1990 650 SJ Knocking
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  1. #1
    PWCToday Newbie Tr565's Avatar
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    1990 650 SJ Knocking

    Hi all,

    I picked up a 1990 square nose last year from a guy I knows sister who bought it new for $300. Hasn't been ran in a few years.

    Took the engine hood off and mold on the entire engine. Everything inside was gross. He said his sister used to race it. Looked stock on the outside minus air intake. I pulled the engine, cleaned hull and fuel take all out spotless. Next I took intake manifold off and saw a tiny bit of rust on one of the cams so I figured I better dig in. Turns out, all the cooling sleeves were completely oxidized and almost full of dust. So I cleaned everything, used a scotch bright to clean the small amount of rust off of the one cam. Everything felt very good and everything was in spec according to the service manual so I proceeded to re assembling. Had to buy a new OEM carburetor (Primer Kit version). Top end appeared to have recently been rebuilt so I checked specs and put it back together. Flywheel was completely corroded so I cleaned that up really good, also had to put a new stator in because of the corrosion. All new gaskets and seals obviously as well (there was no seal between upper and lower crank cases? odd). Everything was done step by step according to the service manual.

    Went to start up and it fired right up immediately. Shut it down after 30 seconds. Checked compression and was at 146PSI in front and 145PSI in rear. Used garden hose and started it up and it idled completely normal. However, the problem I am having is I have a knocking in the engine that only makes noise when engine is revved up anywhere past idle. Ran for 15 minutes then shut down. Top end and exhaust never got over 50 degrees F (ground is still cold here in MI), front of bottom end was at 100 degrees F and rear of bottom end was at 90 degrees F.

    Was curious if those temps are normal. I have never checked it on my 2016 SJ and it is still in storage. Also my new ski does not have the knock obviously.

    Any help would be great......

    Also If you email me I can send you the video of what it sounds like because I do not know how to attach videos.

    ranckt@yahoo.com

  2. #2
    PWCToday.com Is My Home Away From Home
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    Re: 1990 650 SJ Knocking

    It's probably bad cams from the factory. Never trust girls about jet skis.

  3. #3
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 1990 650 SJ Knocking

    I think you mean crank journals as there are no cams. I suspect the knocking is either loose piston to cylinder wall clearance or a loose lower rod bearing.
    http://www.facebook.com/twinlakesjetskirepair

    '89 Kawi 650SX 42.4 GPS
    +3" stock pipe, ported ex. manifold, drilled waterbox, blueprinted pump, Ocean Pro ride plate

    '99 Yama GP1200 65U 61.8 GPS
    ported cylinders, matched cases, milled head, blueprinted pump, long ride plate

    '96 Seadoo HX 717 53.13 GPS
    light porting, massaged cases, lightened flywheel, port matched manifolds, Rossier pipe, stubby pump cone

  4. #4
    I dream skis needforspeed's Avatar
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    Re: 1990 650 SJ Knocking

    If it aint broke...don't fix it!!!!

  5. #5
    PWCToday Newbie Tr565's Avatar
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    Re: 1990 650 SJ Knocking

    Quote Originally Posted by Myself View Post
    I think you mean crank journals as there are no cams. I suspect the knocking is either loose piston to cylinder wall clearance or a loose lower rod bearing.

    Would I be able to feel a loose rod by turning flywheel back and forth by hand?

  6. #6
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 1990 650 SJ Knocking

    Maybe with a long screwdriver down the plug hole and resting on the piston at top or bottom of the stroke you might be able to feel it. Now, with the piston at tdc you can probably use the screwdriver to move the piston in the bore and see how much play there is.
    http://www.facebook.com/twinlakesjetskirepair

    '89 Kawi 650SX 42.4 GPS
    +3" stock pipe, ported ex. manifold, drilled waterbox, blueprinted pump, Ocean Pro ride plate

    '99 Yama GP1200 65U 61.8 GPS
    ported cylinders, matched cases, milled head, blueprinted pump, long ride plate

    '96 Seadoo HX 717 53.13 GPS
    light porting, massaged cases, lightened flywheel, port matched manifolds, Rossier pipe, stubby pump cone

  7. #7
    Top Dog Bionic racing's Avatar
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    Re: 1990 650 SJ Knocking

    Have seen high hour yamaha cranks wear out the small end , wrist pin , egg shape , and knock like crazy , plan on a tear down , check piston to bore clearence and crank for wear

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