Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Broken Head Bolt

Alright, I commenced reassembling my engine after replacing the head gasket, and lo and behold if the torque wrench i got from Auto Zone was defective, and snapped the head bolt in the block. What do I do? An extractor set hasn’t been able to pull it, and wrenches and pliers are eating the bolt away. I’ve got about 1 cm of bolt sticking out of the short block. Help!

Does this engine use “stretch bolts”?? These are not reusable. you must buy a new set. But that’s not the issue here is it…If a new set of real Vice-Grips will not turn it out, the threads are badly galled/buggered and the services of an automotive machine shop may be required…Have you tried tightening the bolt a little while flooding the hole with penetrating oil? Since there is no torque on the bolt now, it should turn out easily…

vice grips could work, There have been previous posts about looseners Maybe someone can do a refresher course.

You can try grinding a flat on each side of the part that is protruding and try removing it with a small pipe wrench.

It’s also unlikely the torque wrench is defective. If you reused Torque to Yield headbolts you should keep in mind that these bolts are designed to stretch. Try stretching them too much or repeatedly and something like this can happen.
Any severe overheating problems that may have existed can also lead to weakened bolts.

Vice have been used to no avail, but i hadn’t thought of grinding a flat on each side. The extractor broke off in the hole i drilled, so no more drilling.

If you want it out?


Is the block aluminum or cast iron?

And what difference would that make?


Since the bolt was just reinserted and snapped off, it would seem to me that it should not take much effort to remove it once a bite can be gotten on it.
It’s not like it has been in place for a decade and suffering thread corrosion.

Here is a trick I have used before but you need a mig welder to do it. I have welded a larger nut over the broken bolt, one that will slide down over the bolt instead of threading to it. Jam nuts work well because they are about half the thickness of a standard nut and it is easier to weld to the broken bolt if the nut is not so deep. Try and remove it while the bolt is still warm from welding and it should come right out, that is if you have access to a mig welder.

I just now looked at the previous post with the link and what he is doing with the welder is what I was talking about. The washer is a good idea because you can get a very good weld to the bolt and then weld the nut to the washer.

I can see some reason for Caddymans question. If the threads were buggered up (in an iron block) perhaps the bolt broke due to excess torque used to run this bolt through the threads. I can see less of a chance for this happening with an aluminum block.

So my reasoning for the bolt breaking was thread interference due to rust. If this is the case it won’t just back out either.Perhaps the bottom of the bolt hole was filled with rust and the bolt bottomed out.

Another reason to chase those headbolt threads and blow out the debris.It still doesn’t explain why when excess torque was being applied you did not stop.

As to why i didn’t stop when excess torque was being applied- I’ve never used a torque wrench, nor have i replaced a head gasket before, so I do not know what it should feel like when it is at the correct torque. the 4g63 block is iron. Also, I cleared all the holes and threads of debris before beginning reassembling everything.

I can see if I get a welder to put a nut on the bolt. I’ve already tried flattening two sides of the bolts, and the vice grips and channel locks I used just couldn’t turn it.

I would say heat on the block might help, too. I use an electric heat gun to really warm things up, but I suppose even a propane torch on the iron block, along the side nearest the bolt.

As per your previous comment, you MUST use a torque wrench on the head bolts. Period. Under torqued, and they back off. Over-torqued, and they snap under load. If the torque specs call for a final angle turn, these are torque-to-yield (TTY) bolts, and MUST be replaced once used. They will never achieve proper tension again.

As far as the broken bolt, I’ve had good luck with my 18" pipe wrench.

The torque specs are listed in 5 steps.

  1. 58 ft pounds
  2. Back off all bolts
  3. Tighten to 15 ft pounds
  4. Tighten 90 degrees
  5. Tighten 90 degress

How much of this do i need to do?

when i say need to do, i realize there is a reason for this. I’m more just curious about what this procedure achieves.