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Rating: 2
BSA gearbox sprocket. #600970
05/24/15 1:00 pm
05/24/15 1:00 pm
Joined: May 2015
Posts: 4
Geelong Australia.
T
Tribsa norton 21 Offline OP
BritBike Forum member
Tribsa norton 21  Offline OP
BritBike Forum member
T

Joined: May 2015
Posts: 4
Geelong Australia.
I'm new to the BSA A65 after having owned Nortons and triumphs for many years.

My current bike, a 1967 lightning is too low geared for my taste and I wish to gear it up a bit. Currently it is pulling 4000 rpm at 60 mph approx. In Australia we have a ridiculous 60 mph speed limit and so I want to get the revs down for a less busy feel on the freeway and highways. I'm thinking of a 21 tooth gear for the gearbox sprocket.

The vibes don't seem that bad to me, but at speeds up to 80 mph I start to lose bits and pieces! I have lost 2 rear numberplates already!

I had the same issue with my 70 Triumph and made it a much nicer bike to own with the addition of a larger gearbox sprocket which I fitted myself.

Question is, what special tools do I need to get to the sprocket? I will also fit a 7 plate clutch at the same time.
I remember when I did my Triumph that I needed 2 pullers to remove the alternator and primary drive/clutch basket, plus a pretty large socket/box spanner to remove the nut holding the sprocket on.

All help appreciated.


Triumph developed the oil leak and BSA perfected it.
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Re: BSA gearbox sprocket. [Re: Tribsa norton 21] #600981
05/24/15 2:04 pm
05/24/15 2:04 pm
Joined: Jul 2001
Posts: 13,050
Central Virginia
Lannis Online content

Well'ard Rocker
Lannis  Online Content

Well'ard Rocker

Joined: Jul 2001
Posts: 13,050
Central Virginia
What sprocket have you got now?

They came with a 17T for sidecar work, 18T for Western US desert racing, 19T Western standard and 20T Eastern US standard.

A 21T will fit through the inner primary onto the gearbox with no machining. A 22T will required machining the inner primary to fit.

I have a 21T on my Firebird Scrambler and have for years. For highway work, it's pretty good - I see about 3600 - 3700 RPM for 60 MPH.

But for more general riding, when I replace it, I'll probably go with a 20T.

The difference you see will depend on what you've got now, which is why I ask. I don't know what went to Oz or whether it's been changed in 48 years .... !

Lannis


I stopped believing for a little while this morning. Journey is really going to be upset.
Re: BSA gearbox sprocket. [Re: Lannis] #601021
05/24/15 6:21 pm
05/24/15 6:21 pm
Joined: Aug 2014
Posts: 313
Bowral NSW Australia
John Goodwin Offline
BritBike Forum member
John Goodwin  Offline
BritBike Forum member

Joined: Aug 2014
Posts: 313
Bowral NSW Australia
According to the parts manual for 67 the Lightning, Thunderbird and Spitfire share the 20T gearbox sprocket. The 21T was listed as an alternative. 47T rear as standard factory fitment.



If you've got a Triumph clutch hub puller it may work on the BSA clutch as I think they share the same clutch hub center.
The gearbox sprocket nut is 1 1/2" AF

While you're in there it may be worthwhile looking at an outrigger bearing for the mainshaft, they go in the sprocket access window and can be sourced from the US as a combined new access cover plate & bearing assembly. lots of pluses doing that mod.

Hope that helps


Current: 2 x 1966 A65S, 1 x 1967 A65SA, 1 x 69/70? A65LA space Y, 1 X D14/4 & 1 x B175
Past: 4 x 1976 T160V, 1 74/5 T150V, 83 model GSX 750 ESD, Z650, Katana 1100(Bathurst Model), 79 T140V, 70's TR6, 2 x 1971 BSA 250 Gold Stars, 50's 350 Goldie, A65 Spitfire semi basket case, 1965/6? A65 LC, Tiger 21 350 & a D14/4 Bantam, 175 Bridgestone Twin with Zimmerman discs!
Re: BSA gearbox sprocket. [Re: Lannis] #601116
05/25/15 10:24 am
05/25/15 10:24 am
Joined: May 2015
Posts: 4
Geelong Australia.
T
Tribsa norton 21 Offline OP
BritBike Forum member
Tribsa norton 21  Offline OP
BritBike Forum member
T

Joined: May 2015
Posts: 4
Geelong Australia.
Thanks for that Lannis. I think I have a 20T sprocket which was classed as "standard" in the UK. The small drop in revs will be most welcome at 60MPH (currently 4000 rpm) but hopefully the bike will still have good overtaking potential.

Last edited by Tribsa norton 21; 05/25/15 10:44 am.

Triumph developed the oil leak and BSA perfected it.
Re: BSA gearbox sprocket. [Re: NickL] #601117
05/25/15 10:26 am
05/25/15 10:26 am
Joined: May 2015
Posts: 4
Geelong Australia.
T
Tribsa norton 21 Offline OP
BritBike Forum member
Tribsa norton 21  Offline OP
BritBike Forum member
T

Joined: May 2015
Posts: 4
Geelong Australia.
Yes I have planned to change the gearbox seal as it certainly makes sense at this stage.

Craig.


