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  1. #1

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    ZXi 1100 Wiseco piston damage

    In pulling my exhaust manifold due to a hairline crack and leaking all over, I decided to throw a DI exhaust onto my non-DI ZXi, and do some stage2 modifications to the port runners and elbow while I was at it. (opening up 2mm) I have good compression @125psi+/- on all three cylinders, and she has run strong for the 2 years I owned her. Only issue has been tuning the CDKii carbs I put on her.

    But in doing the exhaust manifold change and upgrade, I pulled the piston sleeves off to get at the exhaust ports more easily. Looks like good color and piston wash (pictures below). Much to my surprise, I found what looked like molten/smashed metal pressed into the wall of the front cylinder, and then looking at the front piston, saw what looks like scraping damage from this on the carb side of the piston, with some damage on the exhaust side too.(pictures below)

    Does anyone know what causes this exactly? Was this a rogue piece of metal from a previous rebuild in the crank that got pressed up and obliterated into the cylinder wall, causing a high spot that the piston scraped against? Or is this the wiseco piston failing and falling apart? Or is it maybe a bad wrist pin bearing causing too much wobble in the piston?

    I cannot find any chips or missing material from this piston, nor are the rings broken, so I am baffled at what causes this, but I can only assume is from some foreign bit of metal. The previous owner had Wiseco pistons and a hotrods crank put in this,(any way to identify HR crank?) so I can only assume the motor was blown at some point, and the crankcase probably not cleaned thoroughly, leaving a bit or bits of metal that caused this.

    As always, any advice is greatly appreciated!










  2. #2

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    Took a picture for reference of where the metal was pressed into the cylinder wall. I already took a round file and smoothed it out, but circled where it was at. Below the water jacket, so although possible, don't think it's a hot spot.


  3. #3
    steve45's Avatar
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    Lack of oil? That piston has gotten hot and rubbed the cylinder. Do you warm it up for a few minutes before you run it hard? Failure to do this can cause a 'cold seizure', where the pistons expand faster than the cylinders. Are you running chokes on the carbs? Removing the chokes can make it hard to tune the carbs.

    An exhaust leak can do strange things. It can make an outdoor engine run lean. However, inside the hull, it will start breathing exhaust, which reduces the oxygen concentration getting to the engine.

    At least you caught it before major damage was done.

  4. #4

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    Thanks for replying Steve45... I appreciate the insight...

    I kinda wondered that @ getting hot and the aluminum actually melting onto the cylinder wall, having read a few postings about piston/cylinder damage. But given the amount of oil in the crank case of each cylinder, and the oil burn off on this front piston head heavier than other 2, plus this ski just smokes pretty bad, so it's hard to see it coming from a lack of lubrication, but I guess at higher RPMs, its completely possible... and I do warm my skis up before jumping on them, as I understand the cold seize concept, especially with these Wiseco forged pistons.

    Yes.. running chokes, and per a couple of threads, found never to remove the chokes, even if doing primer kit. But these 96 CDKii carbs I got have the accelerator pump on them, so a quick shot of the throttle there and she starts almost the first time.

    I put all new blue oil lines on her last year, and recently changed from cheap Walmart Penzoil 2stroke to Maxima Race oil, completely draining and replacing with new. Also made sure no air bubbles in lines, etc. This oil pump is not adjustable, from what I understand, and is driven off the rpms of the motor, not cable driven off throttle like old Seadoos. I will probably pull the oil pump and see if it can be cleaned or at least check it over, given that this seems a heat based problem. The front piston exhaust manifold is also where the hairline crack occurred in the outer jacket. I'm getting a bit nervous looking at these facts now.

    But you're right... glad I pulled all this apart to make the mods and caught it before catastrophic failure, which knowing my luck would have been a mile offshore or something. The front cylinder always seems to run hotter on this ski, which from what I have also read is common. But again, now with these facts laid out, I almost wonder if the water jacket on this cylinder has sand or shells lodged from something previous and blocking in/out. Might not be a lubrication issue but a cooling one. (hairline crack on outer jacket of exhaust manifold, piston that looks melted) I installed dual cooling, and get crazy water pressure through the engine + stinger mod, but if it was pre-existing blockage, then it doesn't matter how good cooling intake is....

