Top end rebuild

[DirtDaddy]

How often (in hours or miles) does the top end need rebuilding on a KDX200? How big of a job is it and what all does it include? (Just cylinder honing and new rings or...?) How often does the cylinder need to actually be replaced vs. just cleaned up? How about the cost of a top end rebuild? Trying to get an idea of the maintainance involved with two strokes. This is assuming "normal" trail riding and no racing. Thanks!

[KDXGarage]

With a normal amount of normal trail riding, you may want to take apart the top end in the winter when it is too cold to ride. You may need to replace the rings at that time. Due to Kawasaki's Electrofusion coating on the cylinder, they suggest not to hone the cylinder walls. Some have used a green Scotch-Brite pad to remove any glaze. I can't remember anyone replacing a cylinder due to normal wear. I have heard of people getting it replated due to piston failure or something like that, but not through normal use with good air filter maintenance.

Normal top end service includes cleaning the power valve components. Carbon can build up on the valves and after a few years of neglect can cause the system to break or fail otherwise. It is one of those things that if done yearly, you shouldn't have to worry about it.

The engine coolant is drained during this time, so you would have the cost of replacing it ($3 or so, as it is roughl 1/3 of a gallon, and you can just buy a gallon of 50/50 coolant pre-mix for example). An aftermarket top end gasket kit is around $30. OEM rings are around $35?? Someone help me out on that. I would suggest you take the piston off during top end service and clean the carbon off it. When you do that, you need at least one new circlip $2.50-ish for OEM. All in all, probably $80-ish for doing just the rings, then the next winter, you can do rings, along with piston, pin, circlips and pin. That would put you at about $175-ish OEM and $150-ish aftermarket (Wiseco brand piston kit for example).

Compared to your previous WR, I would imagine it to be a bit less "high-maintenance" and cost less when it is due.

All the above costs are assuming you do the work yourself instead of a motorcycle repair shop.

I hope this helps.

[NM_KDX200]

I ride 2-3x a week for 1-2 hours each time, varying between play biking in the creek to running hard down jeep roads in the woods. I've put 2 pistons in my bike on an every-other year schedule and in both cases, the rings were not even worn out of the "new" specifications. I use Pro-X pistons and Yamalube 2R at 32:1.

The only reason I can see to replace a cylinder is in case of an accident- loose circlip, dirt, busted piston, etc.

[DirtDaddy]

Thanks guys! Doesn't sound like it's that big of a deal with normal trail riding.

[NM_KDX200]

Naw, not a big deal.

Prior to the KDX I had a '92 Yamaha YZ250WR and it was the same story. I changed piston/rings pretty quick upon getting it. Previous owner had been using Bel-Ray MC1 at 40 or 50:1 and there was heavy carbon on everything. Powervalve was stuck. I put a Pro-X in, switched to Yamalube 2R at 32:1. A year later, I tore it down and the rings were still well w/in new specs and the powervalve was sliding slick as can be. Almost NO carbon build-up anywhere. I put a new Pro-X in since I'd already ordered one. Rode it another 18 months and sold it.

When I got my KDX in '01, it was in great shape. Original graphics, original jets, everything stock (except someone must've worked on the suspension 'cause the forks are NOT soft at all. Jason's gonna find out the truth for me pretty soon). Owner was using BelRay MC-1 at 40:1. Tore it down. Carbon everywhere. Powervalve working but heavily carboned (those are my pictures on the Just KDX site, BTW). Cleaned it up, put a Pro-X in, ran it for 2 years. Tore it down again. Still w/in new specs but on the outer end, no carbon at all, very clean. Put a new Pro-X in. It's coming up on 2 years this spring.

Got my KX125 in Sept. Original owner put a Wiseco piston in and was using....you guessed it!!! Bel-Ray MC-1 at 40:1!!! Being a 125, I figured I'd better get in there, so after a few rides, I tore it down. Heavy carbon, powervalve stuck and disconnected (KX has a spring loaded opener that'll pop off before causing damage). Put a Pro-X piston in, switched to Yamalube 2R at 32:1. Ran it for 2 months (months!!), approx 20 hrs. Tore it down Sunday evening, ring was at the end of "new" specs, powervalve was sliding slick as can be, everything looked great- very little blow-by on the piston. Wiped the top of the piston clean with my finger. Put a new ring on, buttoned it back, started 3rd kick. Started 1st kick today.

That's my experience with modern 2-strokes.

[fuzzy]

FWIW, I change the top-end when the bike won't idle anymore or get's hard to start...Lack of compression will show up more at these RPM's. Well...IT does show itself in peak power loss long before that, but I never really care. The 250 has top-end to spare...