2 fast 4 u

i have a full Yoshimura exhaust

Dyno Jet kit

K/N air filter with sleeve

Hot camshaft 

cylinder works 479cc big bore kit (Getting put in within this week)

So i recently bought a Honda TRX 450r 05 kick start model i am the 3rd owner. this bike ripped when it was running but i ceased it.I freed up the piston but there is little compression now. i think i ran it out of oil but it was like 20hrs or so since the last oil change. My real question is that i heard you have to rebuild the top end every 15 hours is this true? Now i have bought a new big bore kit to replace the cylinder and the piston but i dont really want to have to rebuild it every 15hrs.