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  1. #1

    1989 650SX - Which pistons to buy?

    Picked up a 1989 650SX in great condition. Engine was run low on oil briefly and rear piston was slightly damaged. Front piston has great compression while rear piston has about 1/3 of front. Pulled it apart and indeed the rear piston has some scoring. Machine shop only needed 0.002" to clean it up. Figure I can go with 0.25mm over pistons to fix this. There are a lot of vendors with 0.50 and 1.00mm top end rebuild sets but just a few with the 0.25mm.

    I know Wiseco pistons are good, but can get pricey. What about WSM pr PRO-X?

    Also are there vendors to stay away from? PWC engine list WSM, Pro-X and Wiseco. Is this a reputable vendor?

    Thanks in advance!


  2. #2
    steve45's Avatar
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    Don't know that it's critical on a 650. On an Ultra 150, I'd only use OEM Kawi. I've used Wiseco, and WSM in the past, and have Pro-X and WSM in boxes ready to go into a couple of project engines as soon as I can get to them.

  3. #3
    badjoka's Avatar
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    Wiseco in mine, 15 years+

  4. #4
    steve45's Avatar
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    I don't like the Wiseco gasket sets that come in their overhaul kit, but pistons are OK.

  5. #5
    thanks guys

  6. #6
    john zigler's Avatar
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    Be careful with Wiseco's. They are an excellent piston, light and strong, BUT they are a forged piston, and will expand at a quicker rate. If not properly set up, they will seize. Because of the higher piston to cyl wall clearances, you will need to rebuild sooner. Also be sure to let your motor fully warm up before going wide open throttle, or you can cold seize.

    WSM, & Pro-X are a "cast" OE type piston. Pro-X are actually the same as OE. If you look under, inside the piston it will say "art" same as OE. WSM is an OK alternative, in a stock motor.

    I can help with pistons, rings, gaskets, etc if you need. I have lots in stock, and if I do not can get them in a few days.

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  8. #7
    thanks watcon, checked your new parts website and did not see a top end rebuild kit and just saw new pistons on the used part site

  9. #8
    john zigler's Avatar
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    I have MANY more parts here than listed on the site.

    Feel free to call 608-743-1305 or email [email protected]

  10. #9
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    Quote Originally Posted by vwztips View Post
    Picked up a 1989 650SX in great condition. Engine was run low on oil briefly and rear piston was slightly damaged. Front piston has great compression while rear piston has about 1/3 of front. Pulled it apart and indeed the rear piston has some scoring. Machine shop only needed 0.002" to clean it up. Figure I can go with 0.25mm over pistons to fix this. There are a lot of vendors with 0.50 and 1.00mm top end rebuild sets but just a few with the 0.25mm.

    I know Wiseco pistons are good, but can get pricey. What about WSM pr PRO-X?

    Also are there vendors to stay away from? PWC engine list WSM, Pro-X and Wiseco. Is this a reputable vendor?

    Thanks in advance!

    If your machinist only took .002 out of the bore to clean it up, a .25mm over piston will be too big. Measure your cylinder diameter and the piston you plan to use to determine the clearance. I am afraid you may be too tight if you buy a .25 over piston, yet you may be too loose with a standard piston.

  11. #10
    john zigler's Avatar
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    Quote Originally Posted by BryanP View Post
    Quote Originally Posted by vwztips View Post
    Picked up a 1989 650SX in great condition. Engine was run low on oil briefly and rear piston was slightly damaged. Front piston has great compression while rear piston has about 1/3 of front. Pulled it apart and indeed the rear piston has some scoring. Machine shop only needed 0.002" to clean it up. Figure I can go with 0.25mm over pistons to fix this. There are a lot of vendors with 0.50 and 1.00mm top end rebuild sets but just a few with the 0.25mm.

    I know Wiseco pistons are good, but can get pricey. What about WSM pr PRO-X?

    Also are there vendors to stay away from? PWC engine list WSM, Pro-X and Wiseco. Is this a reputable vendor?

    Thanks in advance!

    If your machinist only took .002 out of the bore to clean it up, a .25mm over piston will be too big. Measure your cylinder diameter and the piston you plan to use to determine the clearance. I am afraid you may be too tight if you buy a .25 over piston, yet you may be too loose with a standard piston.
    I assume he did this to see how much material needed to be removed to fix the bore and scoring. He will now order pistons, and finish bore to match the new pistons.

    I do this all the time, to make sure I do not order a .25mm piston, when I actually needed a .50mm

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