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Thread: Where can I find 30 over piston and rings for my Tri-Z???

  1. #1
    Join Date
    Jun 2014
    Location
    Pittsburgh
    --
    108

    Where can I find 30 over piston and rings for my Tri-Z???

    So I went to put new piston and rings in my 85 Tri-Z. When I took it apart I noticed that it already had a .010 over piston in it. Also the sidewalls looked a little scratchy so I wanted to have it bored out so I could get it back to running 100%. The guy at the machine shop said it would be best to do 30 over because 20 over might not be quite enough. So now I have a fresh jug that's .030 over or 68.75mm instead of the stock 68mm. My problem is I can only find the stock 68 size and the 2nd overbore 68.5 size. Where the heck can I find a 3rd overbore size piston and rings? I looked on Google, eBay, Rocky Mountain ATV, ect..... Everybody has 68mm and 68.5mm but nobody seems to have 68.75mm? Am I not using the correct numbers or terms? Can anybody help a brother out on this one?
    '' Mixin gas N haulin _ss''

    1985 250R-310
    1985 Tri-Z
    1985 Tri Zinger-X's 4
    1973 atc70

  2. #2
    Join Date
    Jun 2014
    Location
    SW PA
    --
    128
    I found an old 3wheelerworld discussion on this...Click image for larger version. 

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    Try this...Search 515p3...I found this site...
    http://www.powersportsnetwork.com/en...tCategoryCode=

    ‘84 Big Red
    ‘85 250R
    ‘86 XR600R(I know, not a trike, but an 80’s beast)
    Survived: Breezewood - April 2016
    Trikefest 2015, 2016, 2017, 2018

  3. #3
    Join Date
    Jun 2014
    Location
    SW PA
    --
    128
    I guess that's only helping confirm the part number. I can't find where it's available yet either.

    ‘84 Big Red
    ‘85 250R
    ‘86 XR600R(I know, not a trike, but an 80’s beast)
    Survived: Breezewood - April 2016
    Trikefest 2015, 2016, 2017, 2018

  4. #4
    Join Date
    Apr 2014
    Location
    Edmond, KS
    --
    2,531
    I'd be careful of that machine shop if I was you. It sounds to me like your cylinder was "bored out and ready to go". The piston manufacturer always sends clearance specs with their pistons. How does this person know what your clearance is if you don't even have a piston to be measured?

  5. #5
    Join Date
    Mar 2010
    Location
    Slidell, LA
    --
    4,737
    X2......next time buy the next size piston first then have the shop bore to that piston.
    Feedback for yaegerb: Click Here

    Need something blasted or polished or both? Send me a PM

  6. #6
    Join Date
    Aug 2015
    Location
    Portland Oregon
    --
    174
    Any shop who doesn’t preorder a piston needs to be replaced. How in the heck could your cylinder be bored without a piston; these little cylinders only need a +.0015” skirt clearance.
    Wiesco pistons are sized in .5mm steps; I never bore a cylinder without a piston in my hands. Since your cylinder is a 4 stroke? It could have very well have been honed to the next size. I only purchase Wiesco pistons direct from the factory in order to check on the stock on hand.
    If you send me your cylinder I’ll bore or hone your cylinder FREE if you order a piston from me? Check out my site, we are always looking for people who are interested in the trade.

    John Tice
    503-593-2908 Alternate 541-595-0310
    www.smallenginemachineworks.com & www.nwsleeve.com
    Turning Custom Cylinder Sleeves Since 1971
    http://forums.everything2stroke.com/...d-the-Shop.com


  7. #7
    Join Date
    Jun 2014
    Location
    Pittsburgh
    --
    108
    Well he just measured what it was and compared that to the stock 68mm. Also he had some banshee heads and what not there but it's not a motorycle based shop by any means. But anyway. I found that wiseco website shows one that's for 69mm. So I'm going to double check this out to be 100% sure and just have them bore it out one more time to 69mm. At least if this works out it, I think it will technically be 255cc's instead of 248cc's. I couldn't really find an 85 yz250 jug to see if maybe that would work either. So it's either this or I find a whole other jug the surely will need work and be 1 of 4 for sale on the planet hahaha. But FYI don't ever bore your Z 30 over.
    '' Mixin gas N haulin _ss''

    1985 250R-310
    1985 Tri-Z
    1985 Tri Zinger-X's 4
    1973 atc70

  8. #8
    Join Date
    Mar 2010
    Location
    Slidell, LA
    --
    4,737
    69mm is actually a 1mm overbore on a z. Dem walls gonna be thin plus it's your last bore. Maybe consider a sleeve for more life?
    Feedback for yaegerb: Click Here

    Need something blasted or polished or both? Send me a PM

  9. #9
    barnett468 is offline FACT ! I have no edit button Arm chair racerThe day begins with 3WW
    Join Date
    Jan 2013
    Location
    minnesota
    --
    5,911
    Well, it looks like Yamaha did not even offer a 3rd over for the tri z . I would call Wiseco like Hunting Chip suggested and ask them if they have one since they didn't list the size along with the part numbers.

    FROM THE 1985 TRI Z PARTS FICHE

    https://www.cmsnl.com/yamaha-ytz250n...6.html#results



    PREVIOUS KAWASAKI INTERNATIONAL R & D PROJECT ENGINEER AND ATV DEPARTMENT SUPERVISOR

  10. #10
    barnett468 is offline FACT ! I have no edit button Arm chair racerThe day begins with 3WW
    Join Date
    Jan 2013
    Location
    minnesota
    --
    5,911
    Ok, I decided to not be lazy and I looked it up . The last number of the Wiseco part number is the size in inches.

    515PS = STD
    515P1 = .010" or .25 mm
    515P2 = .020" or .50 mm
    515P3 = .020" or .75 mm
    515P4 = .040" or 1.0 mm

    In your case, you need a 515P3.



    PREVIOUS KAWASAKI INTERNATIONAL R & D PROJECT ENGINEER AND ATV DEPARTMENT SUPERVISOR

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