Broken stud

Richard/Ca

Richard/Ca

Senior Member
Surprise ! Surprise ! I broke a head stud on my engine block. Now I have already drilled it out and retreaded it. My problem is apparently I not not drill deep enough because when I screw the new stud in it stops three threads short. Any ideas? Maybe cut three threads off the bottom of the stud???. Really don't want to mess up the new threads.
 
never use heli coil, please look into time serts far far away better, I do not understand the three threads, Does the stud stand up taller than the rest if so and you have tapped, yes i would feel ok about removeing just three, I think this would leave you over 3/4 of the stud in hole, al
 
Did you use a BOTTOMING TAP? This is what you need to get the threads down to the bottom on a closed hole. And, be sure to blow the hole clean.
 
M,M,M, My first question would be what is the overall length of the new stud in comparison to the others? The number of threads on the stud can vary from one supplier to the next. The real concern is how far does the new stud rise above the head in comparison to the rest? If it is just a few threads too high then Tom’s remark about using a bottoming tap is right on the mark.
 
I seem to remember a while ago that some people on here or the old Fordbarn, said that you should never use a tap to clean the threads in the block. It did something to the threads??? (weakened them) I don't know, I didn't understand it then, and I don't now...
 
Right, a tap can enlarge the threads, but in this case a broken stud was drilled and tapped. I would try the welded washer and nut process to remove the broken stud first. If that didn't work, I'd carefully drill the exact center of the broken stud with a 1/8" drill bit and keep increasing the size until the edge of the ole just got to the threads. Then I'd use a dental pick to carefully peel away the remaining thread.

Use an old bolt with 4 slots cut in it to clean threads.
 
I think what he is saying is he did not drill deep enough so when he tapped he ran out of hole, Now he will have to drill and keep away from threads which will be tough road to haul, This is why i said cut to fit might work for him,

I would like to respectfully disagree with tapping is a bad thing, After 80 years of debris in the holes I would think there would be no way you could torque to 55 pounds with crud in the holes, I tap and die every bolt every hole that would require torque, As always the knowledge on the board as my respect
 
Ford used taps that were way more percise then generally available today.

There are 3 classes of fit, 1 for loose tolerance. 2 for general purpose. 3 for tight tolerance.
 
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Thank You all for some very interesting answer. No I did not used an heli coil I drilled the hole out with different size bits until I finished with a 3/8 bit. Then I could run a 7/16-14NC tap to clean the threads. But apparently I did not drill deep enough to thread the full 21/32 which is how deep the hole should be at least. As stated in George Miller's post. I did use a bottom tap. I went back out to my shop and was thinking of try my Drimrel tool with a small grinding bit.Working very carefully I managed to get about two more threads deeper.Now I think I had better leave will enough alone. Once again Thanks Richard
 
When I drill a broken head stud I start with a 1/8" bit and drill until I feel the bit go through the bottom end of the stud and hit the casting of the block. I never measured but I'd guess the bit drops about an 1/8" to 1/4" after it leaves the bottom of the stud.
 
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