The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: sprint on 31.07. 2013 10:18
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I currently have the RGS on std A10 sprockets, 21T E/S, 43T Clutch, 19T G/B and 42T Rear Wheel but with the RR2T G/B.
I am finding that the milometer is reading short, 1.8 is recorded as 1.4 and I get the feeling that the speedo is giving a lower speed that it actually is.
Don't know what speedo drive gear I currently have or what the gear is on the end of the L/S?
Can somebody advise what I should have or need for the above configuration? Do both the L/S gear and Speedo drive gears need to be replaced and if so what do I need?
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This could get complicated.
First you need to know your speedo ratio in revs per mile. This may be printed on the speedo face. If you have the original RGS speedo, it should be in the order of 1600.
Now you calculate. 42/19 x sleevegear/layshaft x layshaft worm/speedo drive x 800.
I suppose that you still have the RRT2 sleevegear and layshaft with the original speedo drive and if the speedo is the correct one, all you have to do to get it back to the correct reading is change the rear sprocket to 46T.
Easy?
Trev.
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This could get complicated.
First you need to know your speedo ratio in revs per mile. This may be printed on the speedo face. If you have the original RGS speedo, it should be in the order of 1600.
Now you calculate. 42/19 x sleevegear/layshaft x layshaft worm/speedo drive x 800.
I suppose that you still have the RRT2 sleevegear and layshaft with the original speedo drive and if the speedo is the correct one, all you have to do to get it back to the correct reading is change the rear sprocket to 46T.
Easy?
Trev.
Thanks Trev
Speedo details as on pic which shows 1620 as you indicated.
Unfortunately I do not know what the worm dive gears are on the end of the L/S or Speedo drive but it is my understanding that the L/S gear is normally 6T and the Speedo drive 10T or 11T unless there are other alternatives?
I still have all the std RRT2 M/S and L/S gear ratios except for 1st gear which I have currently changed to std A10 ratios.
So from what you have indicated all I need to do is change the rear wheel sprocket to 46T? Will having the engine sprocket at 21T instead of 23T have no impact and will this not just only correct the mileage reading or will that also correct any speedo error as well or do I need different layshaft worm/speedo drive gears?
Andy
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Andy,
The RGS ratios are 46/19 x 25/18 x 6/10 x 800 which gives a final cable speed of 1612 revs per mile.
The STD ratios are 42/19 x 26/17 x 6/11 x 800 which gives a final cable speed of 1473 revs per mile.
With the 42 rear sprocket substituted you get 42/19 x 25/18 x 6/10 x 800 which gives you 1473 revs per mile.
Your options are:- replace the rear sprocket with a 46T and the engine sprocket to 23T or replace the speedo head with a standard Rocket one.
I suppose that your speed indication would be low as at 60MPH the speedo cable should be revolving at 1612 RPM but is only doing 1473 RPM.
You need to change the engine sprocket to suit the rear sprocket to keep the overall engine/speed ratio correct.
Trev.
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Yes, changing the engine sprocket won't change the speedo ratio, but gearbox and rear sprocket will.
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Thanks for the replies.
What will be the impact of leaving the E/S at 21T if I change the rear wheel sprocket to 46T and leave the RRT2 box as is? Will it be detrimental to the engine/clutch or just simply give a higher engine speed for any given road speed, ie instead of say 15 mph/1000 rev in top to 12 mph/1000 rev?
I'm trying to make the bike more usable on the road without having to resort to fitting a std G/B, if possible?
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It will accelerate very well but will be a bit busy at normal road speeds.
By changing the engine sprocket to 23T with a 46T rear sprocket, you are just bringing the overall ratio to the same as with a 21T engine sprocket/42 rear sprocket.
That is, it will be exactly the same as it is now.
Trev.
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If you want a higher tooth count on your engine sprocket just get an original one rebanded. Greg Ditchfield does it for me.
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If you want a higher tooth count on your engine sprocket just get an original one rebanded. Greg Ditchfield does it for me.
Thanks Wilko.
I have both 21T and 23T E/S's.
The bike is fitted with a RRT2 box which is not very practical for road use, so I am trying to see if having a 21T E/S (instead of the std 23T) with the 46T rear wheel sprocket is a practical alternative way to make it more usable other than having to fit a std G/B?