OK....Drilled 21/64 hole for fitting...all ok.....Am trying to start 1/8" npt tap...
cast iron hard as a rock or EITHER my Great Neck 19.95 tap & die I got from
AutoZone yesterday is not worth 10 cents. I have tried starting it with a variable speed drill, tried tapping it with a hammer,oiled it,etc...

I had to cut off the ends of the tap wrench so I could get a good twist down
in the hole....every time I think its gonna catch I twist with lotsa' pressure
and it doesn't....just starts a death wobble...

 

Man, while doing both of mine I was kept thinking how SOFT the cast was!

I used the same size bit, but I know of many people who have used the next size up.

Remember, these are tapered pipe threads, don't run the tap all the way in!

 

It will go. It took me 2 hours and 2 taps to do my buddys 3rd gen. I think the manifolds on them are harder. My ats one was a breeze, tho it was on my work bench. I Used a cordless drill on slowest setting and once it started i would only turn a half turn back it out, and kept at that pace. Be paitent.

 

Thought a 5/16 bit was used for 1/8 npt tap. Guess there really isn't a whole lot of difference, only 1/64. 21/64 is slightly larger anyway. It took us a few seconds to get mine tapped. It took us about a half hour to go from squeezing the trigger on the drill to getting the pyro in.

 

Try another tap, it could be a bad one.

 

First, get a good, sharp tap. I tapped mine with a hand tap and handle, it cut like butter with a new, sharp tap.

Second, make sure you are running the tap in straight, (on the same axis as the drilled hole). It kinda sounds like the tap may be going in crooked.

If you have cut a thread or two with the tap and it is binding, try removing the tap, use a countersink drill bit and put a slight chamfer on the leading edge of the hole, then try the tap again, keeping the tap aligned with the hole as you turn it. Cast generally taps very easy, it'll go.

 

MIne tapped in very well... I went to a true value hardware and asked for the best quality one they had.. I think it cost me $10.00 for both the tao and bit.. Make sure the tap you have is NPT.. should be a lot of taper on it and go in easy..

Gerry

 

If you don't go in at the angle that you drilled tap will not start. Put the drill in the hole and ream a little than try again at the angle that you drilled. I used a cheap $5 tap on my 3rd gen. and cut great.

 

Worked on this thing all day ... Manifold HAS GOT TO BE MADE OF
CONCRETE REINFORCED TITANIUM ...

Guys, thanx a bunch for the responses .....Go to 3rd gen perf while I blow
some steam

 

my chart calls for a 11/32 drill for 1/8 pipe tap

 

Yes sir,you are correct. Thats what I ended up using but my STUPID directions had me starting with a 5/16. No wonder I couldn't
start the tap......

 

Your directions were not totally wrong. The standard pipe thread taps correspond with Briggs Standard Pipe Taps, or Whitworth Standard Pipe Taps.

1/8" NPT = 11/32" drill for Briggs, or 5/16" drill Whitworth taps
1/4" NPT = 7/16" drill for Briggs, or 27/64" drill for Whitworth taps

 

Don't always trust what the charts say. Most taps say right on the side what size drill to use and they aren't all the same depending on the tap.

 

For a 1/8" NPT hole in a manifold - you should have been using an "R" drill bit:

http://www.newmantools.com/tapdrill.htm

 

This can sometimes be handy, especially on awkward angles of attack.
Drill hole for tap, drill same size hole in a block of wood that can be clamped to material being tapped, align holes and secure/clamp wood to object(duct tape may even hold well enough). Increase hole in wood to the o.d. of the tap, use said hole in wood as a guide to align tap while turning.
I've used this to tap holes I could only see in a mirror.. Happy tapping