Vibration problem in 1st gear

[Richyryder]

Hi, I have a 150cc chinese-made, general-purpose street bike. It had some general vibration issues relating to the engine. I took it to the dealer and he tightened all the engine bolts. This didnt help so he replaced the drive sprocket with one that had 1 extra tooth. I dont know if he did anything else, but after that, the vibration issue was solved!

A short while later, I wanted to pop a wheelie so I put the bike into 1st gear, revved the engine, and popped the clutch. As I popped the clutch, I heard a stange noise from the engine area, and since then the bike has had a vibration issue. In 1st gear, when I accelerate at full throttle, there is a bad vibration when the revs get to about 7k (handle bars, seat, foot pegs and tank vibrate). This vibration gets weaker when the bike is in the higher gears.

I just had all the engine bolts tightened at the dealer and the problem is still present. I think it could have some thing to do with the drive sprocket. Any suggestions to help will be appreciated.

Richy

[katoranger]

I would check to make sure a mounting bolt has not broken first.

[Richyryder]

Thanks for the reply, but I just had the dealer check and tighten the engine mounting bolts.

[Richyryder]

I removed the sprocket cover to check the front sprocket. There is a small but noticable amount of play between it and the shaft (radial play as well as "wobble" play). The retaining bolts on the sprocket were both tight.

[Weldangrind]

That's by design. If the sprocket was solid mounted to the countershaft, it would probably break the chain or sprocket teeth.

[clippedwings]

It could be your chains slack hitting the sprocket cover. Sounds ridiculous I know but check the slack in your chain. If its been doing it long enoough you may even notice wear on the outside of the chain. I had this happen with one of my bikes where I actually had to grind away a bit of the sprocket cover for it to stop.