Tapping Freeze Plug Holes

[blykins]

I started tapping a freeze plug hole the other day on my FE block. Dennis with DSC Motorsport said I needed to use a 1-1/2, 11.5 NPT tap. I borrowed one and went to town.

Has anyone ever done this? I made sure to get it square, but since the tap is tapered, I really don't know how far to go. The freeze plugs haven't arrived yet, so I've stopped work.

It's getting pretty rough to turn.....I'm using a 3/4" drive breaker bar and socket with some Tap-Eze.

I have a piece of 1-1/2 NPT pipe that's threaded....and I can just barely get it started....so I guess I need to go further with it. I'm afraid I'll run out of room though since the cylinder walls are pretty close....

Any advice?

[Rick Parker]

Brent:

I did this on my 289 block. You'll need to tap all the holes as far as you can, being carefull as the tap will contact the cylinder walls, stop turning and go to the next hole. After all holes are done cut a few threads off the end of the tap with a thin abrasive wheel. Then go back and continue tapping each hole. The finished tap size & depth will need to be continually checked with the screw in plugs. If you get the holes too big the plugs will fall inside the water jackets. (not good!) If you ar planning on removing the plugs, mark each plug for its respective hole as they will all fit differently due to variences in the plug threads.

Rick

[blykins]

Thanks Rick...

What sucks now is I have a borrowed tap.....hehehe....can't cut the end off of that one....

[trularin]

You will need to buy a tap and cut off the bottom.

You may be able to get one off ebay or a China import place like Harbor Freight.

I'd let you borrow mine, but I don't want the end cut off.

[Aussie Mike]

You can buy taps with different lead tapers on them. You probably have a taper or intermediate tap. You can buy what is called a bottom tap which has almost no taper on the lead in.

Get all the holes started with the intermediate tap you have and then Buy yourself a bottom tap to finish the holes off. A better option than destroying a good intermediate tap.

edit: I found this picture which shows the different lead tapes on the taps:


Cheers

[DAVID GAGNARD]

I did just what Rick did,first tap was too "tight",then got an old rusty one and cut some threads of after cleaning it up and re-tapped the holes,you will have to go in till the tap bottoms out on the cylinder wall,sometimes hard to "feel" so I backed it 2 or 3 times to check the cylinder wall..................

BTW: You can still buy the original type screw-in freeze plugs from Ford Motorsports for about 12 to 15 bucks per block.........

Look in my gallery,that's a plain jane 1971 302 block,looks just like a Boss block though............

Only reason I tapped mine was when I took the engine down to have machined,the machinest told me two of the freeze plug holes had a lot of pitting on the edges and thought they would surely leak with use,so we tapped them cause at the time,that was the only good block I had,total cost about 20 bucks............



David

[Rick Parker]

Aussie Mike:

We're talking about tapered pipe taps here. You're comments are well founded but do not apply with this application.

Rick

[Aussie Mike]

You are correct. I realised my mistake when I got home tonight and had a look at some of my NPT taps.

Grind away.

[blykins]

I got high bid on a tap on Ebay.....It's only $14, so I wouldn't feel bad about knocking the end off of it....

[trularin]

There is no "bottoming" tap in pipe threads that I am aware of.

Do not grind off the bottom, It would be better to cut it off as there will be less heat and less chance of messing up the metal.

And, do not cut off too much.