[Johnny406]

I'm trying to get a better understanding/grasp of this bearing modification.

See picture, on a unmodified bearing, the oil hole is dead center and aligned with the camshaft lube hole. On the crudely modified bearing, I drilled a larger hole to represent the modification with a bit approximately the size of the actual oil passage inlet hole where the hole aligns with the block.

Question #1: Would doing this modification, with more oil flow and less restriction at the mains, be a de-facto oil restriction for the top end/valvetrain? Will this hurt HFT cam engines?

Question #2: Will I need to shim the pump spring to slightly raise the pressure to compensage for the pressure drop at the mains?

Question #3: With more oil circulating on the bottom end, will it all get back to the pan in time so the pump doesn't cavitate?

Question #4: On the front main, should I just enlarge the center hole?

Question #5: Any negative effects from doing this modification?

If I do this mod, I will certainly buy new/sharp drillbits and use my press. This bit in a hand drill sucked...

[Skip Fix]

To me the issue potentially is the "wall" shown in the other thread obstructing the main feed hole if nor ground down like Steve25 said. Otherwise that "wall" is the restrictive factor of oil getting too the bearing hole.

I have seen one old RAV block the cam feed holes were drilled and tapped for restrictors!

[steve25]

I would drill it but start with a much smaller bit.

Once it starts to nose thru the other side then switch to drilling out that side.

Then step up to the final size of bit you need and do the same process.

Note that with any drill bit it will not pull itself thru until it’s whole face is cutting .

[Dragncar]

Originally Posted by Johnny406

I'm trying to get a better understanding/grasp of this bearing modification.

See picture, on a unmodified bearing, the oil hole is dead center and aligned with the camshaft lube hole. On the crudely modified bearing, I drilled a larger hole to represent the modification with a bit approximately the size of the actual oil passage inlet hole where the hole aligns with the block.

Question #1: Would doing this modification, with more oil flow and less restriction at the mains, be a de-facto oil restriction for the top end/valvetrain? Will this hurt HFT cam engines?

Question #2: Will I need to shim the pump spring to slightly raise the pressure to compensage for the pressure drop at the mains?

Question #3: With more oil circulating on the bottom end, will it all get back to the pan in time so the pump doesn't cavitate?

Question #4: On the front main, should I just enlarge the center hole?

Question #5: Any negative effects from doing this modification?

If I do this mod, I will certainly buy new/sharp drillbits and use my press. This bit in a hand drill sucked...

This modification will not hurt anything in any way. It will not put too much oil in one place and less in the other. Will not hurt any hft cam/lifters. The pump does not need any shims.
You can enlarge the front main if you want to but not needed. I asked D Whitmore that very question, the person who told me about doing this 40 years ago and he told me its not needed. But I have done it both ways.

I have done this with a hand drill every time. Bearing wrapped with a rag in a vise. You need to be careful with your first tiny little punch mark to start your first bit. I simply press a very small/sharp center punch in the back of the bearing by hand. Thus a very small punch mark so starting out with a very small drill bit is needed unless you want to deal with a drill bit walking around.

I start out with the smallest bit I can chuck in a 3/8 hand drill. Then go up one size at a time until I get to 9/32. Drill from the back all the way through and dress with jewlers file.
I see no reason to use a drill press. And with a drill press you might have a hard time getting a smaller than 1/8" drill bit chucked. You can use a pin vise in that drill press check to use a small drill bit.

This mod can not hurt a thing. All we are doing is doing what the bearing manufacture should have done in the first place if they took the time to actually understand a Pontiac's oiling system.
I have never ground down the Vee in a OEM block like in the other thread. Its not needed once you do this mod. The hole on the tab side now has a hole lining up with the main oil shot and the center hole is already lined up.
And the center hole already is in the right spot.
IMO its just not worth sticking a die grinder down there and risking it catching and contacting the main journal in the block.
A some risk and zero benefit deal.