China Girl Motorized Bicyle Build

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biknut

biknut

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I'm planning to build a China motor from parts. I want it to be as quality as possible, but I'm not that interested in building a HP monster. My emphisis is going to be on quality performance, rather than all out performance.

I'm hoping to build a motor that will be smooth, last a long time, and has a little better than avarage power.

The first thing I'd like to do is balance the crank. How? Does anyone know of a shop that works on China Girl cranks? Suggestions?

This is where I'm at right now. This is a motor I just took apart.




http://www.youtube.com/watch?v=NGJwoiU1CFs

Here it is after the build. Looks better now doesn't it?

 
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chainmaker

chainmaker

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Re: China Girl Motor Build

Cool Bikenut. I have a china sitting in the basement I was thinking of doing the same over the winter, will be following this one,
 
biknut

biknut

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Re: China Girl Motor Build

What I found out today at the bearing house, was that the 6202 crank bearings are common and easy to find. I bought NSK (Japan) for $8 each. The clutch shaft bearings are the same 6202 except the only difference is the 2 bearings on the clutch shaft have plastic seals, but on the crank no seals. They told me to just pull the seals off for the crank.

No luck with the crank seals, or the small end rod bearing. They are definitely not common size, and probably like a Chinese OEM.
 
2door

2door

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Re: China Girl Motor Build

biknut said:
No luck with the crank seals, or the small end rod bearing. They are definitely not common size, and probably like a Chinese OEM.
Click to expand...
I had trouble finding crank seals too. The HT seals are a non-standard size and very hard to find at seal suppliers. I found them at PistonBikes, one of our sponsors. Others might carry them too but that's where I got mine.
http://www.pistonbikes.com/category-s/10.htm
Tom
 
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biknut

biknut

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Re: China Girl Motor Build

2door said:
I had trouble finding crank seals too. The HT seals are a non-standard size and very hard to find at seal suppliers. I found them at PistonBikes, one of our sponsors. Others might carry them too but that's where I got mine.
Gaskets and Seals
Tom
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Thanks Tom. That's what I do. I try to buy local, and then I start spreading the money around the forum sponsors. I'm very thankful they're here for us.

By the time I get through with this motor, I'll probably have enough parts to build four more lol. So far I've ordered a new motor kit, a new crankshaft, a short block, a piston and cylinder set, 4 sets of oil seals, a gasket set, 2 more gasket sets, a stator, a ignition, extra puller tool, 2 sets of bearings, a MM gen 2 head, a MM shorty manifold, a fancy carb from DAX, and about a dozen other parts I can't remember right now.

 
GearNut

GearNut

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Re: China Girl Motor Build

Ask some motorcycle shops about folks who can balance your crank.
The shop may or may not do it themselves, but they most likely know someone who can.

Some electric motor rebuilding shops will balance small engine crankshafts as well. The principals are quite similar.
Do bear in mind that the balance factor will be a percentage of the weight of the piston, piston pin, pin bearing, pin retaining clips, and the weight of the connecting rod as weighed 90* from the crank installed.
Balancing the crank in a single cylinder engine will always be a compromise. You will never be able to get rid of all the inherent vibration, just tune the balance factor to place the vibration where you want it to be most reduced. High RPM or low RPM.
 
biknut

biknut

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Re: China Girl Motor Build

GearNut said:
Ask some motorcycle shops about folks who can balance your crank.
The shop may or may not do it themselves, but they most likely know someone who can.

Some electric motor rebuilding shops will balance small engine crankshafts as well. The principals are quite similar.
Do bear in mind that the balance factor will be a percentage of the weight of the piston, piston pin, pin bearing, pin retaining clips, and the weight of the connecting rod as weighed 90* from the crank installed.
Balancing the crank in a single cylinder engine will always be a compromise. You will never be able to get rid of all the inherent vibration, just tune the balance factor to place the vibration where you want it to be most reduced. High RPM or low RPM.
Click to expand...
I just got some information from a local motorcycle shop about balancing cranks. They said they can't balance it with the rod on it.
 
GearNut

GearNut

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Re: China Girl Motor Build

Nobody can balance it with the rod on. That's not how it's done anyways.
Here's a condensed version of what is involved:
Press apart the flywheels.
Weigh all parts attached to the crank pin. (connecting rod, piston, and every little other part involved)
Put the weight total through a balance factor formula.
Reassemble and true the flywheels with a bob weight, weighing the proper amount as determined by the formula, used in place of the connecting rod.
Either static balance or dynamic balance the flywheels.
Press apart the flywheels and remove bob weight.
Reassemble and true the flywheels with connecting rod/ bearings installed.
Done.

Any motorcycle shop that deals with building performance motorcycle engines can easily balance your crank, whether the farm out the job or do it in house.
It is not really that hard to do, you just need the know how and tools to do it.
 
