67 427 Engine Threaded Plugs into the Block

[Thomas N.]

Hi:
I'm putting a 67 427 engine together, and put the hex threaded plugs into the oil gallery on the LHS of the block. There are also two more threaded plugs on that LH side (see picture with my pinky and thumb pointing to the two plugs in question) and one more plug on the RHS (see pointer finger pointing in 2nd picture). Do these get hex plugs also, or do they get square headed plugs, or something else? It looks like they are coolant jacket related. Thanks for any responses.

[Carl S.]

Re: 67 427 Engine Threaded Plugs into the Block

Hi Tom,

I believe that the correct type of drain plug is the cast iron NPT plug with the large allen wrench opening in the center. The other option would be just hex head stainless steel NPT plug. Although not NCRS correct, the stainless steel plug has the advantage of not rusting in place and becoming part of the block and also having the hex head is easier to manipulate with a socket wrench rather than stripping out the allen wrench opening in the cast iron plug; which is what usually happens.

I have attached a picture of each for your perusal. I hope this helps. C.J.

[Jim D.]

Re: 67 427 Engine Threaded Plugs into the Block

The hole on the drivers side that your thumb is pointing to is for the clutch cross shaft pivot ball. The other two are coolant drain holes that take a NPT hex head plug.

[Thomas N.]

Re: 67 427 Engine Threaded Plugs into the Block

Thanks so much!
It's been a while since I've done any big block work, and the cross shaft was one of those duh moments. I will install NPT hex head plugs.

[Duke W.]

Re: 67 427 Engine Threaded Plugs into the Block

Use 9/16" hex head brass plugs with plenty of "pipe dope" on the threads - the type for water and steam pipes, and just install "snug" like 5-10 lb-ft. The factory installed plugs were steel and I don't think they used any dope on them, so if they weren't regularly removed for coolant changes (typical) after a decade or two they were pretty much seized and difficult to remove.

The thread size is either 1/4 or 3/8 NPT, I'm not sure.

When you paint the engine be sure to cover the brass fully. I don't think the judges will test them with a magnet. On small blocks with radios they are under the "boomerang" RFI shields and aren't visible.

Duke

[Gary J.]

Re: 67 427 Engine Threaded Plugs into the Block

What is the best way to remove these plugs? Any tricks?

[Jim D.]

Re: 67 427 Engine Threaded Plugs into the Block

What is the best way to remove these plugs? Any tricks?

If they're really stubborn, use a torch to heat the plug up, tap it a few times with a hammer and use a 6 point socket. They come out easily. When you replace them, use a little anti-seize on the plug and don't over tighten them.

[Dick W.]

Re: 67 427 Engine Threaded Plugs into the Block

Best product to use when reinstalling the plugs is Loctite Pipe Sealant with Teflon (PST) Takes care of possible leaks and lubricates the thread if you should ever need to remove them again. Plumbers pipe dope somewhat hardens and does not provide any lubrication for removal.

[Mark M.]

Re: 67 427 Engine Threaded Plugs into the Block

From what I've seen on original 396 and 427 engines is a square drive plug in the oil galleries at bottom of the block and around the front and rear of the cam. 1/4" and some 3/16" square drive. Replacements are often hex drive. The coolant plugs are bigger and hex drive.

[Joe L.]

Re: 67 427 Engine Threaded Plugs into the Block

From what I've seen on original 396 and 427 engines is a square drive plug in the oil galleries at bottom of the block and around the front and rear of the cam. 1/4" and some 3/16" square drive. Replacements are often hex drive. The coolant plugs are bigger and hex drive.

Mark------


The lifter oil gallery plugs on big blocks are 1/4" NPT, front and rear. The main oil gallery plug located on the front of the left side oil pan rail is also 1/4" NPT. All of the plugs I have ever seen use a 1/4" internal square drive. I've never seen a 3/16" internal square drive but I suppose it's possible they exist. As far as drive size or whether square or hex, the only one that matters is the main gallery plug. All the others cannot be seen with an installed engine.

By the way, small blocks also use the same plug as above for the 3 REAR oil gallery plugs. However, the front 3 are cup-type drive plugs which are factory staked.