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  1. #1

    I need help with piston clearances plz

    Okay...

    So I have:
    2003 Ultra 150
    Bore Gauge
    Micrometers (3")
    Factory Service Manual

    Here is whats going on... This is a newer boat for me. I bought the boat with a terrible, rebuild job done to it. I ripped the motor down because I thought I was hearing some slap. Sure enough slap was there. One of my pistons had .013 clearance to cylinder. It was surely the culprit. Interestingly enough, the cylinder with the slap has a different stamping near the head. Two of the cylinders have a "B" stamp whereas the one that was looser had a "C" stamp. Dunno if the stamping makes a difference, but it was bigger than the "B" Cyls. So I got a Nikasiled "B" cylinder to match the others. Now are the cylinders are the same. So now... I got the book, some tools, and some parts.

    My pistons read 3.141

    FSM says:
    Piston Diameter
    Standard: 79.865 ∼ 79.880 mm
    (3.14429 ∼ 3.14488 in.)

    Service Limit: 79.72 mm (3.1386 in.)
    ○If the measurement is less than the service limit, replace
    the piston.

    Fair enough... but the pistons look super clean, yet still bigger than the service limit

    My cylinders read 3.150 on the nose

    FSM says:
    Cylinder Inside Diameter
    Standard: 80.000 ∼ 80.015 mm (3.14961 ∼ 3.15019
    in.) and less than 0.01 mm difference
    between any two measurements

    Service Limit: 80.10 mm (3.1535 in.), or more than
    0.05 mm (0.0020 in.) difference
    between any two measurements

    So it appears my Cylinders are good, Pistons??? dunno. This puts my Cyl to Piston clearance at .009 in.

    FSM says:
    Piston/Cylinder Clearance
    0.130 ∼ 0.140 mm (0.005118 ∼ 0.005512 in.)

    What to do? The pistons look so new, but I have no way to get to the .005 number. I think my cylinders are so close to stock that I don't need to worry about replating. Anyone have any advice?

    Thanks,
    Jason


  2. #2

    Join Date
    Jan 2006
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    Taylor, MI 48180
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    Hey Jason, a new stock Kaw piston mikes out at 3.1435. That still puts you at 6.5 thou. Sounds like you also need a renik to make it right.

  3. #3
    Okay thanks... I was worried that was the case.

    Anyone have any thoughts on piston selection? OEM, Wiseco, WSM, Pro-X?

  4. #4
    btldigger's Avatar
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    lebanon tn.
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    I have used oem and wsm with good results. Actually i really like wsm top end rebuild kits

  5. #5
    How many times have you used WSM. I was considering them but I have heard from some that they are cheap quality and from some they are ok.

    I also have a cylinder from a guy that had one break apart on him and the other pistons have fractures throughout the skirt. I can actually see light through the skirt of the piston. It was only a matter of time before that one went too. The piston to cylinder clearance was within the service limit too. It made me leary of buying WSM or cast pistons in general. I have never used or had them. I have always used forged.

    I am interested to hear about your experience with them, because they are a much more affordable route than going with Wisecos. I know Wiseco is pretty much top of the line, and I have never had issues with them in dirt bikes and such, but I have never used them in a jet ski. I haven't rebuilt a jet ski top end before. I am working on my first one. I will fork out the extra money for the Wisecos if it means I don't have to replace the cylinder.

    Thanks in advance.

  6. #6
    btldigger's Avatar
    Join Date
    Feb 2007
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    lebanon tn.
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    1,641
    I havent had a problem that wasnt caused by other issues such as water injestion. That can wash the lube off the cylinder walls and cause the skirt to break up.

  7. #7
    you know... I actually already have (2) STD Wiesco pistons. They are in really good shape. I am wondering if these are the route to go. I have seen so many debates about pistons, clearances, skirts breaking, and seizing. I dont want the skirts to break... I had that happen to a 750 and it shot through the bottom of the case. I have heard that WSM's are a little more brittle on the skirt than a forged piston like the Wiescos. With my clearances, I think the Wisecos will run just fine. Do you think I should go that route? Others say stick with the OEM Kawi pistons. Those are the best period....

    Opinions please! I want to move on this (the sensible/right way) and get back on the water.

    Thanks, JP
    Jason

  8. #8

    Join Date
    Jan 2006
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    I would call Wiseco and have them Mic a piston for you. I would not run a cast piston with .006 + clearance. Unless you like your cases with windows in them!

  9. #9
    Wiseco forged pistons usually run 0.0045 ~ 0.005 inch clearance fresh. Call them and match one if you go that route. Their technical support is very helpful and they will give you exact measurements if you ask for them. That's what I did for mine.

  10. #10
    good news is that Wiseco is about a half an hour from my house. I may just drive up tomorrow and ask them.

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