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    '99 ZL 500 EFI Rebuild

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    • Member since
      March 2016
    '99 ZL 500 EFI Rebuild
    Posted by abaker262 on Tuesday, March 1, 2016 9:16 AM


    I have a '99 ZL 500 EFI with around 5300 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 cross-hatch 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 reman/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 at very least.  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.

    Any help or advice would be greatly appreciated!

    • Member since
      July 2005
    Posted by dyna-tek racing on Friday, March 4, 2016 8:54 AM

    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. Youcan 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 cross hatch 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 thats sleds days.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 melt down in the motor.With todays 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 you had gotten a large load of ethanol or a bad batch of low octane fuel.hope this helps you get this project done if you have any more tech questions feel free to call or phone it wont cost you a thing to ask questions and get the right info,thanks todd ,dyna-tek performance 1-260-316-2839

    master mechanic-outboard,sterndrive,pwc,snowmobile. dynamometer facility -crank repair -cylinder repair-trail and race motors-shock service clutch machining and balancing. complete racer support- free technical support-racer discount programs Todd Guthrie 1-260-316-2839 or like us on face book and keep up to date on monthly specials using our facebook page.See new innovative product as soon as it gets built

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