Another question on drilling/tapping oil passages

[fairlaniac]

Just taking one hole at a time. The arrow points to the oil passage on the front of the block. The block is rotated on my stand, hence the angle of the picture. This hole has a larger opening and necks down. Is this one to be tapped for a 3/8" plug or go into the small diameter and tap for 1/4" plug? I'm not sue that is the way to go as I can pass a 15/32" drill thru the smaller passage. the 1/4" NPT tap requires a 7/16" hole.


Thanks,

[Ranch]

Doug,  Looks like the main galley that runs down the top center of the block, so yes it would be tapped and plugged. You can see where it accepted a Welch Plug

[fairlaniac]

Do you tap the large hole, possibly a 3/8" or the small hole? A little loose for a 1/4" plug.

[BattlestarGalactic]

As long as there is meat around the hole, go 3/8" npt.  That's 37/64"  What is the large hole size?
My block is at home apart, have to see what was done to it tonight.  I'm thinking they are 3/8". (it's been 19 years since I did the work)