine. Above the barrels, studs and bolts still had Cycle threads and a need forBSF/WW spanners.But below the exhausts UNF ruled except for those studs holding the cases together.

This state of affairs did not last and as the 850 bikes appeared on the scene more cycle threads disappeared leaving just a few survivors holding the cylinder head in place. AF spanners could be used on almost every external nut or bolt head but strangely inside the engine, Cycle threads continued to rule on the crankshaft, the rockersand inside the Timing Cover.However just before the Commndo ceased production even the rocker adjuster nutshad succumbedandyou needed a1/2" AF spanner to reset the valve gaps.