Ok, lets talk chains for a minute here...and not the fancy gold chains that Kelsow wore back in his 80's Disco phase. We're talking motorcycle chain here. Chain drives are something that we all must live with, but are often (in fact normally...) misunderstood. I apologize in advance for the length of this dissertation, but it's the only way I know to make it clear. If you suffer any attention deficit disorders, please feel free to stop and grab a coffee at any stage.
First thing to understand is how to adjust your chain. I'm not talking about the mechanics of loosening the axle and such, as if you haven't gotten that far yet, please stop reading now and go to your local bike shop for ALL service. How tight a chain should be is determined by the geometry of your given bike. When in doubt, READ THE MANUAL. Never mind what anyone else with a different bike is doing, as the geometry of theirs may be very different from your. What's right for one is not necessarily right for all. The owner's manual will give you the manufacturer's recommended tension for your model.
If you do not have a manual, or want to understand how they achieve this mysterious number, I'll briefly roll it out for you. As the suspension compresses the swingarm travels in an arc around the swingarm pivot at the frame. If our front sprocket was located precisely at this pivot all our tensioning issues would be easy, but it's not. As the swingarm travels through its path, the relationship in length between the center of the front sprocket and the rear axle (center of rear sprocket) varies. This means the chain is getting tighter and looser as the suspension travels through it's range. The position of the front sprocket in relation to the swingarm pivot is the key here and what will make one bike's ideal tension different from others.
To accurately measure correct tension, you need to remove the shock and move the swingarm through its range seeking the point of greatest tension in the chain. At this point there should be about 1/2-3/8" of slack in the chain from center (center being a straight edge running from the front to rear sprocket).
Now that we've adjusted the chain, how do we know when it's worn out? Well, there's lots of backyard methods...pulling chain off rear sprocket, removing it and looking for how much bend you can put on it sideways, etc. Well, I'm here to tell you the right way to do it and the only truly accurate way to tell.
Chains are made to a specific pitch (that's the 520 part of the chain size). What is critical is the distance from pin to pin. Contrary to popular opinion, chains do not stretch. They can potentially, but no dirtbike is going to be capable of stretching that steel link...even KLRs. What really happens is the pin wears against the bushing it ride on, this makes the chain appear longer, as the pin to pin distance increases with this wear. As this wear occurs and the pitch changes accordingly, the loads on the sprocket teeth dramatically change. This is the hooking you will see on worn sprocket teeth. That wear (hooking) is because the chain has worn and no longer has the pitch to precisely match the sprocket teeth, so it start to wear it's own into the sprocket. A hooked sprocket is a sure sign your chain is dead. If you monitor it closely for the very first signs of sprocket wear, it can also tell you when it's time to change chains, before the sprocket is destroyed...and yes, you can change chains without changing sprockets, as long as you do it before the sprocket is worn out of pitch. Remember its pitch is what makes the difference.
So, with that little tidbit of knowledge, we measure the chain. Count out 10 pins, starting at zero (0, 1, 2...10). Now tension the chain. An easy way is to put the bike in gear and roll back on the tire. Measure the distance from the 0 pin to the 10 pin. Write it down. One a brand new 520 chain, that measurement will be 15.875mm Once your chain reaches a measurement of 161.925mm, or 2% over it's original length, it's time to get ready to buy a new one. The measurement should also be taken at several places in the chain to ensure consistency. If you carefully monitor this measurement through the life of your chain and sprockets you will find that your sprocket will likely rarely show wear and maybe reused responsible with the new chain. If you let it go too far, you'll be buying sprockets too.
Due to this critical pitch we just talked about, you can see why it's also very unwise to put a new chain on worn sprockets, as your forcing the chain to conform with the sprocket which will prematurely wear it out.
Ok, go get that coffee, juice or beer that you need to get through the rest of this...
Back now and refreshed? Now, let's talk about chains themselves. All are not created equal. There are two basic varieties, o-ring and non-o-ring. Each have their place. Remember how we said chains wear? The pin and bushing area. Well, on an o-ring chain, this is packed with grease and sealed in there with little tiny rubber o-rings. On a standard, non-ring chain, this is reliant on you lubricating it. Does this mean that o-ring chains are maintenance free? NO, they still need lubrication. Those little rings still need help, as to the rollers that actually contact the sprocket.
For an MX application where a chain is run for short periods before it can be re-lubricated, non-ring chains make a lot of sense. For Dual sporting and extended trail riding in muddy conditions (not that we ever have muddy conditions in NS) o-ring chains probably going to be more suitable.
Even within the o-ring group of chains there are many variances. The construction and materials in the chain makes a huge difference in the performance you will see from it. Does this mean to run out and buy the most expensive chain on the market? NO. Dirtbikes just do not generate that huge of forces on a chain, due to their relative light weight (KLRs excluded) and relatively low power output. Ah, so we only need to buy cheap chains? NO, again. Cheap chains will use lower quality materials in the pin and bushing areas as well as ring quality. You will not get nearly as good a service life out of a $89 o-ring chain, as you will from a say, $140 o-ring chain. You could spend $200 on a fancy o-ring chain but not see any improvement in performance over the middle of the road $140 one but it will probably come with a nice sticker, if some kid at the dealership didn't steal it out of the box.
Next, chain maintenance...just as you Mom used to tell you, cleanliness is next to Godliness. Chain lube, as we are all aware is a sticky, messy nightmare. Take the time, when washing your bike, to wash the chain and sprockets carefully. Use a stiff nylon brush with nice soapy water, or Simple Green or the like. Scrub it lovingly oops, sorry, wrong article. Anyways, scrub it clean so there is no accumulation of that gunk on there. Consider this gunk to be what it is, grinding paste. It's a whole bunch of grit and dirt caught up in that sticky chain lube and will wear the heck out of everything it touches.
Now the chain and your bike are nice and clean. Now, immediately after washing, dry that chain with a rag or paper towel, or even compressed air if you're fortunate enough to have access. It's now time to lube the chain. Here, quality, not quantity is the key. Spray the chain lube of your choice at the area between the links (remember those little o-rings?). Some will also be directed down the link to the rollers in the process. It is preferable to put the lube on the sprocket side of the chain, as opposed to the outer diameter, as the centrifugal force will force the lube deeper into the chain, as opposed to away from the chain.
After you thoroughly lube the chain, give the rear wheel a few good hard spins to use that centrifugal force to your favour and more evenly distribute lube. Now, take that rag, and wipe off the excess lube from the chain. Yes, that's right, wipe it off! Remember the points you're trying to lube are out of sight, inside the chain. All that stuff on the outside is nothing more than a dirt magnet and doesn't do your chain any good. You're now ready to tuck the bike in for the night and get yourself a beverage of your choice and relax.
The cleaning and maintenance takes a few moments to do, but will save you money period. Being a cheapskate myself, it pays far more than it costs (and certainly more than you saved with the cheap chain).