SII Head Stud Broken

That is the issue. I need to get to the stud behind the hex fitting as that is the one that has broken off. The hex fitting is fitted in the location where the core plug would be. I tried an endoscope down the stud hole but it is difficult to see what is going on. So hoping removing the hex plug will at least let me get more visibility into the stud break.


Jay. If I can offer a suggestion you are probably only going to get one good chance at removing this plug. If you rush it chances are you will round off the socket and then things become more complicated. You need to devise a method to get that plug soaked with penetrating fluid and keep it soaking for at least 2 weeks before violent action. I think you are going to have to pull the engine to do this job properly. Lay the engine on its side with the plug up. Pack cotton wool, cloth etc around the plug and then soak the material with your penetrant of choice. I like acetone/ATF. It has worked for me where others have not and it is cheap. Resoak the material daily and cover the area with an old coffee cup to slow down evaporation of the acetone. If you have access to a torch periodically heat the plug .(clean up all fluid before each heating. It is flammable). After 2 weeks then use your big air impact or a long breaker bar. While the engine is out you can then attend to the rest of the studs. I would remove the rest of the frost plugs and soak each of the studs before attempting to remove them. Time is your friend with penetrating fluids. Give it lots of time to creep.

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I will add to Geoff’s good advice, except I don’t know that an engine pull would be necessary. I do agree they all should be replaced, one at a time.

Well I have been adding penetrating oil, heating with a propane torch and using a long breaker bar with about 3 ft arm but have not been able to remove the plug. I also tried a 1/2 impact wrench but did not budget. At this point I have decided to remove the engine so I can get better access.
Plan is to continue to spray with penetrating oil, and heat and then try a much longer arm and hang a bucket of bricks or similar from it for a few days. May also try renting a 1" impact wrench for a bit more oomph (technical term).

Any success stories of people removing this plug would be helpful at this time as it feels like I am banging my head against a wall :disappointed:.


Worst case you could drill, and carefully cut out the plug, cut just short of threads, crack it out with a punch, or cold chisel.

All I can add is that I’ve been told you can sometimes break a fastener loose by first trying to move it opposite the rotation you would use to loosen it. I don’t see why the same wouldn’t apply to the plug in question.

More specifically, drill a half inch hole in the center of the lug. Cut with hacksaw blade, dremel, mini grinder, or whatever, an “x” just to the threads. Then take a punch, and tap hard next to the drill hole on the remaining wedges. One will cave in, the rest will pull right out. It’s not as hazardous as it sounds.

Note this is a screw in steel plug (see earlier photo) and not the normal freeze plugs, so it is not possible to knock it out with a punch. Cutting and taking out the parts is a last resort option if the 7/8" hex key rounds off, but hopefully it won’t come to that.
Got to get the engine out first which is in process, but some bolts have not been touched in 50 years so taking a while to get stuff off, like the exhaust.


Jay, yes, I know it is the screw out plug. It can be drilled and parted out.

My fault, I misread your response. I saw the “One will cave in, the rest will pull right out.” and thought freeze plugs, but you were talking about the parts of the steel plug. Its been a long day :sleepy:

Hi Jay…have you considered welding a nut onto the plug…the heat could possibly break the seal and give you a better head to fix a tool to undo…Steve

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Ingenious. Apart from the fact threaded rod is normally mild steel I don’t see too much of a problem if the gasket doesn’t blow medium-term. Maybe there’s a new market out there for a high tensile ‘repair stud’. :slight_smile:

The socket ( as opposed to hex head ) plugs I have seen were brass.

Grade 5 and Grade 8 threaded rod is readily available from most any fastener supply store…

After a couple of weeks of penetrating oil and heating, the plug finally came free with the impact driver. Unfortunately part of the plug broke off while it was being removed so I will need to locate a new plug when I put it back together. Are these available anywhere or would this need to be custom made ?
Now I have the plug removed I cleaned out the debris and can see the remaining part of the stud that broke. It is very close to being broken off flush but I think there may be enough to be able to weld a nut or something on so I can try to extract. I am going to keep spraying with penetrating oil for a week or so and maybe add some heat from a propane torch. At least with the engine out I have a lot to work on while I’m waiting.



Congratulations. Glad to hear it finally came out.

I would put a dremel or chisel on that and see where the steel is. Hopefully there is enough to weld a bolt onto!

Monte is a very smart Patent Attorney and very creative, I worked closely with him and lent him my revealing gun drill for the studs, I highly recommend his method.
Mike Moore

The threaded boss was to take a heating element made by the Bray electrical company UK. I expect it will be a standard British thread of some sort. Can you work out how many threads per inch there are.?

I would grind that flush, so that there is shiny steel…if you choose not to drill from above;

place a thin copper washer to prevent welding stud to block

sit a steel washer on top, and mig the stud to the steel washer

mig a nut to the steel washer, and while its still very hot, wind it out

well done getting that plug out