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  1. #1

    Join Date
    Oct 2009
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    NE Wisconsin
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    27

    Piston Issue and More

    Had a problem with my 1996 SLT780. It seemed to run fine then went to ride again and it started fine but would not get on plane, took it back to the trailer and checked compression with the MAG cylinder having 60 psi. Pulled the head and found the piston damaged (see photos). The rings are still in place but the connecting rod has vertical movement. I have not had any experience with working on these but from researching these forums I think that the connecting rod to crank bearings let loose, does this sound correct? Can they get to the top of the piston? How do you get the connecting rod off of the crankshaft? Do you need to pull the engine? Thanks for any help!
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  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
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    Cleveland OH
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    Wow, that's some damage....


    Connecting rods need to be professionally done. Polaris uses a press fit crank, and yes the engine needs to come out.

  3. #3

    Join Date
    Sep 2009
    Location
    St. Louis, MO
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    220
    Holy crap! That looks horrible, sorry to hear about it.

    Someone will correct me, but from what I know the crank is pressed together and the only way to replace the connecting rod is to split the crank apart and then press it back together. Not a small job from my reading.

  4. #4

    Join Date
    Oct 2009
    Location
    NE Wisconsin
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    So to inspect the crankshaft I need to remove the engine and remove it? Will I be able to take the connecting rods off or are special tools required? Any idea if it is worth rebuilding if the crankshaft is damaged?

  5. #5
    johnsonmtz's Avatar
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    Oct 2006
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    Mt. Zion Illinois
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    Quote Originally Posted by Wiweeds View Post
    So to inspect the crankshaft I need to remove the engine and remove it? Will I be able to take the connecting rods off or are special tools required? Any idea if it is worth rebuilding if the crankshaft is damaged?
    Yes, to inspect the crank fully you need to pull the engine and split the case in half. If you have vertical play there is no doubt that rod bearing is shot. Unless you have a fully outfitted machine shop and the proper jigs you will not be able to service the crank. There are no bolted caps on these rods. On these engines the crank is a multi-part unit that is assembled and pressed together. The bearing is pressed into the rod then slid onto the crank journal and then the entire assembly is pressed together with each journal 120 degrees from each other.

    Your engine may be worth salvaging. You could send you crank out to be refurbished, you could buy a used crank (John Zigler at Rock County Jet Ski is a good place to look), you could buy a remanufactured crank, or you could by a reman engine.

    KJ

  6. #6
    Clayton G's Avatar
    Join Date
    Apr 2009
    Location
    Upper Peninsula of Michigan
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    143
    Where in NE Wis are you located? Jeff at Midwest Crankshaft can do the rebuild for you. He is just north of Green Bay on Lineville Rd. I arrainged for him to rebuild a crank for me while we were shopping in GB. Took him about 3 hours, called my cell when he was done. Call him at 1-920-434-3630.

  7. #7

    Join Date
    Oct 2009
    Location
    NE Wisconsin
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    Was hoping for better news. I am in Appleton just south of Green Bay. I will give Jeff a call at Midwest crankshaft if I decide to rebuild it. Did he provide all of the parts or did you? I need to decide if it is worth it to rebuild it or buy a reconditioned one from SBT at $245. Thanks for the information all!

  8. #8
    Clayton G's Avatar
    Join Date
    Apr 2009
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    Upper Peninsula of Michigan
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    143
    If you call Jeff and give him enough lead time he will order the parts if he doesn't have them already. He has shelfs full of used cranks that he uses for parts incase you need to replace any section of your crank. I needed to replace the mag end on my SLTX crank. He had good used ones there. I'm sure he would have what ever you would need.

  9. #9

    Join Date
    Oct 2009
    Location
    NE Wisconsin
    Posts
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    Can anyone suggest what would of done this type of damage. I have read connecting rod bearings can, but how could it get into the cylinder? All of the rings seem to be on the piston. I am about to pull the engine and would like to know what to look for.

    Thanks

  10. #10

    Join Date
    Oct 2009
    Location
    NE Wisconsin
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    27
    Could this be caused by a lean condition?

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