Lifter shims/oil holes in head??

[Robby Camero]

I installed some reground 272's and while inserting the shims into the lifter hole in the head, I noticed the oil hole at the bottom was covered now, well not all of it but most of it. I made the shims to fit in the hole perfectly with almost no clearance.

I noticed that the lifters fit into the hole with a very tight clearance so I dont see how oil needs to pass from the bottom to the top.

I also noticed that there is a huge oil port in the lifter hole (head) right where the oil hole on the side of the lifter is, which by the way is undercut on the diameter of the lifter. This leads me to believe that that this area is the only place where the passing of oil is required, because of the big port in the head and the relitive hole and undercuting of the lifter. Also my reasoning for this is due to the previously mentioned TIGHT clearance for the lifter to fit into the head (oil cant pass through from bottom of hole in head to anywhere along lifter "efficiantly" enough to make a difference)

One last thing I noticed is that the hole on the bottom of the lifter port is drilled from the top, right in the oil journal, which makes me think it was mostly just a manufacturing thing and the hole at the bottom of the lifter port does nothing much.

So if you follow my poor explaination here, I basicly want to know if I am ok or do I have to pull all the shims out and make them not cover most of that little hole in the bottom of the lifter hole in the head.

 

[pneumo]

The hole in the bottom of the lifter hole is there to relieve pressure so the lifter won't get pushed up. That hole doesn't go into the pressureized oil galley, it vents through a small hole located more towards the midline of the head, next to the spark plug well. If your shims cover that hole you could get a type of lifter pump, which could hold the valves open and smack the pistons.

I recomend cutting several notches in the shims so that if they rotate during use there will always be an open notch to releive pressure through the bottom hole. Make sure the edges are smooth, you don't want to turn it into a mini sawblade.