Trying to get/create a motorized 2-stroke 50cc bicycle

jman116

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Jul 20, 2019
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What sort of bikes should I look for, is there any significance in the frame design? Is there any "pre-built" bikes that you recommend?
From what I've gathered, aluminum frames aren't good because the aluminum weakens due to the motor vibrations, and smooth city tires are better because of their traction, except in snow. I am going to use this bike to traverse back and forth between two campuses about a mile apart, five days a week. The campus is situated in Nebraska, and Nebraska bike laws state that the motor has to be less than 50cc and max unassisted speed of 30 mph. I'm a big guy, at 180lbs, so a 50cc probably won't be able to propel me that fast, and I'm not very concerned about any legal issues. I'm well versed in mechanical engineering and prototyping so building the bike isn't an issue.
(sorry for the info dump)
 
The beauty of building a motorized bicycle is you have almost no limits on what bike you can use as a base. As long as it's not a BMX and it's a hardtail, you can slap a 66/80cc 2 stroke on it without much issue.

There doesn't appear to be much in the way of prebuilt bikes and the ones that are offered typically come unassembled and have a fairly high premium attached. You'll be better off finding a bike you enjoy riding then sourcing a motor kit to bolt-on.

For motors personally, I prefer Zeda 80 triple 40s as they have a higher output than most and typically are fairly stout.
 
The most important is if the engine will fit. My engine barely fit in this frame. I had to buy an offset intake.
IMG_20190720_153706.jpg

Take into consideration the ride. You are going to be travelling faster so bumps are bumpier. A bike with a decent front suspension, and tires that will cushion your ride. I got that bike off Craigslist for under 100 bucks and it rides great But the wheels are crap. I also didn't prepare them, I should have taken them apart and inspected / greased them. I've ordered wheels to replace them.
 
I wouldn't worry too much about the engine size. The cops will never know how big it is. Just slap a 49cc sticker on it if your that concerned about it. Add far as frames go, some guys like cruiser frames and others like mountain bikes. A steel frame is the way to in my opinion.
 
Your requirements exactly match a pure electric bike. I mean I went to university a while ago and I understand your needs. By the time you get your gas bike choked properly, warmed up, and moving, you might as well just walk and be half way to your next class/building, LOL. Just get a 1000W rear hub and 48V 12-15aH detachable battery and you will be all good throughout the year. It starts in 0 seconds and you are zipping to your next class/building.

1000W rear hub = $140
48V 12-15aH = $220-300 (domestic Chinese cells)
 
I wouldn't worry too much about the engine size. The cops will never know how big it is. Just slap a 49cc sticker on it if your that concerned about it. Add far as frames go, some guys like cruiser frames and others like mountain bikes. A steel frame is the way to in my opinion.
Grubee sells 49cc tags. Might get one for the new bike.
 
Your requirements exactly match a pure electric bike. I mean I went to university a while ago and I understand your needs. By the time you get your gas bike choked properly, warmed up, and moving, you might as well just walk and be half way to your next class/building, LOL. Just get a 1000W rear hub and 48V 12-15aH detachable battery and you will be all good throughout the year. It starts in 0 seconds and you are zipping to your next class/building.

1000W rear hub = $140
48V 12-15aH = $220-300 (domestic Chinese cells)
My college doesn't allow electric vehicles, otherwise I'd have bought one already :(
 
Your requirements exactly match a pure electric bike. I mean I went to university a while ago and I understand your needs. By the time you get your gas bike choked properly, warmed up, and moving, you might as well just walk and be half way to your next class/building, LOL. Just get a 1000W rear hub and 48V 12-15aH detachable battery and you will be all good throughout the year. It starts in 0 seconds and you are zipping to your next class/building.

1000W rear hub = $140
48V 12-15aH = $220-300 (domestic Chinese cells)

Wait, people actually need to use the choke to get their bike running? Both my $80 ebay crap motor and my zeda 80 will typically pop off almost instantly when dead cold (Phoenix cold, aka 90-100f) on both the stock NT and the PHBG 21mm racing clone.

Gotta say, I agree with bakeneko here. 2 strokes are fun as a hobby but they are grueling as a daily rider. They fail constantly due to the low build quality, cheap materials and the fact these motors vibrate like crazy. Not to mention that they can be super touchy and not run for the dumbest reasons.

For a rough example at what can go wrong and in what kind of time span, I had to deal with the following over the course of 2 months

March - April
Petcock broke off (dumping all my fuel onto my right leg)
Fuel tank mounting lug ripped (dumping all my fuel onto my left leg)
Blown headgasket
Fried CDI (two in a week)
Chain tensioner shifting (like 5 goddamn times)
Chain stretching
Rubber sprocket mounts getting cut by spokes causing the sprocket to wobble and throw the chain
Carb leaking where it mounts (mix leaned and it wouldn't run)
Main jet housing unscrewing and falling into the bowl (on 2 f***ing carbs in one day)
Engine mounting bolts rattling loose and falling off despite locktite
Engine mounting bolts snapping mid ride (cheap ebay motor)
Engine seizing because of too little oil in the mix (Thought I could make the .6 mile ride from the gas station to my oil bottle, in hind sight running it balls out was stupid. This was on the garbage ebay motor) After cooling off for 5 mins it cycled freely, has some deep scoring on the exhaust side of the piston now.
Intake rattling loose (mix leaned out, it wouldn't run)
Sparkplug rattled loose and fell out (NEVER grab a plug that just popped out of the motor, smoke came off of my finger tips when I touched it)
Exhaust rattling loose (killed the motor to pedal home as the studs were to hot to touch and I didn't want to have the pipe fall off)
Head vibrating loose and losing compression despite red locktite
Had to adjust the flower nut on the clutch plate since it wouldn't release.
Petcock handle broke off
Had to adjust the flower nut tighter by literally 1/6th of a turn to keep the clutch from slipping on acceleration.
Had to retighten the locktite'd motor mounts, again.
Clear fuel line turned rock hard, cracked, and started leaking like a sieve.
Clutch flower nut adjustment, AGAIN.
Had to replace the rear brake pads, the stock ones burnt up in just 2 months (I've NEVER in my life had to replace bike brake pads)

