Clearancing Pushrod Holes

This question pertains to which directions do I need to open the pushrod holes for extra clearance when swapping from a SFT to a SR cam.

I am trying to get some of the dirty work done before my rotating assembly is ready (340/418) at the machine shop. I now want to try and open the push rod holes ahead of time so that most of that is done before my parts show up. I am currently trying to determine which direction I should be opening the pushrod holes. I am thinking that the top of the pushrod hole may be ok and the bottom needs to be clearanced towards the intake an inch or so upward.

Between the SFT lifters that I was using to the new SR lifters, the pushrod seat will be setting approximately .27” higher with the new lifter. The attached picture shows where the 5/16” pushrod was located in the hole with the SFT setup. I don’t recall where in the lift process this picture was taken (maybe at full lift referencing the rocker), but at that time, the clearance was checked all around the pushrods at about every 45 degrees of turning the crank.

Since the SR lifter will be taller, then my assumption would be to pre-clearance the pushrod holes inward at the bottom as mentioned.

I will be using 11/32” or 3/8” pushrods and the lift will be about .07” more with the SR. I will set up the rockers with my existing B3 shim kit to see what the wipe pattern looks like.

So where should I start clearancing the pushrod holes ahead of time?

Thanks!

My machine shop usually does it, I am pretty sure they open the hole the entire length towards the intake manifold. I have a set of heads for the engine I am assembling now, I will double check. I know that the hole is into the gasket surface for the valve cover. And with 5/16 pushrods it is still close.

Thanks Sterling!
Referencing my picture, I was also thinking of working on the top too just up to that valve cover lip. I may just go all the way thru with my hand grinder.

Depending on the solid roller spring pressures you will be using, you may not need anything bigger than a good 5/16 wall push rod. I would consult Smith Brothers with your specs to see if it is needed/required. I say that because you may not need to clearance the heads with a 5/16 push rod (I didn't on my 408).

With that said, I would wait until you have answers to all that so you have a definitive game plan, rather than cutting when you don't need to. Just my 2 cents.

Spring pressures would be 230/540lbs at 6300rpms max. I have been consulting with Manton and they suggested their 5/16” x .118" or their 11/32” x .120" Stage 5’s. These are rated at 275,000psi.

Thanks

Thank you for the pictures Sterling.

Your welcome. These heads were already modified when I received them. The pedestals for the rocker arms were already milled off, so I am using Harland Sharp rockers and offset shafts, which makes the clearence to the intake side less