This is dished (lipped) washer that fits under the Lower Bevel (twin) ball bearing on all SOHC bottom bevel castings. Designed to capture any errant balls that should drop from the bearing (a very common fault) and an absolute essential to fit. Price is each.
This washer has a slight dishing in its central part, and is designed to be fitted in the machined bearing recess in the SOHC lower bevel casting, just before the double row ball bearing is dropped in (this best being done when the casting is heated). The special twin row ball bearing had a well earned reputation for shedding its balls and often when they do - they can drop down in to the bottom bevel case where they can break the teeth off the lower bevels. I heard from an old friend that was in the trade when Norton's still made the SOHC model - that Norton's service department were pretty much kept in business by those balls dropping and the damage they subsequently did!
Although not totally foolproof - this dished washer is an essential fitment in the lower bevel (under the ball bearing) - as if balls do drop from the cage, they will hopefully sit on top of the dished washer, instead of dropping into the bevel chamber below. When stripping your engine, and removing the bottom bevel casting, you should always carefully check that none of the ball bearing balls have dropped and become trapped in the dish washer area (and obvsiously if they have - remove the balls!)
April 2021 Update: Apologies, these have been out of stock for some time, but we are pleased to say we have just had a new batch manufactured and they are now in stock. If you have been on the waiting list for these - Steph, will be contacting you in the next 2 weeks. Apologies price has risen - but I noticed price had not been amended since 2009 and was very out of date!