JHZR2
Staff member
To just take out a bit more of the remnant piece down in the hole?
Broken exhaust stud removal
- Thread starter JHZR2
- Start date
To just take out a bit more of the remnant piece down in the hole?
Just grind it out yes
JHZR2
Staff member
Waste of my life…
Can you tap it? Size ok?
JHZR2
Staff member
TBD on size. Had to leave for kids event. Will have to see if 6.8mm bit drops through. If so I have a 21/64 cobalt bit that is appropriate for the helicoil tap.
It’s a blind hole so I’m kind of scared…
JHZR2
Staff member
Sooooo… not quite.
Got a 6.8 mm bit. I figured for the first non-blind hole, I might just have a solid stainless/cast mix and cut new threads in it. The hole was less than 6.8, so I drilled it.
But when I just went to check both holes, I found the hole is too big!
The bit can rattle around in the hole a bit.
So then I went to check the other one that I haven’t drilled but got the stud out tonight.
The top is wider than further down.
So deeper in the hole is only 6.8 which would be ok to tap.
But I’m not sure I should at this point…
So why was the first hole too big? I checked runout.
So 0.008” runout? If I’m not mistaken, it’s 0.008x25.4=0.203mm.
But somehow that very top photo where I drilled out the hole is more than 7.0mm,
I guess the hole would be 2x the runout that is measured in one spot? So the hole will be 7.2mm on a 6.8mm drill with 0.2mm min to max runout?
Does that mean I should have bought a 6.4mm drill? And when I drill for the helicoil, I should account for this in the drill size?
Last edited:
I think at this point i would either buy a new manifold ( or good used one), or take it to someone that knows how to weld cast iron ( its not that easy unless you have done it before). Weld the holes up completely, resurface the manifold, then using a gasket as a template, re-drill the holes. A machine shop might drill this better with less run-out.
JHZR2
Staff member
I don’t know any good shops, I’d like to learn, I’ve had a horrible time finding an exact manifold because they tend to stay with the engine.
If my grandfathers old 1950s drill press has too much runout that’s a solvable problem. Ideally I can fix that but of course a new drill press is also in the cards if need be.
The recommendation was always to helicoil. I was going to see if it was viable to drill and tap for m8, with the assumption of no. I was surprised it took the effort it did. Reality is that for a Helicoil, I need to drill larger anyway. Just don’t want to mess up the hole by letting it become larger than the Helicoil tap requires…
Try to tap as is.
The reason i suggested that, is the hole in one picture looks oval to my eye, unless its the angle, i'm not sure you can helicoil that and it be tight in the hole.
JHZR2
Staff member
That hole is about 7.2mm at the top, 6.8 inside (see photos in prior post). To drill out to tap for a helicoil that will accept an M8x1.25 bolt, I need to drill it with a 21/64” drill then tap. 21/64=0.328 0.328x25.4=8.331mm. So there’s a lot of material I need to remove to be ready to tap for a helicoil.
I saw the oval but I think it’s a bit of an optical illusion tbh. There was a stud solidly in there and nothing done that could have made it oval.
I’m thinking to do so for two reasons.
1) it will still be smaller diameter than the drilled out hole required to tap for a helicoil
2) it will give me tap practice. I’ve done it many times before but I think this one is more reliant on perfect straightness.
Similar threads
