Adjusting rear tyre and chain tension

[Buddy]

Guys

Have just replaced the tube in the young fellas thumpa and have to put the rear tyre back on.
Is there any tricks to adjusting the line up of the rear tyre. It seems to be a bit tricky working out if it is sitting straight.
I have a two to three finger movement in the chain, but when he rides it now, the chain comes off every now and again.
Any info would be much appreciated.
Its a chinese import from ebusiness off ebay.

Regards

Buddy

 

[Mack]

Run a straight edge of some sort across the rear sprocket to the front sprocket. A large builders square is pretty good for this or one of those 1 metre steel rulers. Sounds like you may have mixed the spacers up on reassembly...

 

[Flarry]

On the swingarm above the chain adjusters there should be markings, each about half a centimetre apart, if not you can put some on. Line them up so each adjuster is in the same place and it will be straight.

 

[numroe]

Sorry flarry, but that'd be a big call to trust those axle markers on a china bike. They will line up in most cases, but Mack's suggestion is the quickest and easiest way to be really sure.

Buddy, with your chain slack, the problem is that the swing arm geometries differ a bit from bike to bike. Generally on these pitbikes the chain tightens considerably as the swing arm comes up to a more horizontal angle. Which (if you think your boy needs that travel) means your chain must look kinda loose when the swing arm is down/hanging. Which makes it all the more important that you line up your sprockets. Also be sure you put the correct axle/bearing spacers on each side, in case yours are not equal thickness left and right. If the chain still keeps coming off then try a new chain (get a real good one like an RK) which has less lateral slop. Plus you could also start to fiddle with your chain guide - as in put a new nylon guide in there or something.

 

[I_THUMP]

Yeah I wouldnt trust the swingarm markings either (which his bike wouldnt have) coz iv seen china bikes where the motor wasnt straight so that threw out the swinger alignment with the wheel and so on.