Topic: Remove broken bolt in cylinder head :(

[Teddyhoeg1982]

This is a ‘77 CB550. When removing the valve cover two bolts broke due to being stuck from corrosion. So I have two stumps left in the aluminium now.

Best way to remove them?

I have given them penetrant oil and left them overnight for now.

[MauiK3]

They look like they are below the surface which could give you a good chance to center punch and drill it out with a left hand drill bit which may spin it out

[Sw1ssdude]

+1 on the left hand drill bits.

if you use EZ-out on small (M6 or smaller) bolts there is a high chance of snapping off the tip of the EZ-Out. then you have half a bolt AND a hardened piece of steel stuck in that hole.

[willbird]

They look like they are below the surface which could give you a good chance to center punch and drill it out with a left hand drill bit which may spin it out

Normally when we drill we try to NOT have the drill grab, the trick with the LH drill bits IMHO is to GET them to grab and unscrew the bolt.

[Kelly E]

As soon as a bolt acts like it is stuck we stop and break out the LH drill bits. Drill only until the screw/bolt starts to turn or the head pops off. Then the remains of the bolt will still be sticking out to deal with after the cover is off. Most of the time they start to unscrew just before the head pops off. We successfully drilled out 30 case cover screws on the 78' KL 250 that were stuck with LH drill bits.

[beemerbum]

You might look into electrical discharge machining to remove the bolts

[ts354]

What ever way you decide, let us know how it goes.  Just curious, is that grease all over the pucks? and if so, why?

[craz1]

I would center punch that one and use left hand bits which should twist it out as you get close to the 6mm size. The trick is to get that punch at center. If you bugger it up then install a Timesert. Looks like there are Helicoils on some of those other threads. looks like it's a pretty flat break. If you are removing the head bring it to a machine shop. Here is a broken cylinder stud bolt removed from a case using EDM

[willbird]

The "weld a nut" on procedure may have been around a long time but I have only heard of it within the last decade.

Going back to the 1970's I never saw any other methods that were really effective if galvanic corrosion had firmly taken hold between the bolt threads and the aluminum. That stuff is a really effective chemical thread locker for sure. it would also establish itself on long straight portions of bolts too, there was some hope there anyway LOL.

[WideAWAKE]

I’ve met a ton of broken and stuck bolts.

Never has anything ever required an EDM.

Punch it, center drill it, cut your bit so you don’t have wobble.

If you can throw it on a drill press or mill, figure out a way to clamp your drill to a vertical post to drive it dead on straight.

Think through it.

It’s not a crazy repair.

[Redline it]

pay close attention to that, if you're not an experienced welder, and you try your luck at the drilling, the avalanche that you finally stop, because your whole thumb can fit in the hole, with 2 threads left, by then you can use that case for practice, timeserts ezy outs, and new set of threads can't be glued or welded back in. find a welder that's got good eyes, owns a home, organized and that's done it before. don't let anybody learn how its done it before you bring over a lawn mower motor found on the street cut a bolt in half and screw into a threaded case hole, center punch that, and let him show you he can do it. i've only had luck 1 time removing a skid plate 6mm bolt in 40yrs and the near toothpick size ez out was twisted 10 degrees i thought i was over and it snapped out, 1 time. i was so happy i saved the ez out still wedged in the broken stud. 

[WideAWAKE]

Punch it, center drill it, cut your bit so you don’t have wobble.

If you can throw it on a drill press or mill, figure out a way to clamp your drill to a vertical post to drive it dead on straight.

Without refuting any response, the most common problem with "punching it and drilling it" is that all too often the bolt sheared in a way that does not leave a flat, perpendicular surface to the shank of the bolt. It is for this very reason, that drill bits wander despite having a "centered punch". Hand drilling these out is possible, using a drill press improves the chances, but even LH drill bits approach the same margin of error.

Heating the bolts up prior to removal ALWAYS helps, but it does not ensure a successful removal. Welding an extension shank, nut, build-up is probably the easiest "home" method if you have access to welding equipment. There's little to no danger of damaging anything since steel and aluminum are not compatible materials for welding filler wire. Even if the bolt is sheared below the surface, building up the bolt above the surface is quite easy to do.

Having said all that, milling it out (conventional or EDM) is absolutely the best method. Not available to all, and it does cost money. But so will damaging the head (over-drilling, tapping and installing a threadsert). But, given the average Joe has cheap "Home Center" bits and likely doesnt have a true centering punch, the potential for self-inflicted damage is high. Weld it up (MIG, TIG or hell, even FC). You'll be done in less time than punching, drilling and re-tapping.

This is why we think first.

All your issues stated above are fairly easily correctable.

I’d guess 90+% of the time the problems listed above happen they can be seen starting to happen a mile away and there is no course correction, just soldier on ahead.

Be smart about it.

It’s not a crazy repair.

[willbird]

Punch it, center drill it, cut your bit so you don’t have wobble.

If you can throw it on a drill press or mill, figure out a way to clamp your drill to a vertical post to drive it dead on straight.

Without refuting any response, the most common problem with "punching it and drilling it" is that all too often the bolt sheared in a way that does not leave a flat, perpendicular surface to the shank of the bolt. It is for this very reason, that drill bits wander despite having a "centered punch". Hand drilling these out is possible, using a drill press improves the chances, but even LH drill bits approach the same margin of error.

Heating the bolts up prior to removal ALWAYS helps, but it does not ensure a successful removal. Welding an extension shank, nut, build-up is probably the easiest "home" method if you have access to welding equipment. There's little to no danger of damaging anything since steel and aluminum are not compatible materials for welding filler wire. Even if the bolt is sheared below the surface, building up the bolt above the surface is quite easy to do.

Having said all that, milling it out (conventional or EDM) is absolutely the best method. Not available to all, and it does cost money. But so will damaging the head (over-drilling, tapping and installing a threadsert). But, given the average Joe has cheap "Home Center" bits and likely doesnt have a true centering punch, the potential for self-inflicted damage is high. Weld it up (MIG, TIG or hell, even FC). You'll be done in less time than punching, drilling and re-tapping.

There are a lot of tricks I have learned over the years. One has to do with centering up a hole to an existing part. Several ways to do this and I have tried both ways.

1. Drill you new part with the tap drill size of your bolt, if we were bolting it on with 3/8-16 this would be a 5/16" drill. Then clamp your part place and spot one hole with a 5/16 drill. remove part, drill the mounting point 5/16 and tap 3/8-16...then open up the hole in the part bolting on the 3/8, and bolt it in place, then do the rest of the holes, if you are being ultra careful do them 1 at a time.

2. drill 13/32 holes in your part that will be bolting on. Clamp the part in place and spot each hole using a 13/32 drill. Then drill each spot location 5/16 and tap 3/8-16, then bolt your part on. This method applies to our repair. if we can bolt our part on with all of the bolts BUT a few broken ones, say they are M6 holes and the clearance hole is 7mm we can take a 7mm drill, or the drill that JUST slips in the bolt hole and we can carefully spot the broken bolt as long as it is not way down in the hole. Then once we have established our position we can drill at that location.

I have a knee mill at work that I CAN use....but often it is 1/4 mile away from where I am working so I have found ways to get stuff done where I find myself.

Many times just paying a person who HAS a knee mill is the best answer ;-).