DIY Honda 4-Stroke on 20" bike

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TFroehlichIII

New Member
Dec 27, 2013
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Lansing MI, USA
Hey everyone,
I'm going to be building a rear mounted 4-stroke motorized bicycle with a Honda engine. What I'm wanting to know is about how fast will my bike go with the 20" wheels and the Honda 4-Stroke, it's a 1.3hp engine. Or would it be better if I got a bigger engine?

The other question I have is, are all the chains that I can buy on these motorized bicycle sites be cut to any length? The distance from the rear mount to the center of the wheel is about 10" or less. Will this be an issue?


Hope to hear from you!
 
maniac57

maniac57

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Oct 8, 2011
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Speed will depend on gearing. You can gear the engine however you please. I'd start by deciding what kind of clutch and drivetrain you will be using.
Most transmission setups have a reduction so you need to know where to start.
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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memphis Tn
Well, a china two stroke has a built in 4:1 gear reduction. This allows a reasonable size rear sprocket without losing acceleration. Running chain direct from motor to wheel would require a huge wheel sprocket to get any kind of useable gear ratio. Most four stroke setups have built in clutch and reduction before the final drive chain.
If it were as easy as just bolting a motor and chain on, everyone would do it.
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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memphis Tn
Basically yes.
Depends a lot on the wheel diameter too.
Figure a stock ht uses a 10 front-44 rear on 26'' rims WITH a built in 4:1 gear reduction.
Maybe a 10 front-32 rear with a 20'' rim WITH a built in 4:1 reduction.
Running direct from clutch, I'd guess you would need something like a 12 front- 60rear with a 20'' rim. Probably take some fine tuning adjustment depending on how powerful your engine is down low and what rpm your particular clutch engages at.
 
16v4nrbrgr

16v4nrbrgr

Active Member
Mar 17, 2012
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North Bay
There are some pocket bike 5:1 gear reductions and a 7:1-3:1 CVT that will fit or the EZM kit also works well for motorbikes. I'm playing around with using my spare auger tranny which is 33:1 on a HS49 4 stroke in the future, the nice thing about that is the gear reduction is all done in the tranny so you can use bike sprockets for BMX chain for the power transmission, not big motorbike ones.
 
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T

TFroehlichIII

New Member
Dec 27, 2013
16
0
0
Lansing MI, USA
I'm looking to rear mount the engine which is a GX35 Honda 4-stroke. After doing a little research this is what I have come up with.

The GX35 (35CC) 1.6hp engine [rear mounted]
A 4-stroke transmission (link listed below)

I'm still not sure what sprocket to use on the rear wheel.
Also, how will that GX35 mount on the rear? I'm going to be using a heavy duty rear bike rack.

http://www.bikeberry.com/engine-kit-parts/4-stroke-parts/4-stroke-transmission.html
 
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