KDXRIDER.NET

WOW!!! My Bike is a 2003 KDX220 and when I bought it it had maybe 5 hours or less ride time on it. It has been nothing but rock-solid reliable and other than regular maintenance it has been the most reliable bike out of the 20+ bikes I have owned so far in my life. I blew out my water pump seals last October and as a consequence coolant got in the engine and I guess pressurized the engine so the oil/coolant mixture, what I thought at the time, blew by the top of the right outside case gasket in the area next to the cylinder. Note that this engine has never been opened in it's life. So I opened the outside case the other day and found the factory installed case gasket totally mis-installed at the top. Must have been late Friday in Japan back in 2003 when this thing was installed! Anybody else ever see a screw up of an install inside the engine of any part of these bikes? I was really surprised seeing that it would have been pretty hard to mess up installing that gasket especially missing the pin like it did.
Funny thing is that until the water pump seals blew there was never an oil leak in that area. When it did blow however, oil was actually pumping out of that area at a furious rate, which was surprising as I would have thought that a crankcase vent tube would have relieved any excess pressure or is there not a vent tube like that on these engines? Another weird thing is that the weep hole under the water pump never leaked any coolant after the seal failed. I checked the hole after removing the side case and the hole wasn't plugged with anything. Odd... this ever happen to anyone else where the water pump seal failed, flooded coolant into the engine but never came out that indicator hole?

Yup, i've seen a small screw up in mine (probably) - the mechanic that was rebuilding my engine said that the engine appeared to have never been open as in the 35 years of the existence of my bike the bottom end has never been replaced- ( not one 3rd party part in sight) - and a washer was misplaced in the transmission - where it should have not been there

I have seen this mistake on rebuilds done by a professional shop on my current bike by the previous owners' full rebuild performed at a professional well-regarded shop. It took several seasons for it to be an issue, but when I slammed the bike down really hard on a rocky climb on the clutch case housing side, it then began leaking significantly. I also have been thinking I might have had a very slight head gasket leak for a while as well as I am at 465 hours on my top end under my ownerhip...
But the gasket on the top left side in your first and last photo has sagged down before on me, for that previous owner's shop's rebuild. That definitely is an area that needs to be watched when you install the clutchcase housing aka "inner clutch cover" as some refer to it as.

Have you changed the piston in your 220 yet? Or at least verify that you have an SK Pistons OEM version (very rare but very reliable) or the ART Pistons OEM version (very common and a ticking time bomb, highly unreliable)????

It's really important to look at the underside of the piston to determine which one you have. The ART Pistons version should be replaced immediately with a Wossner forged or even a Wiseco forged. You should have a cylinder professionally measured with a dial bore gauge or inside bore telescoping calipers, not just regular micrometer calipers at the top of the cylinder where it doesn't get any wear. Wiseco only makes A-sized 69.00mm bore pistons, and their quality control is not as high quality as it used to be so there is some size variation versus advertised.
Wossner is much higher quality and comes in A, B, and C bore sizes 69.00, 69.01, & 69.02mm measured bores. It's very beneficial to get the proper size and can be detrimental to not measure things ahead of time. Wossner forged always for the win. Wiseco makes great clutch baskets for our bikes, but I prefer to not use their pistons with Wossner available as a much better alternative