My ABC jigsaw

Can anyone explain this bearing attached to rear of my flywheel,can find no reference anywhere,is it  factory upgrade?,my jigsaw continues

Dunno how to put this to you Dell...your clutch-release system is entirely bogus! 
Its style is borrowed from, for instance, a post-war Douglas (although some prewar Duggies used it too).
However, the rest of these clutch systems were totally different to the Sopwith, and couldn't realistically be applied.
My advice...ditch your system pronto, and in total!
The Sopwith clutch and its release system are far simpler, and that includes better. 

Thanks Paul the reply I was hoping for as I had already decided,although I will have to use a different crankcase as this has been altered as well
It must have been run as this came from the only nearly complete engine I had
Merry Christmas to everyone Dell

if it works leave it alone, it is part of its history, someone may not have been able to get the correct one so used a douglas ?

Hi I will try and explain this addition to my crankshaft although I am not an engineer,it consists of a circular plate attached to the rear of the flywheel contiang a bearing and another plate which is cut and chamfered and free running on the crankshaft allowing movement back and forth approx 1 inch,I remember reading some where that this could be a shock absorber to relieve load on the crankshaft at startup and on high revving engines
on further conversation with Paul he describes it as an adjustable thrust carrier ,normally thrust from the clutch disengagement is transmitted through the crankshaft to the front main bearing (so yes a type of shock absorber)

I do believe it to be a period supposedly upgrade to the ABC as this engine had been in a bike stored in a celler since 1932 when the tax run out till I purchased it in 1985,since then it has been in various sheds garages stores until I recently started restoration
i am thinking should i retain it as it is part of the engines history as Keith says
Or go for the easier option and bin it
I would be interested in any comments views or history
Derek
 

Hi Derek

Please add my vote to the "keep it" tally. Its a nice period remedy to prevent the potential failure of the woodruff key on the end of the crank shaft. Hopefully, you can get it all work as the previous owner intended. Will we see the completed machine at Founders Day this year?