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  1. #1

    2007 Kawasaki STX-12F Project (Auckland, New Zealand)

    Hi All,

    I picked up this STX-12F last week, and i'm looking to get it back on the water in time for summer here.

    The person i got it from didn't have too much background info on it as he got it as part of a deal for a trailer. The motor has been taken apart already and I've not found out what the reason for that was. The only thing I've noticed so far is that the impeller was seized, i managed to work it free but it's still sticking when rotating the coupling.

    I'm planning on making a start on it this week, so far I've got a service manual and that's about it. I'm a newbie when it comes to working on these things, with some previous experience working on a few cars.

    I'm sure i'll be asking some obvious questions but i'm hoping you can all help out when required. I'll take an inventory of what parts i have and make sure nothings missing in the boxes I've got.

    Whats parts should i be replacing as a general rule when rebuilding this motor?

    Thanks!





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  2. #2
    Ultra 15f's Avatar
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    If the impeller moved forward I'm sure it trashed the crank and crankcase be sure to check them.

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  4. #3
    Thanks.

    What’s the best way to check them? Anything obvious I should be looking for?

  5. #4
    steve45's Avatar
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    If the impeller was seized, that would prevent it from cranking. A lot of newbies don't realize that and they assume the engine is seized. Perhaps this is what happened in your case. If the engine was really torn down (crank exposed, etc.), look for wear around the crank journals.

    The -12Fs had some trouble with pistons, I believe, so that would be something to address, too.

  6. #5
    This is what the pistons looked like when i got them



    I've since cleaned them up a little and the first piston on the pics above is quite pitted, would this be detonation?



    As the pistons were already out the cylinders i'm not sure what one each belonged to. I've had a quick look at the cylinders, they need a clean but from first looks they seem in good condition with only 1 of them showing a slightly pitted imperfection. Whats the best course of action, re-hone the cylinders and stick with the standard size pistons or have the cylinders re-bored and go with the larger pistons? i'm planning on rebuilding the top end anyway.

    I've had a look at the crank and only the rod journals are visible, i'll need to split the case to get a look at the main journals, from the pictures below, do you think the rod journals look okay?

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  7. #6
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  8. #7
    steve45's Avatar
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    I think the crank looks fine. I haven't worked on one of these engines that has had the pump push against the crank, but I've seen it on a different engine. There was definite evidence of damage in the form of 'steel wool' type particles all around the bearings.

    I'm not knowledgeable about the -12F pistons, but I've read about cracking and/or broken ring lands. Do a search on this site for better info. Also, I believe the cylinders are nikasil plated and can't be bored, but verify that, too, before you spend a bunch of money on it.

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  10. #8
    dcuhpw's Avatar
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    The jet pump liners can swell with salt water and cause the impeller to seize. They can be replaced fairly easily.

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  12. #9

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    These pumps are very easy to rebuild. I did a complete post on this forum from replacing the liner and building up the impeller edges and re-machining it back to size.

  13. #10
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    The pistons are normal for a 12f, they are just cast pistons.

    If you had a bad one, you would know it, they burn through the upper ring land and eat the side of the piston.

    As for cylinders, you can hone them if you have the right hone for it, you can also have them replated but its expensive. Measure the piston to wall clearance, and if its in spec, pickup a flex hone and give it a quick spin to knock the glaze off. Then toss in a fresh set of oem rings and send it.

    The rod bolts are torque to yield so since they are off, you need to replace them. Single use only.

    Sean

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