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Time for a top end

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Hey guys, so this is the first time I've ever owened or tinkered with a dirt bike. Since I'm able to kick start my YZ125 with my hand, and only have 120PSI of compression I believe it's time for a top end. Before I go out and buy a top end kit, I read something about getting the cylinder replated or honed. Is this a must? Or can I just buy the top end kit? I've only put 5 hours on her and only intend to single track ride it so I'm not looking to spend tons of cash. Also, would looking through the exhaust port give me any valuable information towards doing a topend? 

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I read something about getting the cylinder replated or honed. Is this a must? Or can I just buy the top end kit? 

 

Also, would looking through the exhaust port give me any valuable information towards doing a topend? 

 

Only if there is damage to your cylinder. Since you said its running good, probably no damage and you are good to go. Won't know until you remove and inspect.

 

No, looking won't do much. Best indicator is to put on an hour meter and do a top end every 40-50 hours.

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Would it be a good idea to order a D sized piston and just install it? 

 

No, I would check the etching on the cylinder for manufacture size. Even that won't tell you much if the previous owner installed an over-sized piston instead of OEM size.

 

I would recommend a Wiseco kit. It only comes in one OEM size for the yz125

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A bore gauge is the only way to accurately measure the bore

 

mainclearance2fs.jpg

 

Thank you very much, I'll invest in one.

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