Need to tap into the ONSC wisdom (1 Viewer)

[adman02]

I'm in the middle of swapping an LS into my FJ62. The donor engine is an LM7 from a 2006 Yukon. There's some differences with this engine vs early LS IIIs (e.g,. return-less fuel rail, hydroboost PS pump, different bolt pattern for the oil pan, etc.)

My question is about the vacuum ports, though. I know there's one at the back of the engine for the brake booster. BUT, there's another about midway on the passenger side of the intake. Traditionally, you can break off a plastic tab and voila - you have a vacuum port nipple. With my engine, though, there's no plastic nipple - just a steel block off plug. I need to know the size of that plug so I can buy a fitting. This will power my xfer case vacuum system. 1/4 in is too small; 3/8 seems too big.

Any guesses on size?

 

[White Sheep]

Can you take a picture?

 

[fourtrax]

are you measuring in like 1/4 bolt size or NPT size? it's probably 1/8" NPT

 

[GLTHFJ60]

Tapping plastic is asking for trouble imo.

Like fourtrax says, npt ports are measured in through hole size, not thread size. Some common npt sizes:

1/8npt, 27tpi, 21/64 drill size
1/4npt, 18tpi, 27/64 drill size

Etc...
3/8 18 9/16
1/2 14 11 /16

 

[adman02]

FWIW, the hole was tapped already (maybe from the factory). I fully intended to just snap off the plastic tab and go. Then I found a steel plug rather than a plastic tab. I did try 1/4 NPT and it was too small. I have a 3/8 vacuum port, but I can see with my naked eye that it's slightly bigger than the plug. Wasn't sure if there was an in-between size. I'll post some pics tomorrow.

 

[GLTHFJ60]

There is no inbetween npt thread. Could be bst I suppose, but that would be weird, and they fairly closely follow npt sizes.

Npt reference:

NPT-National Pipe Thread Chart - Squarespace https://static1.squarespace.com/sta...59419833/National+Pipe+Thread+Chart+OPT+P.pdf

 

[adman02]

Some pics in case they're helpful...

 

[adman02]

Disregard. I'm an idiot.

Hole was 1/4 NPT –– I mistook a 1/8 NPT plug for a 1/4 NPT, which is why I thought 1/4 was too small.