What replacement chain/sprockets should I consider?
Any O/X/W-ring chain should give you 25-30,000 miles of use with proper care. Those same chains should give you 10-13,000 miles with only the most minimal care possible, that being adjusting it from time to time when it gets so loose as to slap the swingarm.
A non-o-ring chain is old-tech for street riders. Don't consider getting one. The o-rings seal lubricant in the chain where it is most needed. The o-ring chain makes life easy for a motorcycle rider compared to the constant lubing and adjusting required for a non-o-ring chain.
Most chains used in industrial applications are non-o-ring but they (are supposed to) receive lots of lube, which is very messy, much more than you want to have on a motorcycle.
RK chains are recommended by experienced board members. A lot of people like DID chains, but RKs are usually cheaper and last every bit as long. In fact, many people have found that RKs last longer than DIDs. EK (makers of the OEM chain) is also recommended by some. However, there are always dissenters. A couple of our admins really like DID chains.
RK has phased out their standard O-ring chain, the SO. The newer mainstay in their lineup is the XSO. This uses an X shaped O-ring. Their more expensive, high-speed GXW is unnecessary for the Ninja 250.
The theory behind X-ring chains, as opposed to O-ring ones, is that the X ring has 2 sealing surfaces for retaining the factory lube. This is vs. just one sealing surface on O rings. This supposedly allows for longer life by retaining more lube for a longer period of time. That's seriously the only difference.
One of our tight-fisted administrators has a good idea. He buys stock chains off of low-mileage crashed bikes (salvage yards, eBay). Of course, you'll have to drop your swingarm to install it, as it won't have a master link, but the swingarm isn't that hard to remove, and should be done every 6000 miles, anyway.
Go to the chain replacement article for more information on master links and what you are going to need to install your chain.
Make sure your new chain comes with a riveting master link, as opposed to the kind that just clips on. Check with your retailer if it's unclear what is included with your chain. Clip-type master links are not recommended. This is what a clip master link looks like. Remember, this is what you don't want.
Note that, as of August 2008, the RK website had its XSO chain listed as coming with a clip master link. We have been assured by the US distributor that this is incorrect, and that the XSO is supplied with a riveting link. Make sure before you buy.
The clip-on master link on this bike, with only about 250 miles on it, came off when the rider was going in the high 80s (mph). It was just his lucky day that the chain only hit metal, and that he managed to get the bike stopped without any further disaster occurring. In addition to the visible damage, the chain put several holes through the rear tail, the wheel is now about 2" off center, and the dog bones are bent.
Buying a chain
If you're shopping online, search high; search low. There can be a difference of $20-30 from one site to another on the same chain. Check with your local dealer and eBay, too.
DID O-ring chains may still be available and aren't too expensive. Their X-rings, on the other hand, are not what you would call affordable.
Some companies sell kits that have a chain and both sprockets all in one package. You might be able to find one for the EX250, but don't hold your breath. And you can't use an EX500 kit, either. The chain is too short. You'll most likely have to source them separately. And it'll be a good day for you, too, if you can find one vendor who has both the chain and sprockets that you want.
The best way to find a chain on the net is to be very specific at first, then get more general. You can look at your favorite store first if you want, but then Google, say, RK XSO and see what happens. This might save you some time. You'll need it when you start looking for sprockets.
You need a 520-106 chain. 106 is the number of links you need. The chain size is 520. What the zero means is an ancient British secret and doesn't matter. The other two numbers represent link size, in eighths of an inch. The "5" is the length of a link from pin to pin (5/8"), and the "2" is the width of the link (2/8, or, if you were there in third grade when they taught you how to reduce fractions, 1/4").
If you have an EX250H (ZZR250), you need a 520-108.
Generally speaking, it's an exceptionally good idea to replace both sprockets along with a new chain. Not doing so will promote advanced chain wear. This is even more true when you have a completely shot chain that's being replaced. Some people replace the rear sprocket every 2 chains, but you'll be better off just spending the dough and changing it.
On a worn sprocket the teeth get thin and hooked, kinda looking like the dorsal fin on a shark, or the teeth on a saw blade. When that happens, the sprocket is SHOT and will kill any new chain in short order (a couple thousand miles).
It's strongly recommended that you stay away from aluminum (a.k.a. alloy) sprockets (yes, even the hardened/anodized sprockets) as they wear quickly and take out the chain when they go. There's a tiny amount of weight savings that maybe a racer could use, but it's not useful on the street.
There are many choices when it comes to sprockets. Those most used by board members are JT and AFAM. Both are of good quality and will last the life of your chain. AFAM gets a better nod on quality, but JTs aren't nearly as expensive.
Here's a list of the manufacturers that make sprockets that fit the Ninja 250, from least to most expensive:
Sprockets Hints & Tips
Finding sprockets online
Finding a front sprocket from any of the brands listed above is pretty simple. Getting a steel rear one is getting harder, as many people have jumped on the aluminum bandwagon. JT and Sunstar are readily available, so it's not too bad. Just be forewarned that many of the stores that come up on a Google search have websites that are hard to use. The bigger, more well-known sites are usually easier to navigate. What really helps is having the part number, and some patience. Do either a part number search or a search-by-bike.
By the time you factor in shipping, your local shop might not seem so expensive. They'll have to order them, too, but it shouldn't take too long, and there's no freight charge. Check the manufacturer's online dealer locator to find a dealer near you. It doesn't have to be a Kawasaki dealer.
Kawasaki sells only stock sprocket sizes. If you want different gearing, you'll have to buy aftermarket.
Sprocket Part Numbers
A Great Big Hint: For REAR sprockets, EX500 and EX250 have the same part numbers. So, if you can't find what you're looking for listed under EX250, try EX500. It will bolt right up. Not applicable to front sprockets or chains.
Note: For any of these part numbers, XX means the number of teeth you want.
Front: JTF 516.xx