Push rods on a 390 with stock heads.

[mrtleavitt]

I had a miss on the left bank of my 390 the other day so I gave it a tune up (plugs, wires, rotor, cap) and after that it was still missing. So I checked out my push rods to find 2 bent ones. They were just slightly bent as I rolled them across the wood floor in our living room. Anyways, I replaced the 2 and noticed as I was looking them up on the computer at Autozone, they offer the standard sized rods as well as rods that are 0.060 oversize length. Now why would they make those? The only thing I could figure is if you used a super thick head gasket. But then how would you know to use the longer ones? Can anyone shed some light on this for me?

[AlleyCat]

The oversize pushrods are used to make up for differences in valve train tolerances. For example if a valve stem tip was ground too far it would cause the rocker arm to travel a bit farther. This in turn will push the hydraulic lifter to it's upper limit to compensate. If the distance is beyond what the lifter can compensate for the rocker arm will make noise every time it opens the valve. The oversize pushrods will make up the difference and allow the lifter to work as it's supposed to.

FE engines can have any combination of standard and oversize pushrods making it a good idea to keep push rods in order anytime they are removed.

Also if you are doing a build adjustable rocker arms are a good investment.