New Member Pocket bike engine BMX

[ac4life00]

Hey so this is my first post but I have looked around at alot of the builds people have done. Im currently working on my own build using a BMX frame and a 49cc pocket bike engine. My goal with this project was to use a pocket bike engine and still be able to pedal the bicycle. I still need to make a jackshaft from the engine to the drive sprockets mounted on the crank freewheel. The other problem I need to tackle next is mounting my exhaust since there is not much room between the frame and the header. Also on the list of things to do is put a 3 speed internal rear hub. I plan on making the top bar of the frame into the gas tank. I may abandon this bmx frame and go to a mountain bike frame that is a little bigger not sure yet still tinkering. Let me know what you think or any suggestions or if you have any parts. Thanks and go COUGS!!

 

[professor]

Hi Ac welcome to Motoredbikes! Looks like a challenging project.

 

[wheelbender6]

I dig it!

 

[ac4life00]

Yeah its been a bit of a challenge so far especially since i have been building it in my bedroom at college haha....but it should be a fun little ride to zoom around campus on

 

[deXtrous]

How do you intend hooking up the chain to that drive sprocket? I have the same motor and it seems you would have to cut the sprocket off and fashion a bigger one to it which will fit the rear sprocket????

 

[ac4life00]

I am going to build a jack shaft that will have a chain running from the engine sprocket to the jackshaft then across to the other side of the crank where there are two sprockets on the crank. One sprocket uses the same chain as the pocket bike engine the other sprocket uses a standard bicycle chain. Both sprockets are mounted on a freewheel and can spin without the pedals moving. From engine to jackshaft will be a 1:1 ratio (small sprocket to small sprocket)...from jack shaft to crank small sprocket to a big 65 tooth sprocket which will drive the regular bicycle drive sprockets.

 

[ac4life00]

Dextrous just out of curiosity what kind of build are you doing using the pocket bike engine..do you have any pics of your build?

 

[deXtrous]

Mate I've just stripped the engine down, haven't started to construct anything yet.

Just toying around with the best way to mount the thing as the motors are a bit wide.

 

[ac4life00]

I think i might change the way mine is mounted also. Im contemplating doing a bent downtube like old board track racers did then using flat iron straps bolted to the frame downtube and seat post tube above the crank for an engine mount. I am having trouble finding a way to bend steel tube for the frame though. The motors are a bit wide i agree thats why i had to make my crank using 5/8 steel rod and drilling out my crank arms to 5/8. To narrow mine down a bit i removed the pull start cover and I plan on shaving the flywheel fins off...perhaps i can use my shoe on the flywheel to kind of kick start it or i might try to mount a small belt drive to the flywheel that i can manually wrap a cord around and give it a pull.

 

[Alaskavan]

From what I've read, internal 3-speed hubs don't last long in a motorized application.