Can head bolts get so hot that they weld themselves in?

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With the exhaust manifold off. If there is some of the bolt sticking out. You'll need a torch to heat the head up, red hot around the bolt. Also a pair of needle nose vise grips to grab it with and turn it out. You'll have to heat it several times to get out. No bolt showing, you best bet it to pull the head. Drill the bolt and extract it.

If all of that fails, try a miniature butain torch aimed at the part of the block were the bolt threads into. Try heating around as much of the area as u can, moving bak&forth to heat evenly, do this may take 3to5 minutes. To ckeck temp i lick finger real good then touch area 1to2" away frm where i heated. If u get a sizzle, then its hot enough 4 an attempt. I found butain works better than propane, but not as good as oxy-acataline. These lil butains are also great 4 breaking bleader screws loose. Dont pretend its hot enough and make shure wires&combustables r outta the way. A buddy on fire watch, also hehpful. PS. If head of bolt is boogered up & wont grab frm thoes pliars, u can weld a socket or wrench 2 the head & proceed frm there. No weilder? Epoxy

First, don't hold bar on cog as you will damage those and ruin it. Using the starter is a good way to damage starter or flywheel.

Soak the bolt with PB Blaster or WD40 and let is soak for a day. Use a large impact gun (3/4 or 1") with plenty of air flow and pressure.
If that does not work, then use a torch to heat the bolt head (not red hot or anything like that), then strike the bolt head straight on with a brass rod using a heavy hammer (32oz or so). This will break any corrosion that has welded the bolt head to the balancer.
Then use your wrenches again.
If that does not work, then try this: How to remove stuck harmonic balancer bolt

There are several ways: you could
- weld a new head on what has remained of the shaft using a pressure welder.
- heat the bolt with a welding torch until it's red hot (this will burn the rust), allow it to cool, apply some WD40 and let it penetrate, then try to unscrew it.
- grind the remaining head flat, drill a hole in the center of the bolt then hammer an EZ Out bit into the hole until it wedges then use it to unscrew the bolt.
Or try to use all of then in this order.
If nothing works you will have to drill the bolt out then tap a slightly larger threaded hole and install a larger bolt in its place.

weld nuts to them.or pound socket over top.drilling last resort

The threads or the head off the bolt? none the less, try to find a way to cut the bolt but if the head is stripped you can weld a nut and ratchet it out (works for when the bolt itself snaps) maybe a combo off cutting off the end and putting a new nut and weld it to shaft to get it out

To remove the bolt with the rounded head I would try cutting a slot in the top of the bolt head. Cut the slot to fit the largest straight tip screwdriver that you can find. then use a pair of pliers or vise grips to grip the shaft of the screwdriver to put more torque on the screwdriver (it helps if the screwdriver has a square shaft. If you think that the bolt is too seized into the engine block to try that, another thing to try is to weld another bolt to the head of the original bolt, (I would use a wire feed welder) so that you have an undamaged bolt head to use a wrench on (preferably a strong socket wrench). If you do weld another bolt onto the original bolt, make sure that you let the bolt cool down completely because when you get the bolt hot, it will expand and will not break loose until it has cooled. Have a fire extinguisher handy and good luck. Hope this helps.

You can try to drill out the broken bolts, or you can use heat, if you can grasp the bit of bolt poking out the back side of the plate. Get the bolt tips red hot with a torch or as hot as you can. Grab the parts of the bolt with a vise grip pliers and try and turn it out. If this does not work, you will have to drill a small starter hole in the bolt to weaken them and allow it to shrink a-bit and turn out.

if you can access the bolt with a dremel tool, you can grind new flats in the sides and try a slightly smaller six pointed socket. If you have an arc welder, you can weld another good bolt to the top of the rounded off bolt head and use the head of the good bolt to undo it.