What are these brass plugs on the left side of the block?

[MarcDeSoto]

  I started to fill my radiator to check for leaks, and water started to pour out the side of the block.  I know I have to install the temp. gauge, but these are little brass plugs.  They must be for draining the block.  I'm missing a couple of plugs, so I need to know the size and thread, probably pipe thread.  I unscrewed the plug that you see on the left of the first pic, but found it was too small for the missing plug.  The second pic shows another missing plug just under the oil filter.  Does anyone know the size?  I could not find it in the Parts Book.  

 

 

[Sam Buchanan]

Marc, go to a parts or hardware store and buy 1/8", 1/4" and 3/8" NPT plugs and keep them in your shop for "gauges". That way you can skip the parts book and internet back-and-forth and know instantly the size of the threads.

[Sniper]

It's the hole for a block drain.  I put one of these in so I could drain it and use a hose to direct the flow

 

https://www.amazon.com/dp/B07Q2NGJV7?psc=1&ref=ppx_yo2ov_dt_b_product_details

 

It's 1/4" NPT

[wagoneer]

@MarcDeSoto those brass plugs are for bearing oil passages and are 1/8 “ npt for the sides.

 

see my thread from earlier this week

[wagoneer]

one more thing - oil should be coming out of that hole NOT coolant. If coolant is coming then there may be a deeper issue. Mine is open at the moment and when I crank oil comes out.

[Sniper]

not sure what hole y'all are talking about, none of the open ones shown intersect the oiling system.

 

First pic shows the block drain hole, the one with the pipe plug in it is the oiling system hole.

 

The second pic shows what looks like an attaching hole for some sort of bracketry.

[MarcDeSoto]

I think you are both right.  Oil comes out of the smaller holes, and coolant out of the larger plugs.  And I think Sniper is right about the second pic being for some alternate type of oil filter mount.  thanks.  

[RobertKB]

3 hours ago, Sam Buchanan said:

Marc, go to a parts or hardware store and buy 1/8", 1/4" and 3/8" NPT plugs and keep them in your shop for "gauges". That way you can skip the parts book and internet back-and-forth and know instantly the size of the threads.

Totally agree!!
 

It’s always good to have a healthy supply of various bolts, plugs, nuts, etc. I never throw away any of those items but put them in a can, or in my case cans. In the last 30 years there have only been a couple of times I couldn’t find what I needed, even specialty items. Mind you, I’ve been pulling old Mopar stuff apart for years. 

[keithb7]

When I have to go the store to buy brass fittings or plugs I always buy extra and store them in my storage containers. Inverted flare, pipe, 90 deg, straight etc. Lots of them in our old Mopars.

[MarcDeSoto]

Went to HD to buy some NPT 14" plugs.  Instead of NPT fittings, they had MIP plugs.  I learned that MIP means male iron pipe, as opposed to FIP, which means female iron pipe.  Otherwise it is NPT.  My brass plug 1/4" would not screw into the hole in the block.  I think the hole needs to tapped.  I'm not sure, but I think the other hole below the oil filter may be 1/8" NPT, as the 1/4" didn't seem to fit.  It is not a bracket fitting, as I was able to push a screwdriver all the way in to the cylinder wall.  

[MarcDeSoto]

Found out my Tap and Die set doesn't include taps for NPT.  So I ordered a Pipe Tap Set that includes 1/4" and 1/8" taps from Ebay.  

 

 

[RobertKB]

I wouldn’t be tapping holes unless you know exactly what they are. If you use a wrong tap, which initially seemed ok, you can break it in the hole and you are basically screwed. 

[MarcDeSoto]

Well, a couple people told me the hole is 1/4" npt.  I checked the thread count in the hole and it is 18 tpi.  So I think I'm OK.  If I don't tap it, I can't screw the plug in.  

[chris 48 P15]

use the taps to clean the threads

[Kilgore47]

8 hours ago, MarcDeSoto said:

It is not a bracket fitting, as I was able to push a screwdriver all the way in to the cylinder wall.

Many of the bolts on these blocks goes through to the cooling jacket.  So it could be for a bracket.  Don't know what yours are for.  It's always a good idea to add thread sealant to avoid future coolant leaks.  

[keithb7]

Just confirming that you are not planning to tap any ⅛ pipe threads in the main oil pressure gallery. Its too late for that in my opinion. You do those threads before the block gets hot tanked. You cannot afford to risk metal, dirt and rust entry into the oil gallery. That would be very bad. 
 

 

[MarcDeSoto]

I tapped the water jacket hole shown above in the first pic with a new brass plug, but I guess I should have screwed in a spigot like on Keith's block shown above.  This hole toward the back of my block, shown below, was giving me trouble.  I couldn't tap a 1/8" pipe thread tap into it because the tap was too big.  So I experimented with different bolts untill I found a 3/8 bolt with 16 thread!  It worked, but why does a 16 thread bolt work here, unless Sniper was right about it being an alternate hole for a different oil filter housing.  Anyway, the hole went into the water jacket, so it had to be plugged.  

 

 

[wallytoo]

in the photo above this post, that is a boss mount for something, not a coolant passage/drain nor oil gallery.  you don't need to put anything in it to use the engine.

 

neither my 237 nor my 251 has that boss, however.

 

Edited August 5, 2022 by wallytoo

[MarcDeSoto]

But wouldn't coolant come out of it.  I put a screwdriver in the hole and it went all the way to the cylinder wall.  

[kencombs]

17 hours ago, MarcDeSoto said:

But wouldn't coolant come out of it.  I put a screwdriver in the hole and it went all the way to the cylinder wall.  

Just use a bolt that fits, with the same thread sealer you used on manifold and head bolts that enter the water jacket.  Or use a copper sealing washer under the head if you prefer.  Not a big deal.

[Bryan]

What my 49 Plymouth block looks like.  Maybe use it for a modern temperature gauge?