water passages next to header bolt hole?

[Craig 94 TA GT]

How close are the water passages next to the exhaust manifold/header bolt holes, if there are any? The hole in front of #7 has been stripped, and I was going to retap it with a 7/16" tap. I know this is only 1/16" bigger than stock, but would I be OK doing this? Thanks in advance.

[Z Ya Later]

How close are the water passages next to the exhaust manifold/header bolt holes, if there are any? The hole in front of #7 has been stripped, and I was going to retap it with a 7/16" tap. I know this is only 1/16" bigger than stock, but would I be OK doing this? Thanks in advance.

So, I'm guessing the bolt is out?

[Craig 94 TA GT]

Nope, but there is still 1/4" of the old bolt in there There is maybe 1/2" to the old bolt though. The drill is walking again, and I think that 1/2" should be enough, temporarily, until I pull the heads to do a full port job.

[Jeff_in_Atl]

Why don't you helicoil it instead of tapping it bigger. I don't know what the stock head bolt is but by that statement I assume it is 3/8".

Tip for drilling the screw out. Drill a hole in the middle of the screw with a center drill. They don't walk as bad as a regular drill. Then drill the center drilled hole with the tap drill size. I think a #4 center drill may be about a 1/4 inch in diameter and the threads on the 3/8" tapped hole will help to center the drill. Maybe it's a #3. I don't remember.

[Craig 94 TA GT]

Thanks for the tips.
You're right, the bolts are 3/8". Doesn't the helicoil need to be threaded into 7/16" or larger to regain the original 3/8" inside diameter?

I drilled a pilot hole dead center (with a Cobalt bit), but after it got down so far, it just stopped. It was extremely hard material there for some reason. The only thing that seemed to be making progress is a tungsten carbide tipped 1/4" drill bit. It's starting to walk up the hole a tiny bit...I'm getting a bit scared. I think it's mainly due to poor access though. I have a right hand drill attachment that barely fits.

Can I hack the center drill to be < 2" due to the limited space? And do they come in extra hard material? Thanks...

[Cerwin Vega Fan]

Reading threads like this make me scared to install my own headers.

[Jeff_in_Atl]

Thanks for the tips.
You're right, the bolts are 3/8". Doesn't the helicoil need to be threaded into 7/16" or larger to regain the original 3/8" inside diameter?

I drilled a pilot hole dead center (with a Cobalt bit), but after it got down so far, it just stopped. It was extremely hard material there for some reason. The only thing that seemed to be making progress is a tungsten carbide tipped 1/4" drill bit. It's starting to walk up the hole a tiny bit...I'm getting a bit scared. I think it's mainly due to poor access though. I have a right hand drill attachment that barely fits.

Can I hack the center drill to be < 2" due to the limited space? And do they come in extra hard material? Thanks...

No. A 3/8-16 helicoil is drilled larger than 3/8" (I don't know the size off hand) and tapped with a helicoil tap that is 16 threads per inch. It's not the same thing as a 7/16" tap which would have a different threads per inch. You'll need a tap drill, helicoil tap, the helicoil and a helicoil insertion tool. I've made insertion tools out of a bolt with a pedestal grinder but you have to know how to do it. If you tap the hole with a 7/16" tap you will have to drill out the head for that one bolt to use a 7/16" bolt. That's not the right way to do it.

You can use a carbide drill to drill out the bolt. A head bolt is hardened. That's why you can't drill it with a steal bit.

If you already have a hole in it the center drill won't do you any good. That may be the hardest part. (You can cut a center drill with a cut off wheel or a pedestal grinder.)

[Jeff_in_Atl]

Here is your drill chart for helicoil taps.
http://www.carbidedepot.com/formulas-tap-helicoil.htm

[Jeff_in_Atl]

Here is info on helicoils. We use Emhart all the time where I work.
http://www.emhart.com/products/helicoil.html

[Craig 94 TA GT]

OK, thanks Jeff, I appreciate your help. I'll just get the helicoil and follow the chart. Dumb me always assumed that drilling and using a 7/16" tap was the same thing as the helicoil for that size.

[Jeff_in_Atl]

OK, thanks Jeff, I appreciate your help. I'll just get the helicoil and follow the chart. Dumb me always assumed that drilling and using a 7/16" tap was the same thing as the helicoil for that size.

The only place that works is a #10-32 tap is almost exactly the same size as a #8-32 helicoil tap. The key is the thread pitch is the same.

Good luck.

[Craig 94 TA GT]

I just got the whole heli-coil repair kit at Ace. It's for 3/8 x 16 and comes with the tap, screw in device and many coils. Thanks for wishing me luck...I'll need it

[Z Ya Later]

I just got the whole heli-coil repair kit at Ace. It's for 3/8 x 16 and comes with the tap, screw in device and many coils. Thanks for wishing me luck...I'll need it

Gee, I wonder what I should prepare for tonight lol

[Craig 94 TA GT]

Well, here's another obstacle. The drill bit required needs to be 25/64" for a 3/8" helicoil. I grinded one down short enough to fit, but had to cut it past the smooth shank. So now the bit is held by the chuck unevenly...due to it only holding the "spiral" part of the bit. I guess I need to either find a short 25/64" bit (which I can't seem to find in that odd size), or get a smaller right angle drill attachment.

Edit:
The only solution seems to be...purchase this: http://www.dremel.com/productdisplay...5&Color=009933
and somehow grind the extra 1/64" around the hole to make up for the 25/64" - 3/8" difference. I know it's a real hack job, but I can't figure out any other way to do this. Nobody seems to sell a 25/64" short bit, and the smallest right angle attachment will not fit the huge 25/64" bit. I'll be really careful, and if my luck turns around, hopefully get it done well.

[Jeff_in_Atl]

Well, here's another obstacle. The drill bit required needs to be 25/64" for a 3/8" helicoil. I grinded one down short enough to fit, but had to cut it past the smooth shank. So now the bit is held by the chuck unevenly...due to it only holding the "spiral" part of the bit. I guess I need to either find a short 25/64" bit (which I can't seem to find in that odd size), or get a smaller right angle drill attachment.

Edit:
The only solution seems to be...purchase this: http://www.dremel.com/productdisplay...5&Color=009933
and somehow grind the extra 1/64" around the hole to make up for the 25/64" - 3/8" difference. I know it's a real hack job, but I can't figure out any other way to do this. Nobody seems to sell a 25/64" short bit, and the smallest right angle attachment will not fit the huge 25/64" bit. I'll be really careful, and if my luck turns around, hopefully get it done well.

If you can find someone with a pedestal grinder they can shorten it. Any machine should be able to shorten it and probably not charge you for it. I wouldn't. Spend the time and do it right.