I know it’s June 15th and it’s going to be 80 degrees but I’m starting to get the itch to work on my sled.
The basics: 1999 ZR 500 efi w/ approx 4800 miles on it. The motor has never been rebuilt as far as I was told by the dealer.

I apologize in advance for all these questions but I can think of no where else where I can ask a group with as much knowledge as we’v got here! SWRules

Questions:
1. I’m sure with 4800 miles and it’s compression a little low it’s time to “freshen it up.” The problem is, I don’t know what “freshen up” means. A set of pistons and a gasket kit? I hear stock arctic cat pistons should be replaced at about 4k miles so I think that’s definitely overdue. I look up part numbers and I can order two pistons easy enough but what else is required? There are two gasket kits and do I need a writst pin/bearing of some sort? (I plan on ordering OEM pistons.)

2. If I am going to perform the rebuild above, I need a book. I’ve had no luck finding a 99’ specific book. Anyone have any idea where I can find instructions of some sort? (Don’t worry, I’ve rebuilt car engines before just never a high-strung 2 stroke.) Any special tools if there is no scoring of the cylinder walls? What is they are scratched? Get it honed somewhere? Do I need bigger pistons if it gets honed?

3. I’d assume I should remove the clutches and replace at least the springs which I’ve heard can become weak over time. What else is replaceable in there? (I’ve read a LOT about clutching and still don’t know much so I’m going to replace worn parts rather than try tuning right now unless anone has any easy setups for this sled!!)

4. In my reading I have seen many times that stock sleds are geared for worse case conditions to avoid overrev. Since We have no -20 degree conditions and no frozen lakes to race on, I figure I may benefit from regearing. I’ve seen some pretty complicated stuff on determining gearing and am curious if anyone has done this on a similar sled and to what effect?

5. What are some other things tha should be addressed on a sled of this age with this many miles? (They aren’t “highway miles” like you guys in Michigan or Canada.) I replaced the chaincase fluid with synthetic as soon as I bought it and did the same with the brake fluid. I also replaced a bunch of wheels/bearings in the rear skid that looked questionable. I think I can wait until next summer to rebuild the fox shocks. Anything else that should be addressed?

Well, you do have a lot of questions but maybe I can help.

Freshen up can mean different things to different people. To me a freshen up is Rings only. You will need a new Base Gasket and I always replace the upper O-rings. If you want to do a complete top end, buy Pistons, Rings, Wrist Pin and Wrist Pin Bearing and Gaskets.

Now to the Clutch. Pull it out and take the cover off of it. Be careful as you know it is spring loaded........

Check out the Rollers and the slop in the Weights. You will probably with out even looking at it need those parts.

The Secondary will probably require new Rollers in it.

Note how you take both of them apart. Mark the Covers as well as the main section with a sharpie so you can line them up again. They are balanced for a reason......

REBUILD YOUR SHOCKS!!!!!!!!!!!!!!!

Let us know what else you need to know, nothing you are talking about is Rocket Science, take your time and note what you do(or take pictures also).

Ryan

A fresh top end will require at least new pistons and rings and a resurface on the cylinders. The cylinders are nicasil plated so honing in the manner applied to cast iron bores is not permitted. When I say resurfacing the cylinder I am referring to the light use of a ball hone to put a fresh crosshatch on the cylinder walls. This does not increase the bore size and gives the proper surface for the new rings to seat against. Resurfacing is not the same thing as replating. If the nicasil plating is damaged, gouged, peeled then you can send the cylinder out for repair and replating.

I have rebuilt the top end in my 580 numerous times and have never found it necessary to replace the piston pin and pin bearings. Inspect them and determine if the wear is excessive. Replace as necessary. The base gasket and head o-rings can be reused if they are not damaged during disassembly. If the base gaskets are the metal type the factory service manual will tell you to use a little sealer on the gasket and reassemble, however, there is never a problem with buying new. A top end gasket kit will include all gaskets for the complete top end.

