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  1. #1

    GP1200R Rebuilding after WSM piston failure; back to OEM

    As some of you may have seen I posted a thread a week or so ago inquiring about a fuel issue on my PTO cylinder.... As it turns out, that piston was fried and only making 5psi. At this point I think the culprit was a hung ring or ring failure of some sort (ill let everyone here help me with that judgement). Thanks to pierowman for pointing out that it could be a larger issue and reminding me to compression test again.

    On to more current business.

    I purchased this ski in late May and have put around 30 hours on the motor (including regular flushing after each outing). I bought the ski under the impression that it was a completely stock motor with a d-plate and pre-mix, it turns out this thing is anything but and is starting to look like the seller pulled off a convincing patch and punt leaving me with the wreckage.

    For the hours I ran it, the ski performed great. My first few rides revealed a bad PV Servo and a terrible wear ring and impeller. I changed those out and the ski really started to haul. Im thinking now that the smaller issues that I fixed allowed the ski to finally run to it full potential which ultimately caused the failure.


    When cracking open the motor I found the rear piston and head beaten up pretty bad (Props to Osidebill for a nice machined head that should be on its way ) After closer inspection I find that the entire motor had be rebuild with WSM components. Crank (welded), rods, pistons gaskets etc. The other two cylinders/pistons looked great and still have some of the crosshatch on the nikasil cylinders. I will be posting more pics tomorrow. Everything aside from the rear piston and jug look good, but Im pretty confident the small end rod play on the failed cylinder is way too much. After searching around and asking where I could I haven't been able to get any reviews of the WSM crank so I plan on documenting this rebuild to shed some light on this low cost alternative. Hopefully with the help of the folks here at greenhulk we can determine whether this was an assembly/fitment error (ill get to my suspicions there later) or a failure of sub par parts.


    I plan on rebuilding and restoring the motor with stock internals and maybe pro-x pistons. I have the head on the way, and will use millennium for my cylinder repair/replate. Im assuming I will need a new crank (anyone out there with a good oem crank pm me) and am thinking about refreshing the reeds and testing the carbs (pics to come). I have several questions about matching the cylinders and whether I should hone/replate the good cylinders or just get the one done. I plan on flooding this thread with pics so we can A- make a determination on WSM quality and B - figure out what caused the failure in the first place.

    Here are the pics I have so far...

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    Here she is all gutted

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    Tomorrow I will post better pics of the good cylinders pistons and crank.

  2. #2
    Hello Integragated, I am doing the same engine rebuild that you are doing. The PTO piston went dead on me. my was because the crank seal let water inside the engine and the lubrication holes to the bottom of the crank were cloged. So it overheated and there it went. I had the same questions as you and so far the answer is that you could do just the one that failed but it depends on how the other two look. In my case the damage was only to the PTo cyl. I broke the cylinder case by mistake so I bought one in ebay and I am in the process of re- sleeving it with a used sleeve. I am planing on puting a new OEM piston on it and new gaskets all around. Are you sure that it was the ring that failed? I wish you the best of luck in your rebuild and if you find any good deals let me know cause I am also doing this as cheap as possible.

  3. #3
    Thanks ccameselle best of luck to you too! Just a thought... be careful sleeving the new cylinder if the others are oem nikasil, it seems mix and matching isnt a good idea. I will be getting my cylinders re-nikasiled by millennium to restore for maximum longevity. I want to decide on pistons before sending it out though.

    As of right now Im not positive what cause the failure. I do know that all of the rollers on the piston rod bearings are present and accounted for (both on the piston side and crank side) and I haven't seen any metal in the crank case. It doesnt seem to have been leaning out either. I will have to check the piston to wall clearance as it seems that the pistons may not have been sized appropriately to the cylinders and may have exposed to much of the ring causing a failure.

    Others feel free to chime in with probable causes.