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biknut

biknut

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Re: China Girl Motor Build

GearNut said:
Nobody can balance it with the rod on. That's not how it's done anyways.
Here's a condensed version of what is involved:
Press apart the flywheels.
Weigh all parts attached to the crank pin. (connecting rod, piston, and every little other part involved)
Put the weight total through a balance factor formula.
Reassemble and true the flywheels with a bob weight, weighing the proper amount as determined by the formula, used in place of the connecting rod.
Either static balance or dynamic balance the flywheels.
Press apart the flywheels and remove bob weight.
Reassemble and true the flywheels with connecting rod/ bearings installed.
Done.

Any motorcycle shop that deals with building performance motorcycle engines can easily balance your crank, whether the farm out the job or do it in house.
It is not really that hard to do, you just need the know how and tools to do it.
Click to expand...
Thanks for the good explanation. I'm going to need to study up on balance factors. I only have a vague idea. Me and Bruce made this vid of when I got my Sportster balanced at T&O.

http://www.youtube.com/watch?v=Jn50F_yKW0s
 
GearNut

GearNut

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Re: China Girl Motor Build

Very cool video! That is dynamic balancing.

As stated before, I only shared a condensed version of how its' done.
If you want to do it yourself, you can do static balancing in your own garage. It will not be nearly as accurate as dynamic balancing, but should be plenty good enough for these China engines.
Educate yourself thoroughly before attempting though!

Edit: I wish I could afford to have T&O build dynamically balanced, 4 5/8 stroked Torque Monster flywheels for my Shovelhead!
 
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biknut

biknut

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Re: China Girl Motor Build

GearNut said:
Very cool video! That is dynamic balancing.

As stated before, I only shared a condensed version of how its' done.
If you want to do it yourself, you can do static balancing in your own garage. It will not be nearly as accurate as dynamic balancing, but should be plenty good enough for these China engines.
Educate yourself thoroughly before attempting though!

Edit: I wish I could afford to have T&O build dynamically balanced, 4 5/8 stroked Torque Monster flywheels for my Shovelhead!
Click to expand...
I think maybe I could do something like this. I'm guessing the weight he adds to the rod weighs the same as the piston assembly? That's the only way that makes sense to me with a single.

Static crank balance - YouTube
 
GearNut

GearNut

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Re: China Girl Motor Build

No, the weight that he added to the small end of the connecting rod is still determined by using a formula. The exact equation I have written down somewhere in my library of books and notes.

Remember, when balancing a single pin crankshaft you can only balance it to reduce the vibration in a particular RPM range. Sometimes you can get it to the point where the RPM speed of serious vibration is well above the redline. You will never see it before the engine self destructs. This would be a perfectly balanced flywheel. (Read dynamically balanced.) Folks who are experts at static balancing can get it damm close to that too. I am not one of those people. I have done static balancing in school and on Hodaka dirt bikes. I was pleased with the new found smoothness, but that is also weighed in with the fact that is was a homemade balance job. I have never professionally balanced fl ywheels for a living. The shops I worked for always farmed out balancing jobs.
 
biknut

biknut

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Re: China Girl Motor Build

GearNut said:
No, the weight that he added to the small end of the connecting rod is still determined by using a formula. The exact equation I have written down somewhere in my library of books and notes.
Click to expand...
Looks like you're right. This is how he says he figured out how to balance it. I guess I'm going to have to figure it out too.

"Piston_motion_equations@wikipe*dia is a good site to see what I used as input to balance the crank. After taking the second derivative from the position equations for both x and y axis to get the acceleration, I used Matlab to simulate different crank weights to get the least vibration. But the main thing was that my crank was unevenly unbalanced as why I drilled 90 degrees from the top of the crank and not 180 degrees and as you can see it is pretty evenly unbalanced now."
 
biknut

biknut

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Re: China Girl Motor Build

What a surprise, Powroll called me back today and said they're willing to take a look at my crank. They say if I send them the crank and piston assembly with wrist pin, they'll see about trying to balance and true it.

I think I'll do that with at least one crank just to see what happens.
 
GearNut

GearNut

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Re: China Girl Motor Build

Don't leave out the wrist pin bearing! Every teeny little part involved in the assembly needs to be weighed. Leave out even a wrist pin clip during the balancing step and you will end up with the wrong measure of weight to do the balance factor equation.
 
biknut

biknut

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Re: China Girl Motor Build

GearNut said:
Don't leave out the wrist pin bearing! Every teeny little part involved in the assembly needs to be weighed. Leave out even a wrist pin clip during the balancing step and you will end up with the wrong measure of weight to do the balance factor equation.
Click to expand...
Yep they mentioned the clips and wrist pin bearing. The lady said a lot of the time when she gets asked about odd ball stuff like this the shop techs say forget it, but in this case she thought the fact that I said it's a for motor bicycle might have pict their interest. I told her there's thousands of them in this country and most of them need balancing lol. They haven't promised to do anything, but at least they're willing to take a look at it.
 
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