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  1. #1

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    Another Spun Ring - GP1300R

    Just had another spun ring, this time on cyl #2 at 132 hours.
    The first spun ring was couple years ago on cyl #3 at 88 hours.
    In both cases the ring locating pin was loose which allowed the ring to spin and catch exhaust port.
    I also checked piston #1 (front) and the pin is loose on that one also but no damage, yet.
    Searched the forum and it appears this is a known weakness of the oem pistons.
    Are there any other known causes of this?
    How to prevent this?
    Since the first one failed at 88 hours I suppose I could replace pistons every 80 hours which is expensive but maybe prevent cyl or crank damage.
    Please advise.

    Thanks, Ceril

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  2. #2
    How is the repair job going

  3. #3

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    Slow and methodical.
    Sent my crank out also to CrankWorks for inspect, true and weld so the bottom end will be healthy.

    The spun ring has happened to me twice now and after close inspection of the loose ring locating pins I completely understand the cause now.
    The yamaha oem piston has a design flaw in my opinion. The ring locating pin is not centered in the ring groove, see first pic.
    Over time, the forces from the ring on the sides of the pin cause it to loosen and then the pin works its way up into the ring groove.
    Eventually the pin raises to the point where the ring spins under it and results in ring ends in exhaust port, kapow.
    The second picture shows the ring locating pin has worked its way up into the ring groove.
    Both pistons that failed had the exact same failure signature with the loose pin.

    I discussed this with the machine shop guy at work and he showed me a piston from a 250cc 2 stroke dirt bike where the locating pin is centered in the ring groove.
    This is a much stronger design since the pin is supported equally on top and bottom of the ring groove.
    I just got the 3 new oem pistons and plan to replace the stock pins with a larger diameter slotted spring pin (www.mcmaster.com/#91611a154/=skc7x1).
    A slotted pin has an advantage over the solid oem pin where it will be able to grow as the piston heats up to retain the press fit.
    The machine shop guy will do this for me on his mill so he can accurately mill the larger pin holes in the pistons.
    Anyway this is not something you do in your garage.
    My other choice is to replace pistons every 40 to 50 hours or risk the same piston+cyl damage.

    Ceril




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  4. #4
    BahamasGPR's Avatar
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    I think personally I would be using a different piston - Wiseco, Pro-X etc

    Used Wiseco Forged pistons in MX racing for many years and never had an issue with piston itself.

  5. #5
    Almost's Avatar
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    Sorry you didn't hear about this the first time you rebuilt. I thought it was common knowledge in the GPR world, but I don't think there is any stickys about it unfortunately. Carl at Island Racing explained this issue when he was rebuilding my motor and I only wanted OEM. He talked me to going with pro-x so I wouldn't have this issue, matter of fact it's the whole reason I needed a rebuild in the first place. I spun a ring on the 3rd cylinder at 167 Hrs. Pro-x pistons are made by ART which just so happens to be the people that make OEM pistons, they are almost identical but better designed locating pin. So yeah go with pro-x.
    Last edited by Almost; 06-25-2014 at 07:22 PM.

  6. #6
    Just out of curiosity is this piston evidence of a possible same issue ?? I have the pro x pistons I am about to install after getting all cylinders back ski had 165 hrs
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  7. #7
    Almost's Avatar
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    I would say no since since it has a hole in the side, that was caused by heat. This is what mine looked like, that was after riding on it for about 20 min to get back to my dock on 2 cylinders.
    .
    Click image for larger version. 

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  8. #8
    I u look at first piston photo of thread that one has a hole in it too in the exact same place once compression is lost doesn't heat burn the hole In the side and due to combustion loss oil does not circulate through cylinder

  9. #9
    Almost's Avatar
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    I think his is the hole in the third pic blown out on the other side, i could be wrong. Is yours a new hole or in the same place?

  10. #10
    read the comments about welded top pin pistons, once done piston pin issues will be a thing of the past.

    http://www.us1.cc/ { I am not affiliated and have no special interest so I gain absolutely nothing !

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