  4. #4

    More pics

    Good #2 Jug- Still debating whether I can reuse or get them all replated and matched to pistons
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    Burn marks on Underside of PTO piston
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    Good Front Jug - still has a bit of original hone marks
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    OEM has thrust washers on either side of the bearing... Nothing here.. Could this be an issue?
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    Wearing on the PTO Rod- looks like bearings dug a groove
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  5. #5
    Top of Good Front Piston
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    Top of Good #2 Piston - Do these look lean?
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    Failed PTO Piston Pin (notice the grooves that the bearing made..Similar pitting on the bearing itself, both good cylinders do not show this wear
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    Intake side of PTO Piston (hairline crack on the skirt)
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    Exhaust side of PTO piston (OUCH)
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  6. #6
    PolarisNut's Avatar
    Join Date
    Dec 2006
    Lower Michigan
    Those are the non Platinum series WSM pistons. There have been some reported failures with those ones. I've used several sets of late model Platinum series, including ones in my 80+MPH triple pipe GPR, without issue (even though most on this site won't use them). It does look like it may have spun a ring and snagged it, but the $150 OEM ones are known to do this as well. That cylinder was clearly lean, as evidenced by the burnt oil on the underside of the dome. This probably resulted in some mild detonation, which hammered the ring locator loose. Most piston failures that I've experienced with 2 strokes is due to lack of fuel/oil, detonation, or water/snow ingestion. Very rarely have I attributed the actual failure to poor quality parts, although it has happened.

    As for the damage to the wrist pin and pin bearing...It looks like there was possibly an oil starvation issue, or water ingestion/hydrolock at one time. Getting water into the cylinder and forcing the piston to compress it, can flatten the needle bearings and wash the oil off of everything. Also, if the cylinder gets water in it, and then sits, the rust will pit the bearings, and eventually cause failure that looks similar to yours. Sometimes the failure will take 10+ hours to show up. I used OEM wrist pins and bearings in all of my personal builds, but have used WSM in some cheap rebuilds for friends without issue.

    Do I think WSM Platinums are as good as the stock ART pistons?, but they are a decent low cost alternative, IMO. Now that these skis are dropping in value, and they are 10+ years old, I just can't justify spending $150+ ea. for pistons. If it were a fairly new $8000 ski, then that would be a different story.

  7. #7
    Interesting... I tried to look up the part number on the tops of the pistons and all I can find is "Platinum Series" maybe they don't make the originals anymore..

    On the hydrolock issue.. I will confess the motor did have fresh water in it at one time earlier this season. I did my best to fountain it out, then ran it like hell to burn up anything left. Guess that didn't work so well...

    I was thinking that underside burn came from excess heat that built up when the motor was run with the failed piston as is. The other two cylinders have a much smaller brown dot on the underside in the center, I was told that this is normal for two strokes. Can anyone else confirm that the two good pistons look as if they were running lean?

    I will be taking some pictures of the WSM crank tonight as well as my recently discovered warped case.. Warped right under the failed piston.

  8. #8
    This never ends.....

    Another issue I just came across is that the two remaining "good" jugs are two different sizes... Now after buying a fresh jug from Mikegp (thanks mike) two jugs will be #10's which maps to one size oem piston (orange; diameter 79.903 ~ 79.906). The other jug is a 14 which maps to the next piston size bigger (green; diameter 79.907 ~ 79.910). I realize there is some overlap of the sizes so basically I'm left with three possible choices;

    Should I get two orange pistons and one green, and if so do i need to worry about balancing them given the slightly larger size?

    Should I just get 3 of the same, maybe green if there is enough clearance and call it a day?

    Should I just get the largest OEM piston size and send all three jugs and pistons to Millennium for a renik and match? (would really prefer to avoid this)

    Im probably being neurotic but Id love to get some opinions.

  9. #9
    A child of five would understand this. Go get one. pierowman's Avatar
    Join Date
    Sep 2011
    Seattle, WA
    Im no mechanic but what i have been told is you want the pistons to match otherwise the engine will be out of balance causing various issues. Thats not to say it wouldnt work. It seems though that the size difference you have wouldnt be that big a deal.

    The main issue would be premature failure of crank and or seals.

  10. #10
    I agree with that being a weakness of using different (albeit slightly) sized pistons. I was most concerned with preventing a situation where I have too much gap between the piston and the cylinder which could potentially cause a ring to fail. I will get the pistons matched by my machine shop. After talking with a few people (thanks OsideBill) I will be getting 2 orange and 1 green to best match my cylinders. Ill have the whole rotating assembly balanced to make sure everything is even.

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