Morris Minor Owners Club

Hello all,

I’ve been taking my (spare) head apart, and unfortunately I managed to snap a thermostat stud just below the surface after successfully doing battle with the thermostat itself.

I’ve tried using a left handed drill bit to encourage it to rotate out. I’ve also tried a ‘stud extractor’… but now I’ve been left with a ‘hollow’ stud clinging to the threads in the stud hole

I’m not sure what to try next. Perhaps I could ‘tap’ the threads to remove the old stud material? I’m worried I’d end up just mashing the existing thread up

TYIA

you can get diamond tipped drill relatively cheap. The one I purchased was hollow, like a mini hole saw, so the material came out through the centre.
My minor had a broken of thread tap in the thermostat bolt hole, in the head and I managed to drill it out. Someone had bonded a cut off stud in, so it just came away when I tried to undo the nut.Take you time and keep plenty of water to lubricate and cool. I then ran a tap down the hole and restored the original thread size.
https://www.ebay.co.uk/itm/222645770011 ... media=COPY

The thermostat studs are only mild steel so should easily drill out with a normal HSS drill.
I would gradually increase the size of the drill to get rid of the remains of the stud until you can see a start of the threads in the head. Then you may be able to rethread the head using those original threads as a start guide.
If the worst comes the worst you can always go up to a 3/8" stud and drill the thermostat housing hole to suit.
It helps if you drill the three holes in the thermostat housing out to 3/8" as it makes it easier to remove the thermostat housing cover and reduces the risk of corrosion seizure. Always give the studs a good smear with copper ease.
Ditch the cork gasket and fit one of the latest paper gaskets.
https://www.ebay.co.uk/itm/356466217216 ... R_Tas5XEZQ
The stud(s) that goes into the cylinder head water jacket should be sealed in the head as coolant can leak past the stud threads and appear at the top of the stud.

philthehill wrote: ↑Thu Apr 10, 2025 9:10 pm
The stud(s) that goes into the cylinder head water jacket should be sealed in the head as coolant can leak past the stud threads and appear at the top of the stud.

Yes. Same with the heater tap studs. I used Permatex on mine and no leaks. For years I did not know this and wasted time with new gaskets and totally unnecessary goo.

I’ve tried using a left handed drill bit to encourage it to rotate out.

Continue with left-handed drill bits of increasing size. Stub will usually screw out as you approach the minor diameter of the broken bolt.

This is all very useful, thank you!

I will continue on my drilling path, and see what happens. One of my drill bits just fits down the other holes, so hopefully that will be the key

Hello, me again.

So, I've drilled the stud about as much as I can without it impacting the threads (I think). The remains of the stud seem to be holding on for dear life as though it's become fused to the head.

Would running something like https://amzn.eu/d/giBSYnz down the hold clear out all the stud metal?

Yes but you need to be careful otherwise you could end up with no thread or a double thread.
As I said above if you can see a thread to use as a start for the tap so much the better.
You could if you wanted to put a repair thread (helicoil) insert into the hole. You will need a special size drill and tap to do that though.

philthehill wrote: ↑Fri Apr 11, 2025 5:56 pm Yes but you need to be careful otherwise you could end up with no thread or a double thread.
As I said above if you can see a thread to use as a start for the tap so much the better.
You could if you wanted to put a repair thread (helicoil) insert into the hole. You will need a special size drill and tap to do that though.

Thank you, I will heed your warning and go carefully. There’s a tiny bit of thread, so I’ll see if I can use that. If that fails I’ll either give up, use a helicoil or go up a stud size.

Hello again

I was able to tap the stud hole reasonably successfully. It seems a bit looser than the others. I suspect in the process of drilling out the stud I’ve taken the tops of the threads off (if that makes sense?).

I can however do up the stud tight so hopefully it’s okay. I guess there’s a danger of striping the thread when I torque down the thermostat or it coming loose (maybe some thread lock would be wise?)

Thanks

Well done. There’s no great torque required on the thermostat studs. They often leak where the stud screws into the head so some thread sealant is a good idea anyway.

Stephen

svenedin wrote: ↑Wed Apr 23, 2025 8:05 am Well done. There’s no great torque required on the thermostat studs. They often leak where the stud screws into the head so some thread sealant is a good idea anyway.

Stephen

Thank you. That's all reassuring!