Play with your clutching before you worry about changing gearing. Stock gearing is usually good for most riding, but the clutching will be the biggest bang for your buck. Like the other guy said, rebuild your shocks. They should be done every year and in the spring is the best time to do them to minimize internal corrossion.

I can address the gearing issue. Your gearing determines your absolute top speed at your peak RPM when fully shifted out. Now if you gear to 100 MPH, that doesn't mean your engine has what it takes to get you there. So if you can only get to 80 on your sled but you are geared to 100, you are never fully shifting out and you're losing some effeciency in your clutching. You can overrev if you try to go faster than what you are geared to, like if you're geared to top out at 70 and you try to go 80: The clutch shifts all the way and then the engine start revving up higher until it passes the top of its power band and can't pull any harder.

There is a sweet gearing calculator here on SW under "Tech tools". Play with that to get a feel for it.

So with gearing, it depends on what kind of riding you are doing. If you are trying to go for max top speed then the stock gearing is probably the right choice, though as you said it may be still higher than ideal to keep people from overrevving easliy. It does become a tuning issue. Gearing for a lower top speed gives you better acceleration, especially the holeshot, and more climbing power, and the clutch is more effecient in it's operating range because it's got the same amount of clutch surface area but now it's dealing with a smaller total range of speeds. The drivetrain simply has to do less work when you gear to a lower top speed. It's easier on the belt since it takes less power to move you from a stop. Since I mostly ride mountain and am afraid to go over 70 on the lake, I have geared my Vmax to the lowest top speed configuration that the service manual specifies, about 77mph according to the calculator.

I have to agree that getting the clutching right is more important. The CVT clutch will make the gearing seem unimportant. However, once your clutch is dialed you should at least take a look at your gearing and use that calculator and see if it matches your riding style.

Thanks guys!

Is a ball hone of the cylinder walls something that has to be done by a shop or is this very light work something I can do with a proper tool/bit/attchment? I'm really excited to try to rebuild this thing myself, I just don't want to do something stupid and have to buy a new cylinder or something. Are there any special tools needed for removing anything on the top end? (I'm probably making this too complicated I know.) Anyone know where i can get a shop manual for a 99?

You guys are probably right. The dealer said the shocks were recently service (and I only got about 5-600 miles on last year) but I think that guy lied to me quite a few times anyway. No wonder they were out of business in less than a year. (A-holes still owe me a set of skis too.)

I think I'd like to experiment with gearing in the future but as you guys said, I think the clutch is where I should start.

The proper ball hone for your bore is probably not worth buying for one, or occasional use. You might be able to find the ball hone online at Brown's Leisure World, in the tools section. Some guys will do the crosshatch by hand with a scotchbrite pad, but I've always had my dealer do mine. It takes the tech a minute of two to do it and I buy all my other parts there, so they have never charged me for the resurfacing. You will need metric sockets and wrenches for the engine nuts and bolts, and a torque wrench, but that is about as special as it gets. A factroy service manual will take you through the process step-by-step, with pictures too, and give you all the torque specs. That is well worth the money.

Thanks, I'll take it to the dealer to have that part done. I'd hate to buy an expensive tool and then screw it up!

....and I have a torque wrench and a bunch of sockets so all I need to do is find the book and I'm good to go. I'm sure once I get all the parts together and start on this I'll have more questions. As usual, you guys are awesome!

With that many miles on it, seeing it's summer. I would replace all the bearings in the idlers for the track and drive train....

To me freshen up has always meant rings,,,, but you will get to see the pistons when you pull them. As for your hone, I picked up a hone at autozone (less than 20$) and use oil and my drill at low speed and have never had a problem with mine. If you do have bad scoring in your cylinder walls, you will need to have it renicked,,, lots of good companies out there than can take care of it, (millenium technologies is who I use). To me, 4800 mile on a sled with good oil, I wouldnt worry about the pistons unless they look bad,,, others feel that if your already that far and it isnt really expensive, just change them. I do know if your changing one piston, DO THEM BOTH. I also run stock pistons over the aftermarket ones,,, I know some disagree with that, but I have had pretty good luck taking care of them this way.

You will have to pull the pistons and make the decision yourself.