Originally Posted by koltonmoe
please help me i am 17 and i am rebuilding the motor in my 72 chevy blazer. its a 350 small block and i put a roller cam in it and roller lifters and roller rocker arms but i can not figure out how to find the right size pushrod length because iv bought 2 sets and one was to big and the other was to small...please help and my name is moe
First question has to do with process. Here's a link to Comp Cams and the instruction for determining push rod length. Are you following this method?
You'll see they recommend an adjustable push rod length checker, as has also been recommended in the responses to you. The pain of this is that push rod checkers aren't all that strong so you need a light weight spring which drives you into an assembly and disassembly of the head to set this up, check, then tear the set up down to replace it with the intended service spring. This can be done with the head on by bringing the piston almost to TDC then filling the combustion space with rope to support the valve to have the springs replaced then using a tool make for this purpose to compress the spring to be removed and its replacement for service installed. Don't forget to take the rope out of the chamber when you're done.
As you're seeing, getting a hot rod engine built is not all that easy. As you move away from the factory design you spend a lot of time having to mock the engine up to check dimensions then tear it down to put it back together again. Once you get the push rod lengths correct you'll need to go back and check for piston to valve clearance which is likely to involve another top end assembly-disassembly-reassembly routine. An aftermarket roller cam is very likely to have piston to valve clearance issues because of the higher lifts and longer durations involved. You have to go at it carefully you can't assume that everything just fits together.