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Discussion Starter #1 (Edited)
I was looking at going down a couple of teeth in the front or up a few teeth in the rear. Ive heard rumors that going down on the front sprocket places extra stress on the crank espeacilly on 929's. I would appreciate anyones help or opinion on this situation.
 

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Two less teeth on the front sprocket is a big change in gearing, but it shouldn't hurt the gearbox and definitely won't hurt the crank. It might stress your chain a bit more though because of the reduced diameter of the sprocket. If it was me, I'd go -1 on the front and +3 on the rear sprocket instead (but I still think this is too much personally).
 

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-2 front could damage the swingarm the chain would probably rub against it a lot. I would go -1 front and the rest on the rear. With stock chain 108 you can go 15 45 wich is almost like 14 43.
 

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Yes....a smaller front sprocket will add proportionally more overhung load to your countershaft snout and more importantly the bearings...

But there are other more pertinent reasons for not going too small, such as swingarm clearance, increased component wear due to chordal action...yadda, yadda, yadda....

Of course it is all relative, but as a rule of thumb a 15t is the smallest "practical" choice...and even then it's a bit of a compromise.... :twocents:


Edit:
Fixed typo - from "crankshaft" to "countershaft".
 

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Coming in on this a little late, but on a previous Yamaha that i owned, i changed from a 15 to a 14 on the front. as stated, keep an eye out for premature wear on the swingarm guard and always make sure your chain is adjusted/maintained correctly.

also, driveline noise becomes more obvious, (especially when driving next to a cement median, or center guardrail) due to the now, tighter, radius the chain has to turn, causing premature chain wear in some cases.
 

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I don't follow how a reduction in countershaft sprocket size can have any affect on the crankshaft. Perhaps the transmission output shaft/bearing, but how would that cause any harm to the crank? The crankshaft output to the transmission (clutch basket) isn't even on the same side.

I'm sure Honda quality is better, but there was a problem several years ago with the old air cooled Suzuki engines (mostly Katana, but also some GSXR)developing cracks around the output shaft bearing, which was mostly blamed on the chain being adjusted too tight and stressing the cases.
 

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evl_twn said:
I don't follow how a reduction in countershaft sprocket size can have any affect on the crankshaft. Perhaps the transmission output shaft/bearing, but how would that cause any harm to the crank? The crankshaft output to the transmission (clutch basket) isn't even on the same side.
That was a typo in my post...I meant to say "countershaft snout" instead of crankshaft....fixed it accordingly.... :thumb:
 

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Just do it man - youre going to sell the bike one day anyway - or die on it or it will get stolen, so just get on with it !!!!!

Jon
 

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A friend put a 12 tooth on his Honda 750 back in 1970. It was an old clapped out bike to begin with, but it didn't take long for the chain to break and get shot through the cases.

I'd stick with 15 teeth for efficiency and swingarm clearance.
 

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DavidW said:
If it was me, I'd go -1 on the front and +3 on the rear sprocket instead (but I still think this is too much personally).
this is what i'm running right now, and am very pleased with it...still does 85mph at 6.5k

as others have said 14t on the front is probably not so good of an idea, more for chain reasons than crank reasons though...
 

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Baketech said:
Yes....a smaller front sprocket will add proportionally more overhung load to your countershaft snout and more importantly the bearings...
Any Mechanical engineers in the house that can explaine this?... I dont see how shortening the leverage arm off a rotating mass attached to a driven shaft is going to change the load on the shaft. The shaft is getting the same amount of power from the engine side. I do understand more leverage being asserted on the chain, and its increased travel speed...but not the shaft itself. :idunno: Or are we talking about increasing the load on the outer bearing, the one closest to the sprocket?
 

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the wear occurs on the chain, then the chain breaks. That will be bad maintenance. If you wanna mod the thing the you have to look after it. No extra wear will occur on the shaft - thats crap, however making the front smaller will kill the chain.
 

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G-Force Junkie said:
Any Mechanical engineers in the house that can explaine this?... I dont see how shortening the leverage arm off a rotating mass attached to a driven shaft is going to change the load on the shaft. The shaft is getting the same amount of power from the engine side. I do understand more leverage being asserted on the chain, and its increased travel speed...but not the shaft itself. :idunno: Or are we talking about increasing the load on the outer bearing, the one closest to the sprocket?
Sure....

T=F*d
-or-
Torque = Force x Distance

In this case:
1. Force = Tension in the chain
2. Distance is equal to 1/2(Pitch Diameter) of the sprocket.
For a 15t this = 1.50"
For a 16t this = 1.60"

Let's assume an output torque of 80lb*ft to make the math easy.
80lb*ft = 960lb*in

From T=F*d:
For a 15t (1.5"), F = 640lbs.
For a 16t (1.6"), F = 600lbs.

This is the resultant chain tension....and the difference in numbers is due to the smaller pitch diameter (ie more leverage). It's also why you feel more "squirt" when riding.

The Force "F" (chain tension) acts on the countershaft, creating a proportionally larger load on the output bearing, and in addition a larger moment in the shaft itself.

*I want to reiterate, that all things are relative. Within reason the higher loads created by a smaller sprocket fit within the design parameters of the drive. But it should be noted that the difference is real, and does have an effect on longevity and wear.
 

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An Engineer's opinon:One tooth smaller on the c-shaft sprocket won't cause you any problems with the chain, counter shaft, cases etc. Just watch those full throttle power shifts from 1st to 2nd (@ the track of course) and remember your speedo will now show some really impressive (and incorrect) speeds and mileage. My solution to the speedo inaccuracy is to apply a piece of duct tape over it.........Works every time!
 

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Steve Kratz said:
An Engineer's opinon:One tooth smaller on the c-shaft sprocket won't cause you any problems with the chain, counter shaft, cases etc. Just watch those full throttle power shifts from 1st to 2nd (@ the track of course) and remember your speedo will now show some really impressive (and incorrect) speeds and mileage. My solution to the speedo inaccuracy is to apply a piece of duct tape over it.........Works every time!
Or, you could be like the rest of us mod freaks and get a Jim Ahlman's Speedo Recalibrator! :D
 

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Thanks for the suggestion but I find that duct tape is by far the best value, since it not only renders the speedo error irrelevent and keeps me from looking at the stupid thing while I'm riding @ the track but it's cheaper than a "recalibrator"..........Not ot mention, easy to install.
 

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CBRBob said:
On a bike like the 929/954 andything more than -1f OR +3r is too much if you plan on riding it on the highway.

how come? mine does just fine at -1 +3...the biggest problem i have is that it needs the speedo recalibrated
 

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It's a subjective thing....I have 15/45 on my 929, and I think it's perfect road gearing... :thumb:
 

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Steve Kratz said:
Thanks for the suggestion but I find that duct tape is by far the best value, since it not only renders the speedo error irrelevent and keeps me from looking at the stupid thing while I'm riding @ the track but it's cheaper than a "recalibrator"..........Not ot mention, easy to install.
True, and that's fine as long as you don't care if your odometer has more miles showing on it than the bike really has. Some folks care about that for resale value, but it doesn't seem like a big deal.
 
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