Which engine?

I have some experiencie with industrial (sorry but I don´t know the name of the device... electric generators? The engines used to power factories in case of a blackout), 4-stroke, low size (125 to 500 cc) engines. I think the "metals" (crankshaft, pistons, rings, cylinders) are WAY more resistant than the "china girl" equivalents. The engine is a bit more complex as well, and it is heavier and lower-performing.

However, if only u$200 are to be spent, and this is the first engine he´ll buy... I would advise for a good china girl kit. I have the cheapest 48 cc engine with bearings (not bushigs) that I could find, I haven´t had a problem in 4 gas tanks. That should be enough to get some advertisment going with his proyect, I guess! He can always change the motor later on.

Oh, and then there´s the sound issue. In my humble opinion, in small displacements, 2-stroke engines do sound a bit better!

None of the chinagirls are industrial/commercial-rated engines. None of them. They aren't designed to run all day. See what happens when you run them at their power peak for a an hour or two straight. See what happens when you do that every day. I have, and I was constantly wrenching! Some people get/build a gem of a 2-stroke, but most don't. In the end, it's still an engine that wasn't designed to run all day.

OTOH just about every 4-stroke is. HS, GX, HF, Predator are all industrial/commercial engines. Most of them have their own cooling fan, iron cylinder liner, and pretty much guaranteed to run all day long at their power peak. And there's always the not fiddling around with oil all the time bonus, too.

My years of experience with these have led me to this opinion: if one is intending to build a cheap toy to have fun with now and then, a chinagirl is great for that. But if you intend on relying on your MaB to get you to important places, then you should go 4-stroke. It costs more now, but less later.

"If you can't afford to do it right the first time, you must afford to do it twice."

Bottom line, you might get an ok working 2 stroke with no problems and have a great time with the build and use of the engine, but the word here is "Might" If your going to spend money on a project why it not be something that "will" work. I don"t want to tear down an engine every couple of hours, or check every bolt after every ride I want to be out riding, not wrenching, unless its putting together a new bike or normal service. the reliably of the 6 builds we at design logic bikes have put together have all been 4 strokes with Staton gearboxes and have never had any issues with the engines or trans, they start everytime, do 25-30 mph, give 125-150 mpg and take me on 20 mile rides every other couple of days and bring me home with a smile on my face ear to ear, whats not to like about that?

im no expert having only two builds up to now,i do like the simplicity of the two stroke also the price not bad, if you grenade one trying to hop it up.the weight isnt too much for the bike frame.having only two so far. first is 66cc from bgf on e bay,cheap acessories but decent motor and price. second is a pk 80 silver with upgraded hardware and sproket adapter from pirate cycles,well worth the extra money,anyway my 2 cents, welcome aboard

When I first started building bikes I was told you get what your willing to pay for. My guidelines for building bikes is predominant riding terrain, legal requirements, rider and budget. My personal choice are 4 strokes. Get an hour/tachometer gauge so that you keep the oil changed and the air filter cleaned on schedule and these engines will last far beyond any two stroke engine.

Motorvator said:

Hello everyone, my name is Chad and I come from the bicycle industry. I actually still work in the industry. I am very interested in creating my version of what a motorized bicycle should be, and hope to change some of your minds about your bicycle set ups. Inversely, I need to know about motors. It seems to me there is not a whole lot of difference from one motor to the next, and am trying to decide which to get. I definately want a chain drive as I will be using a disc brake hub to bolt a king cog to, so the simplicity of the cheap 2 stroke motors is very appealing. I don't want to spend more than 200.00 on a motor, but am very open to a four stroke motor that installs the same way as the 2 strokes do. I definately DO NOT want a friction drive, as I believe from my experience in loaded touring, that is way too much weight on the back of the bicycle and I do plan on laying this thing over through the turns flat track style. So, which engine for around 200?

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If your budget for engine only is $200, you can buy 2hp-6hp engines for much less than that.

Then it's up to you and your friends' skills and more $$ to harness that awesome power. The more skills and access to resources you have, the less your motorized bike will cost you. Let's see, the clutch, jackshaft and the right combination of sprockets will power you down the road with great speed. Of course, the rest of your bike would be built with stronger brakes, wheels, etc. to safely harness the beast.

You weren't thinking of a $200 build, were you?

One other thing, you talk about riding over on your side. I hope you mean on some kind of a race track. We have enough problems with the law as it is keeping our bikes on the road. Please don't make things worse for us. Ride safe and enjoy the hobby.

I've been riding my china girl to work everyday (lol) since august 2011 and it has never taken a dive on me. I did blueprint it like biknut mentioned (opened up the engine, did a quick portjob, smoothed everything out and replaced all the nuts and bolts with ones of higher quality) although I did not do anything as extensive as he has to his. My total cost was probably about $200 including. Although I must point out that I've been building and porting high performance 2 stroke engines for a couple of years now so this kind of work is not beyond me. To someone less experienced this may seem daunting so a china girl might not be the best choice.

From my experience china girls are not so bad but unfortunately you must be willing to open up and work on these little beasts if you want to make sure they won't bail out on you. I do not think that china girls are necessarily "plug and play." But for the mechanically inclined they offer a nice affordable way to motorize your bicycle.


EDIT: Damn I didn't see the date. Sorry for bumping an old thread >.<