riding my mc21 today. leaked a bit of coolent yesterday though it would be sweet today just riding for about 10-15 mins on the there noticed it was overheating severly, i pulled over and the coolent hose going to the low barrel had come off. i put it back on the best i could, (had no cellphone, no tools on me) on my way back home must have popped off again over heating and blowing a gasket.
Does this mean its game over for the engine? or can i replace a few crutuel parts, thinking off getting the tyga big bore kit. advice would be much appreciated, cheers.

Until you take it apart you won't know what is wrong with it. Start with pulling the plugs and see how they look. Then pull the pipes and look up the exhaust port. You can usally see any damage that way. Was the bike still running when you got home??
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nah fully died out had to push it for about 30 minutes, its at some fellas place at the moment, gotta pic it up today had oil and coolant pissing out of the top cylinder gasket.

May have done terminal top end damage.

Follow Steve C's advice for a rough idea, but you'll really need to pull the cylinders off to get a proper idea of what's going on.

You might be lucky in that it didn't seize, but you'll need to check the flatness of the heads as they may have distorted. Also worth looking closely at the bog and small ends. Any signs of discolouration? This is not a good thing and means they've overheated and could possibly be out of round. Dothe bearings show any signs of blueness?

In the best case you'll probably find that the heads have warped a little.

The NSR doesn't like to over heat. No two stroke does, so don't take a water leak lightly. If it leaks then stop.....fix it....and go out and play again. Cheaper and much less frutrating than having to pull it apart.

Hells teeth, this is exactly what happened to mine recently.

I think it might be prudent for those who haven't suffered to check the lower coolant hose, and ensure that it's well secured to the barrel!

Mine screwed the top barrel and piston. Everything else seems ok (though I'm not 100% sure about the crank).
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

yeah, that bottom hose you really have to watch, im not even sure the last mechanic to look at mine done the job properly because the hose clamp nut were you tighten it was sticking straight up into tthe radiator. the hose had deatached itself from the cylenderhead. i can still push it though so that got to be a good sign, anyways guys cheers for the info, think i might just cut the shite and get a tyga 300cc kit. cheers.