1999 Arctic Cat ZL 500 Rebuild

Start by finding out why the motor failed in the first place
1999 Arctic Cat ZL 500 EFI snowmobile rebuild
Q: I have a 1999 ZL 500 EFI with around 5,300 miles that I burnt the PTO side cylinder down on over the weekend. I am looking for some advice on standard/best practice as I go about the rebuild. I pulled the head last night and this is what I know so far:
  • It appears to have melted down due to a lean burn on the PTO side. I noticed it was down on power when riding, and upon shutting it down, the spark plug and top of the piston were white. Also, when I pulled the head, it looks like the piston had a hot spot that melted right near the intake port closest to the throttle body.
  • It appears that a ring was broken and debris from it got slammed around in the combustion chamber for a bit.  Definitely will need a new cylinder as it is pretty badly scored. Also will need a new piston and head.
  • Mag side cylinder looks good. I have yet to check the crosshatch closely, but everything was clean with no noticeable (to the eye or to feel) grooves or major wear.
I have rebuilt several old snowmobile engines and other small engines, but have never dealt with EFI or coated pistons. Here are my questions as far as proper procedure from here:
  1. Can I just replace the bad cylinder with a remanufactured/replated one, or should I replace both so that they are both fresh?
  2. If I do not replace the mag side cylinder (the “good” one), should I at least have it honed? How careful do I (or a machine shop) have to be about burning through the cylinder coating?
  3. As long as I am in this deep, I plan to split the case and check out the bottom end for shrapnel. I will definitely replace the seals, but is it necessary to replace bearings (crank and/or rod) as well?
  4. I am going to replace the pistons and rings on both cylinders. Are there any aftermarket companies that are particularly good or bad? Take into account that this is my backup machine and I am really looking for a just a budget-conscious, reliable setup, not a fancy high-performance race setup.
– abaker262
1999 Arctic Cat ZL 500 EFI snowmobile engine rebuild
A: First and foremost, on any motor rebuild that is being done by necessity, figure out what the reason was that it failed in the first place, or you will be doing a second overhaul shortly after the first one. You can use the undamaged cylinder with a fresh replated cylinder, but it is suggested to hone the cylinder to remove any glazing and renew some good crosshatch in it for lubrication purposes. That can be done with a good solid stone diamond hone. Also, verify sizing and that the cylinder is still round when you have it apart. I would suggest finding a good used cylinder head with no damage to it just so you can have a quality rebuild that will last the rest of that sled’s life. Next, I would suggest having the injectors cleaned and flow tested to make sure the engine is getting the correct amount of fuel during operation, and also verify fuel pressure and volume from the pump. Going through the bottom end is a good idea and always should be on the list if you have had a bad meltdown in the motor. With today’s inferior fuel quality, I also suggest making sure that you test the fuel in the sled at the time of its demise to see if it had fallen victim to a large load of ethanol or a bad batch of low octane fuel. Hope this helps you get this project done.
– Todd Guthrie, Dyna-tek Performance
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