FrankenBike Idea

[rottyfan]

A little background first. I am a new rider and the only experience I've had really was riding a 1981 Honda C70 Passport I brought back to life after sitting in a garage for over 25 years. I ended up selling it last week and it got me thinking of getting a 50cc bike/scooter. Here in Connecticut you don't need a motorcycle license to operate one, just a drivers license. Nor do you need to register or insure one.

So here's what I'm thinking: Pick up a relatively whole pre-gen parts bike. I see them for sale really cheap because they don't have a title and the engines are blown. I would remove all of the bodywork, the only thing I'd keep on it would be the seat and tank.

I was thinking of sticking a 50cc motor, probably a cheap Chinese knock-off, with a clutch and electric start on it. I wouldn't have to worry about a title because the bike wouldn't need to be registered. And instead of a flimsy scooter with tiny wheels, it would have a real and sturdy frame along with superior suspension and braking for its weight.

The most difficult part would be aligning the front sprocket and fabbing new motor mounts, but that would have to be done no matter what engine you swap. Might be easier because there would so much more room to work with. I'm thinking something like this can be built pretty cheap and that's the only way I'll take a stab at it. Right now I can get a 50cc engine for ~$100 and an almost whole parts bike for ~$200.

I kind of got this idea when I found a post where someone stuffed a Ninja 250 engine into a little Yamaha YSR50 so I figured heck, then maybe that little 50cc engine can bolt into a Ninja 250 without much problems. So what do you guys think?

[csmith12]

DEW ET!

In for the pics.

[The Red Scourge]

[Racer x]

No don't do it.
First check the law. I scooter and a motorcycle are different. Some laws say 50cc but not with foot pegs. Must have step through architecture.

Most scooters don't have chains so you would need a 50cc dirt bike with a chain. While they can be had. They are usually crap. And most are twist and go. And the go
part is really slow.


Just get a scooter and learn to ride . Or a whole bike.

[TnNinjaGirl]

Do what you want but I can't remember ever being on a 50cc bike and thinking "wow, I wish this thing went slower and handled worse" or conversely on a 250 thinking "man I wish this were a lot slower"

[Geezer-60]

Originally Posted by TnNinjaGirl

Do what you want but I can't remember ever being on a 50cc bike and thinking "wow, I wish this thing went slower and handled worse" or conversely on a 250 thinking "man I wish this were a lot slower"

Funny but true! With the engine being part of the frame, some bracing would be needed, I'd think. Might end up adding weight and still not being as rigid. Depends on your 90% riding style though. Short hops around town might be OK, not much more. I got a 250 because the 125 MadAss I really lusted over didn't have the grunt to do what I wanted it to do. With all of that ... it does sound like a fun project with a lot of machining and metal working. And yes, we all want pictures!!

[ga_drifter]

if you want a scooter and the style of a ninja get something like this..brand new they asking 1800.. personally id rather put that money towards a 250. but thats just me...

[Racer x]

I ride a 50cc scooter all the time. First of all it's a two stroke. That is a big difference. A four stroke 50cc engine might make four hp.

. I like the thinking but for all that work I would not want him to be disappointed. I have had some really cool 50 cc bikes. They are cool because the weight is so low. In the end you would end up with a 300 lb motorcycle that had 26 hp and now has maybe 10.

But it's the out of the box thinking I like.

[subxero]

Just thinking that thing is gonna weight a lot and have very little engine to push it around.

I assume you are talking 2stroke 50cc?

Regardless could be fun little project and end up with a toy that is fun to mess around on although I assume it will leave you wanting more every time you get on it.

[rottyfan]

Originally Posted by Racer x

No don't do it.
First check the law.

Yes, only interested in working within the law here. From my state's DMV website: "You may operate the following on the roadway without registering it:

Motor Driven Cycles are defined as a motor scooter, moped or motorbike having an engine size of less than 50 cc and a seat height of at least 26 inches."

