O.K a little O/T Flathead

OK probly been up before so hear goes changed heads from cast to alum now I gota plug 2 holes right so I tap em out 3/8 x16 go to put i n set screws loose as **** what did I do wrong need this thing running for the 6 th of Aug

 

not sure, couple of things could of went wrong. (wrong drill size before tapping?)

first, how come aluminum heads use less holes than stock heads? are you talking about the two bolts that are at top of water intake?

 

A standard thread will not tighten up as you screw it in. For that you need a pipe thread as the threads taper so it tightens up and seals as you turn it in.

 

It appears to me that you might have "over-engineered" the project. I just used a wooden dowel, took 15 minutes or so.

31acoupe

 

can you braze it with a bit of coat hanger? might tighten it up enough to make you warm & fuzzy

 

You don't say in your post but I am ***uming you are either putting early (59A) aluminum heads on a late (8BA) block and need to plug the two holes in the front of the deck or vice-versa and you need to plug the two holes on the late head to use on the early block. Either way the size is 3/8" NPT (National Pipe Thread) and not a 3/8"-16 bolt thread. The 3/8" NPT thread is the same size as the temperature sender holes of the head. Get a 3/8" NPT tap and it should work.

Since today is the 28th of July you should have it running by the 30th. Don't forget to re-torque your head bolts/stud nuts after each heat/cool cycle for about 4 times.

 

When I did this I had to do is drill the holes to be plugged out to 37/64th, and then run a 3/8"NPT tap in both sides as far as you can until it bottoms out. Then I had to cut the bottom 1" or so off the botom of the tap so that the threads could get cut a little deeper. With out doing this I wouldnt have been able to get the plugs flush with the deck of the head. Prety easy job, I used some grease around the tap to collect the threads and keep them out of the water jacket.

 

Cutting the thread DEEPER created an "oversized" fit. (loose)
The correct way is to TRIM THE PLUGS to get them flush. Or use shorter plugs.

Start over with a 7/16 inch NPT tap (and proper tap drill size) and a 7/16 NPT plug; and TRIM THE PLUG!

If you can't find 7/16" NPT tap and plugs; (VERY hard to find) take it up to 1/2 inch. You have already "shmucked" the holes anyway.

 

Dave I don't think there is such a thing as a 5/16" NPT thread; starts at 1/8" then 1/4" then 3/8". Been doing a lot of plumbing for 50 years

 

Yeah, your right! Shouldn't think NPT sizes before my 3rd cup of coffee!
Now that I think about it; even 7/16" probably doesn't exist either!

Anyway, ended with 1/2 inch!!

 

Saw the 8BA block in question. The two water p***age holes needing to be plugged are indeed tapped out to 3/8-16. but loose. Best solution drill and tap for 1/4 pipe plug. 3/8 pipe would be far too big unless the 1/4 plug gets screwed up.

 

Here's mine and I though I used 3/8" NPT but that was 6 years ago.

 

So ... not ALL is lost.

Going back - poorboy you DID say "and then run a 3/8" NPT tap"
That part threw me.

NPT means National Pipe Thread.

You should be able to solve this problem with a PIPE TAP and a PIPE PLUG.
Just tap a bit at a time; trying the plug. Once the plug is close to the surface, STOP threading.
Pipe thread is tapered and the plug will tighten down into the thread.

Tap drill size for 1/4 " NPT is 7/16 " (without reamer) if the 3/8 holes are already "loose" you may be able to use a 1/4 " NPT tap in them without drilling the holes any larger.

 

You can use small freeze plugs on both the pump side & the head side - hold 'em in with Permatex #2 - you'll be fine....