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85 kx125 top end rebuild question

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I just picked up a project I am hoping to rebuild for my son. The bike has real low compression, (can kick over with hand on kick start) I need to pick up a new top end kit. From what I have gathered, will an 86 piston kit work with an 85 model? I thought 85-87 were pretty much interchangable. The cylinder and piston did not look too bad, no metal or scraping. Anyone been here before??

MattyB

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Measure the cylinder and current piston, ring gap, etc.

Look on the Kawasaki site, or Wiseco site to see what will match up.

Check the crankshaft bearing play while you are at it. If the top end is that worn out, that may mean the bottom end is worn out, too.

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I agree with KDX, you definitely need to measure the parts and not just visually inspect them.

But to answer your question according to the online parts fiche, they use the same part number for the piston.

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The part number for 1985 is the same for 1982 - 1985, with supersession to the 1986 piston part number. 1987 is different! The 1985 diagram shows two rings. 1987 is a single ring. Not only is it on the diagram, but I have a new 1987 OEM piston and four single packs of rings for 1987. They are NOT the same.

Post some pictures of the cylinder and piston. Let us mechanic wannabes try to guess the condition. :thumbsup:

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Yeah I should have clarified, I meant the 1985 and 1986 use the same numbers, sorry about that, lol.

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GetAttachmentaspx.jpg

Thanks for all the info so far. The bottom end feels pretty tight and moves fine. The piston on it only had one ring, so it has been replaced by someone with prob the 86 version.

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