250-500cc 3rd seizure on a 12 wr300

Did you check your main seal under the magneto?
HS, I read through your thread and your issue is not oil related. Your piston temperature was too high and expanded into the cylinder wall.

I sprayed stater fluid behind the stator while bike was running. And nothing happened. I held the throttle at a high rpm, and still nothing changed. I also sprayed it around the the intake boot. Nothing changed. Pre-Detention? Could this cause the high heat?

It could leak air in from the intake boot, base gasket, center spit of cases, etc. Husky did have an issue with crank seals, how long has it been since replaced? What is heat range of plug>?

Never replaced, bike is a 2012. 20-25 hours. Heat range of 9.

What kind of riding where you doing when you had wall contact? Were you running 87 octane fuel or higher?

High speed desert riding. I was running 91.

You may of have just got it really hot/detonation. In order to run higher mixtures of oil, you must jet richer. Not only because you are displacing a little more fuel, but because the oil will actually lower your octane down. Modern oils are not as effected as the old ones, but it may still of lowered you down below 85. If 927 is available, it will protect better than M. Lucas octane boost will push you up three numbers and is inexpensive. We also run waterless coolant, there is no hot spots and it helps for high speed desert.

Has anyone mentioned timing yet?

What's the approximate octane rating for premix oil? Seems like it would have to be really low for it to have a real influence on overall octane...

The difference in fuel delivery from 24:1 to 50:1 is really small, like 2%.

I'm convinced that a totally hammered piston like that is the result of some major flaw, not a main jet 1 size too small or running 50:1 instead of 40:1. Air leaks or the wrong sized components seem like likely candidates. Wally has also suggested (several times) that the bottom end looks way too dry, I'd take the mans advice and look into that...

personally i would get the cylinder measured and see if its got a taper on it, then i would check the water pump is circulating and that there is no crud in your coolant system.
i would drop a little more oil in every mix, how far into the ride have the seizures occured?
questioning warm up time and thermostat if your 300 has one.

how did the piston rings look were they eaten?
any pictures of the damage would be very helpful.

its truly gutting when the rear locks up you have my sympathy

Being as though it seized, the engine most likely got really hot. Replace all seals, overheating is bad for seals!

Can't change it, i have the same bike, same year. By the way that trans is still going strong!

1.9% actually. I had this argument with management already. Leaning your mixture out is more myth than fact.

I honestly don't know. In the old days before synthetic modern oils, the octane was often reduced from 92 all the way down to 72. This gave the effects of a lean mixture without the understanding of what might really be happening. Older recipes of 2 stroke oils contained octane boosters, such as Blendzall. Modern oils do not effect the octane like this nearly as much, but you could see what would happen if you ran 87 by accident. Because octane has been lowered, more fuel must be delivered to counter the added heat. If your spark plug becomes too wet, adjust your spark plug to match your fuel, never the other way around.

po

possible pre-det caused by erratic spark from faulty ignition.check for consistent & strength of spark.

A big hug goes out to both you guys. It just sucks to have this kind of trouble with such a simple motor. Not to mention the lack of confidence it gives you in your machine. Best of luck in finding this menace.

I rejetted mine and I don't seem to be having any issue. 20 hours on the new top end since. (Have hour meter)