sounds like you could have a real problem, if the push rods are all the same lenth? The problem is either wear in the camshaft followers which is a complete strip down of the engine to repair or that you have wear in the rocker assembly which can be replaced quite easily from a car breakers,or that the push rod has slipped off the cam follower which can be reset in the same procedure as the rocker assembly
Chris rigby
March 2006