Why A Motorized Bicycle and NOT a Moped?

sbest

Member
Nov 3, 2015
343
2
18
Nova Scotia
The China Girl motorized bike engine will take the Puch cylinder if you didn't know?
I am going with a Minarelli cylinder on my China Girl:


This is a cast iron cylinder making 4-7hp, and I have a 70cc Airsal aluminum cylinder that is purported to make 8-12hp. 12hp in an under 50 lbs bike will out perform most mopeds with a big bore kit, AND I can still lift it over a fence or carry it up steps if I need to.

This bike as shown could do over 40mph.
44t sprocket, stock NT carb, stock bottom end, $20 stock Grubee pipe.
All it had was head and porting mods.

I didn't go with a taller sprocket because I used it on trails and I needed low speed torque as well. Also, 40mph on a 50 lbs bicycle is killer fast. I didn't feel the need for anything faster.

If it is speed is what you want, get the moped and modify it. Scooter wheels, brakes and bearings are better for speed.

If you want lightweight and simple, go China Girl and learn what they need to survive.

The 4 strokes will give long life with simple maintenance, but you give up lightness. Everything is a trade off.
 

Mikey_

Member
May 15, 2016
37
0
6
GA
It isn't and either or thing: I'm building both but will start with the Puch because I'm getting a frame at a really low price. I'm going to go K star 70cc kit. I want to do the 74 but I don't want to have to weld or do any boring.

Where can you get a stronger crank and arm to build the China engine up for the Puch 70cc top?
 
Jan 21, 2015
610
23
18
Portland, Oregon
I would disagree about 2 strokes being more fun than 4 strokes. 2 strokes may be more powerful for an engine of the same size, but 4 strokes come much bigger, and are more reliable. I've never seen a 2 stroke go anywhere near as fast as my lifan bike (68 mph), plus it looks cooler:

Heck, I'd wager mine would beat most mopeds in a race as well.
The only reason I'd ever go for a 2 stroke is that they're much cheaper.
 

ultralight01

New Member
Oct 30, 2016
337
0
0
Hood River, Oregon
That bike.
Is insane.
I got to see it in person! Haha
I think if there was a bigger 2 stroke available I'd buy it since they're cheap and easy to mod, but overall, they're just not as... solid. But they're fun in their own way, you can get a lot of power for very little weight. I mean, R125 2 stroke shifter kart engines get up to 115mph. But they're $1500-$3500 because of the sheer amount of design and quality involved to make them...

A Yamaha KT100. That would be fun.
 
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Feb 2, 2017
155
6
18
California
I just see 4 stroke motors as 'cheap' motors in my eyes...... but that's just me. I've always been a 2 stroke guy from my racing kart, to dirt bike, now motorized bicycles. If you've never seen high performance 2 strokes, just take a look at kart motors. The Italian motors can squeeze 46 or was it 48 horses out of a 125cc water-cooled shifter right from the factory. But I understand the motors that we put on these bicycles aren't 'performance' motors and you need to do modifications if you want real horsepower, 2 stroke or 4 stroke. Still, only way to go for me is 2 strokes...... it just makes more sense. Who wants to lug a huge motor around in a bicycle when you can put in one that is half it's size and makes the same (if not more) horsepower?
 

ultralight01

New Member
Oct 30, 2016
337
0
0
Hood River, Oregon
Except for oil mix. But eh.
The thing is China girls take a workshop to make decent. High quality 2 strokes are the best engines out there. There's not very many options for a bike.
If you get a different engine and build from scrap, an engine not from a kit, you'll have something far better in all cases.
 

sbest

Member
Nov 3, 2015
343
2
18
Nova Scotia
It isn't and either or thing: I'm building both but will start with the Puch because I'm getting a frame at a really low price. I'm going to go K star 70cc kit. I want to do the 74 but I don't want to have to weld or do any boring.

Where can you get a stronger crank and arm to build the China engine up for the Puch 70cc top?
Just start with a new well balanced Grubee or other bottom end.
A 40mm crank would be better but the 38mm will work.
I would split the case and blueprint it, drill the case for extra oiling passage.
I have run the Grubee for hundreds of miles at 9000-10,000 rpm.
The new 6203/17mm cranks are plenty tough. Both rod bearings are the only problem.

You can press the Grubee crank apart, even bore it for 40 or 42mm stroke and install a better rod and big end bearing if you like. Cost would be about $250-$500.

The answer starts at the question. What do you want to do with it?
Absolute reliability? stock 4t moped
Lightest weight? 2t China Girl on a bare 10sp frame
Cheapest? 2t China Girl on a bargain 10sp frame
Most versatile lightweight? modified 2t China Girl shifter on a Mountain Bike frame
Stealthy? Electric
Longest range? 30-49cc 4t
Weight is no object and full compensation? 4t big bore
I'm not a hobbyist and I just want it to work? 49cc 4t on a plain bike
Full motor bike performance in a cheater bike? Motoped 2t or 4t
Top speed? big 4t or highly modified 2t, probably a shifter, and full survivor benefits

I'll try to get some pictures of the Airsal cylinder up.
 

Mikey_

Member
May 15, 2016
37
0
6
GA
I've changed my mind! LOL I think that i get more of what i want and what is actually useful for riding in traffic with a MB. the taller height and longer frame will give a better experience.

Now I'm at the point where I'm choosing between 2 frames; Slugo or a Huntington, both Micargi.

Engine wise, predator 79cc or Lifan. I was thinking about putting a Lifan on a Puch Maxi or Magnum frame but MB just gives better real work riding comfort and visibility.

