Fork pinch bolts (in yoke) rounded off

[KoalaBiker]

Hi all,

While working on a bike I bought a few years ago, I figured I may as well change the fork oil seeing as the maintenance interval was coming up.

However, it looks like the previous owner managed to round off the allen heads for 2 of the 4 M8 bolts which clamp the fork legs in the lower yoke. I tried hammering in an allen key which was 1mm larger, but that just rounded off too when any force was applied - the bolts didn't even budge.

I've been treating it with penetrating oil twice daily for a few days now, but there's no sign of any improvement (although there's also no sign of any rust or corrosion anyway, so not convinced it's really going to help).

Annoyingly, the bolts are recessed into the yoke, which makes it very hard to just cut a line across and use a flat screwdriver to extract the bolt. I'm also very reluctant to use a screw extractor because if it snaps off in-situ then I'm going to have an even worse problem.

Part of me is tempted to drill off the bolt head, as I've heard a few people say it's only the clamping tension that prevents the bolt from easily coming out. If that's the case, once the head is removed, the rest of the bolt should theoretically be quite easy to remove.

I've got a set of replacement bolts, so not bothered about destructive techniques. I can even get a new lower yoke relatively cheaply (they're about £50 used online), but I'd like to avoid that if at all possible.

Was wondering if any of the more experienced people on this forum might have any advice - or whether it might be time to just give up and go to a shop.

Thanks in advance

[Islander]

Try hammering in a Torx bit, or if the size doesn't suit, a spline bit. Make sure it goes in well before you attempt to turn it.

[Riejufixing]

[Tankie]

If you fail with using Torx /spline drives you could do the sacrificial method which is to weld in an old piece of hex key ,or even a nut on the top of the offending item
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[colink98]

[Riejufixing]

[1198]

Were you to drill off the head would the remaining threaded stud part not be concealed in the yoke?

[stinkwheel]

Shouldn't matter what it's made of, heat will help anyway. The expansion differential will still loosen the grip of the corrosion.

Welding a short hex-bolt to the end of the allen head and using that to wind it out would probably work too. Umm, with a recessed allen head, might be easier to weld a nut to it but you get the idea.

Another thought is that used bottom yokes aren't necessarily all that expensive so do you just want to cut the bolt with a hacksaw, pull out your forks and replace the yoke. Save yourself a load of hassle.

You can get a used bottom yoke for my bike for a tenner delivered.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.