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My 04 200 has approximately 100 hours on a fresh replate and Pro-x piston. Most of my riding is low RPM technical trail, with logging roads between to clear it out. It runs great, no power loss, just wondering how long do most run a piston and rings?

In my racing past it was always changed every 5 races or 15 hours whichever came first. I think Pro-X recommends like 25 hours. Nowadays I run it until I see a noticeable decrease in compression. I check compression every few rides and keep notes. My current piston/rings have about 75 hours on them and have no noticeable loss in compression.

I run only forged pistons in the 220 and I go until I start getting towards the lower end of compression spec. I think I'm over 400 hours on my current Wiseco and she is about due. Oh, and I don't ride my bike easy! If I was running a cast, which you should never use in a 220, I would go no more than 100 hours or so.

If I had a fresh replate, I sure as hell would not let it run real long.Even at 1,000 RPM, the piston is riding against the thin film of oil between it and the cylinder... 16.6 times per second! Rip it to 10k RPM for 166 per second.

KDXGarage wrote: 10:16 pm Aug 04 2022 If I had a fresh replate, I sure as hell would not let it run real long.Even at 1,000 RPM, the piston is riding against the thin film of oil between it and the cylinder... 16.6 times per second! Rip it to 10k RPM for 166 per second.

I know not an apples to apples comparison but here in Thailand there are many many 2 stroke scooters with 70,000klms and never had a rebuild, seems a bit extreme to be changing pistons often

Maybe I take a slightly different approach. I'll change rings on an existing piston that is still good. It's the rings that ride on the cylinder walls so I always want to make sure i have good solid ones in the bike. A broken ring is a big time problem. Generally I would put in new rings about every 3-5 races, maybe more often if doing a lot of hard riding between races. I also watch compression; not so much the specific number but how much it changes over time. I always kept a notebook that gave me a running history of compression so I could see a trend. As long as we're talking, fresh oil every race, plug every other. Fresh premix using 93 octane alcohol-free pump gas.

Compression is 135 psi, the usable range stated in the manual is 95 -151psi . This is the first check on this top end so I don't have a reference but will keep track from here on.

Forgot,, Compression corrected for altitude is 122 psi @ 3500' elev. so right in the middle of the service range.

I know this is dragging up an old thread, but it may be useful for some. And sometimes, people should read old threads. They are kept for a reason.

I have a 2005 KDX200 that I bought about 2 years ago and it just blew it's head gasket at a race meet, so I take the top end apart for the first time (since I've owned it) and find that it's been bored and sleeved and has a 70mm bore (which actually makes it a 223cc).

So I'm trying to find a 70 mm piston for a KDX and the only one I can find online is a Wiseco which is for a KDX220 with a +1mm overbore. But here in NZ or Australia, no one has one. It's in the catalogue, but not very common.

And that is actually the piston that was already in it. It already had this rare 70mm Wiseco piston. So I check this piston over and it doesn't look too bad. Just a bit of carbon on the crown. The rings look ok too, They are free and shiny. Though I have no idea what bad rings would actually look like. I also have no idea how many hours this piston has on it. But it is a forged Wiseco, so it's going back in.
I got a new top end bearing and wire clips. It's going back together this weekend and I expect it to perform just as good as it did before the head gasket blew. Let's see how long it lasts.

Thoroughly clean the piston and meticulously inspect it for any signs of cracking or deformation. The biggest thing for me is to look at the skirt for wear and measure the cylinder bore to ensure that it still has a good piston to wall clearance specification. The problem with all Wiseco pistons for our bikes is that they only come in overboard sizes, they do not come in B, C, or D sizes to compensate for cylinder plating or sleeve wear. Wossner do have 69.01mm A-oversize, & 69.02mm C-oversize, but Wiseco only offer stock bore A-size & then overbore sizes (only +1.00mm overbore @ 70.00mm for the 220, no 69.01mm or 70.01mm nor 70.02mm. this means that you must receive if the sleeve is worn, which will wear significantly faster than plating, however, a chromoly sleeve will last a bit longer before wearing, a bit closer to the original electrofusion plating.

Your best bet would be to find another stock cylinder and have it stripped and replated, that way you can run a Wossner or Wiseco A-size and then once the cylinder has a slight bit of wear, you can run a 69.01mm Wissner B-size.

The 70.00mm Wiseco is a commonly available piston here in the USA. You could have one imported if your cylinder measures up to spec. I would imagine you can get by with just cleaning the top end, particularly the power valve components, and cleaning the Piston Ring grooves in the piston and reinstalling the stock rings if they check out to have proper gap specification, as long as the compression still felt good.

SS109 wrote: 05:31 pm Aug 04 2022 I run only forged pistons in the 220 and I go until I start getting towards the lower end of compression spec. I think I'm over 400 hours on my current Wiseco and she is about due. Oh, and I don't ride my bike easy! If I was running a cast, which you should never use in a 220, I would go no more than 100 hours or so.

SS109, I'm at nearly 460+ hours on the Wiseco that the previous owner installed, and I definitely run it quite hard, but at 40:1 high flashpoint oil in order to get the best protection.
At this point I believe I can hear a very slight bit of piston slap, but last time I had the exhaust off the season, the piston skirt still looked almost like new. It might be time for a Wossner B-size piston, perhaps. Much to my surprise, compression is still well within spec despite the long hours and hard use / high revs on this 220.