Seeking any advice on getting a badly stripped brake caliper bolt out! I’ve tried extractor and used a cutting wheel to notch a place where I could break loose with a chisel. To no avail… please help

ouch!...I think the last couple of these instructions might just work for ya....
Good luck.

I think at 6:42 is where ya want to try.

I think you're saying the bolt head(allen)is rounded out.Is this right?At least you have a 'guide' to help you keep the drill going in straight.You MAY have to go all the way down till you hit the fork mount hole bottom.Long as you pay attention,you won't dig into the fork mount assembly but barely.Which would be okay.Watch for aluminum chips.Stop when ya see em.You could also measure the other bolt then maybe put a mark on the other fork mount and measure the drill bit and adjust before drilling.Yer gonna have to ream that bolt out all the way I think.
I think a few times(at least once) I firmly hit the bolt with something and a heavy ball peen hammer.To shock it a bit.I think it helped to jar it enough to turn it.But the allen was fine.Just gotta be real careful.
If the allen's rounded,then a heavy punch should fit and help,maybe.OR..take it to a pro and pay them to do it.I would consider this route if you have any real doubts about doing this.I know I would if I didn't think I could pull it off.
In fact I did...with a lower fork clamp bolt that refused to budge.Tried vise grips(after the socket and open end wrenches failed to move it(and me rounding off the hex head).

* Last updated by: Grn14 on 12/18/2021 @ 12:11 AM *

I think you're saying the bolt head(allen)is rounded out.Is this right?

Good clarification, I though he meant the threads were stripped and the bolt wouldn't come out.

Hopefully an easy-out will help to remove that bolt. That is a big M8 bolt and the large diameter will be in your favor if your drill isn't perfectly parallel to the axis of the bolt. I don't know that you would need to drill much more than 2 inches deep to use an easy-out on a bolt of that diameter....but 2 inches is still a pretty deep hole if the drill is not parallel to the threads or if the drill bit is off center. The allen head should help in keeping the bit centered and parallel. If the bit chews away at the side of the hole in the caliper just a little, I don't think that would render the caliper useless. The bolthole in the caliper is just a guide, it has no threads in it.

The bolt threads in the fork bottom must be seized. I doubt you would need to drill deep enough to touch the fork bottom. If you do need to drill past the caliper guide hole and the drill cuts into the threads in the fork bottom, I believe that would mean you would need to remove the fork and replace the fork bottom. I don't know if it's possible to replace the fork bottoms though, you might need to buy a whole new fork in which case, I'd get a set of Ohlins forks instead of stock.

If the threads in the caliper bolthole are damaged you might try to repair them with a thread restoring tap. If that is to no avail, there are thread replacement plugs available which have both internal and external threads. You drill out a larger hole and tap female threads in the fork bottom bolthole. Then thread the male plug in using permanent thread locking agent. The plug you would select for this project would have female threads of the proper pitch to match the caliper bolt. Voila-- new threads.

If you go with the easy-out, I'd strongly consider using an impact wrench to turn it. It doesn't look like penetrating oil or heat will help a great deal with a bolt that is positioned as the front caliper bolts are. You could try heating the fork bottom with a torch but that will destroy the paint finish. It would be an easy thing to repaint. I guess you would not want to heat aluminum too much or it will melt.

My caliper bolts were extremely tight from the factory. This is why I never tighten them to full spec. I believe I went about 2/3 of spec and used blue locktight. Never had a problem getting them out and they never came loose.

* Last updated by: Rook on 12/18/2021 @ 8:56 AM *

The only problem I see with replacing the whole fork is...he still has to get that bolt out.Unless of course he cuts the forward portion of the fork mount part right where it mates to the caliper,inboard maybe a couple of centimeters so he doesn't damage the caliper.Probably with a hand held cutting wheel.If he goes that route,he may as well leave everything as is,and just replace the whole fork.That may be overkill though.It's possible he could get that bolt out as we mentioned.But like you say...they're WAY tight in there all the way down.I don't tighten those bolts down all the way either.

* Last updated by: Grn14 on 12/18/2021 @ 10:15 AM *

The head of the bolt is in a recess in the brake caliper. It would be a tedious job to drill and grind the head off but that would be the least invasive procedure if the bolt has to be cut. I guess I'd drill the head away as much as possible and dremmel enough out so that I could break the last fragments of bolt head off with a needle nose pliers. The only thing that would get destroyed would be the bolt. You could grind opposite sides of the bolt shank flat and try turning it with a couple adjustable wrenches. That might get the bolt out as a last resort.

If he cuts the bolt off through the fork bottom, whatever portion of the bolt hole was left, That could be ground down thin enough to pull off with a pliers. The fork bottom would be scrap, maybe the whole fork if the fork bottom alone can't be replaced.

No matter what method, maybe use a heat gun tio get everything warm before applying preassure . Not a torch but a heat gun, just hot air.

"I guess I'd drill the head away as much as possible and dremmel enough out so that I could break the last fragments of bolt head off with a needle nose pliers."

BINGO...winner!That sounds like the easiest and 'safest' way to not damage anything.It might shave a bit off the flange in there,but that could be repainted.Good idea rookster!If it were me,that's how I'd do it.At least the other bolt can be removed.

With those hex bolts, the deal on those are to act the torsion bar, not full power down all at once. You want to wrinkle the neck of that head bolt. Like a push down then unload, push, unload, repeat, and eventually it breaks loose.

Removal:
1. Hammer the hex back into shape. Line up the hex tool and hammer that socket end so it has more 'lock' around the hex sides.
2. More like a half inch breaker bar and a long handle for the fulcrum is one, then it's easier to be parallel with the hex, meaning, the 90° to the hex is square around the hex, not at an angle and it pops out of the hex, tears that up on the head bolt, etc.
3. No joy above are now the hack jobs:
a. Let's say the hex is useless, and this is my #1, always bails me out, the super sharp ground flat blade punch, big brass hammer. A hammer is limited in weight. The heavy can be controlled from light to way too much. Then the 45° at the edge of the head. Let's say again, I don't need the center so why not drill the hex hole and just keep going deep into the bolt shaft. I'm using a stout small drill to start out with, and snapping off is good luck.

Brand new drills of the same steps, because I am going to make the head have more give with the hollow shaft. Then with all that meat on the bolt head, my sharp hit is the 45 to get that angle pealed up under that hood you made. And now don't leave that angle at any other degree sort of speak, here comes the heavy hitter one after the other, and hope it does not slip out of the hood or you shave head and now it's too close to the caliper, and the dig is going there?

So you more sacrifice what is hard to get at on the counter clockwise. Sheer that off, the lower, easier side to get at is another chance. Get what I mean?

b. This is back to drilling the center shaft with new bits after bits. Now the trick is not to leave center drilling down the shaft. And this is a left hand drill and bits. To the point of thinning out the head so the load is less, or less material at that pressure point.

c. Same drill out opening procedure, but with a one way drill&bits, this one now calls for the easy-out set and choose the big one that fits. This might take a 3rd hand, but I'd have the load (torsion here too) on the easy-out, the other set of hands at the non-ground down hex head, and 45 that sucker on a tag team basis.

If you use a heat gun(s), I think you're going to need to heat it up enough to damage the paint if that technique is goin to loosen up the threads. A little heat couldn't hurt though. ...just you don't have much left to that bolt head to be going light on the heat.