2003 KX 100 rebuild need help

[rick64n]

Just finished rebuilding my 10 son’s kx100 top end. The piston was badly pitted, as was the head cover. Before rebuilding the bike it started smoking badly and had a bad engine rattle. I got metal shavings out of the crankcase, inspected the crankshaft bearing, as it appeared to be okay (it moved freely w/no grinding). I cleaned out the crankcase until I did not see any more shavings by filling with oil, rotating crankshaft, and then turning bike upside down and allowed to drain. Talk to mechanic at shop about replacing head cover, he said it was okay to reuse. Proceeded with rebuild w/all new piston, rings, bearing, ring-snaps, and gaskets. Started right up, but with engine rattle. Turned off immediately. What is causing the engine rattle? How should I proceed?

Thanks for any help!!

 

[Tony Eeds]

Welcome to the site :cool:

I am going to move this over to the General Bike Repair forum. You will get many more views and much more info there.

Be sure and go to your User CP and update information relating to your location, type of riding, etc. After that grab a spot on the couch and tell us a bit about yourself. How long you have been riding, what kind of riding you prefer, where you are located, etc. We will do our best to hook you up with some fellow dirt bike enthusiasts.

Again, welcome to the site, and shout if you have any questions!

 

[Radiator Ron]

Rich metal shavings came from somewhere, you have to find it. I would suspect rod or main bearing, smoking sounds like a right side crank seal, or maybe coolant leak. Inspect the lower end by disassembly, i would also either replace or repair that head. Depending on severity of gouges eric gore might be able to recut head for you and clean it up for about 50.00 from what i've seen. Dont run bike or you'll be buying another piston.

 

[gwcrim]

Finding metal shavings but no source would scare the heck out of me. I'd want an answer before I started it up again.

 

[nickyd]

he told us right where the shavings came from - the head and the crown of piston...that's b/c the air filter was neglected and the motor was sucking in dirt when it was running and the motor created a bead blaster in the cylinder......the rattling you hear could be a number of things - how bad was the piston worn? did you measure it? what is the clearance between the piston and cylinder? Does the cylinder need to be bored? If you've got a worn cylinder and you slap a stock bore piston back in it, you're going to have a new piston in an old bore - and she will rock and rattle just like with the old piston....if you didn't measure or don't have the tools, pull the head, move the piston all the way down in its stroke...run your finger up the bore - feel a "LIP" near the top? if yes, that's a sure sign you need to bore it out as the cylinder has worn out and has created a taper. let us know what is up with it.