Please help!

I already posted this question on a different thread but then I saw this thread and seems like it will put me in a better place being I have a trx450er.

2 problems

1. I just shimmed my valves a month and a half ago and i just had to do them again last night. The clearances were way off and after every ride i clean my airfilter and reoil it. I dont understand why this happened so quick?

2. My intake valves are on their last shim, 1.20, so next time i need to replace valves and lap them, but my question is will i need any head work done aside of lapping the valves?