Hi gang,

A friend has a small Chinese bike. He recently found that his front drive sprocket was about to fall off and did not know what to do. I drafted a response for him. I thought it may be useful to post here in case someone else had a similar problem. Note: I have been kind enough to sanitize my respone of <u>most</u> of my "Chinese engineering" editorial comments. :-)

We have one small Chinese bike like you describe. My 7-year old "baby girl" rides it. For the price you can't beat them, especially since the kids grow out of them quickly. However, the engineering (and manufacturing) are not up to U.S., Japanese, or European standards.

Almost all of these small Chinese bikes use the same parts and design patterns regardless of how they were marketed (i.e. Kazuma, Meerkat, Falcon, Yamoto, etc.)

The part you pictured in your email is called the drive sprocket. The drive sprocket on our bike wobbles a bit. It is not perfectly solid on the shaft like you would expect (and like it should be!) Most good designs use a "collar" device that locks onto the shaft in a solid manner such as a set screw or bolt in the end of the shaft.

Anyway, here is the tech story on your bike.... You can see a diagram at this address: (See diagram below) I pulled it off the Internet at the following European site. http://stores.channeladvisor.c...nsmission%20Mechanism


The home page is http://www.petrolscooter.co.uk/ This site has parts schematics for Chinese bikes... very helpful.

The splines on the shaft only go so far back toward the oil seal in the engine casing. As a result, the drive sprocket can only slide onto the shaft (toward the engine) so far. (i.e. it must stop where the splines stop). This is the mechanical construct for keeping the drive sprocket from moving toward the engine.

So you slide the drive sprocket onto the shaft as far as it will go. The "trick" to keeping the drive sprocket from sliding off the outer end of the shaft is something called a "fixing plate". It slides just over the outer end of the shaft. You will notice that the shaft has a groove or split all the way around near the end of the shaft. You then turn the fixing plate in the groove so that the "teeth" on the inside of the fixing plate are counter to the splines on the very end of the shaft. It simply "rides in that groove. You then run the bolts through the holes in the fixing plate... screwing them into the threaded holes in the drive sprocket. Because the drive sprocket has teeth (splines) on the the inside, it cannot rotate or slip around the shaft when the shaft turns. Since the fixing plate is bolted to the drive sprocket, it will not slip around the shaft either. As a result, the teeth (splines) on the inside of the Fixing Plate remain counter to the outermost splines on the shaft. Presto! The sprocket cannot slide off the outer end of the shaft.

So at the end of the day... the fixing plate acts much like a traditional spring steel retaining clip that rides in the groove of a shaft. If you think about this design or actually see it in action, you will realize that you simply have a Drive Sprocket sandwiched between the stopping point of the shaft splines (on the inside) and a Fixing Plate (i.e "retaining clip of sorts") on the outside. So... the Drive Sprocket sort of "floats" between these too stopping points. It is NOT fixed in a hard manner to the shaft like you would find in a design that uses a shaft collar or other more "solid" construct. The Drive Sprocket on my daughter's bike is sloppy! ... as the tolerances are relatively large. (i.e. it "wobbles") ...amazing it works at all.

I suspect that the bolts holding the Fixing Plate to the Drive Sprocket came out and you lost your Fixing Plate. (note: my friend confirmed that this is exactly what happened. The bolts and fixing plate are missing)

So... another note. It is well-documented that these Chinese bikes have a lot of problems with loose bolts. You need to check them often and do any reassembly with liberal amounts of Loctite (threadlocker). Believe me. I ignored this warning from several forums ...then began losing bolts on my daughter's bike.

Final note: Some of the smaller bikes ACTUALLY use a simple spring-steel retaining clip to hold the Drive Sprocket on the shaft. The schematics call it a "Spring Washer". If this "Spring Washer" pops off the shaft, you obviously have the same problem described above with a missing "Fixing Plate".

I hope this helps someone who may have a similar Drive Sprocket problem.