Gearing insight....

#21
Using the calculator I listed above I get a 9-1 ratio by dropping from 13 teeth to 10 teeth on the output (jackshaft to wheel). If I go from an 18 tooth to a 24 tooth on the input (motor to jackshaft) I get a 9.23-1 ratio. There is some chain clearance potential issues on the jackshaft to wheel if I change that sprocket while no issues with the larger input sprocket change.

So...two more questions....

1. Is going from a 6.923-1 ration to a 9.23-1 a real world, significant change? Yes...I know numerically it is...the question is will it really make a real world difference?

2. The other "question" (which is really an out loud thought) is that would the current set up work for say an average weight adult (say 180lbs)? If so, I will be selling this bike and I better off just leaving it as is. I wish I had a 180lb tester here......my kid is 6'5 220lb so he would be better than me I guess.
 

mustangfrank

Well-Known Member
#24
Using the calculator I listed above I get a 9-1 ratio by dropping from 13 teeth to 10 teeth on the output (jackshaft to wheel). If I go from an 18 tooth to a 24 tooth on the input (motor to jackshaft) I get a 9.23-1 ratio. There is some chain clearance potential issues on the jackshaft to wheel if I change that sprocket while no issues with the larger input sprocket change.

So...two more questions....

1. Is going from a 6.923-1 ration to a 9.23-1 a real world, significant change? Yes...I know numerically it is...the question is will it really make a real world difference?

2. The other "question" (which is really an out loud thought) is that would the current set up work for say an average weight adult (say 180lbs)? If so, I will be selling this bike and I better off just leaving it as is. I wish I had a 180lb tester here......my kid is 6'5 220lb so he would be better than me I guess.
Yep to above (again), torque converter will get you moving yet still keep your top speed. Gearing the jackshaft gears in either position to get you to 9:1 will work but at the sacrifice of top speed, making the outer larger is easier for clearance reasons.

Compression is OK at 90psi and YES, weight is a factor in your issue...at a deuce and a half I only ride a couple centrifugal equipped bikes with gearing both around 9:1...and I still give them a decent two footed push off before hammering it.
 
#25
The "two footed push off" is about where I am at right now. Looks like we will keep the clutch unless the new owner wants a TAV installed. Will use this learning experience for the next build
 
#26
So...because I had the time and the parts I swapped out the motor I had in the bike with another Tecumseh 5hp I had laying around. Same result.

With the Torque Master clutch I am getting more move movement. Once it gets warm and with a little push I can get up to speed on a flat but it won't make it up a hill.

So...now I need to decide if I change it or leave it. Couple of questions...

1. If I go to a new jackshaft input gear of 24 teeth (from the 18 currently) I get the ratio up to around 9.23/1. I do have 15" tall tires. Odds that this simple switch will get me moving round a sloped yard?

or

2. Install a torque converter. Since I have never retrofitted one before I admit I am a little confused as to how the chain would ultimately drive my jackshaft. Would I get a longer jackshaft and run it through the rear of the torque converter and eliminate the sprocket/chain on the torque converter side? Or would I run a small chain from the torque converter sprocket to the jackshaft.

Which is the better solution. I want to make sure I give the new owner a well sorted bike.
 
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