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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.

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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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    Thanks!


  2. #2
    THE PLATE MAN JIM'S PERFORMANCE's Avatar
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    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
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    +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?
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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
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    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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