I recently rebuilt my son's top end only needed piston and rings. I have it back together and it will not start have spark, compression, and getting fuel. I think I may have it out of time at the valves. Is it possible to set this timing with out taking the cylinder back off. Any tips would be greatly appreciated.

 

Its been awhile since I've worked on a kx bike. There is no timing on a 2stroke. Unless the KIPS valves can be put in wrong which I dont think so. If in fact this is a 2 stroke. Now if it was a kx250f or 450f, then timing is involved. Did you check your reed valves?? Might not be closed all the way. Might have a lil gap or chips or broken pieces. What caused you to put a top end kit in it??

 

hmm, you may want to back track some and check the sealing of components. The cylinder, head, kips re-install, reed cage (torqued properly and checked for being warped), the spark plug loose.

Welcome to KF

 

first yes it is a 2 stroke. I bought the bike this summer my son was at friends riding for two weeks and called me up to say bike wont run . he is 17 and a bit clueless if you know what I mean.There was little or no compression so I took it apart after looking all over the net for a service manual that I could afford. I found a hole in the piston where the valve ports are in cyl. it got hot piston was kind of melted a little it looked like. cylinder looked fine I did not measure it but it was clean and shiny. I didn't see any signs of anything in crank case and ring was all there. so that is why the new top end. My son did put a performance reed valve kit in it so maybe I need to start there today.. I never did one is there only one way they can go in like a check valve type?

 

I did torque everything I worked on to spec but like I said I didn't even touch the reeds.

 

FYI I took the reed valves out and put them back in retightened everything and still no run. So as was staring at the bike and touching stuff I figured I would check governor to see if it was working and it was. Since I had exhaust pipe off I looked up into cyl. and felt up in there with finger and found alot of oil. I had asked a couple friends if I should fill valve area with oil they said yes. well the answer is actually no. I drained the oil out of valves made sure carb was tight put pipe back on and she fired right up. It runs very nice. Thank you for your replys you did send me in the right direction.

 

Did you hone the cylinder? Nice and shiny is actually a bad thing. You want crosshatch marks in a cylinder so the rings seat in properly.

 

No I did not hone the cylinder hope it lasts awhile. I guess next top end rebuild I will hone the cylinder thanks for giving me something else to worry about lol

 

Thats what we are here for haha. U can get a hone stone and if u have a drill you can do it easy or just take it to an engine shop and they can do it.

 

hahaha, if you take the top end off the ride, will you post up some pics of the cylinder and assembly?