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Thread: rod seized

  1. #1
    Junior Member turbosixgn's Avatar
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    rod seized

    My motor
    Honda TRX250r oem cylinder-ported mid/high by Neil
    69mm bore
    Oem crank stroked +2mm by crank works
    Connecting rod is a new hot rod
    ESR mid/high pipe
    ESR reed cage
    38mm carb
    Cool head with race dome

    This setup is tuned well and runs/ran great, out pulls my buddies banshee and quadzilla. I had about 30 gallons of gas thru it when it seized. After taking it apart I found that it was the bottom end rod bearing that seized. When I put the motor together the bottom of the rod sticks out below the crank shaft but cleared the case. However the rod had been hitting about a 3 inch section of the case on the down stroke and about a 1 inch section on the up stroke side. The fine aluminum dust eventually seized the rod bearing.

    I have read on this site that people have put in a +4mm stroke and not have to modify the case. Then why is my +2mm stroke hitting the case?

  2. #2
    Super Moderator C-Leigh Racing's Avatar
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    Normally a +4 stroker crank, like a Hot Rods or ESR, will have a clearanced big end rod & no case trenching is needed, but with a rod that the big is left stock, theres not enough room under the crank to clear that unclearanced rod.
    Neil

  3. #3
    Senior Member DnB_racing's Avatar
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    I kinda surprised you didn't see evidence of the aluminum dust on the spark plug, or felt any unusual vibrations well before any chance of seizure???

    I would have thought that there would be at least something noticeably strange,

    was the plug fine, and no noises to raise any warning signs?

  4. #4
    Junior Member turbosixgn's Avatar
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    How much clearance is needed between the rod end and the case?

    Neil Thanks for the work that you did on the cylinder! this motor ran so sweet!

    Kevin

  5. #5
    Senior Member american opel's Avatar
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    sorry to hear.hopefully you and neil can figure out what happened,so it won't happen again.

  6. #6
    Junior Member turbosixgn's Avatar
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    Quote Originally Posted by DnB_racing View Post
    I kinda surprised you didn't see evidence of the aluminum dust on the spark plug, or felt any unusual vibrations well before any chance of seizure???

    I would have thought that there would be at least something noticeably strange,

    was the plug fine, and no noises to raise any warning signs?


    When i put the motor together there was clearance, however small obviously not enough. So under idle there was no vibration and hard to tell under hard throttle/riding. The plugs were slightly black but nothing that looked concerning. Most the aluminum dust was oil coated and stayed in the bottom.

  7. #7
    Super Moderator C-Leigh Racing's Avatar
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    Quote Originally Posted by turbosixgn View Post
    How much clearance is needed between the rod end and the case?

    Neil Thanks for the work that you did on the cylinder! this motor ran so sweet!

    Kevin
    You'll probably need at least 1.5mm of clearance, trenched into the cases to clear the rods big end, but it depends of which replacement rod kit you use.
    You could get a rod kit from ESR, that has already been clearanced & not need to do any case trenching. They have those in stock & are the Pro-x brand.
    Neil


 

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