I've been going through a few maintenance items on my 95 XT225 I bought a few weeks ago. Last weekend I uncovered the upper cam sprocket to take a look at the timing chain and sprocket condition. The metal parts looked fine, but the plastic (hardened rubber?) material bonded to the sprocket had started cracking and chipping off. Since this debris would potentially cause problems circulating around the engine, I obviously wanted to replace the sprocket. This job is pretty simple, but since the bike has 7200 miles (fairly hard miles I think), and I don't know any history, I thought it would be a good time to also replace the cam/timing chain.
This process is pretty straight-forward, and I had a little while last night to take care of it. I decided to try and document the process since I know that step-by-step procedures with pictures can be really helpful. Some of my pictures are a little blurry since they were just one-handed snap shots, so sorry about that. Also, realize this just happened to be the method I used and I'm sure it could be improved, so please use your own judgment. As with any maintenance work there's always some risk involved, so proceed with caution.
Disclaimers notwithstanding, the entire process from laying the bike over to standing it back up was right at one hour (including taking pictures), so I did not find this to be a difficult job.
Starting out I decided to lay the bike over as far as possible to avoid draining the oil and also to ease access. I laid it over on a padded shop stool, but obviously lots of things would work as a support. Put the bike in neutral.
Remove skid plate (10mm bolt).
Crankcase cover bolts are phillips-head, and are pretty soft. Someone has already had this cover off in the past, and as usual they weren't really careful with the bolts. You could use a JIS-standard screwdriver, but I used a decent quality #3 phillips (pretty fat head) which fit tight in the slots. I used a crescent wrench here also so I could concentrate more on down force rather than turning. The horizontal position of the bike helps here too.
If you are new to this type of work, one tip is to bear down hard and turn slightly clockwise first if it won't immediately break loose. Usually phillips-head screws/bolts are worn more in the counter-clockwise direction, so twisting clockwise first will often break the bolt loose, and then you can proceed with the normal counter-clockwise removal. On tight bolts you might have to alternate right, left, right, etc. until you hear the bolt break loose. Whatever you do, don't use a small screwdriver or let the head slip and round off the slots. If all else fails, you might have to use a set of vice grips to grab the head of the bolt or even use a screw extractor (Easy Out, etc.).
Crankcase cover is not too pretty; maybe I'll repaint it some day. Anyway, remove the sprocket cover. No big deal here, just two screws.
Tap gently around the cover using a soft mallet or similar. The screwdriver handle works fine too. Go easy on this since the stator is housed inside. I left the bolts in place during removal, but it might be less cumbersome to pull them all out. Be aware that the lengths are not all the same, so mark or arrange them so they go back in the same holes.
Very gently start pulling the cover straight toward you. You'll have to wiggle it a little to get it moving, and there's a magnetic resistance from the rotor inside. The only thing tricky here is the thin paper gasket. The shop manual will say to replace this, but you might be able to re-use it if you are careful. It would be best though to order a new gasket when buying the sprocket and chain. Gently still, lay it to the side and avoid stressing the stator wires. It can rest in this position for the rest of the job.
If you have an impact wrench, removing the rotor bolt is trivial (standard counter-clockwise threads). Bolt head size is 17mm. If you don't have an impact driver, use a 3/8 or 1/2 inch ratchet with a 17mm deep-well socket, hold it straight down tight with one hand so the socket will not slip off the bolt head, and tap the end of the ratchet several times with a rubber mallet. The compression of the engine will resist well enough that the bolt should break loose after a few hits. This is all the impact wrench is doing, but it will take a little more time.
I didn't need to use this approach, but there's an alternate method if it's really tight. Notice the flat shoulders on the rotor shaft. Use an open-end wrench on the shaft (not sure of the exact size, but would guess something like 22 or 24mm) to hold it in place while loosening with the ratchet.
Should look like this now. The bolt is out but the rotor is still tight on the crankshaft. Notice that the rotor has two sets of threads, one for the bolt itself and a larger diameter threaded area in the top portion. I believe an M16 bolt X 1.5 thread pitch will fit here, and I thought I could scrounge one up, but I couldn't find anything handy to fit.
I then remembered my handy Harbor Freight "Heavy Duty Chain Breaker" (item number 66488) I used a couple of weeks ago when replacing my drive chain.
Perfect fit in the rotor.
When tightened, the bottom of the tool pushes against the crankshaft and the rotor is pulled loose. Again using the impact wrench. If using a ratchet, tapping in a clockwise direction should also work. Alternatively, like the bolt in the above step, if it's really tight you can use an open-end wrench to hold it in place while tightening with the ratchet.
Avoid the temptation to hit the rotor since the magnets will likely be damaged and cost around $200 to replace.
Rotor removed with bolt/chain breaker tool still attached.
