E-Type 4.2 cylinder head stud

E-Type
1

Need help gentlemen. I am currently rebuilding the 4.2 engine from my '71 2+2, and I have managed to drill out the broken cylinder head stud from the bottom of the water jacket, but no I need to tap the threads. The new stud threads do not fit any of the taps in my kit (SAE), could anyone tell me the tap I need?
Thanks
Mike

2

Working from memory - 7/16" UNF. I used a lengthened tap - welded a shaft on the end of a standard plug tap with a T bar welded to top. This way can work above the deck. Paul

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3

Thanks Paul, I hope my wedding skills are up to it!
Mike

4

I guess that one does get married to a project of this scope!:wink:

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5

GD autocorrect!!! Please read welding.

6

Have you considered a helicoil, or is that not an option with the long stud engine?

7

As I recently recommended for another fix- you may want to look at Time-Sert (no affiliation):

http://www.timesert.com/html/inchsert.html

Either way, good luck.

Huff
69 2+2

8

Success!! Local tool store had 12" drill bits, so drilling was easy. Tap square head fit my 1/4 drive extension, so no need to weld, held in place by a dab of dum dum. Threads cut easily, and new stud in place.
This is an engine out job, and a frost plug hole was directly in front of the broken stud, so I could see what I was doing.
Thanks to all helpers
Mike

9

69 Coupe
Need some clarification.

  1. Did you re-tap to the original thread size? If so, are the resulting threads as strong as original because of the “rust” damage??

or

  1. If you used a helicoil drill and tap, does it fit down thru the top or do you have to somehow put in thru the side and then connect to an extensio from the top, etc??
10

You have two options. The first is to chase the threads with a chaser tap that removes a minimal amount of spalled iron. If you use a regular tap you will likely remove too much material and make a sloppy fit. If the fit is sloppy there’s a chance the stud will shear the threads once torqued to 55-58 ftlbs, depending on the spec you choose to apply. If that fails a helicoil will remedy it, but you will have wasted a head gasket. So, my free advice is to chase the threads and then dry fit the stud without the head in place. If there’s the sightest movement in the stud afterward, go with the helicoil. YMMV.

11

Mark, yes, I used 7/16 NF tap, and the new stud is solid, no wiggle or play. I was fortunate that the broken stud was centered on a frost plug, which I will leave open when I install the head, to see how it fares. Waiting for new valves to arrive to rebuild the head.

Mike

12

I’m not so sure that you were fortunate. That’s the way they are. I think that all 10 long studs are centered on a frost plug, They added the extra plugs when they went to the long studs.

13

Thank you. What size drill bit did you use before tapping PC721? That’s my concern! I’m hoping that I can grind the nub off to about 1/8th" above the block and then use a smaller bit than would be required for a tap and “hope” that maybe an extractor will get the remnants out. I’ve been daily soaking all the long studs for about 4 months now and not even a budge!! The one that broke was the most deteriorated at the base. It was about 1/3rd gone. All the rest are surface corroded, but not to the point that they would likely fail if put back in service.

Mark

14

Hi Mark, I had about 3/8" stud left, and I found a compression nut for 1/4" copper tubing that was a snug fit over it, to centre the drill bit, so I used 3/16 first, then 1/4, and then tried an extractor without success. (I was afraid to lean on it too much, if it broke I was really buggered!)

Final drill was 3/8, then the 7/16 tap went fairly easily with a little oil. I did take photographs, and if I can figure out how to download them to this computer, I will send them.

Good luck

Mike

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15

Thanks David, my luck doesn’t seem to work on the lottery either!

Mike