Run in Reverse?

FatLazyAndStupid

New Member
Oct 22, 2008
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Missouri
I have some ideas about putting a motor on a bike. I want to mount a 49cc 2cycle engine to the frame with the drive shaft on the right side of a bike with 2 sprockets in the front and 3 or 4 in the back. With the setup I'm thinking of I could change what gear I'm in and theoretically achieve greater speeds or lots of torque depending on the gear. The engine would connect to the larger of the front sprockets and the smaller front sprocket would be connected to the back sprockets. I would have a pull, kick or electric start with the pedals removed. With a chainsaw style clutch so I can start it in place then go. All of the kits and motors I have seen are made to drive an additional sprocket added to the left side of the rear wheel. I have seen some Chinese kits that look pretty good and I would need most of the parts from the kit to make it work, but there is one main question that is keeping me from starting: Is it possible to run a 2cycle engine backwards or am I out of luck?
 

FatLazyAndStupid

New Member
Oct 22, 2008
4
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Missouri
Thank you now I know its at lest possible to do, I suppose I will figure out how to set the timing whenever I purchase it.

Which would be best for a motored bike disk or rim brakes?
 

jerseykat1

New Member
Thank you now I know its at lest possible to do, I suppose I will figure out how to set the timing whenever I purchase it.

Which would be best for a motored bike disk or rim brakes?
if you click the link a the top left that says "looking for performance" in red you will see a kit that allows you to properly mount the motor, and use your bikes rear gears to shift. It is called a shifting kit. I have one installed on my bike, and it makes the ride so much smoother, not to mention you can change gears.

disc is best if you don't get the cheapest ones you can find. But V brakes are best on a budget, provided your frame has the attachments on it for v brakes. unless you ride in wet or humid conditions i would just go with v brakes and a good set of pads.
 

NEAT TIMES

New Member
May 28, 2008
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PENSACOLA, FL
LAZY , JUST KIDDING. WELCOME TO THE FORUM . YOU WILL LIKE IT HERE. I THINK "SICK BIKE PARTS" HAS ADD IN LEFT COLOMN. SEE THEIR WEB SITE AND VIDEO`S THEY HAVE A NICE SHIFT KIT. I BOUGHT ONE , HAVE NOT INSTALLED IT YET. I THINK THE PRICE IS GREAT WITH THE QUALITY OF THE PARTS. HOPE THIS HELPS. MANY ON THE FORUM LIKE THEIRS. RON:bike2:
 

FatLazyAndStupid

New Member
Oct 22, 2008
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Missouri
chainsaws will likely have a sproket already mounted. No it won't be too difficult just have to relocate the carburator so that it is not upside down.

Chainsaws don't come with sprockets but this is the best picture I could find of what a chainsaw does have. Here is a picture of the chain that chainsaws have, the chains on chainsaws work differently than bike chains do and that is why I asked about connecting a regular sprocket.

welcome, and did you read any of our responses?

The shifter kit is too expensive and I'm just trying to figure out a cheap and easy way to motorize a bicycle and make it go fast. I don't have much money to throw around and buy all the odds and ends that will fit together like a hand and glove so I have to make things work. I just figured a chainsaw with a sprocket attached would be the easiest way to make it work.
 

rrraul

New Member
Oct 29, 2008
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New York
Hey. I love the idea of timing the engine to run backwards. The shift kits are cool but it means that you have three chains on your bike. I think it would be much more efficient to have fewer chains and fewer moving parts. Another solution would be to put all the gears on the left side of the bicycle. But I haven't found any parts like that so I like your idea the best.
 

Technocyclist

Motorized Bicycle Senior Technologist
Jul 7, 2008
463
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Asia
I don't think running the engine in reverse is advisable. You need to reduce the RPM for your bottom end or else you would not have enough torque. So if your budget is low, you can use a spare rear hub to mount it on your seat post to act as the jack shaft, similar with SBP. You will need to fabricate a mounting plate to attach the hub to your seat post. You need to attach a sprocket ring from a front sprocket to the left side of the hub. You can reshape the gear on the clutch of the chainsaw to look like a sprocket by grinding the inner edges of the gear.

But this might be too much work if you're lazy...:D
 

rrraul

New Member
Oct 29, 2008
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New York
I dunno I think a jack shaft would be pretty inefficient. You are adding an extra chain and set of bearings. Im pretty sure you should be able to run the engine backwards as long as you adjust the timing properly. Then you can flip it around and attach it directly to the front gears. You would have to modify things slightly of course.
 

Ghost0

New Member
Mar 7, 2008
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Bellingham, WA
Actually chains are pretty darn efficient if tensioned, aligned and lubed properly, at 30mph the resistance of the drive train is insignificant compared to aerodynamic drag.
 

rrraul

New Member
Oct 29, 2008
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New York
Couldn't you use the front gears to gear it down? You would need to have the engine turning a large gear, then use a smaller gear to turn the rear wheel.
 

rrraul

New Member
Oct 29, 2008
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New York
Actually chains are pretty darn efficient if tensioned, aligned and lubed properly, at 30mph the resistance of the drive train is insignificant compared to aerodynamic drag.
True, and the jack shaft kit is awesome but it seems like there must be a simpler solution with fewer moving parts.
 

jasonh

New Member
Jun 23, 2008
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For timing, I think you can just use the white wire off of the mag instead of the blue wire, since it's running backwards...they're just mounted on opposite ends of the coil.

The only thing is, you would actually have to mount the HT motor upside-down because of the location of the drive sprocket and the magneto. Not an issue though, just need to flip the carb over, and come up with a custom exhaust since it'll be coming out of the back.
 

rrraul

New Member
Oct 29, 2008
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0
0
New York
upside-down? wouldn't you just want to mirror it so that the drive sprocket is on the right side of the bike? But I believe you are correct about the exhaust.
 

jasonh

New Member
Jun 23, 2008
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upside-down? wouldn't you just want to mirror it so that the drive sprocket is on the right side of the bike? But I believe you are correct about the exhaust.
If you simply flip the motor around, the drive sprocket will be in towards the front of the motor. On most bikes except some stretch cruisers, this would also be in front of the chainrings.
 

ebmvegan

New Member
Jul 15, 2008
283
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OC, Ca
FatLAzy, If this is your first build, set it up as it was intended to be and run it for a a few tanks. Just so you can get to know your motor and bike. Then if you're not content, start doing the mods your were thinking of. All the instructions on the HT kits state that some mechanical know how will take about 5 hours. My first bike took 10 hours total and I'm pretty mechanically inclined. We have all run into problems but have checked with our peers for solutions. Get to know your motor and bike then do the mods. No amount of money can replace knowledge and experience. Have fun and good luck.
 

jasonh

New Member
Jun 23, 2008
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Oh, and also...you will need to either add a sprocket for 415 chain to the crank, or change out the drive sprocket on the motor to one that accepts bicycle chain.