BSA Owners' Club Forum

The BSA Workshop => Singles => Topic started by: BeenyBoy on 23 July, 2017, 15:47:28

Title: B31 Cush Drive Nut
Post by: BeenyBoy on 23 July, 2017, 15:47:28
I cant get the cush dive nut off (B31 1955  Plunger) ...its been really butchered by a previous owner but I cant get it to move; There doesn't appear to be a tab washer behind it- between the nut and the spring- I've tried stiltsons and a big hammer but cant shift it.......any tips gratefully received !!

Title: Re: B31 Cush Drive Nut
Post by: om15 on 23 July, 2017, 16:03:39
It's not a left hand thread by any chance? 

If it is seized you could try heat, if you have good access use a socket rather than stilson's for better grip, heat the assembly using a hot air gun, (the sort electricians use to shrink plastic heat shrink) then shock the socket bar with a hammer. Applying heat to the nut expands it more than the threads it is screwed onto.
Title: Re: B31 Cush Drive Nut
Post by: JulianS on 23 July, 2017, 17:01:43
These nuts can be done up very tight  and have often been done up and undone over the years with drifts and chisels.

The nut is a right hand thread 3/4 inch x 20 tpi cycle.

There is provision for a lock washer between nut and cush drive sleeve. They get left out sometimes. It folds into the back of the nut where the arrow points on photo.

A soft drift and hammer is the tool of necessity if the nut is too damaged to get the tool on it but locking the shaft against rotation can be a problem. If loctite has been used you may need heat to break it. Locking on the clutch sometimes just causes the cush drive to operate - you might stop this using a suitable strip of metal between the spring coils or you might have to lock it through the small end eye.
Title: Re: B31 Cush Drive Nut
Post by: BeenyBoy on 23 July, 2017, 17:50:53
Thanks guys...I'll have another go in the morning

Title: Re: B31 Cush Drive Nut
Post by: STAR TWIN on 23 July, 2017, 22:28:06
I don't think a hot air gun will be up to the  task. You may need a propane/butane gas torch and get the nut good and hot. If it's hot enough for oil to sizzle out of the threads a good clout with a hammer and a drift should shift it.
Title: Re: B31 Cush Drive Nut
Post by: BeenyBoy on 25 July, 2017, 18:56:07
Well that proved to be a real **********.... got it off eventually ...lots of heat and a big hammer !... the nut is completely butchered but at least its off.  A lot of the problem was stopping things moving- the rear brake has seized so couldn't use that so ended up cutting a large wedge of wood and wedging this - with a rubber mat, between the rear wheel and the gearbox/frame.

Anyhoo ...thanks for you help guys   :)