All 2st Piston/Cylinder Help !

09 WR 300. Need some advice here. Piston obviously bad. Wore completely through the rings on one side. The cylinder is scarred also but I have no idea if it is bad enough to re-plate / sleeve. I have been told by a few that it can't just be honed but needs to be re-plated. Question is - where do I send it to be re-plated. I have called Halls and they suggest I send it to them and they will send it out and get it back.
More important question is how did this happen - This is an 09 wr300 with only 300 miles on it. When i pulled it apart - the radiator was nearly dry. I noticed that the O-ring on the cylinder head was torn (see pic). could this have allowed coolant to leak and dry up my radiator??? Any help would be appreciated.

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I would try cleaning up the cyclinder with WD40 and paper towels and then green scotchbrite and soapy water. Keep repeating until nothing comes off on a white paper towel. Sometimes a lot of what you see in there is metal from the piston. Then when it is completely clean you can see if the nikasil is damaged.

Just my opinion it looks like the inner O ring has failed letting coolant into bore and thats what has caused the damage you are seeing. I would do as utopia says give it a good clean and then see what its like.

So assuming the O-ring is the culprit - the next question is - what would cause that O-ring to fail especially with so few hours on this bike??

Possible assembly error. The o-ring may not have been seated 100% correctly into the groove and the coolant pressure was finally too much for it to handle.
OR maybe you got one of the bikes with a bad seal at the reed block. Get 2 Honda 250R reed gaskets and seal both sides of the reed block with them.

I would get the jug fixed (Poweseal is who I use for replating), check the coolant passages to ensure they're flowing and then reassemble. After that I would be checking the coolant level often to ensure the problem is solved.

That brings up another interesting phenomenon now that you mention reed gaskets. I noticed when I first bought the bike that the boot covering the reeds was beginning to wear out. Almost to the point of a hole in it. I replaced it and have hardly wridden it since and It is beginning to do the same thing again. Seems to be cracking around the square portion.???? I know it only has a gasket on the jug side now.

I cant remember exactly what the problem was, but I think it had to do with Moto Tassani (or whomever makes the reed cage) stamping the part number into the mating surface, which made for a bad seal. I caught wind of this issue early and put the Honda 250 gaskets on both sides of my reed cage on my 09' wr300. I just sold the bike a few weeks ago with 140hrs and no issues.

In fact, I spent 2 weeks riding in the Sierra with a busted radiator and sometimes it would bone dry when I checked it. These motors are tough as nails, so I'm really wondering if you're suffering from the reed block leak issue. Air leak caused too much heat in the head and the o-ring went AWOL

I have the 300 sitting in my garage now and just checked the square boot you were speaking of and it looks fine on my (old) bike. No cracks, holes or anything out of the norm.

From looking at the picture of the head it would appear that you had an o-ring failure, which resulted in a very bad leak. The o-ring is broken and you can see where the gases have passed into the cooling jacket.

The piston and cylinder are the part that looks funny. One, normally a leak of the magnitude would cause the exhaust side of the piston to burn, not the intake side.

Secondly, the ring end gaps appear to be in the wrong place. Normally they are a little further to the left and right of center.

I guess it could have been that there was a very bad leak around the reed gasket that started it all and made the piston cold seize on the intake side and cause a lean condition that made a lean condition that made the head / o-ring fail.

But, with all that, I would still expect to see some exhaust side burn / seizing of the piston. Hard to tell sometimes from pictures.

It that bike have a high, uncontrollable idle before this happened?

The piston wasn't in backwards, was it?

I really appreciate all the feedback here to help me piece together the story here. So in answer to your ?s - I do recall one quick ride recently whe I seem to recall that my idle was quite high. I even remember getting out the tools to adjust it down a bit. The biggest mystery has been the continued gas leak every time I have turned the gas on lately. The bike sat for most of the summer. When I finally got it out and turned on the gas - it was just pouring out of the overflow tube until I shut the pet-cock off. I cleaned out the carb and checke the floats and put it back together and it still leaked. As far as the piston in backwards - the side you see in the picture above was on the intake side by the reeds. ??? I am planning on sending it to Millenium Technologies for the re-plating and new Wossner piston.