24 Tooth Countershaft Sprocket

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chasesa

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I would like to hear comments (especially actual experience) regarding the merits & demerits of using a 24 tooth countershaft sprocket on a stock 850 Mark lll.
Thanks,
Stephen
 
That is what I will be usung. But my situation is special, 2:1 belt primary and 17" wheels.
 
I've been running a 24-tooth sprocket with a Combat 750 for about twenty years now. I'll probably never go back to something smaller. Zero-to-60 times remain comparable because you don't change out of first gear. Gas mileage improves, highway revs go way down--and if you need it there's always third gear. Having an optional overdrive is useful almost every day--with my tall 18-inch tire 4000 rpm is a leisurely 89 mph on the tollway. My rebuilds seem to last a lot longer as well.


Tim Kraakevik
kraakevik@voyager.net
Three Commandos
 
Yes, I like mine geared way tall. It kills the first gear wheelies and I find myself using 3rd a lot in the mountains but if you see a lot of highway miles it is worth it. Jim
 
I've been running a 23 tooth for some time now and with the standard head found it a bit breathless at times, but with the Fullauto head on with everything else standard apart from the Tri Spark and a 34 Mikuni it is a great combo. When I changed my gearbox over to my spare recently, the 23 tooth was knackered so I used the 21 that was on the other gearbox and it's a hoot with so much low end and midrange grunt. Having said that, when I recon my gearbox and refit it I'll be going back to the 23 tooth. At 70 mph it's turning over at 3500 rpm with 80mph at 4000 rpm. I have noticed that I use more fuel now with the 21 fitted. I haven't tried the 24 tooth but I would think that it probably would be going too far. I love tall gearing, but.......... I also like good throttle response when I pull the trigger. With a standard motor, especially with the extra weight of the MK3, I would think that the standard ( for MK3 anyway) 22 tooth would be the ideal compromise.
 
And . . . . to think that a 19 tooth was stock on some models . . . . .
I'm running a 20 tooth and since it pulls past 7000 in 4th, I really should go to a 21.
 
You guys must not like to dance the front wheel on acceleration!

Russ --- still 19T combat
 
Depends on what kind of riding you like to do. I have an 850 with a 22T sprocket and ride mostly on backroads at 60-70 mph. Acceleration is still crisp enough for me. Bike came with a 20T and I found that too low for comfortable highway cruising. I find the 22 a bit tall for the kind of roads I ride as I rarely get out of third. However, above 70 mph or so, the bike is much more relaxed. So if you are riding a lot on slabs at 75-80, 22T would be ideal. For me, I think the 21T on an 850 is ideal compromise and will likely go to that at some point in the future. I would think 23 or 24 would be way too tall for almost any kind of riding but some folks seem to like it.
 
Doesn't the higher the number of teeth on the gearbox output sprocket, put that much more of a load on the main and layshaft bearings ??? ( in our already stressed AMC gearboxes; originally designed for 30 BHP motors ?) I've got a 21 tooth on mine and the layshaft NJ203 C3 roller bearing upgrade; so I think I'm relatively "safe". However, appears like several have went the more teeth thus higher gearing route; and had no problems. I'm hesitant to go higher than the 21 tooth myself though. Just my 2 cents ...
 
The amount of torque applied to the gearbox is dependent on the primary drive ratio and the riders throttle hand. Changing the rear drive sprocket doesn't change the amount of torque the engine produces.
Yes I have read the part about bigger rear drive sprockets being the cause of layshaft bearing failure on the MK3 850. Poppycock. It was dodgy bearings. Jim
 
Appreciate the thoughts on tall sprockets as I'm in quandry what to use on Ms Peel.
I liked 20T with factory Combats, plenty of pull, no need to down shift to accel up hwy steeps but nicer to run 80's. On peppy Peel liked 21T+taller belt drive as could still creep around in 1st, lift front in 1st and 2nd approaching 7000 but cruise 80's+ in mid rpm range. Peel did pop the teeth off 3rd gear playing catch up with Duci Monster 900, I'd slowed up behind a car for.

