Tell me about bicycle engine kits!
September 14, 2008 9:04 PM   Subscribe

Hey dudes! I want to mount a big, ridiculous engine to this racing bike I have. Tell me about that.

I recently inherited another bicycle. It's a racing/street bike, and I think it has an aluminum frame - it's really light, probably less than thirty pounds. I want to stick the biggest, baddest, most inappropriate engine I can on it. What do I need? I have a motorcycle license, so I'm not concerned about the size. I'm also not too concerned about practicality - I know that it'll be harder to pedal, but as long as the thing is ridable I'm happy.

There are a lot of 80cc kits on ebay for about $150, are these worth buying? Are there better ones for a bit more? What should I look out for?
posted by borkingchikapa to Sports, Hobbies, & Recreation (5 answers total) 1 user marked this as a favorite
I've seen a few around, they look and sound like someone took a lawnmower engine and strapped it on. They look pretty ridiculous.
posted by axltea at 10:21 PM on September 14, 2008

What you're trying to create is known as a "moped". That term has been coopted to refer to motor scooters as well, but the original meaning of the term was "motor + pedal".

Apparently now they're called "motorized bicycles".
posted by Class Goat at 12:03 AM on September 15, 2008

Wouldn't motorizing a bicycle create the need for brake lights, turn signals and such to make it street legal?
posted by jon1270 at 3:19 AM on September 15, 2008

Best answer: Hey so hi I have one of the 80cc kits. They're generally called "Happy Time" motors, and come entirely from China. They're not 80cc, they're somewhere between 49 and 59cc's.

Before you do anything else, get the to and learn about your options.

Let me tell you about my experience:
I put mine on a 1997 Specialized RockHopper. I will put it on a street bike when I get one.

Things to know: The mounts generally require modification. LOTS of people drill through the frame...not me. I just ground out the mount to make it bigger. On a racing bike you'll probably need to make it smaller. It does NOT include rubber pieces for the frame mounts, which are absolutely required for vibration dampening. The default electrical system sucks. Under no circumstances should you use the included kill switch, instead buy your own toggle switch. Reason being that the included switch actually shorts out the magneto, which kills it by about the 20th use. If you can find instructions to install your own, let me know and I'll tell you how. It are teh ez. Next---the throttles are super stupid. I will at some point replace mine with a thumb throttle. Next, the spark plug is shit and is gapped wrong. There's a $1.09 NGK that's way better that you can pick up. The gas tank is also shit, looks stupid, and interferes with cables running on the upper bar. I've modified an old Nalgene bottle as my fuel tank, and it hangs behind my seat, out of the way. It's extra hawt because now I see how much fuel I use in CC's.

The hardest part about installation is the chain tensioner. It's 10 kinds of a pain in the ass to get right, and as the chain stretches you'll have to re-adjust it. You can do it---it's just a pain.

The up sides: On the flat, my bike hums along at about 32mph. Realize that you've only got one drive sproket from the motor---it does NOT make use of your gear system. The motor stays running up hills if you just give it a little assistance to keep it turning. I live in the mountains, and its lack of hill climbing ability is the worst thing about it. There are jackshaft kits available so that you can use your gears, but they're an extra $200. That gives you more gears than a Honda Ruckus with about the same motor's supposed to make the motor hill climb like a freak and take flat top speed up to closer to 50mph. It does get good gas mileage, but you have to break it in first with a higher oil/gas ratio. I'm still in the break in period on mine, and on flat I'm getting about 50mpg, and I didn't change the spark plug right off the bat, so that's not quite accurate. There are also all kinds of aftermarket shit you can get for it, like boost tubes (prevented wasted gas when the motor aspirates), goped pipes, etc etc. The motor does give you a 12v lead you can use to power a headlight/tail lights...whatever.

The down sides: Installation is a pain if you're not technically inclined. The little bastard gets HOT, as it has no fairing or anything anywhere on it. It's air cooled, so you can't box it in. It's not quiet, but it's also not super loud. They exist in a gray area of the law. In most places they're legal only because they're not illegal. People look at you like you're nuts, but then they generally smile at you and ask how you did it. Most of the motor nuts/bolts are loose when you get the motor. You MUST check EVERY ONE before you try to ride. It is a 2 stroke motor, so it is dirty, but it'll also get up to about 100-120mpg and you can park it on the sidewalk.

I guess that's about it, feel free to MeFi mail me with questions.

Happy Times are kind of the bargain basement. Golden Eagles are really where it's at, but they're also 3x as expensive. They're using 4 stroke Robin/Subaru's though.

Really I bought mine so that I have a point of reference for making some from scratch. I have a semi-unlimited access to 50cc chainsaw engines. :)
posted by TomMelee at 5:26 AM on September 15, 2008 [2 favorites]

Take some pictures or better yet video and post it when you are done. It'll be fun whe you get the thing going much faster and with more mass than the rim brakes were designed for. Have fun.
posted by fixedgear at 8:56 AM on September 15, 2008

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