With that said, 50cc motorcycles have been factory produced and a few that come to mind are the Aprilia RS50, Suzuki AS50, and Honda MB5. The Aprilia is the most modern one and the Suzuki and Honda were made in the 60s or 70s; all of them, in decent condition, are pretty pricey. So it's not like it's never been done, I'm just looking for an affordable option that will provide modern safety and handling rather than 60s technology.

Weight shouldn't be an issue. I'd get rid of the plastics like everyone else cafe'ing or streetfighting their 250s and that should be good for 30 lbs. I would also be getting rid of the 250cc motor and cooling system, not sure how much that weighs, but my all in I wouldn't be surprised if the total weight reduction would around 100 lbs.

No worries about wishing for a 250, I already have one. There are no pretensions here; I'm interested in building a 50cc bike and my expectations on how it performs will be just that, that of a bike powered by a 50cc motor. The best analogy I can think of is that my daily driver is a Dodge Magnum RT AWD that came from the factory with 340hp and 390 ft/lbs torque. Mods done to it are cam, ported heads, and headers. Although it hasn't been on a dyno, that combo is usually good for 75hp and will put these big beasts into the 12s. On the other hand, for a few years I owned a 1985 Suzuki Carry. That's a Japanese mini Kei truck that had a 550cc 3 cylinder engine and 4 speed stick. I had school buses pass me it was that slow, but that little truck sure got a LOT of attention. The one thing I told everyone when chatting about the truck was that it was the most fun I ever had driving slow. Keeping your expectations rooted in reality will spare you from a lot of disappointment.

[Racer x]

You won't get it to 100 lb. The frame is steel. And even at 100 lb it would not go 40 mph up hill. If you can find an RS50 grab it. They rock, but are still slow. They hold speed on a race track. But on the street. From a dead stop they be to be at 10000 rpm to get moving.

[rottyfan]

100 lb weight reduction, not 100 lb bike.

[jkv45]

You'd be way better off finding a pregen that needed some work and fixing it. Installing a 50cc 4-stroke into a Ninja 250 frame would be a terrible idea. The Ninja isn't that small and light. Plus it would be registered as a motorcycle (frame number) - not a scooter - if that matters to you.

I have a 75cc 2-stroke street bike, and it's usable on the road, but a bike the size of a Ninja 250 with a 50cc 4-stroke would be painfully slow - and dangerous to ride in traffic.

[garth285]

Why dont you get a 250 and put like a 2 stroke 250 or 500 in it :-p

[subxero]

Originally Posted by rottyfan

100 lb weight reduction, not 100 lb bike.

the problem is most of the weight is in the frame, wheels, forks, swing arm.

The only thing you would really be losing is the engine.

You could maybe drop 100lbs total between cutting anything and everything off, tabs, back part of frame, and then the difference in the engine weight but still. A 260lb bike with that small of an engine? Gonna be a dog.

Might be better off finding a smallish dirtbike frame to swap the motor into and make a mini motard

Could probably get it to be in the 160lb range maybe less if you get the right starter bike.

[Racer x]

I striped my bike to the bone. Aluminum tank small radiator and no fairings. No lights front breaks or seat. Still only able to remove 70-80 lb. that got the bike down to 290 lb on a scale. I don't know what a stock bike tips the scale at. I'll sell you a perfect 2007 new top end on the engine. And in great shape for 1500 or even less. The bikes are out there. If you don't just want a project.

[TnNinjaGirl]

I can't see any benefits of the project other it being a project. Sometimes that is all one wants though.

I have a ysr50 with an 80cc 2 stroke sitting in the garage. The technology is not that far off from a pregen 250 abd and it's ****in nuts

[spooph]

If I were you, I'd build this on an old mountain bike frame... Like Britton Bees or something. If you want to put in the time, that's fine, but might as well put into something that's worth while, as you'll be dissapointed within the first 5 seconds of riding it. But don't let us stop you..

[csmith12]

^^^^ That would be a cool project.