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  1. #1

    Piston pin free play

    Hello, this is my first time rebuilding a two-stroke engine and I have a couple questions.

    I ordered a crank from SBT and now I'm in the process of assembling the engine and I noticed a tiny bit twist/rotation so I was wondering if I need to order new piston/pins or just pins.

    Click image for larger version. 

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    Is the wrist pin supposed to be free floating when fully in the piston like mine or do they need to be press fit/snug the whole time?

    Click image for larger version. 

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    I also noticed the rod bearings seems to move side to side a lot, is this safe for these SBT pistons?
    I noticed in the OEM Yamaha parts diagram that theirs a washer/shim on each side of the bearings.
    Click image for larger version. 

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  2. #2
    Join Date
    Nov 2005
    the pin is suppose to free float you are missing the washers that go on each end of the bearing.

  3. #3
    A child of five would understand this. Go get one. pierowman's Avatar
    Join Date
    Sep 2011
    Seattle, WA
    +1 missing two washers

  4. #4
    Thanks for the fast replies!

    Just looked on their site and it doesn't show the piston kit comes with those washers but the 1200R does..interesting.

    I didn't know it was an SBT rebuilt engine until I took it out to rebuild it and this is why.. missing washer on #1 rod and It's actually missing one on #3 also but theirs no discoloration.

    Also do you think I'll still need to get a new wrist pin to fix the free play in the piston?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  5. #5
    Apparently SBT doesn't use those washers but I read that Riva sells wider bearings so you don't need the thrust washers.

  6. #6
    A child of five would understand this. Go get one. pierowman's Avatar
    Join Date
    Sep 2011
    Seattle, WA
    Someone correct me if im wrong but the coloration on the rod there is a bad sign and looks to be due to not having a washer there. I would install washers where they need to be dispite SBT not installing them. They arent exactly known for quality.

  7. #7
    Yeah that's the old crank from the rebuilt SBT engine, just showing what I found wrong with it.

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