Tapping for threaded plugs

[Sport/Truck]

I want to tap the three holes under the timing gear (oil passages). I went to measure the hole size before I started and they all are .510. The drill needed for a 1/4 pipe thread is .437 (7/16).
Can anyone confirm how do this? Just tap it anyway? I think I’ll drill a .510 hole in a block and try the tap.
If anyone has a link or info on this process can you post it?
Thanks,
s/t

[jamesi20]

you really should use a tapered reamer before tapping a pipe thread and .073 oversize on the hole may be to much

[FLEET72]

Bill Jenkins has a different opinion regarding the need to use threaded plugs:

[RACINJASON22]

Bill Jenkins method is still very commonly used today. there is a actual tool to perform this task avalible through many performance suppliers.

[Sport/Truck]

Originally Posted by jamesi20

you really should use a tapered reamer before tapping a pipe thread and .073 oversize on the hole may be to much

Originally Posted by FLEET72

Bill Jenkins has a different opinion regarding the need to use threaded plugs:

Thanks for the reply; I have the tapered reamer, tap and a good tap handle. I checked the chart for the drill size, after measuring I found it to be too big. I stuck my tapered reamer in and it goes all the way in. I’m not sure what to do at this point.
What is the reason to go with threaded plugs? I mean, is it because they will pop out with a high-flow oil pump? FWIW I’m going to use a stock oil pump. Is this a non issue since I’m not going with a high flow?
Staking seems to be a good alternative though.
Thanks.
s/t

[Sport/Truck]

Is the standard press in plugs ok for a stock oil pump?
I’m just wondering why this is necessary. What is everyone else doing?
The one above looks like a small cold chisel was used for staking. I’m concerned about messing this thing up, because once I tap it there’s no going back.
I’m not sure why the hole size is measuring so big, and yet people say to tap it? The ID from the hole and the OD of the plug is only .020 difference.
I guess if I only start the tap, then let the plug bottom out on the uncut area then it will get tight. But that would be ghetto IMO.
Any thoughts on this?
I’m going to call NAPA and get size of there press in plug to make sure I don’t have something different.
s/t

[FLEET72]

Originally Posted by Sport/Truck

Is the standard press in plugs ok for a stock oil pump?

Yes, just think of how many millions of SBC's there are out there without failures. I'm using a melling hv55 and haven't had any issues even with 80+ psi on cold mornings. My plugs are staked stockers.

Originally Posted by Sport/Truck

I’m just wondering why this is necessary.

It's not. It is just an option that some people choose to do.

Originally Posted by Sport/Truck

What is everyone else doing?

I'm using pressed in plugs like stated above.

Originally Posted by Sport/Truck

The one above looks like a small cold chisel was used for staking. I’m concerned about messing this thing up, because once I tap it there’s no going back.

Quote below is from Bill Jenkins' book "The Chevrolet Racing Engine" (1976) Yes, I am that old.