I love that Lifan build Necro and I wonder if a Lifan will fit in the Slugo or Huntington. I also like the idea of running a China 2 stroke but with a Puch head-- I just worry about the bottom end internals.

I want easy power not tune tune tune tune tune power so the 4 strokes seem like the better option.
 

ultralight01

New Member
Oct 30, 2016
337
0
0
Hood River, Oregon
YES
Someone make this guy a senior member just cause.
I say huntington all the way. Fat tires and ape bars? No thank you.
The Lifan is a beast. For a build like that, you're talking a frame that can fit an engine over 17" long, with components that can take up to 70mph. You'll need a shift arm and various parts. Necro has over 2K in his bike. I think it could be done for less, you just need to be thrifty and very good at fabricating parts.

The 79ccs have easy power with little tuning. Have you seen scotto's 99cc build thread? (99ccs are discontinued but perform nearly identically to the 79)
https://www.google.com/url?sa=t&rct...RKMJLX_dVBq8Bf2ZQ&sig2=QNdqkjFIBiiC_rQeBrJ9OQ

Edit: Just looked up Georgia's laws. In georgia, anything must be registered as a motorcycle. Motor assisted scooters are considered motorcycles and must have a title and registration to be legal. So I guess, if you build a lifann bike and manage to get it registered, you'll have a legal homemade motorcycle. But you'll want to engrave the tires with "DOT", add turn signals and lights, all of that stuff.

Or label it 50cc, then call it a moped and have fun
 
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Mikey_

Member
May 15, 2016
37
0
6
GA
I don't really care about registering it! I'll only do that if the cops stop me, if they figure out it is over 50cc and if they care enough to give me a ticket. THe cops are pretty cool here. We have hundreds of guys rolling around on dirtbikes that are not street legal cruising the streets every Sunday. The cops don't bother them unless they are being reckless or rude.

The 79cc might be the best choice, I can buy a mounting kit for it, many ppl have shared their builds so the ability to siphon collective knowledge is high. It is only $99 too. I like the slugo but I like the Huntington even more. I've seen some really nice builds on the Huntington frame.
 

ultralight01

New Member
Oct 30, 2016
337
0
0
Hood River, Oregon
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Jan 21, 2015
610
23
18
Portland, Oregon
The predator mounts are overpriced. You can make the same thing functionality wise with about $20 worth of angle iron and fasteners. It might not look as pretty if you do it lazily, but if you powder coat or paint it and round the corners it will look just fine. In terms of building predator bikes, I have put together instructions on how to do it: http://www.instructables.com/id/79cc-Motorized-Bicycle-From-Scratch/

I'd not recommend going with the lifan for a first build, it's rather complicated and likely to get you killed if you don't know what you're doing. It's more of a motorcycle than a bike at this point. Also really expensive, as ultralight said, I've got over $2,000 in mine, and it's not quite finished yet. I doubt you could do it for cheaper unless you either skimped on parts and made a deathtrap, or you can manufacture your own sprockets and wheels and the like, and I basically have a whole machine shop in my garage and I can't even do that. I made all the mounting hardware and the jackshaft myself, only things I ordered were things like sprockets, chains, the engine itself, and bicycle parts like wheels and brakes.
 

Mikey_

Member
May 15, 2016
37
0
6
GA
I want to do something like this Huntington with a 79cc Predator or even try some sort of Frankenstein China Girl with a larger head like a member showed a few posts back but most likely just with the predator but I've been studying 2 stroke performance so much that I want to build up a 2 stroke. Blame it on the Puch forums.

I'll order everything next Monday and start building. .shft.




***Image from http://www.pistonbikes.com/Articles.asp?ID=249 I hope they don't mind me posting their race bike.***
 
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Mikey_

Member
May 15, 2016
37
0
6
GA
The China Girl motorized bike engine will take the Puch cylinder if you didn't know?
I am going with a Minarelli cylinder on my China Girl:


This is a cast iron cylinder making 4-7hp, and I have a 70cc Airsal aluminum cylinder that is purported to make 8-12hp. 12hp in an under 50 lbs bike will out perform most mopeds with a big bore kit, AND I can still lift it over a fence or carry it up steps if I need to.

This bike as shown could do over 40mph.
44t sprocket, stock NT carb, stock bottom end, $20 stock Grubee pipe.
All it had was head and porting mods.

I didn't go with a taller sprocket because I used it on trails and I needed low speed torque as well. Also, 40mph on a 50 lbs bicycle is killer fast. I didn't feel the need for anything faster.

If it is speed is what you want, get the moped and modify it. Scooter wheels, brakes and bearings are better for speed.

If you want lightweight and simple, go China Girl and learn what they need to survive.

The 4 strokes will give long life with simple maintenance, but you give up lightness. Everything is a trade off.
What all besides case matching do you need to get the Puch 70cc heads to mate to a China Girl without any leaks? I'm still worried about the bottom end holding up to so much more power.
 

ultralight01

New Member
Oct 30, 2016
337
0
0
Hood River, Oregon
Well...
Ok.
The bottom end will hold up, no one really replaces those. The crank bearings are what need to be replaced with better quality ones, or just replaced when your engine blows up.

I'm considering building a 2 stroke for a homemade paramotor.
 
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Mikey_

Member
May 15, 2016
37
0
6
GA
Sorry guys for not being able to make up my mind! I was impulsive and went ahead and bought a Puch Maxi frame for $50 from a really cool guy. I'm going to build this out just to cruise around my neighborhood and then start on the MB project late spring/early summer.