Hope that's all it is,no bent valves or other damage.

 

What causes this? Oil delivery issues I assume?
What oil were you running?

 

Several reasons for a lifter to fail. Seems like on a lot of these people have been having problems with the steel pressure relief valves that were used that would stick in the aluminum cases especially if they were neglected and never cleaned.This can cause a drop in oil pressure. On some engines piston/ring seizure can happen,lifters can stick as he says his has,plus on a lot of the 700s rod bearing failures. I had a couple on the 500 engines that I had to replace simply by going through regular maintenance and found them sticking. My guess is either a fluke lifter collapse that might be an easy fix or a sticking relief valve that he may not have checked out yet could have caused it.

Possible causes of internal engine parts failures from the manual. * items usually can go hand in hand.
* Oil pump failure
* Oil pressure drop
Wrong oil used
* Sticking oil pressure relief valve

 

Might be a dumb question, but do I have a pressure relief valve on my 06 sportsman 450? How does one clean it?

 

Yes same as the 500 does.Pressure reief valve or one way valve as some call it. On the 500 it's purpose is to keep oil from draining into the engine from the oil tank when the engine is off. If it sticks,problems can happen. Look at page 12 of this engine pdf for its location and page 32 on cleaning/checking.https://www.google.com/url?sa=t&rct=...ZN9jLa7SAHw2aI

 

Thank you, I'll keep an eye on it.