China Girl Chain Sprocket

Discussion in 'Frame Mounted Engines' started by Tyler6357, Sep 4, 2012.

  1. Tyler6357

    Tyler6357 Member

    Hey everyone!

    I got a new 2 stroke china girl but when I mounted it to the frame it didn't quite line up with the rear wheel sprocket as well as the old one did and the large stock chain that came with the kit was hitting the rear tire. I should say that the frame is an old classic 80s mountain bike frame. I have very few options for remounting the engine and still clear the pedals so I decided to replace the large stock chain with a smaller but very strong BMX 1/8-1/2 chain (breaking load of 12,500 Newton). After I got the chain I realized that the chain sprocket that came on my new engine was too fat to fit the chain. The chain links wouldn't fit into the gear teeth because the metal was forged too thick (wide). I took the sprocket off the engine and compared it to the one on my old engine and discovered that the one from my old engine was forged much thinner and the new chain runs smoothly through it with no problems. I decided to install the old sprocket on the new engine and use the new chain to clear the tire. Simple enough? Not so fast! The sprocket is held to the drive shaft with a small piece of half moon shaped medal that fits in the slot on the sprocket as well as the slot on the drive shaft. I found that this piece of medal was much thicker on my new engine and it was too large to fit the slot on the older sprocket so I decided to replace the new half moon shaped piece of medal with the one from my old engine as well. Of course, it fits the slot on the sprocket perfectly but when sits in the slot on the drive shaft it is not very snug. I screwed the nuts back on to secure the sprocket to the engine and installed the new chain. Everything seems to to running fine. I mean, the chain is very smooth in its rotation and clears the tire fine. The chain sprocket on the motor seems to turn fine with a load on it while riding. The engine seems to run ok (I'm still breaking it in). But my question is: could that loose fitting half moon shaped piece of metal become a problem? How important is it that it fit totally snug in the slot on the drive shaft? Should I take it apart again and grind down the larger piece of metal that came with my new engine to fit my old sprocket or is that not really necessary?

    I should also say that I am very happy with the smaller chain. It creates a much smoother chain rotation through the engine as well as the chain tensioner. I don't want to go back to the large chain if I can help it.