Am I missing a part here?

[Billeverhart]

I got this pit bike new for my son last Christmas. He rode it a couple of times and said the chain keeps coming off. So we tightened the chain. But now when we put weight on the bike the chain slips where it meets the motor. I'm wondering if there is a missing piece that the chain should go onto? Sorry I don't know all of the part names but I took pictures of it.

 

[Billeverhart]

If you look at the picture, the shaft that the chain is on turns but the chain doesn't not when there is weight on the bike

 

[AntNZ]

YES!!!, you are definitely missing an important part....The drive sprocket!!!, looks like you have already caused damage to the shaft but you might get away with it....

 

[Billeverhart]

The bike is a "RX1 Traxxis Mini Dirt Bike". Do you know what size sprocket I need to buy? Is the shaft a replaceable part if it's already too messed up? Also, do I need to buy something to hold the sprocket onto the shaft? This thing has only been ridden 3 times so I'm guessing the original one wasn't attached correctly.

 

[Billeverhart]

The bike is a "RX1 Traxxis Mini Dirt Bike". Do you know what size sprocket I need to buy? Is the shaft a replaceable part if it's already too messed up? Also, do I need to buy something to hold the sprocket onto the shaft? This thing has only been ridden 3 times so I'm guessing the original one wasn't attached correctly.

Here are the bike specs if that helps.



Engine: 40cc, 4-STROKE, ~10,000 RPM, Air Cooled
Fuel: 87+ Unleaded Gas (no oil mixing required)
Starter: Pull Starter
Maximum Speed: up to 45 MPH with Performance Parts
User Adjustable from 10-45 mph
Ignition: CDI, Ultra High Discharge Coil
Transmission: Centrifugal Automatic (transfer case / chain drive)
Maximum Power: 5.3 hp
Brakes: Front & Rear Cross-Drilled, Slotted Discs
Exhaust: Straight Pipe Exhaust, Mandrel Bent

Dimensions

Length: 43"
Width: 23"
Height: 28"
Ground Clearance: 7"
Dry Weight: 46 lbs.
Weight Capacity: 165 lbs, tested up to 250 lbs
Fuel Tank Capacity: 1.8 Liter (All Metal Gas Tank)
Cruising Range: 30 miles per tank
Tires: Pneumatic Knobby All-Terrain Tires

 

[AntNZ]

how many teeth does the rear sprocket have, prob somewhere between 30-40 teeth....
measure the diameter of the drive shaft to get the right front sprocket.
probably want 13 or 14 teeth on the front sprocket with a small engine like that, maybe even less, less teeth on front=more pickup less top speed, its up to you really, I dont really know what combo front and back works well with such a small engine....hope this helps.

 

[motodevo]

If you have a pit bike store locally, take it down they will find one that will fit and be able to judge how many teeth according to chain length, there are only 2 common shaft sizes used, there is a retaining washer that sits in the groove and bolts to the sprocket stopping the sprocket from falling off, might wanna loctite those bolts before the next ride. In saying that, the sprockets aren't tiny, if you know where he threw the chain the first time you should be able to find it, get yourself a new retaining washer and bolts and get going. The shaft is chewed but should be fine for what it has to do. I would suspect it wasnt installed correctly or the clip/washer wasn't there in the first place. Googling it, its an oddball of a minibike but luckily the chinese tend to use the same parts bin to build all their bikes so spares shouldnt be too hard to find.

 

[headsmess]

two or three options spring to mind...

you want a sprocket for either the honda c50 or a sachs madass, etc...just about any bike shop should have from 13t to 16t. stick to the small side for that bike pretty sure every china engine uses the same spline, based off the honda... think about $15.

oh. be careful of the width... try to make sure its for 420 chain... or you may be fitting a new chain as well...

z50, braap, certain yamahas, motovert...its fun finding out who lists the same sprockets! not...

or theres ebay...any generic "pit bike" sprocket will do. again...12-14t, no bigger.

or a local pitbike shop.

or a wrecker. could get messy when you mention pitbike

youre gunna need the retainer plate as well... it screws onto the sprocket and locks into that groove on the shaft... never had to buy one, no idea where to find it...

a circlip will work as well...any old mechanic should have a box of them...

could be lucky with a file or something and rescue the shaft... but it looks ugly...
and no, it isnt a replaceable part...
or it is, but its a challenging job. split the engine, dealing with springs and things that pop apart...

 

[motodevo]

If you look it up, the shaft i on these is easy to replace, its not like a regular pit bike motor, the pic he has taken of the shaft is from the other side of the bike to what you would think compared to a regular pit bike. It has a clutch hanging off the left side of the motor, with a chain(in a covered transfer case) driving the output shaft out behind the motor. You were right about the sprocket, it only has a circlip holding the sprocket on to the shaft

 

[motodevo]

From looking on the net, the 4 stroke uses the same part as the 2 stroke version, probably the easiest option , whatevet you do, I'd lock wire ends of the circlip before it gets ridden again at the very least. Never been a fan of those little 2 stroke bikes and it would seem the 4 stroke version is using most of the same parts. Not the best design, no wonder it came off so easily, not what you want to hear but I'd be going over everything working out what will break/fall off next