Triumph developed the oil leak and BSA perfected it.
Re: BSA gearbox sprocket. [Re: John Goodwin] #601118
05/25/15 10:27 am
05/25/15 10:27 am
Joined: May 2015
Posts: 4
Geelong Australia.
T
Tribsa norton 21 Offline OP
BritBike Forum member
Tribsa norton 21  Offline OP
BritBike Forum member
T

Joined: May 2015
Posts: 4
Geelong Australia.
Originally Posted by John Goodwin
According to the parts manual for 67 the Lightning, Thunderbird and Spitfire share the 20T gearbox sprocket. The 21T was listed as an alternative. 47T rear as standard factory fitment.



If you've got a Triumph clutch hub puller it may work on the BSA clutch as I think they share the same clutch hub center.
The gearbox sprocket nut is 1 1/2" AF

While you're in there it may be worthwhile looking at an outrigger bearing for the mainshaft, they go in the sprocket access window and can be sourced from the US as a combined new access cover plate & bearing assembly. lots of pluses doing that mod.

Hope that helps


Certainly does John...the idea of the outrigger bearing sounds good...do you have a link for this part? [img]https://www.facebook.com/#!/photo.php?fbid=10205466576291966&set=pb.1477483077.-2207520000.1432564421.&type=3&theater[/img]


Triumph developed the oil leak and BSA perfected it.
Re: BSA gearbox sprocket. [Re: Tribsa norton 21] #601166
05/25/15 1:53 pm
05/25/15 1:53 pm
Joined: Jan 2012
Posts: 255
Oahu Hawaii USA
Roger Gulledge Offline
BritBike Forum member
Roger Gulledge  Offline
BritBike Forum member

Joined: Jan 2012
Posts: 255
Oahu Hawaii USA
You can try here for a outrigger bearing e&v engineering Ed is one of the sponsor of this site.

Last edited by Roger Gulledge; 05/25/15 5:18 pm.

Roger G
70 Thunderbolt
Re: BSA gearbox sprocket. [Re: Tribsa norton 21] #601717
05/28/15 3:24 pm
05/28/15 3:24 pm
Joined: Sep 2002
Posts: 7,813
Seattle
Alex Offline

BritBike Forum member
Alex  Offline

BritBike Forum member

Joined: Sep 2002
Posts: 7,813
Seattle
If you remove the gearbox, a standard 1-1/2" socket will work. If you want to leave the gearbox in, you will need a Deeeeeeeeeeep socket. AFAIK, there's not really enough room to get an open ender in there unless it's really thin or you grind one down.

Remember to leave the rear chain on so you can lock the countershaft easily with the rear brake.

You should only need a clutch hub puller. A65 alternators and engine sprockets usually come off fairly easy if they're in good shape.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
Re: BSA gearbox sprocket. [Re: Tribsa norton 21] #601789
05/28/15 11:33 pm
05/28/15 11:33 pm
Joined: Aug 2001
Posts: 4,595
Owego, NY, USA
Mark Z Offline
BritBike Forum member
Mark Z  Offline
BritBike Forum member

Joined: Aug 2001
Posts: 4,595
Owego, NY, USA
I had a 21-tooth sprocket on my A65, and it was good for highway use, but I also regularly traverse hilly, curvy 45-50 mph back roads, and I often found myself stuck in 3rd gear. I'm running a 20-tooth sprocket now, and I'm much happier with it for all-around use. BUT, I also had the crank balanced this time around, so now 70 mph on the highway doesn't put my arse and fingers to sleep anymore.

Yes, if you don't pull the gear cluster, you'll need a very deep socket to get on that sprocket nut. One option is a 3/4"-drive socket with an outer hex fitment at the wrench end. Then the tranny mainshaft can go right through, and you can put a wrench to the outside of the socket. There doesn't need to be a whole lot of torque on the sprocket nut, as it has a locktab washer to hold it in place.



Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: BSA gearbox sprocket. [Re: Mark Z] #601944
05/29/15 7:02 pm
05/29/15 7:02 pm
Joined: Oct 2008
Posts: 5,285
Gnashville
DavidP Offline

BritBike Forum member
DavidP  Offline

BritBike Forum member

Joined: Oct 2008
Posts: 5,285
Gnashville
Originally Posted by Mark Z
There doesn't need to be a whole lot of torque on the sprocket nut, as it has a locktab washer to hold it in place.


Funny, the manual calls for 100 lbs-ft on that nut.
I've never removed mine without removing the gearbox first. Then I use a deep socket, a rattle gun, and my fat arse standing on the brake pedal.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: BSA gearbox sprocket. [Re: Mark Z] #601950
05/29/15 7:47 pm
05/29/15 7:47 pm
Joined: Jan 2012
Posts: 255
Oahu Hawaii USA
Roger Gulledge Offline
BritBike Forum member
Roger Gulledge  Offline
BritBike Forum member

Joined: Jan 2012
Posts: 255
Oahu Hawaii USA
Originally Posted by Mark Z


Yes, if you don't pull the gear cluster, you'll need a very deep socket to get on that sprocket nut. One option is a 3/4"-drive socket with an outer hex fitment at the wrench end. Then the tranny mainshaft can go right through, and you can put a wrench to the outside of the socket.


When I changed my sprocket I got this tip on here somewhere. Every long socket I found cost an arm and a leg, use a water heater heating element cheap-o socket from Home Depot or plumbing supply outlet. Then just weld on an old rusty socket to the end of it. Worked like a charm.

cheap-o 5" long 1 1/2" socket

[Linked Image]


Roger G
70 Thunderbolt

Moderated by  Allan Gill, Jon W. Whitley 


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