New Peel will have hi torque and desire to top 150 but still as rpm limited as any good ole Norton. i've got lots to spend on her yet so no TTI gear box possible for first year of use. What T count should I try first and expect gear box to stand it?
I'm hoping care of throttle and/or tire spin will protect cog and shafts some.
 
If you increase the engine torque with a blower I would suggest going to a taller primary ratio. The gearbox will easily handle the added RPM but are pretty much at their limit as far as torque is concerned. jim
 
Not only does the primary ratio establish the peak torque delivered to the gearbox, the taller sprocket also reduces rpm and torque at any given road speed compared to smaller sprockets. My '72 Combat with a 24-tooth sprocket and tall back tire is pulling 4000 rpm at an indicated 89 mph--2000 rpm below peak torque for that engine.

Bikes with standard gearing and camshafts are pulling around 5000 rpm at that speed, which corresponds to peak torque. It is the surplus torque and horsepower that allows these bikes to pull right on up to redline in top gear. It also contributes to the sense that the engine is "busier" than need be at tollway speeds.

My gearbox has been nearly bulletproof since I put in a roller layshaft bearing twelve years ago. The three sleeve-gear bushings are the components most susceptible to wear. Eliminating the mainshaft circlip and moving the entire primary closer to the center line has extended the bushing life to around 30,000 miles.


Tim Kraakevik
kraakevik@voyager.net
Three Commandos
 
kraakevik said:
... The three sleeve-gear bushings are the components most susceptible to wear. Eliminating the mainshaft circlip and moving the entire primary closer to the center line has extended the bushing life to around 30,000 miles.
Click to expand...

Tim, could you explain that more, please, I'm pretty thick. When I put my new bushings on the mainshaft, I only used 2 (know now I should have used 3) and used the red sleeve retainer on them. My original outer bushing was pretty chewed up by the clip from sliding out at 13K miles. I'm still using the clip, but put a washer between it and the bush.

Dave
69S
 
DogT said:
kraakevik said:
... The three sleeve-gear bushings are the components most susceptible to wear. Eliminating the mainshaft circlip and moving the entire primary closer to the center line has extended the bushing life to around 30,000 miles.
Click to expand...

Tim, could you explain that more, please, I'm pretty thick. When I put my new bushings on the mainshaft, I only used 2 (know now I should have used 3) and used the red sleeve retainer on them. My original outer bushing was pretty chewed up by the clip from sliding out at 13K miles. I'm still using the clip, but put a washer between it and the bush.

Dave
69S
Click to expand...
Hi Dave,
It only calls for 2 bushing but many people fill the area in the middle with a third because they can. No big whoop if you don't. The main support is called for on the ends.
 
I know about the bushings, but that is not my main question, I guess I wasn't clear. What does it mean 'Eliminating the mainshaft circlip and moving the entire primary closer to the center line'.

That's the part I don't get.

Dave
69S
 
DogT said:
I know about the bushings, but that is not my main question, I guess I wasn't clear. What does it mean 'Eliminating the mainshaft circlip and moving the entire primary closer to the center line'.

That's the part I don't get.

Dave
69S
Click to expand...
I found this in a search for "clutch circlip". I know what you are thinking about and I have read about it before in more detail but I cannot remember where. It was something about welding a washer to the back of the hub.

Report this postReply with quoteRe: Clutch woes.......
by kraakevik » Thu Oct 21, 2010 9:31 pm

I don't use the circlip anymore--I just shim to allow the lands and grooves on the mainshaft to solidly locate the clutch center.


Tim Kraakevik
kraakevik@voyager.net
 
I went back and read the whole 'clutch woes' thread. Some information I missed there, like the replacement of the circlip with the one sanded down from the starter. The way I read it, Tim is removing the circlip and adding shims from the lip on the counter shaft to locate the clutch basket lined up with the drive sprocket. If I have the drive sprocket off, I may look into that.

Dave
69S
 
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