Breaking exhaust valve guillotines can be quite comon if you are running on mineral oil, or some semi-synthetic crap for a good mileage..
Say you use <Brand X> mineral/semi-synthetic for 5000 km, you can be quite sure that you will have to change your guillotines and a piston or two quite soon, or allready have..
The reason is that while running on this type of oil, you are getting a coating of exhaust "debrief"? not sure of the word, but you will get a black coating , that can go up to a few millimeters in thickness , this ofcourse will make your sled perform less, and in the end jam/lock the guillotines, which again may result in a breakoff, or a total fuckup of your engine..
I've seen this happen a lot in norway, especially farmers and reindeer farmers who arent concerned about performance, but good gas mileage and cheap oil.
RUN WITH ORIGINAL SYNTHETIC OIL! VES Gold for Polaris works wonders !
Tip for cleaning guillotines on Polaris:
Screw lose the 2 outermost screws on the valve cap, lift up the guillotines carefully..
Then take a really thin knife/razor and carefully cut off the black dirt off 'em, be careful not to scratch the guillotine itself.. After this, take some carb cleansing fluid and wash them with a sponge with raw surface, when the guillotines are shining, mount 'em back on - now enjoy your ride
Check if there's lots of oil around the guillotinecap when you lift it off, if it's running down the sides of the cylinder when you remove the cap , you should adjust your oil pump slightly lower , a single mm on the marking should do.