Cush drive

[Sunbeam]

Hi, the cush drive spring broke on my other bike, BSA Gold Star. I've just bought a new old stock spring..nut and tab washer. On screwing the nut on the crankshaft, it only goes on a few turns till it goes really tight. On inspection, one of the threads has been knocked over to touch the next, probably from the use of a hammer and drift in the past to tighten the nut. Have purchased a 3/4 x 20 tpi die but am now concerned that by chasing the crankshaft, it will remove the damaged thread completely. I would be very grateful if anyone could help on this...thanks.

Howard

[Greybeard]

What about dressing the damage with a thread file?

[Billybream]

I would try and remove the damage with a needle file and then run the die if it's a split type over the thread. With a split die you can control the amount of metal it removes.
It might be safer just to run the die over the thread by hand after removing the damage with a file.

[chaterlea25]

Hi,

I've just bought a new old stock spring..nut and tab washer.

If I'm reading this correctly you have bought a "new " nut?
Does the old nut fit the crank threads ok ?
If it does then I would look at the "new" nut first ???

Using a hammer and drift on the nut is Brutality
Theres no way of knowing how tight you are doing up the nut
Buy or make one of these, (this will fit the BSA nut )
http://www.ebay.co.uk/itm/161272516269?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Torque the nut up to 65ftlbs
I do not bother with the lockwasher, degrease the threads and use some thread locking fluid on them

John

[coater87]

 If one of the threads IS folded over, that portion of the thread is junk anyway. Just like a metal coat hanger when you bend it back and forth the metal cracks and fatigues and eventually fails. It may look fine and last forever, but that part will not hold tension like the undamaged ones.

 Be careful with whatever you use on the single damaged thread so no others are damaged of course. If it were mine, I would start the die  and turn it until it just starts getting tight at the spot of the damage. Back the die off and see if its cutting the bad thread, or "unfolding" the metal. If it is unfolding, just run the die all the way down and be done.

 Either way for me, I would just run the die all the way down and be happy with the results. That thread was already damaged by a hammer blow and you can really do anything at this point to "make it worse".

 Lee

[Sunbeam]

Hi All...thanks for your replies. Yes, bought a new nut but it would only go as far as the damaged thread. Did'nt go down the thread file route but used the 3/4 x 20 tpi HSS die. I opened the die out using the middle screw on the stock so as to remove minimal metal and used plenty of tap / die cutting fluid to stop the threads snagging and the new nut went on great. I believe it was recommended practice to used a hammer and soft drift on the nut to shock it tight, that's how the threads end up damaged. I'm waiting for a BSA A7/ A10 cush drive tool to arrive from JB restorations £24..ebay number 322224770954, I can then torque the nut up to 65 ft /lbs as recommended by SRM....Many thanks for all your help.

Howard.

[RichardL]

I'm confused here. Why spend 24 GBP for a special driver for original-style nut (plus the cost of the nut) instead of 18 GBP for a hex nut from SRM? Is this based on a desire for total originality? Furthermore, the SRM nut is designed to accept a timing disk.

Richard L.

[trevinoz]

It makes sense, Richard, if you own more than one bike.

[muskrat]

Yep, after 30 odd years of using a drift & hammer on the '51 I bought one of those nut sockets. I have the SRM nut on the cafe.
Cheers

[madsens]

Hi
I bought the hex nut from SRM - but it would simply not go on, could not even get it started, so had to return it (no problem) and used the old nut without any problems - and there was no tread damage - leaves the question - are there different sizes?

rgds Joergen

[ellis]

Hi madsens,

I had a similar problem with the Cush drive nut. It would only screw on one complete thread and then would not go on any further. I returned it to SRM with a note explaining the problem and received another nut by return of post and that was also tight. Spoke to them about the problem and apparently the nut threads are slightly undersize to stop it slackening off in service. I used a touch more force and the nut went on ok and a drop of blue Loctite to secure it and it hasn't moved.      Hope this has helped.

[BSA_54A10]

A bit late but you can cut the old nut in 1/2 along the axis.
Then flatten the cut surface down to level with some wet & dry on a glass sheet ( or a scraper if you are a show off ) so the thread edges are sharp.
clamp this onto the shaft below the bad threads with a pair of vicegrips then run it up the shaft with a touch of lube on it.
This will clean up the damaged threads beautifully.

[chaterlea25]

Hi All,

Why spend 24 GBP for a special driver for original-style nut

When the Peugeot tool that fits I linked to costs £8.43

 

John

[muskrat]

Yes, thanks John. It works very well.
Cheers
http://www.ebay.com/itm/161272516269?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT&autorefresh=true

[RichardL]

I'm sure using an adaptor works, but it must be less stable and harder to manage than an SRM nut while torquing to 65 ft-lb. 

Richard L.