For the first time since 1992, I began riding something other than a Honda XR600R - an XR650R, to be exact. So, while a lot of what I have learned about XR600s is still fresh in my mind, I'll pass some of it along. I've owned three of them, and I've come to a few conclusions. From my own personal experiences and from that of others, the Honda XR600 has at least three very predictable wear problems. I'm referring to wear problems that go beyond the usual replacement items, such as chains, brakes and tires.
The first problem usually occurs with the rear hub bearings, which in most cases develops at 6-8,000 off-road miles. You can tell if the bearings are bad by simply grabbing the rear wheel with both hands and applying back and forth pressure to see if there is play. If there is any play, replace the bearings immediately. If they go out on you while you're riding the bike, you'll probably destroy the entire hub assembly, which would be costly. The replacement bearings can be found at almost any auto supply house and will probably last longer than the stock Honda ones. It's not a big problem if you keep and eye on it. You should replace the front hub bearings at the same time. They won't be bad yet, but you can bet they will wear like the rear ones. It just takes a little longer.
The second problem is with the timing-chain tensioner. This is an internal engine mechanism that keeps the timing chain taught. You can tell if it is going out if you hear a clicking noise coming from your engine. It usually occurs at 10-12,000 off-road miles, and will continuously get worse the longer you let it go. Obviously, there are other reasons you can have clicking noises in your engine, but a worn timing-chain tensioner is a very common problem at that mileage. It's not an extremely critical thing to worry about at first, but don't wait too long. The more your timing chain slaps around, the more it will stretch and the more the repair cost. Most shops can do the repair in a few days, and it is covered by an extended warranty plan if you have it, but you'll have to take it to a certified Honda dealer for the repairs.
The last problem is the biggest. It's the most expensive, and if you don't have an extended warranty, you're in real trouble. It's the XR600's third gear. It usually starts going out at about 15-18,000 off-road miles. Many hard-riding racers will tell you even sooner. You'll know its starting to go when you hear the transmission howl when you're in third gear. It's not critical that you have it repaired right away, but again, it's only going to get worse if you let it go.
So, without getting too technical about all this, these three problem areas are something you should look for when purchasing a used XR600, or when you think of selling your bike. This information can give you a way to tell just how much a bike has been ridden. If you're looking to buy a used one, check for ovalling or gouges in the rear hub bearing's outer threaded pressure plate. If it is unmarked and the bearing is solid, chances are the bike has less than 8,000 miles on it. If it is an older bike and you can tell the bearings have be replaced, make sure you ride it and listen to the engine. If you hear that clicking noise, you know it's been ridden at least 10-12,000 miles, and not "just a few times," like the ad probably said. If the third gear is singing to you, it has either been ridden a whole lot, or raced.
If you would like some more information about other ways to tell what kind of condition a bike is in, just give your local motorcycle shop a call. From my experience, they all have knowledgeable people working for them, who would be glad to help you out.