Do I need a top end?

[vort3xr6]

Back story:

My KX-65 was running great for the first half of the season last year. So much power and a very good powerband. After half the season the bike started not hitting redline. It would rev great and right when it would start getting into the powerband, it would hit a false redline. Motor has 28 hours since the last rebuild.

Here are the pictures of the tear down. What information can I get from this? The cylinder has brown marks in between the rings which I think means blowby.

I am gonna post this over on thumpertalk too but I wanted to get some opinions here.








I figured while I have it torn down I would probably just do the top end but a 12 dollar gasket is cheaper than a 130 dollar top end kit.

[highpsi03]

2 strokes need to be rebuilt pretty often, especially one that size. No offense but it is hauling your fat ass around (I'm not even sure if you are fat but on a bike that size a normal adult puts extra stress on it)
There is no way to tell if it needs a rebuild from pictures. A compression test would have told you for sure. IMO i would say, yes rebuild it. At the very least put new rings in it since they are what give you the compression you need. I would also suggest a light hone job to help the new rings seal better, and if needed you can get a slightly oversized piston if the bore is worn.

[vort3xr6]

lol I am a fat ass, but still. I always get told top end 40 hours bottom end 80 hours.

These minimoto's get flogged. Hard. So I guess I shouldn't be surprised.

[mdub]

No offense but it is hauling your fat ass around (I'm not even sure if you are fat but on a bike that size a normal adult puts extra stress on it)

that was why a buddy of mine's father always yelled at us to keep off the 50....lil thing would move, but yes it is working extra hard.

[brennahm]

40 hours? Good god...

[Bueller]

From what I see your cyl. is scored beyond honing, you can mic it but it should probably be bored .01 over. The piston doesn't look too bad (can't really see skirts) but the one before this on probably looked like shit.

[vort3xr6]

I keep getting differing responses on different forums. Thumper talk said the piston is trashed but the cylinder was probably good.

I cleaned up the cylinder a little bit and there was no scoring really. I couldn't snag a nail on the inside of the cylinder. I am taking the cylinder to Jim tomorrow for inspection and measurement. I would rather not spend $250 on replating.

[brennahm]

This is why you don't wait 40 hours.

[CYCLE_MONKEY]

I'm sure it would run better if you could keep all the dirt out of it. Why didn't you clean the exterior of the engine before pulling it apart?

The cylinder looks a little scuffed, but I'm no 2-stroke expert. Take hes parts to a shop that is.