Rear chain

Usually there is a problem with clearance to the gearbox shell or the inner primary case  on other models .

Why bother with 3/8 chain, some high powered modern bikes are going back to using 1/4 wide equivalent chain. 

1/4" chain was always good enough for the 140+ mph Manx. (Last development 1962)

Norton only moved to 3/8" on the twins in 1964. 

No chain issues with my singles all on 1/4"   and no pulling the gearbox back either!!!!!!

My '56 19S has been running 3/8" chain & sprockets since 1976. Only reason for the change was that the hub spigot that extends into the sprocket/drum broke up. I have never seen another one fail like that. Owen Greenwood, who had a motorcyle business in Loughborough, found me a replacement wheel which came with a 3/8" sprocket. He also supplied a matching gearbox sprocket which I think required a spacer behind it. Occasionally I think about putting it back to 1/4" but never get around to it.

I believe that the difference between 1/4" and 3/8" wide chains might be sprocket wear. A modern 1/4 inch is much stronger and better than the ones our Nortons had when new. Modern 100 Hp bikes often comes with 1/4" chains. It is customary to always change chain and sprockets at the same time. Could it be that a wider chain gives less wear on the sprockets? I don't know about what material is used in modern sprockets compared to the ones in our Nortons.

It is not fair to compare with a Manx where we change sprockets to suit different tracks. And the changeable rear sprocket is of different material than the roadgoing Nortons with brake drum and sprocket in one piece.

I am still running the orriginal 1960 sprockets on my 99.  They show little signs of any wear after 50k. The chains are removed a couple of times a year for cleaning in parafin then petrol then soaked in low melting point graphite grease. In use they get EP90 brushed on. They live in one of those much maligned full chaincases  that DO keep the water and muck off mostly.. But only after I added a couple of spray baffles and a drain hole . I have now added a Scottoiler  which is not yet fully effective ,work in progress.  The orriginal sprockets are very tough steel ,nothing like a modern bike.  Its all a bit messy and I will be trying a modern chain next  once I get the oiler  100%.  I can remember once fitting 3/8th chain to 1/4" sprockets. The oiler made a huge difference to an MT09's chain life.

many highly recommend  IWIS chains, which the Chainman supplies. 1/4 will be fine.