The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: Scott and Jay on 04.04. 2024 04:00
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Hi there,
I saw a mention in this thread:- https://www.a7a10.net/forum/index.php?topic=7010.msg48758#msg48758, about the "Disastrous Rebuild" - a Triumph Trident kickstart was going to be tried. This was longer and would give more leverage. I was thinking of getting a longer kick start (lever) somehow, myself. Jay's kickstart, on his A65 Thunderbolt - has much more leverage. This is designed in, internally - and known to be much easier than the A10. My trouble starting, in the recent rally we attended, over 6 days travelling - was partly, now, due to less bodyweight and power in my legs. Even though I have IMD flat-top pistons there was enough skimming necessary, for the flanged liners I got with them and to straighten a crooked barrel base - that I calculate it could be as much as 8.25:1. It feels like that.
I wonder if anyone has any thoughts on this, and if not too frowned-upon - what could be a suitable longer replacement, than the standard A10 item?
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I tried an A65 type kickstart (being sold by dealers as fitting the A10) on my A10 a few years back. About 2 cm longer than the A10. Not quite the same bend, got very close to the silencer and when folded the rubber rested on the oil tank. I did not like it so changed back to the A10 folding type.
A bit easier to kick over than the original but because of the greater length your kickstarting foot moves further for the same angle of movement so your engine spins a little slower and perhaps you get a little weaker spark from the magneto?
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I don't think there are any easy answers. You will see from another thread that I recently rebuilt a Matchless single and couldn't start it because the engine was tight and I could not get enough speed. I ended up getting a paddock starter and using that to get it running, now after about an hours running it starts on the kick start. I too looked at longer kick starts but the mag needs some speed so I'm not sure the trade off for easy kicking works. Fine with a coil but not so sure with a mag.
I'm 69 with dodgy knees and found that a lot of my problem was not really going for it, setting myself up to fail. 10 kicks that never quite spin the engine is exhausting when only one that does is needed. I used to be able to kick a Goldie so I went back to how i used to do that and really jumped on it and of course it started. So I'm working on getting my technique back. My Road Rocket has a center stand (and 9:1 pistons) so my plan is to try starting on the stand. I'm building the bottom end at the moment so I don't know if this is solution or not.
Is yours manual or auto advance? If the mag is a bit tired you get a better spark near full advance.
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i have a long en on mine and no problems starting it, i put the long en on because it worked better for me than the little en.
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I like that, I can see myself looking for something similar in a few weeks *smile*
What was it from or did you make it?
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Rob i cut out a block of steel when i had access to big stuff at work, i drilled out for the kickstart shaft and drilled out for the kicker pin. then slipped the kickstart on and put the pin in and filed a radius to make it clear the edge of the block when folding in and out, then drilled two little cup holes for the ball bearing to locate in when it is folded in or opened out. then i put the block on the shaft and marked where the shaft had to be drilled for the roll pin to get it in the correct position, this can be seen on the shaft where i marked it with a hacksaw blade *bright idea* a 5/16th roll pin was used and it's been like this over 40 years now *yeah* . pics are of my spare block i made at the same time thinking i might need it one day and fit a different japanese bike kickstart. who knows it might get used one day on the berger build, i have a BSA kickstart for the berger build but might do the same as betsy has, i will see when the time comes *beer* hehehe i have just seen my trial and error with the position of the ball bearing when it is folded in, that was when i was 20 years old , oh well not much changes ,i told you i wasn't a real welderer or engineerer , but i can play pool and drink like mario lanzer *beer*
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Hi All,
My 2 cents worth on this, I find that standard gearing on A10's is too low for modern traffic
A side benefit of fitting a 22 or 23 tooth engine sprocket is easier kick starting
John
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thats an interesting option John, is the kicking over significantly easier? would you mind just walking through the effects of this change for me please - I want to be sure that I have grasped the concept before jumping on board because of your comment regarding the std A10's gearing being too low for modern traffic ie the interpretation of too low is often confusing wrt ratios vs effects!
Kicking over is becoming a significant issue for more and more of us as we age *eek* *sad2*
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Very timely discussion. I'm sitting here waiting for a UPs delivery of a 16T engine sprocket for my Matchless green-laner. The 18t makes 1 st too high off road. But of course I completely forgot about the effect on the kickstart ratio (doh) so this could be a challenge. If I can't kick it it's back to 18t and get a larger rear wheel sprocket, a much harder task.
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Scott & Jay, Interesting problem. I also fitted IMD's to my standard 1960 Golden Flash engine (in a 1961 frame) during my rebuild and a very fine hone finish to the bores. It has been almost impossible to kickstart. I can stand on it with full weight for minutes and it just won't move. I had an old A10 owner club member try it and his response was "What pistons have you got in this?". They are the standard 7.25 to 1 flat top pistons on first overbore, but I also had all guides replaced and new valves, and set all ring gaps to 12 thou so I believe there is just no gas leakage. I also have a 21-tooth engine sprocket which I thought might improve the kickstart but no noticeable improvement. Soon after I had a right knee replacement and fitted an electric leg (June 2022). Although the knee now is great, I just kick over to free the clutch and just touch the button. The motor has 850 miles on it now and getting no easier. I think the composite oil rings are partly to blame.
Col
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Hi All,
Jules,
With a 23 tooth engine sprocket and otherwise std gearing my SR indicates approx 3300rpm at 60 mph, 4000 at 70
100/90 X 19 rear tyre
It has no problems with taking off on a hill two up either..
Comparing the effort in kickstartong mine vs a friend's A10 or my brothers SR there is definitely a difference.
Having had the same as Col, right knee replacement, I have an electric starter fitted for the last couple of years
John
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Bergs has an 8ft piece of scaffolding on his *smile*
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Bergs has an 8ft piece of scaffolding on his *smile*
yes worty it brings all the girls to the yard , pun intended ;) :-:
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thanks John, it is indeed worthy of a bit of discussion (for me anyway!) and apologies for asking a simple question too - just what is the standard engine sprocket (I've never thought to count the teeth!)?
I note that Col has a 21 which he thought might help, but didn't, and John, you are using 23, thats a big change in gearing in itself...
Your comment ref hill starting 2 up is a great prompt John, simply because "back in the day" I remember having to slip the clutch quite a lot on hill starting and we certainly didn't talk about changing engine sprocket sizing back then (mind you the magic ton was always the goal back then too)!!
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Thanks for all the replies on this. Very interesting. I have a 22 - tooth drive sprocket. When I got the IMDs Adrian Wright the proprietor said "you don't gap them" (the rings). I noticed they were special, thin and deep and a good 3-piece oil ring. Anyway, I think I will just see if I can swop with Jay's (A65) kickstart, and try that. I might be able to report back..
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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 *roll*.
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
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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.
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Isn't the standard A10 engine sprocket 21 teeth?
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Trev a book i have says 21 and rgs 23 but with 46 rear wheel as opposed to 42rear on A10
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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??
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Yes, I recall 19 for outfits and 21 std.
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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
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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
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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....