A65 alternative gear ratios

[dolomite]

Hi all,

Can anyone please guide me to a list of the various gearbox ratios (with alternative mixing of cogs) for the A65/A50 range.  The nice one from Victory (US) is not available to me (Fault 404)

Happy BSA'ing from Norway.

Helge

[DAVE BRADY]

Hi,

I hope this has worked.  PDF copy of the page.
I have swapped CL 2nd for STD 3rd to open up the gap between 3rd and 4th.
This was to address an issue specifically when in mountains loaded with camping gear.  The STD gap between 2nd and 3rd meant that to maintain a good speed up twisty mountainous roads lots of revs needed in 2nd or labouring in 3rd.  The mod. has made quite a difference to this with little impact on normal riding.

Dave.

[Allan G]

After having this discussion with Dave a few times, I'm looking into having gear sets made up. More to post when I have something to sell. But they will be suitable for anyone that wants to gear the bike up but not loose the nice low
First and second gear, or just anyone who wants a wider spread of ratios.

[DAVE BRADY]

Hi,

I reckon that the CR2nd in place of STD3rd give a ratio of 1.1968 as compared with 1.145 for STD and 1.10 for CR.

It would be interesting to hear from arider who has used the John Hill/PES 5 speed box extensively on the road as it could be that having a lower 1st at a STD 2.513 would make this the ideal box.

Dave.

[Allan G]

The John hill box has a taller first.

I've worked on some Ratio's and I'll ask PES if they can make it work. The overall ratio for a stock late 650 with 20:47 gearing has been used as the model for 1st, then I've back calculated the ratios to match that speed vs rpms as if you were running 23:47 gearing. Which is what I will be doing on my bored and stroked OIF.  My A50 with the lower primary gearing is really nice as a crawler gear in first. So I think my ratios will be quite accepted especially for those participating in club runs (where speeds can get pretty slow at points) but also have enough legs for touring speeds.

[DAVE BRADY]

Hi,

The JH 1st I think is 2.222:1 so not that far from the STD 1st at 2.513:1.  Not being an engineer I do not know how much work there would be re-doing the gears with a few different teeth.
The long legs of the stroked motors almost negates the need for 5 speeds unless performance is the only aim.  I have found that the long stroke 750 pulls so well but a lower 1st would definitely mean a better 'pull off' when fully loaded but a long legged top for cruising.
One thing that keeps coming in the back of my mind is how long do those legs need to be considering the ever reducing speed limits.  At some point the engine will be hardly turning whist cruising at the speed limit.
I suppose determining the optimum RPM for MPH and working from that for gearing a state of tune may help.

Dave.

[Servodyne]

Hi all,

Slightly off at a tangent, but has anybody ever tried fitting a T140 engine sprocket onto an A65/A70. It's one tooth bigger, at 29T compared with 28T on the A65. The splines look about the same so it should only be a matter of machining the boss if required and fitting spacers to get the chain alignment, that's if the chain will clear the chaincase. The effect would be to increase the overall gearing in all the gears which is something that would very much appeal to me. I've looked at going for a 22T sprocket on the gearbox, but this would have a much lesser impact and of course necessitate some significant butchery to the crankcase, or removal of the gearbox, which I would prefer not to do.

Jim   

[DAVE BRADY]

Hi Jim,

Without actually trying I would think that the primary chain would catch the case especially if not adjusted exactly.  Most cases bear the scars as it is.
The 22T gearbox sprocket will also greatly increase contact between the chain and chain guard when the suspension is compressed even a 21T can do this if the suspension is a bit soft.
The other option which I think Allan has tried is to use the combined brake drum sprocket with 42T and then experiment with gear box sprockets.

Dave.

[Allan G]

My Lightning has 19:42 on the back, it's 680cc. The primary is a Bob Newby belt drive unit which gears up the primary by equivalent to one tooth on the back. Depending on your final drive ratio, the BNR primary drops the revs by between 300-500 rpm at 70mph.

However, with the OIF, unless you either got a disc brake rear or fit the earlier QD setup then your limited to changing the primary or fitting a taller gearbox sprocket. My 823cc Thunderbolt has the BNR belt and 21:47 at present. I have got a 22t which I decided not to fit as I thought it might be too tall.
With a standard box, first is a bit tall. But once your rolling you find your self in top way too soon, even without a lot of revs, the big capacity just pulls it with no effort. So I will be changing up, back to a 22t on the gearbox sprocket.

[DAVE BRADY]

Hi,

For slight tweaks to gearing, tyres can play a part.  A modern profile of 110/90-18 compared to 400-18 is quite marked.
The 400-18 has a bigger circumference thus making the gearing feel a bit higher.  Other ways it is manifested is that the centre stand is easier to use but the bike leans over more on the side stand.

Dave.