i dont think i would do it unless i tried it on a spare head.

are you worried about the helicoil pulling out?

personally i think the reason they strip isnt because of the load they are under, its the heat and unalike metals expanding and contracting along with the corrosion with unalike metals that leads them to get stuck and break in the head.

I have a spare 6 bolt head. i will go out and measure them for depth right now and get back to you, because im pretty curious on this too

Ok Just went and measured both a 6 bolt and 7 bolt head and here are the results. This is from the bottom of the hole to the outside of the head

6 BOLT HEAD:

All but one measure between .8"-.83" (13/16"-53/64")
The Lower middle hole (oil hole) Measures 1.057" (Just less than 1 1/16")

7 BOLT HEAD:

Large stud holes measure .967" & .958" (61/64")
Lower Middle hole (oil hole) measures 1.075" (1 5/64")
The rest of the smaller stud holes measure between .813"-.832 (13/16"-53/64")

Here is a link to the conversion chart I used to covert to fractions:http://www.championscrew.com/fractions.htm

I see no reason on any of these holes you couldn't go 5/8" or maybe even 11/16" with out coming close to bottoming on any of the holes. I'm not sure how deep the threads actually go though, that's a little harder to get accurate. But if you were to take a tap and measure up 5/8'" or 11/16" and put a piece of tape as a stopping point, there should be no problems at all going that deep. Hope that's what you were looking for.

-Andy

1995gsx20g you just made my point about the load they are under, well kind of. if you give more threads bolt to, then there is less load on each thread. a helicoil isn't going to be much better because you would still be threading the same depth with the same thread pitch. i am going to helicoil them, just really deep.

thanks for the info redwidow. it looks like i'll be looking for studs that go deeper than stock and i'll probably do around 3/4" deep.

anyone know where to go and buy some m8x1.25 deep thread inserts?

You can not drill any deeper into the head, if you look on the side of it you'll see a little grub that allows you to clean out the oil passage and coolant passages running through the head, one of those runs right behind where the manifold studs are so I would not do that. Going bigger I guess is still a possibility though.

I don't believe he is trying to Drill and farther into the head, just run a tap a little farther in to give each stud one or two more threads for extra grip. Due to the fact that the threads do not go to the bottom of each stud hole, I see no reason why you couldn't run a tap a little farther in. The hole is already there, your just adding threads to it.

correct. since the holes are like twice as deep as the stock studs i am just going to thread as deep as i can and not drill deeper. i may even just flip the stock studs around so i can thread them deeper while still having enough on the outside to thread to.

Flipping the stock studs around will work out great if you tap the holes farther. I actually just did the same thing when i installed my stainless steel studs, and it still gives me enough room to put the nut and washer on.

it seems my problem was warping, and sad to say, the manifold is straight, it's the head that is warped at the exhaust flange...great