    I have the entire exhaust off for these mods, and installing a larger DI exhaust chamber AND muffler, so there will be new gaskets all around, and all tightened to spec. Plus an extra 2mm on the exhaust port runners and 3mm in the elbow. I also have a new piston head, circlips and rings coming to replace this damaged one. Just sucks there's no way to see this stuff without pulling everything. She's been running great, with solid compression, and only 25hrs on the engine/hotrods crank. Just don't know what to look for in the future, honestly, because nothing screamed "the front piston is cooking".... other than maybe the hairline crack, but those are also pretty common on the exhaust manifolds of the ZXi from what I have gathered, so.....

  5. #5
    steve45's Avatar
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    Sorry, I mis-read the carb type, I was thinking of the '98 & later 1100s that had the CV carbs. It's OK to remove the chokes on yours.

    Perhaps the clearance wasn't set correctly between the piston & cylinder for those pistons.

  6. #6

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    Well... yes... the older zxi does come stock with CV carb, but got tired of them and rebuilt a set of 1996 cdkii with oem gaskets. Kept all stock, as i surf jump and wanted to use stock airbox to prevent salt intrusion.

    But how do you "adjust" or set clearance? The cylinders just have to be bored to match the piston right? Is this something i can check with feeler gauge when i put the pistons back in, being that i have everything out? Guess I will have to search the forums on setting piston clearance...

  7. #7
    steve45's Avatar
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    From the service manual, piston/cylinder clearance should be 0.13-0.14 mm; or .005" - .0055". Yes, you can check it with a feeler gauge. Keep in mind that the pistons are tapered slightly, they're larger on the skirt than the top. The 1100 service manual doesn't show it, but if I remember right, put the piston in upside down and measure the clearance between the piston and the cylinder at a point about an inch above the bottom of the piston skirt.

  8. #8

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    Thank you very much for the detailed information Steve45. I really appreciate your assistance.

    I checked the cylinders with a set of internal calipers, and they all measure consistently 80.75mm with no variance that I cen tell when turning them around in a circle to see if high/low spots. The pistons are 81mm, but I will check the clearance all around via the instructions you gave.

    Again... I deeply appreciate your assistance. It's clear by your signature that you have some experience with skis and engines to know.

    I will report back my findings....

  9. #9
    steve45's Avatar
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    There are many others here that know a lot more than I do.

    I'm a bit concerned that your cylinders measure 80.75 and your pistons measure 81. It's gonna be pretty hard to get them in there!

  10. #10

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    Quote Originally Posted by steve45 View Post
    There are many others here that know a lot more than I do.
    While that may or may not be true, I respect and appreciate that you took the time to reply.

    Quote Originally Posted by steve45 View Post
    I'm a bit concerned that your cylinders measure 80.75 and your pistons measure 81. It's gonna be pretty hard to get them in there!
    I will report back when I get the pistons in the cylinders and measure with a feeler gauge. That measurement was just internal caliper then measured with digital outer caliper, so may be incorrect/inaccurate...

    But other boards also feel that #1 was lean by the look of the piston wash, and probably overheated, melting the piston to the wall. Having written all this down here and elsewhere, and reviewing the last month of stuff I have done, I have a feeling the lean condition came when I had switched out the CV intake manifold for 1996 manifold to match the carbs, thinking that CV intake was causing my carb tuning issues. This was not the case, as it ran incredibly poor with 1996 intake, and I ran her for about 30 minutes on the water trying to tune things, knowing it didn't feel right. The damage probably occurred there.

    I have since gone back to the 2001 CV intake with the large crossover tube and crossover channels between the 3 carbs, with all new gaskets, tightened to spec. I will also try to do a leak down test on each cylinder to check for crank case leaks while I hae it all apart. That's gotta be a PITA though...

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