new member with a minibike gearing trouble

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rocketjr2008

New Member
#1
#1
Hello I'm rebuilding a minibike I got when I was 10.I'm now 14 and my original motor (49cc) on it broke so I just switched it to a Honda gc160 I got with my go kart.I want to make it go at least 65mph but I don't know how many teeth my clutch should have my jack shaft in has 21 out is 21 and sprocket is 44. Tk
 
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Havasu Dave

Moderator
#2
#2
rocketjr2008 said:
Hello I'm rebuilding a minibike I got when I was 10.I'm now 14 and my original motor (49cc) on it broke so I just switched it to a Honda gc160 I got with my go kart.I want to make it go at least 65mph but I don't know how many teeth my clutch should have my jack shaft in has 21 out is 21 and sprocket is 44. Tk
Click to expand...
Hi Rocket, How tall is your rear tire?

If you have an overall height of 12 inches on your rear, and use the widely available 12 tooth clutch, you would need to swap out the input jack shaft sprocket from 21 teeth to 11 teeth. (Or do a combination on both jack shaft sprockets) That would give you a theoretical 66 MPH at stock governed RPM of 3600.

Your engine probably doesn't have the torque to maintain power at such a high gear ratio however. Those MPH computations are theoretical and don't address torque.

I recommend you first get that 12t clutch, and get the replacement engine and bike working well together first. Maybe do a bit of wrenching and learning (as we all have done) and maybe plan for a larger engine, or faster setup in the future.

By the way, if you have a 12" rear tire height and go with that 12t clutch, your top speed should be around 35 MPH, which on a mini bike feels pretty fast to me, especially with 12" tires. Also, it doesn't hurt as much as it does at 65 when you crash. :thumbsup:
 
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rocketjr2008

New Member
#4
#4
my first engine time me to 30mph then it broke my uncles a mechanic he used to do all the work it needed but now since I'm older he and my dad want me to learn to do these things and they want me to get optimum performance out of the engine and make it hit at least 60. The rear tire is 12 in. I never fell off the bike or crashed it
 
ludicrous speed

ludicrous speed

New Member
#6
#6
got a picture of the bike you are working on?
sometimes that helps...

i run a gsx160 on my doodlebug and its snappy but you still only gonna go same mph.
you might wanna go scope the doodlebug stickied thread about jackshafts and Promod the guy that sells them,lotta! good info on those threads.
 
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Havasu Dave

Moderator
#9
#9
rocketjr2008 said:
What do you mean a combination]
Click to expand...
I mean you'd need a jack shaft to axle ratio of 2:1 by changing BOTH sprockets.

Also, a total ratio of engine to axle of 1.9:1.

That's with a 12 inch tire, and a 3600 RPM engine.

But none of that is going to happen with a Honda 160, unless you are running down hill.

Inventor pardue posted a very neat spreadsheet that allows you to plug in variables like sprocket teeth, RPM, etc. and arrive at top speeds. There are some on line, but his is the best.

Fun to play around with.

https://sheet.zoho.com/view.do?url=http://www.parduebrothers.com/minibike/ratiospeed.xls

You can spend $1200- $1500 or so on your engine, and get it to spin 6500 RPM and keep the gearing the same and do 65.
 
5horsebriggs

5horsebriggs

New Member
#10
#10
do you have a pic of the bike? im guesin its an apc chopper which are junk, i got one last year and they are crap i sold it to a friend, you will need to weld te frame, and 60 is not anywere near safe for that type of bike, 15mph stock was squirrely enough EDIT i looked at the pic, im alSO 14 and ride te bogger bersion of that bike and i was smoshed im only 5' do you have the capability to stretch the frame?
 
ludicrous speed

ludicrous speed

New Member
#15
#15
well when we tried that with a 10/60? it would really heat up the clutch till you got up to speed.
not a good idea...thats why you need the jackshaft and the right gears.
you did read the replies already right one guy laid it right out...
actually 2 guys did...gave you everything you need..
 
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rocketjr2008

New Member
#16
#16
Yep thanks I just wanted to see all my possibilities and I've decided to just put a 12t clutch and leave everything else alone thanks for the help guys I'll try to post pics and a video when I finish
 
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