Rear sprocket

[Rusty nuts]

Has anyone tried running a 42 tooth rear sprocket with a longstroke engine?
Am thinking of trying this for the new project.

Reason being I find the plunger with a 46 tooth rear undergeared, need to change into top @ 35 -40 max & she revs out @55 & vibrates a lot up to flat out @60.
She's happy to pootle along @45-50, but would prefer to pootle slightly faster, say 55-60!
Now for the new project I am using a Star Twin longstroke with HC pistons, twin amal 275's in a rigid frame with plunger hub, a swinging arm spindle & modified spacers. Phew!
 The only small problem is a 46 tooth  sprocket (67-6123) which would be correct for the engine will necessitate either sleeving the bearing or finding one that has the OD of the plunger sprocket bearing housing & ID of the S/A spindle.

Before I do that I'd be interested to hear from anyone who has tried a 42 tooth S/A sprocket as this would remove the bearing issue & potentially improve pootling speed!

Not holding my breath

Cheers

Rusty

[tombeau]

Hi,
My swing arm A10 was fitted with either a rigid or plunger drum sprocket 46 tooth.I'm not sure of the parentage of the stub axle, but I did get a bearing to fit it all together.
I can check the bearing no. for you next time I go to the shed.
Dont quite understand this though:

The only small problem is a 46 tooth  sprocket (67-6123) which would be correct for the engine will necessitate either sleeving the bearing or finding one that has the OD of the plunger sprocket bearing housing & ID of the S/A spindle.

Before I do that I'd be interested to hear from anyone who has tried a 42 tooth S/A sprocket as this would remove the bearing issue & potentially improve pootling speed!

I thought you had got the 46t hub to fit already? Can you not machine an old hub for a "bolt on" 42 tooth sprocket?
I have 2 46t drum sprockets. One worn, and another one with about 500km on it, fitted with a new bearing to take a swing arm spindle. sitting, doing nothing, in a box under my bench. They're cast offs from my mission to get a working back brake out of a mish mash of components.
Trouble is, posting them to you would cost about the same as buying them in GB. You're not planning a trip over here are you?
Cheers,
Iain

[Rusty nuts]

Iain

Yes, I have a new 46T & it will fit but need right bearing.
I can if I want exchange no prob for the 42T which I'm hoping will address the gearing issue.
The plunger 46T, oops correction, "sprocket" bearing housing is bigger than the 42T

Both options available if I use the 42T I can use 3 x 65-5883 bearings, easy!
if I stick with 46T that requires bearing 89-3022 whose inside diameter is larger (to accept a plunger spindle) than the short spindle passing through it so would need to sleeve or find alt.

Rusty

[tombeau]

Ok I have a stub spindle which takes a swing arm axle, and its narrow enough to pass through the slot in a swinging arm, but its outside diameter fits the bearing in a plunger hub. Any use to you?
Cheers,
Iain

[Rusty nuts]

Iain

Many thanks for that, much appreciated.
 Firstly I will go to local (ish) bearing factors to see if they have anything.
But I'm getting really tempted to exchange 46 for a 42 tooth. 
May end up changing gear a lot depending on the wind direction,
but I figure if sidecar outfits ran 49 teeth, moving down from 46 to 42 is not too radical.
Hills could be a problem but hey I could always move to Holland

Cheers
Rusty

[tombeau]

Give us a shout if you want it.
Its just sitting there. I'd be very surprised if anyone here ever needs it.
All it'll cost you is a packet of ginger nuts!
Cheers,
Iain

[Brian]

Assuming you still have either a 18 or 19 tooth on the gearbox then a 42 rear will be way too high gearing for a A7.

I have related the story before on the forum but that how I came to own my 51' A7, the previous owner had put a 19t on the gearbox and a 42t rear and kept seizing the motor and couldnt work out why.

BSA put the gearing they did on their bikes for very good reasons and while sometimes it can have a slight advantage to slightly raise the gearing the std ratios are fine. My 50' Star Twin has a 19t gearbox and 46t rear and will cruise quite comfortably at 60mph. If yours is flat out and vibrating badly at that speed then you have a problem.

[Rusty nuts]

Give us a shout if you want it.
Its just sitting there. I'd be very surprised if anyone here ever needs it.
All it'll cost you is a packet of ginger nuts!
Cheers,
Iain

Bought my first packet in 25 years today, must  be some kind of omen.
Will be in touch.

Cheers

[Rusty nuts]

BSA put the gearing they did on their bikes for very good reasons and while sometimes it can have a slight advantage to slightly raise the gearing the std ratios are fine. My 50' Star Twin has a 19t gearbox and 46t rear and will cruise quite comfortably at 60mph. If yours is flat out and vibrating badly at that speed then you have a problem.

Thanks Brian, that very thought occurred to me & I was looking for some first hand experience.
The low top speed & vibes is on the current A7 plunger & it could well be something in the gearbox, as it runs a 19 tooth front & 46 tooth rear which is pretty standard.
I have to say the vibes are not as bad as on the 5TA I had back in the 70's but she just doesn't seem happy over 50, up to that she is very sweet, at 55 I'm getting the kind of vibrations a teenager would enjoy. She just won't get past 60.

If sanity prevails I 'll stick with the 46 tooth for the new one put a 19 on the front  & hope to lose a few pounds over the winter

Cheers

Rusty

[trevinoz]

Rusty,
            If your A7 wont go over 60, there is something seriously wrong.
I haven't got mine running yet but have seen these long stroke bikes in action. When put together carefully they run beautifully and easily top 60.
 Trev.