Take care when removing the rotor since it has three bearings and springs which like to fall out. The springs fit in a small hole and have a metal cap which keep pressure on the bearings. Pay attention to these since there's nothing other than very slight friction retaining them. If they fall out, just carefully locate the hole where the spring goes, fit on the cap, and then fit the bearing back in place. We'll talk about these again in a few minutes (during reassembly).
No tools here. Just lift out the small starter gear along with the spacer on top.
Woodruff key on the crankshaft needs to be removed to get the larger idler gear out. This is easy since the gear is loose and can be used to tap out the key.
Key removed. Gear will lift out now.
Finally a look at the lower sprocket and chain.
Remove timing cover plate. This could have been done as step one, but it doesn't really matter. 8mm socket on 1/4 inch drive ratchet.
Cover off and top sprocket exposed.
Impact wrench again (same 17mm socket). Using a ratchet, use the same method as above for the rotor.
I put off the chain tensioner until the last step since I didn't want the chain moving around too much. This is easy to remove with an allen wrench (I don't remember the size, probably 5 or 6mm). Since it has an internal spring to keep tension on the chain, hold the tensioner in place with one hand and remove the two loosened bolts with your other hand. If you don't relieve the spring tension by holding it in place, you'll need to use the allen wrench to back the bolts all the way out which will take forever, especially since the carb is kind of in the way. You'll see when you get to this point it's no big deal to get it off (back on is only slightly harder).
The upper sprocket will slip right off now since there's little chain tension. However, FROM THIS POINT FORWARD DON'T ROTATE THE ENGINE (CRANKSHAFT OR CAM SHAFT). IF THE BIKE'S STILL IN GEAR, DON'T LET THE REAR WHEEL ROTATE. Since the starter gear is disconnected, there's no real danger if the rear wheel is stationary or if the transmission is in neutral. If either the camshaft or crankshaft rotates for any reason, the timing will be off which will likely result in bent valves. Fixing this situation is not difficult, but you'll need to rotate the engine to perfect TDC and align the top sprocket with it's TDC timing marks.
Cam chain will fall out now. This is the last stage of disassembly, and reassembly is just the opposite procedure. This is a good time however to inspect everything (including the chain tensioner guides I've circled below).
After comparing your old chain to the new one (to ensure the same size, etc.), feed the new chain from the top.
Route chain around bottom sprocket.
While keeping tension on the chain, mesh the new sprocket into the chain while paying attention to the notch which fits around the small pin on the cam shaft. You might need to re-align the sprocket in the chain a couple of times until the notch fits perfectly around the pin. Again, don't rotate the camshaft or crankshaft and don't force anything. The sprocket should fit in place with moderate tension on the chain (to take up the slack).
Thread the bolt in by hand, but I would suggest not tightening it at this point to avoid rotating the engine. Since the chain is not tensioned yet, it could still slip a tooth on the lower sprocket especially.
Remove the 10mm bolt on the end of the tensioner (this bolt is really just a dust cover). You'll need a small flat-headed screwdriver to turn the adjuster inside the tensioner.
As you tighten the screw, you'll be able to push in on the shaft at the other end. When you release the screw, it'll pop back to it's original position. So the trick here is to tighten it and compress the shaft while you install the tensioner. This is really not difficult, and you'll see how it works if you experiment with it.
The easiest way to install it is to slip in the tensioner and then fit the screwdriver as shown so you can turn it and hold it in place while running down the allen bolts. I couldn't picture that part too well since it requires two hands, but you'll get the idea.
Bolts tightened and 10mm cap bolt reinstalled. After you have it in place, verify that the chain is tight.
Now tighten down the top sprocket. No problem rotating the engine now since everything is back in place.
Reinstall big idler gear.
Don't forget the woodruff key. Just tap it in gently.
Reinstall small idler gear and spacer (on top).
Rotor back in place (align it's slot with the woodruff key). The only tricky part here is just keeping the three springs, caps, and bearing sets in place. Again the more-or-less horizontal position of the engine helps, but they still like to slide out onto the floor. It worked for me to flip the rotor over quickly and keep it as horizontal as possible while fitting it over the crankshaft. If a bearing happens to fall out, you'll probably hear it since they are fairly heavy. If that happens, just flip it back over, reassemble the part, and try again.
Before you install the bolt, make sure everything looks right. The bearings are pretty fat so it should be obvious if one happens to slip out of place prevent the rotor from dropping onto the shaft. Tighten the bolt as usual. I'm not sure of the torque, but since this is all high-carbon steel there won't be any danger of stripping threads. Since the engine will want to turn anyway, just tighten it as much as you can using the same tools used during dis-assembly. I left my compressor at around 60 psi and didn't go crazy with the impact.
Finally, I used a 17mm wrench to just do a final check, rotating back and forth a little and checking for any resistance, binding, etc.
The remaining pictures ended up looking just like the first few, so refer to those if needed. If you are installing a new gasket, that would be the next step followed by the reinstalling the covers.
That's about it I think. Start the bike and make sure everything sounds right. Should be good for another 10K miles.