Removing broken head studs from block

[nkaminar]

Yesterday I helped someone in our club who had broken off 3 studs in his block. I welded nuts to the studs, some of which were broken off fairly deep in the holes.

I used my wire welder set for 1/4 inch material, the highest setting on my welder. I cleaned the top of the studs by multiple strikes with a punch. It took 2 or 3 tries to get the studs out.

I also removed 3 intact studs using an induction heater.

Heat is what does the trick. Plus some penetrating oil. The welded nuts are not any stronger than the chuck we used to remove the intact studs. The welding heats the stud and the thread.

I kept the induction heater on the intact studs until we saw some steam rising from the blocks. This induction heater only heats to a dull red.

A flat washer will protect the block from damage from the welder. After building up a weld on top of the stud, a nut for a 1/2 bolt was used. Some aluminum and some backer board were used to protect the valves and the car. The engine was in the car.

There were 4 intact studs and one broke, so a welded nut was used on that one. That means there were a total of 4 studs removed with the welded nut trick.

An Easyout would not have worked. I had to use a 2-foot breaker bar to remove the studs. They were really in there tight.

[alexiskai]

When you say 2 or 3 tries, what was the failure mode? The nut just breaks off the stud and you have to reweld it?

[nkaminar]

Yes. Part of the problem is that the weld does not get good penetration on the stud because it is cold and heat sunk by the block and my little wire welder does not put out enough heat. The other problem is that the stud does not get hot enough on the first try. The heat is really what enables the stud to be removed.

I did not find much rust in the threads. I think either the studs were too large for the threads in the hole, the threads were not cleaned out properly, that someone tightened the studs too tight, or all of the above. The studs should go in a little more than finger tight, assuring that they go in all the way, and anti seize should be used. There was evidence that someone had worked on the engine in the past.

[Joe K]

Put in to the "neck" of the thread is my usual discovery. This would be the two or three threads at the top of the threaded portion where the thread is not fully formed. The thread at that portion "jams" in the correct size hole, and causes an "interference fit" between the stud and block.

My best luck as been in successively "drilling" the stud until you get to a "spiral" of metal. Off center CAN be a problem. And as you say it's the "heat" of the drilling which actually loosens the connection.


Joe K

[Richard Knight]

We used the washer, nut, welder trick on many broken studs at the shop. Works very good on aluminum cylinder heads also. For model As I drilled out many broken studs using the cylinder head as a drill guide. You can also use a drill bushing in the head to start with a smaller drill.

[alexiskai]

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Originally Posted by Joe K

Put in to the "neck" of the thread is my usual discovery. This would be the two or three threads at the top of the threaded portion where the thread is not fully formed. The thread at that portion "jams" in the correct size hole, and causes an "interference fit" between the stud and block.

This is an interesting idea, can you clarify? The problem is that the top threads in the stud bore in the block are not properly formed? What exactly is jamming where?

[katy]

Thanks for the write-up, very informative, I'll keep that in mind, if, when.

[Dan Partain]

Have you tried pre-heating the broken stud with a torch to get better penetration with the mig welder? I haven't tried it yet, but have been thinking about it since I've had similiar negative results in getting the nut to stay attached to the stud from the cold weld.

[JayJay]

Originally Posted by Dan Partain

Have you tried pre-heating the broken stud with a torch to get better penetration with the mig welder? I haven't tried it yet, but have been thinking about it since I've had similiar negative results in getting the nut to stay attached to the stud from the cold weld.

Unless you use a very fine tip, I’d be afraid of heating the block at the same time, thereby negating the differential heat that breaks the stud loose. I’ve used the welded nut method several times on head and manifold studs with good results. I’ve also used a left handed drill if there is no evidence of corrosion, like on a pressure plate to flywheel bolt.

[Joe K]

Originally Posted by alexiskai

This is an interesting idea, can you clarify? The problem is that the top threads in the stud bore in the block are not properly formed? What exactly is jamming where?

Threads for properly formed studs are "rolled." As in the metal is "squeezed" rather than being cut with a die.

BUT - many replacement studs have the threads cut - this is a manufacturing expediency which typically is not as strong as the rolled thread - and CAN break at the stress concentration point at the beginning of the cut threaded portion.

Whether rolled or cut, the part of the thread next to the uncut portion of the stud can be less than 100 percent depth. I liken the unformed thread to a sort of "taper" - which will jam in its matching hole as the thread is "bottomed out."

It pays to have studs formed to the original dimensions - which generally are set with stick-out to a dimension so one or two threads are "proud" of the retaining nut on top. Ford had a dimension for setting of the studs - and IIRC this caused the incomplete thread to NOT enter the block.

One of my reasons for using blue or even green loctite here. Its an assembly which you don't want the studs to "tighten" under torquing of the head, but you MAY want to remove the studs without the extreme heat needed to break loctite red.

https://tameson.com/pages/loctite-color-comparison

The Service Bulletins don't mention the stick out dimension that head studs are installed. Les Andrews in his seminal work Mechanics Handbook calls out all but No. 8,11, and 13 to be 2-3/4" (8 = 2-29/32", 11, 13 to be 5")

But this assumes your studs are made to the Ford drawings...

I can't say I've seen a drawing for a Ford design stud.

Other than the near taper of the unformed thread I haven't really answered your question.

Joe K

[1crosscut]

I've removed quite a few broken off head studs by placing a washer over the broken off stud, filling the hole with weld and then putting on a nut and welding it full too. I often keep adding weld to the top of the nut building it up higher for the sole purpose of getting more heat into the block.
After that I let it cool completely before trying to remove it.
I like to remove the plating from the washer and nut prior to welding them by dipping in a muratic acid and water mixture to help keep the weld clean.

[nkaminar]

In response to Joe, Post #4: Running the nut down on a nub is a good idea, if you have a nub. Some of these broken stubs were broken down in the hole, some as deep as 3/8 inch. In that case I built up the weldment until it was proud of the block and then used this little bit of weldment to locate the nut. I used nuts for 1/2 inch bolts or larger. Crosscut, above, used the same technique.

[Randall]

I also have used the washer nut deal, but lately I drill a hole in a 3/16" or 1/4"x 1" flat bar and lay it over the broken stud and weld, seems to heat it up more ,then hammering back and forth to to break it loose.

[johnneilson]

After many different methods I have found this to work.
Using a TIG welder, heat the broken stud until almost fully molten on top side.
The is enough heat to cause the stud to shrink in the hole as it cools down.
As it is cooling I weld a nut or washer to the top and then let it cool.
Wrench it out, usually very easily.
This also works for valve seats, use an old valve and weld it to the seat, as it shrinks it loosens the seat, knock it out.

J

[Dan McEachern]

Try this next time: Heat the unbroken stud with a torch close to the block and get it hot, then steal some of your kids or grandkids crayons and melt them at the base of the stud, let it cool and then use a stud remover. I prefer the purple ones over blue or green.

[Charlie Stephens]

Ask around at a few local machine shops and see if you can locate someone with a EDM machine to remove the stud. I live in Los Angeles and that type of machine is available from several local shops.

Charlie Stephens

[Bruce of MN]

EDM would work great, but the less extreme methods should be tried first. I had a broken 1/4" stud with broken EZ OUT removed from an aluminum motorcycle transmission case ~45 years ago. A lot less bulky than a Model A block!