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KX65 Engine Problems

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Whats up guys, I'm fairly new to 2 strokes and I just recently purchased a kx65 to ride as a pit bike for fun. I know the previous owner and rode it when it was in good condition but since has had engine problems. I started stripping the bike last weekend and I am going to pull the engine this up coming weekend. While riding in 4th gear the back tire locked up from what seemed like an engine problem and was laid down on the throttle wide open. The bike started the next day but sounded terrible so I have not started it since so I do not damage it anymore. I am hoping it is the top end and I can get a rebuild kit and maybe make a few other minor adjustments and it will be fine? I am looking for some insight on what it might be before I bust into it. Thanks for any ideas/advise!

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There is a fairly good chance the bottom end seized.  The super small bore engines are tough on cranks.  You will know once you get it apart.

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Second that.

Be prepared and expect to find the connecting rod big end bearing roasted, (crank pin end). Once confirmed, get an oem ir Hot-Rods replacement crank kit. DO NOT put a wiseco in, no matter what the price difference is.

Good luck!

 

PS. Do not turn over nor try to start the engine, to prevent further damage. Take it out of the bike and open it up.

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35 minutes ago, turbo dan said:

There is a fairly good chance the bottom end seized.  The super small bore engines are tough on cranks.  You will know once you get it apart.

Would this alone cause the entire back tire to lock up? or would it be a combination of things? I can still put it in to gear but it does not run very well.

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4 minutes ago, FaceDeAce said:

Second that.

Be prepared and expect to find the connecting rod big end bearing roasted, (crank pin end). Once confirmed, get an oem ir Hot-Rods replacement crank kit. DO NOT put a wiseco in, no matter what the price difference is.

Good luck!

 

PS. Do not turn over nor try to start the engine, to prevent further damage. Take it out of the bike and open it up.

Should I expect this fix to be costly?

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5 minutes ago, FaceDeAce said:

Yes to the lockup

 

Costly is a matter of perspective. All in, 300 - 700 depending on how far the cage bits and rollers went.

 

Thank you for the help!

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13 hours ago, FaceDeAce said:

Good luck and let us know what you find.  Pictures are great.

Will do. What could have been the cause of the bottom end seizing up? Staying in power band too long? incorrect fuel to oil ratio? Something else?

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Too little oil in the mix, poor air filtration or it was just way past its service interval.  High strung small bores don't go hundreds of hours on a crank like the big bikes.

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8 minutes ago, turbo dan said:

Too little oil in the mix, poor air filtration or it was just way past its service interval.  High strung small bores don't go hundreds of hours on a crank like the big bikes.

That would make sense.. When i took apart the bike last weekend and got down into it i took the air filter out and it was completely gummed up with oil and totally black

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Bet youll find piston skirt broke and stuck in crank. Usually what wheel lockups are 

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Will do. What could have been the cause of the bottom end seizing up? Staying in power band too long? incorrect fuel to oil ratio? Something else?

 

Another possible: A heavy rider. That puts a lot of load on a very small bearing.

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