Longer Kick Start

[Colsbeeza]

Jules, The standard engine sprocket for my bike was 19-tooth, but I found it revving too much in my view for the work it was doing, so changed to a 21-tooth in July 2018 which is better for my style of riding. So I rode it for 3 years before IMD pistons were fitted. The IMD pistons were fitted in June 2021, so I put up with the difficult kickstarting for 12 months before fitting the electric start in June 2022. It doesn't burn a drop of oil now though.
At 3500rpm, speed is 60mph with standard 3.50 x 19 rear tyre. That is about when the motor starts to feel "busy". All other gears and sprockets are standard. The motor and carbs are also bog standard, unlike John CL's rocket ship .
The only issue now is that I have to ride the clutch to get up my steep driveway.
Unless you fit IMD's, I wouldn't worry about kickstarting. Conventional cast iron rings in a 150 grit bore was easy kickstarting for mine before going overboard with pistons.
Col

[Jules]

thanks Col/John, I've summarised both your findings here and am confused by it unless the 23 tooth makes a significant difference vs 21 and 19 tooth?
I'm thinking that a 19t engine sprocket would give heavier kick/turnover (but more revs/kick than 23t once moving)....
and, the 19t engine sprocket would give lower revs at any given road speed, hence requires more clutch slip/revs to driveaway..
Have I got this wrong?
I'm thinking about using the 23 tooth for easier kickstarting and clutch function, simply because that is more significant for me than being able to drive faster, thoughts??
Col
The standard engine sprocket for my bike was 19-tooth, but I found it revving too much so changed to a 21-tooth .
I also thought the 21-tooth engine sprocket might improve the kickstarting, but no noticeable improvement.
At 3500rpm, speed is 60mph with standard 3.50 x 19 rear tyre and all other std sprockets
The only issue now is that I have to ride the clutch to get up my steep driveway.
John
With a 23 tooth engine sprocket and otherwise std gearing my SR indicates approx 3300rpm at 60 mph, 4000 at 70 with 100/90 X 19 rear tyre
It has no problems with taking off on a hill two up either..
Comparing the effort in kickstarting mine vs a friend's A10 or my brothers SR there is definitely a difference.

[trevinoz]

Isn't the standard A10 engine sprocket 21 teeth?

[berger]

Trev a book i have says 21 and rgs 23 but with 46 rear wheel as opposed to 42rear on A10

[Worty]

Trev a book i have says 21 and rgs 23 but with 46 rear wheel as opposed to 42rear on A10

Was 19 for sidecar use??

[limeyrob]

Yes, I recall 19 for outfits and 21 std.

[Jules]

I just found this on the forum's database for the 55/56 plunger and s/a, says 18t for sidecar and 21t for solo (maybe 19t was used later?), but I'm still confused by the references to the gearing being too low/high - can somebody please explain in engine revs vs road speed for me, starting at the engine sprocket and finishing up at the back wheel, simply because (presumably) you can change the engine sprocket and also the gearbox sprocket and the rear wheel sprocket to achieve many weird and wonderful variations (assuming you can buy the various parts).
In this case though (I think) John is suggesting just a change to the 23t engine sprocket makes kicking over and clutch engagement much easier without changing the on-road drivability... thoughts??
PS also can I fit the 23t without adjusting the primary chain links ie a std chain still fits?? cheers

[Swarfcut]

 To avoid confusion, Plunger bikes all use the same primary transmission, engine/clutch ratio cannot be changed with standard parts, so this is fixed. Gearbox and rear sprocket can be mixed'matched, big gearbox sprocket with small rear gives relaxed high speed cruising, but poor acceleration.  Conversely small gearbox sprocket, big rear give good acceleration, but motor revs its socks off at higher speeds. Latter low gearing set up is used for sidecar work. So for specific functions the ratios of the final drive can be chosen to suit, within reason.

   Bear in mind that in top gear the gearbox mainshaft and output shaft are locked and turn at the same speed. Considering the later S/A models, the same applies to the final drive. But although the S/A clutch chainwheel is the same for all models, the primary crank sprocket can be changed. The above parts list notes several variants, this is because the sprocket and drive sleeve were changed early on, and a mis match brings up all sorts of chain alignment issues, well known on the Forum.

   A smaller crank sprocket lowers the overall gear ratio, in other words the engine must rotate more times for a single turn of the back wheel. For a given engine speed the road speed will be lower. Conversely, a bigger crank sprocket gives higher road speed for a given engine speed, or same road speed, at less revs. Here again, it's all down to riding style and use. Highly geared is fine for high speed work, but less acceleration, and useless for load lugging or slogging up big hills, here the motor will not be able to reach the sweet spot in the power band without constant use of the lower gears at the slightest incline. This is often referred to as being "overgeared"

 The question of ease of starting is down to the larger diameter of the bigger crank sprocket. Simply put there is more leverage applied to the crank. The downside is that it won't turn as quickly or rotate so many times with a single kick.

  Speedo drive ratio is affected by final drive changes. Primary ratio change has no effect, but road speed per 1000 revs will change.

  Swarfy

   

[Jules]

thanks Swarfy, just what I needed to understand whats happening within this change - my interpretation of John and Col's comments was actually the opposite of your explanation hence my confusion, but now it makes sense when I read them in the context of your explanation, thanks....