BritBike Forum logo
BritBike Sponsor BritBike Sponsor BritBike Sponsor
BritBike Sponsor

BritBike Sponsor

BritBike Sponsor
BritBike Sponsor BritBike Sponsor BritBike Sponsor
JWood Auction JRC Engineering dealers JWood Auction
Home | Sponsors, Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons, "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Member Spotlight
Paul G80
Paul G80
Cambridgeshire UK
Posts: 81
Joined: February 2008
Show All Member Profiles 
Shout Box
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
Who's Online Now
208 registered members (57nortonmodel77), 2,344 guests, and 690 spiders.
Key: Admin, Global Mod, Mod
Newest Members
myshootingstar68, Caddy, Spitfiregary, Ashley, HerbertG
10073 Registered Users
Top Posters(30 Days)
Lannis 85
koan58 82
NickL 81
Stuart 64
Popular Topics(Views)
503,260 mail-order LSR
Forum Statistics
Forums34
Topics66,021
Posts638,979
Members10,073
Most Online3,995
Feb 13th, 2017
Like BritBike.com on Facebook

Previous Thread
Next Thread
Print Thread
Rate Thread
BSA b31 engine sprocket #701232
07/09/17 6:03 pm
07/09/17 6:03 pm
Joined: May 2016
Posts: 16
east yorkshire uk
S
stevenick Offline OP
BritBike Forum member
stevenick  Offline OP
BritBike Forum member
S
Joined: May 2016
Posts: 16
east yorkshire uk
Hi, I have a b31 motor fitted into an m20 frame gearbox. , The other year I bored the engine out to 400 cc and fitted touring goldstar cams with an 19 engine sprocket.
I have just got the primary cover off and while I am in the I was wondering if a 21 engine sprocket would be a good idea . I have one .
The bike runs fine but it's high in the rev,s when on the open road . 55/60 mph

Support Your #1 BritBike Forum!
Membership Type! Free
Member
Premium
Member
Premium Life
Member
Vendor
Member
Site
Sponsor
Recognition No Premium Member Premium Life member (5 years) Vendor Member Site Sponsor Membership
Post commercial threads No No No Yes Yes
Custom title No Yes Yes Yes Yes
Upload avatar & photos No Yes Yes Yes Yes
Link avatar & photos Yes Yes Yes Yes Yes
Private Message Storage: 10 100 100 100 100
Length of signatures 255 600 600 600 600
Removes this very advert island between post 1&2 No Yes Yes Yes Yes
Price Free $12.90/year $105.00 No End
$55.00/5 years
$210.00/year
($17.50/month)
Email
Click on button >>
  Premium Member Premium Life member Vendor Member Site Sponsor Membership
Re: BSA b31 engine sprocket [Re: stevenick] #701350
07/10/17 4:16 pm
07/10/17 4:16 pm
Joined: Aug 2001
Posts: 30
Germany
J
Josef2 Offline
BritBike Forum member
Josef2  Offline
BritBike Forum member
J
Joined: Aug 2001
Posts: 30
Germany
hi,

first you have to calculate the overall ratio.
Internal gear ratio for the top gear is always 1, as its a direct gear.

Engine/Clutch and Gear/Rear differs widely.

M20 had 19/43 and 18/42
or 18/43 and 19/42, depending on the year.
The overall ratio is the same = 43/19 * 42/18= 5,281

B31 had some 5,591, B33 had 5,003 and there are some hundred other ratios for B32/B34, sidecars, Gold Stars ..
So you have to calculate your current setting.


The you need the tyre diameter , an Avon 3,50-19 has 682 mm or 26,85 inch.
And the speed, for example 60 mph

The formula to calculate with mph is now
rpm= speed * ratio * 334,4 / diameter.

With ratio 5,281 its 60 * 5,281 * 334,4 / 26,85 = 3946 rpm - So your B31 runs with 3946 rpm at 60 mph in the top gear.

With ratio 5,0 its 60 * 5,0 * 334,4 / 26,85 = 3736 rpm

Josef

Re: BSA b31 engine sprocket [Re: Josef2] #701764
07/14/17 9:34 pm
07/14/17 9:34 pm
Joined: May 2016
Posts: 16
east yorkshire uk
S
stevenick Offline OP
BritBike Forum member
stevenick  Offline OP
BritBike Forum member
S
Joined: May 2016
Posts: 16
east yorkshire uk
Thanks Josef, going to give it a try and see how it goes

Re: BSA b31 engine sprocket [Re: stevenick] #701838
07/15/17 3:22 pm
07/15/17 3:22 pm
Joined: Aug 2015
Posts: 1,057
Bolton Lancs UK
A
Andy Higham Online content
BritBike Forum member
Andy Higham  Online Content
BritBike Forum member
A
Joined: Aug 2015
Posts: 1,057
Bolton Lancs UK
It's easy to get trapped into thinking higher gearing=more relaxed and better MPG.
Very often what it really means is at touring speeds you are constantly shifting between top and third, worse MPG because a wider throttle opening is required for a given speed and a slower top speed because the engine will not pull the gearing


1955 BSA B31 500cc "Stargazer"
1962 Greeves 200cc "Blue Meanie"
1962/67 Greeves 350
1967 Greeves 360 Challenger
1984 Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"

Moderated by  Allan Gill, Jon W. Whitley 


Home | Sponsors | Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons | "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Powered by UBB.threads™ PHP Forum Software 7.6.1.1
(Release build 20180111)
Page Time: 0.206s Queries: 15 (0.006s) Memory: 1.0071 MB (Peak: 1.1493 MB) Zlib disabled. Server Time: 2018-02-21 11:13:45 UTC