Hay,jus replaced my front sprocke n rear sprocket n chain,put all bak n2gether n it wont change gears,theres a littke shaft thing which i think has slipped out,any ideas?thanks

did you turn the locks on the wheels, or check the fuses

This could be a few things:
1) Your clutch plates may have worn out so that even when the bike is in gear, it will just rev, but no power will be transmitted to the drive shaft (smaller front chain sprocket is the driving gear, larger rear sprocket on the back wheel is the driven gear)
2) The front chain drive sprocket has come off under the cover on the motor - if the chain is really slack, have a look.
3) The front chain drive sprocket SHAFT has sheared. (basically, meaning that the shaft has broken into two parts as it couldn't handle the drive power (torque) being delivered through it to the chain drive) With the motor on, listen for grinding noises internally
when you rev, from the vicinity of the front chain drive cover. If its rough and grindy, the shaft may be sheared. Then with the motor off, take the cover off and leverage the small chain drive sprocket away from the motor with a screwdriver, and see if the shaft can just be pulled out of its sealed opening. Unfortunately with these bikes, the metals used in drive shafts and motors are not always heat-treated or hardened to the standard they should be, so shearing and premature failure can happen.
4) The gearbox or something in it has blown, unfortunately for the same reason above, quality related.
Its fair to say that these great little bikes are here for a good time, but not for a long time.

Remove the gearbox sprocket cover, this may mean undoing the gear lever, First put the bike in gear. This will lock the sprocket so you can undo the securing nut, you will also need to loosen the rear axle to allow the chain to be taken off the sprocket. Then remove the sprocket, refit is the same process in reverse. I would suggest you change the complete set (front & rear sprockets and the chain) that way you only have to take it to bits once. And it will also mean the chain lasts longer as the wear will be the same at both ends.

You can add teeth to the front sprocket or take teeth off of the rear sprocket. In the case of your bike , I do not think there is a 17 tooth front available so your best option would be to shorten your chain and drop from the 44 tooth rear sprocket to 40 tooth or a 36 tooth rear sprocket. That would be like adding one or two teeth to the front sprocket. Your stock is 16/44 so decrease from there. Be sure to ID your chain, get a chain breaker, and a new master link.

Wait until you get new chain and sprockets to do it.

OK, for a beginner in the world of 18 speed bikes, put the chain on the big sprocket up front, it should be about 46 teeth, make sure it is center and doesn't make noise, if it does, adjust it just a hair either way, now, the rear, put the chain on the big sprocket in the rear, make sure the front didn't start making noise, if it did, adjust it again. You are now ready to take off, in low gear, as you start out, it is easy to pedal, soon you will be peddling air, shift into second gear in the rear only, don't touch the front. Just a little push with the thumb will make it shift, now were going faster, easy peddling, shift into 3rd, then 4th, etc, coming to a stop, down shift the back sprocket back into low gear (big sprocket) and be ready to take off again. Soon you will be shifting that thing like a Ferrari! The front sprocket, will be used for moderate terrain, wheelies, and mountain climbing, that will come later, learn how to shift the rear first. As each gear climaxes, hit the shifter, it will get smoother as you go, and keep the chain quiet, no climbing on the next sprocket or falling out of gear. Hope this helps.

I'm assuming you bought a mountain type thing with 12 -18 gears on it, It is easy enough to shift it, as long as it is it working right, They should have set the stops on both shifters front and rear for you. They might be a little off, but when in low gear rear, your chain should not go over the limit and fall into the spokes. Like wise in high gear, should not fall off the cluster in high. The front is the same, the chain should stop at the sprockets smoothly, and not crunch into gear. My bike shifts like a car, 1,2,3,etc. Your front sprockets, unless you are mountain climbing, leave it on the big sprocket, about 46 teeth, and get used to running that high gear up front, now the rear sprocket, you start off in low, biggest one, and move your shifter while you are peddling, 2nd, then 3rd, and when you come to a light or have to stop, downshift to low again in the rear and you'll be ready to take right off. There are a lot of people out there who don't know how to shift these things and they leave them in one gear and pedal air. Hope this helps.

Usually, it seems that changing the front sprocket is more cost effective and easier to do. The front sprockets are about $10-$20 and rears are normally around $40-$50. Usually 1T gearing changes made to the front sprocket are the equivilant of a 3T-4T gearing change to the rear. I personally would go up on the front instead of down on the rear. Right now your gear ratio is 3.846 (meaning every 3.846 rotations of the front sprocket, the rear sprocket makes 1 rotation) If you go down 2T in the rear (13/48) your gear ratio would be 3.692 giving you a little less torque and a little more top end. If you go Up 1T in the front (14/50) your gear ratio would be 3.571. This would be about the equivilant of a 46.5T rear sprocket. (If they made it) The nice thing about doing the front sprocket first is the cost. If you decide it's too much difference and you want something in between, you can put the stock 13 back on and then change the rear (and you would only be out the $$ for the front sprocket) If you start with the rear and decide it's not enough then you change the front you're out the $$ for the rear.

This one's a little tricky cause it could be a few things.
I'll try suggestions in the order of probability

• Worn out chain & sprockets.(Or chain too tight or has a tight spot) Check this by raising the rear wheel off the ground,in neutral & spin the back wheel. If the chain & or sprockets are worn you'll feel it & hear it when you spin the wheel. If it has a tight spot,set the chain tension at the tight spot & lubricate well
• Loose engine mounting bolts. If loose re- tighten.
• Worn front sprocket shaft bearing. to check this(if chain seems ok) Remove the chain(note joining link direction of the circlip. The closed end faces the direction of rotation)Bike in neutral, turn the sprocket shaft by hand. It should turn smoothly.If it is notchy thats not good. It is a major job to change & can be expensive(So i hope its the chain &/or sprockets)
• Broken tooth on a gear in the gearbox. I hope not as again a more difficult & expensive repair.

Hope this helps you narrow down your problem
Regards Andrew Porrelli

hi there,

put your bicyles on upside down position,wheel should on top so you can work freelywork on ,then rotate the pedal to check what the problem it should be freely rotating,check break pads if it was engage even w/o pressing control.release brake cable wire to loosen.if not in the break,check the sprocket gear if connecting to the chain belt,check your sprocket release lock,if damage replace sprocket, check the bearing of the two wheel center shafting if worn out replace bearing,on front wheel there are two quick release nuts,loosen and pull out wheel and loosen all nuts and lock plate bearing,pull out shafting with the bearing,examine mostly bearing worn out also shafting in some occasion its worn out also,possible if you want replace one set center shafting and bearing ts not costly,on rear wheel with sprocket it different to disconnect,beacause there is sprocket,you should dismantle the locked plate and lock nuts of sprocket before the shafting assymble same procedure now on front wheel when after disconnecting sprocket on rear wheel.hope this will guide you and solved your problem have anice day.