Had Mike from Lazer Porting install valve guides in a cylinder head - everything looked great, looked like a nice job. Assembled the motor, and once warmed, smoked like a bastard. New pistons, new block, new valve guide seals, etc. Took it apart to find that 75% of the guides were loose in the head, allowing oil to get past, into cylinder and exhaust ports. Even though the head was ice cold on the bench, I was able to knock the guides right out - one shot with a light ball peen hammer.
Good job Mike! You got my business - when it comes to heads, think 'LOSER PORTING" . . .