June - Present
Piston ring got caught on transfer at 7.5k rpm destroying the piston and damaging the cylinder (was able to repair the cylinder)
Constantly fighting clutch adjustment, I think there is something wrong with the shaft
Constant random fuel/oil drips
Have invested 8-10 hours into tuning this f***ing 21mm PHBG racing clone, still runs rough at certain throttle positions
Clutch lever likes to randomly pop out (the locating pin is missing) which is a huge PITA if I don't have my multitool on me. Basically, you stop and now your tasked with starting the bike with the clutch engaged. Not the easiest thing in the world.

As you can obviously see, I had quite a few issues the first couple of months and only a few in the following months. Basically, be prepared for stuff to not go according to plan. Chances are you won't have to deal with even 1/3rd of that list but I figured I would throw that out there.

My college doesn't allow electric vehicles, otherwise I'd have bought one already :(

That is really strange that they would allow a gas motorized bike but not an electric motorized bike. I know most campuses prohibit motorized bicycles from being on campus sidewalks but it wouldn't surprise me to hear specific rules on just electric kits (cant hear em until its too late)
 
Wait, people actually need to use the choke to get their bike running? Both my $80 ebay crap motor and my zeda 80 will typically pop off almost instantly when dead cold (Phoenix cold, aka 90-100f) on both the stock NT and the PHBG 21mm racing clone.

Gotta say, I agree with bakeneko here. 2 strokes are fun as a hobby but they are grueling as a daily rider. They fail constantly due to the low build quality, cheap materials and the fact these motors vibrate like crazy. Not to mention that they can be super touchy and not run for the dumbest reasons.

For a rough example at what can go wrong and in what kind of time span, I had to deal with the following over the course of 2 months

March - April
Petcock broke off (dumping all my fuel onto my right leg)
Fuel tank mounting lug ripped (dumping all my fuel onto my left leg)
Blown headgasket
Fried CDI (two in a week)
Chain tensioner shifting (like 5 goddamn times)
Chain stretching
Rubber sprocket mounts getting cut by spokes causing the sprocket to wobble and throw the chain
Carb leaking where it mounts (mix leaned and it wouldn't run)
Main jet housing unscrewing and falling into the bowl (on 2 f***ing carbs in one day)
Engine mounting bolts rattling loose and falling off despite locktite
Engine mounting bolts snapping mid ride (cheap ebay motor)
Engine seizing because of too little oil in the mix (Thought I could make the .6 mile ride from the gas station to my oil bottle, in hind sight running it balls out was stupid. This was on the garbage ebay motor) After cooling off for 5 mins it cycled freely, has some deep scoring on the exhaust side of the piston now.
Intake rattling loose (mix leaned out, it wouldn't run)
Sparkplug rattled loose and fell out (NEVER grab a plug that just popped out of the motor, smoke came off of my finger tips when I touched it)
Exhaust rattling loose (killed the motor to pedal home as the studs were to hot to touch and I didn't want to have the pipe fall off)
Head vibrating loose and losing compression despite red locktite
Had to adjust the flower nut on the clutch plate since it wouldn't release.
Petcock handle broke off
Had to adjust the flower nut tighter by literally 1/6th of a turn to keep the clutch from slipping on acceleration.
Had to retighten the locktite'd motor mounts, again.
Clear fuel line turned rock hard, cracked, and started leaking like a sieve.
Clutch flower nut adjustment, AGAIN.
Had to replace the rear brake pads, the stock ones burnt up in just 2 months (I've NEVER in my life had to replace bike brake pads)

June - Present
Piston ring got caught on transfer at 7.5k rpm destroying the piston and damaging the cylinder (was able to repair the cylinder)
Constantly fighting clutch adjustment, I think there is something wrong with the shaft
Constant random fuel/oil drips
Have invested 8-10 hours into tuning this f***ing 21mm PHBG racing clone, still runs rough at certain throttle positions
Clutch lever likes to randomly pop out (the locating pin is missing) which is a huge PITA if I don't have my multitool on me. Basically, you stop and now your tasked with starting the bike with the clutch engaged. Not the easiest thing in the world.

As you can obviously see, I had quite a few issues the first couple of months and only a few in the following months. Basically, be prepared for stuff to not go according to plan. Chances are you won't have to deal with even 1/3rd of that list but I figured I would throw that out there.



That is really strange that they would allow a gas motorized bike but not an electric motorized bike. I know most campuses prohibit motorized bicycles from being on campus sidewalks but it wouldn't surprise me to hear specific rules on just electric kits (cant hear em until its too late)
But they allow gas bikes? Quick someone call AOC.

I believe it's due to the hoverboard fires and that one of the dorm buildings has burnt down like 3 times now.. (not due to hoverboards, but...)
 
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