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Hello all,
I thought I would post this here since this is technically a performance "mod".
I have a big block chevy with the cast Iron manifold, and I want to block the 2 little holes at the ends of the exhaust crossover, at the carb mounting (I've already blocked the passage between the head and manifold).
I read that these are 7/16" holes, so I'm looking for brass 7/16 freeze plugs, but I cant find any. Does anyone know a source? I've tried Dorman, Ersco, Sealed Power, and a few others.

I'll settle for aluminum cup plugs too.

I show 555-002 or 555-129 Dorman 7/16 steel, or 550-002 concave type, also steel-book does not show brass available in that size. You could also drill/tap to a plug size like 3/8 NPT.

Do yourself a favor and use a 1/4" NPT tap to thread those holes, then use 1/4" NPT steel Allen plugs in them. Brass or aluminum will melt out eventually if any exhaust gas at all gets to them. Don't ask me how I know this!
Jerry

Wow, just how hot do the exhaust gases get?
That being the case, I'll just go with a steel plug. I would like to thread those holes and use a allen type plug, but I just dont have the proper tap to do the job.

Thanks fleetside, it looks like steel is the way to go here. Steel freeze plug that is.

It just came to me that header paints are advertised to withstand 1200 degrees.

Several years ago we plugged the heat riser passages of a stock Chevy intake manifold on a race engine by pouring them full of molten aluminum- - - -all the way from the cylinder head hole to the carburetor base, from both sides. After one season of racing, the plug was gone! The thermistors we used in the headers during dyno runs on that engine indicated an exaust port temperature at full throttle under load of 2,000 degrees Farenheit.
Jerry

Edit: Any True Value hardware store, or Lowe's, or Home Depot will have the tap, at a cost of about 5 bucks.
Jerry

Depending on the specific alloy, aluminum begins to melt at a temp. just under 900F to around 1200F. Brasses will melt starting at around 1600F, again, depending on alloy.
I would tap 1/4" pipe threads (7/16" is the right size) and put a (steel) socket-head pipe plug in.
And it seems high-temp. paints always burn off...I've been re-painting the pipes on my motorcycle every couple years since installing in the late 70's.

cm

Maybe I will pick up a single tap. I actually have a 7/16 tap, but its the 20 pitch. I read that a 1/4 pipe thread has a 18 pitch thread.

I wanted to avoid pounding on the manifold to get those freeze plugs in. At least with a tap & screw-in plug, there will be less (?) forces applied to the manifold and its gaskets.
When I replaced my intake gaskets, I also installed GMs valley baffle. I had to follow up and retorque the intake manifold 5 times since then. After I install the plugs, I think I will recheck the torque on the manifold bolts, just to be safe.

While I'm on the subject, I used to have an oil consumption problem with my truck, but after replacing the gaskets and retorqing several times, it eliminated the oil consumption. So I strongly recommend to anyone working on their intake manifold to retorque those things several times. Those Hot & Cold cycles really affect the gaskets and settle the manifold.

I sell Century taps(should be a common brand), part #95202 1/4-18 NPT, sells for $5.36 here.

Pipe taps also have tapered threads, to allow the pipe or plug to wedge itself into the hole and make a pressure-tight seal as it's tightened.
Jerry

If possible obtain an interrupted or skip tooth tap which will greatly reduce the possibility of torn threads:

http://www.grainger.com/Grainger/GREENFIELD-TAP-DIE-Interrupted-Thread-Taper-4CPL3?Pid=search

Tapered threads come in 2 forms which determines if sealant is required or not:


NPT - National pipe thread- requires teflon tape or sealant.

NPTF - National pipe thread dryseal(fuel)- metal to metal seal

Ok, thanks all. I might just be going with the tap and screw-in plug. Definitely steel, whatever the case.

Well, the 7/16" freeze plugs were the ticket. They fit perfectly. Just cleaned the carbon from the walls of the holes using carb cleaner, and tapped them in.

In like Flynn. Whos this "Flynn" anyway?

Errol Flynn, the actor? Or is it "Flint"?

Yeah, after I posted that yesterday, I did a quick search on its origin. It turns out that it was Earl Flynns reputation of having it easy with the ladies. Funny thing is, it wasnt until after he was acquitted of statutory rape of a teenage girl (or girls) that "in like Flynn" came to be.

It turns out that the title of the movie "in like Flint" was a modification of an earlier movie title which they combined with the Earl Flynn phrase. A sequel to the first movie titled "Our Man Flint". Love those classics.
I wish that Netflix would get the movie "The Spanish Main". Probably thee best buccaneer movie ever made.