How bad is this?
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  1. #1
    EAJ
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    How bad is this?

    Cb360 is getting a new top end. Starts and runs but compression is way down and can’t get over 55mph.
    Opened the box one of the Pistons arrived in to find this...break out the file? leave it alone? Or absolutely don’t run it?
    Attached Thumbnails Attached Thumbnails How bad is this?-2bb99a67-bf2f-46be-ac41-6e760c5c787c_1571532793328.jpg   How bad is this?-5c7c8749-e155-4953-a70f-0c411802f2d1_1571532814318.jpg   How bad is this?-dc28f32d-b671-410c-8ef0-9bbb6cc04085_1571532837103.jpg  

  2. #2
    Senior Member BlargKing's Avatar
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    I personally wouldn't use it, even if you filed the edge smooth. Would you want to rebuild the top end with that piston only to find that its no good and have to pull the top end back apart?
    1984 Honda CB450SC Nighthawk

  3. #3
    Senior Member 76TWIN's Avatar
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    it's not as bad as you think. The crown of the piston shouldn't be touching the cylinder wall anyway. It's the rings that are in contact with the cylinder and provide the compression needed.

    That said, since it's a newly ordered piston, you should be able to get an exchange for it no?
    oupa likes this.
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  5. #4
    EAJ
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    That’s kinda what I was hoping to hear...and no exchange as it is a NOS Suzuki gs850 piston

  6. #5
    Senior Member 76TWIN's Avatar
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    I would still do some closer inspection with a magnifying glass and see if there are any cracks around the area. If so do not use it.
    Alan F. likes this.
    '76 CB500T Frankenbike
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    Carpe narem.

  7. #6
    Sensei 66Sprint's Avatar
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    Agree with 76TWIN as to the best choice of your three options......

    Send it back for exchange, ....But since that's not feasible.....
    Lightly dress and run it, ( live with it as-is )......
    Fill the ding with Aluminum welding/brazing rod and then dress it......(lots of work for minuscule gain)
    Last edited by 66Sprint; 10-19-2019 at 08:41 PM.
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  8. #7
    EAJ
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    Ok. I will get it under a magnifying glass and check it out, if it seems solid I will lightly dress it and proceed. This is not a race bike nor a spare no expenses type project so I’m not overly concerned with making big performance gains outside of knowing its running as well as it can.
    Alan F. likes this.

  9. #8
    Senior Member oupa's Avatar
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    Wipe or dip it in gasoline, acetone or a similar THIN solvent. Wipe it dry then check closely. If there is a crack, the solvent will be creeping out of it. Old gunsmith trick for checking receivers.
    Bill H likes this.
    "They're not like cars with a body that rusts out in a few years. Keep them tuned and overhauled and they'll last as long as you do. Probably longer." - Robert Pirsig

  10. #9
    EAJ
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    Pro tip! Awesome, I will be sure to do that. Imagine, if I had a perfectly good piston I never would have learned this.

  11. #10
    Supporting Member crazypj's Avatar
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    As NOS Suzuki it's been out of production for years and you know you won't be able to get an exchange. I would try and get a few bucks back from seller. It won't be a problem though so just file it flat with a very fine file and use it. The alloy isn't so brittle it will crack easily and, real kicker for guy I worked with, the pistons for Suzuki GS850 were made by the company that Honda has controlling interest in so it's really a Honda piston anyway (Gerry was 'corporate Suzuki' at one time )

    Oh, it will go over 55 if you rev it to red-line through the gears. Stick it in top at 35, no way ever unless you fall off a cliff. 360 need to be running at more than 6K to get anywhere
    Last edited by crazypj; 10-20-2019 at 01:46 PM.
    ancientdad and oupa like this.
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