Disaster strikes again..

[rgh0]

Sorry I was thinking these thermostat bolt holes went through into the chamber below but of course they do not.

A small tungsten carbide bit will remove both the bolt and drill stem but go carefully as it will remove aluminium even quicker and may be kicked sideways by the hard drill stem. A small ball shaped tip may be your best option

The carbide bits are extremely hard and you can get them in many shapes for a dremel but they are expensive at about $30 each. Used on Aluminium they last forever on steel or cast iron their life is much shorter.

You can also get diamond tipped dremel drilling bits intended for drilling holes in glass and ceramics that may work also.

If you have oil leaks to fix then perhaps best to live with your temporary repair until you have time to pull the engine for the oil leaks and then you can tackle this repair at the same time.

cheers
Rohan

[JonB]

The key to a good job is to have everything held firmly in perfect alignment and location before machining. It's virtually impossible to achieve this with the head in place on the car.

^This. I'd feel much better drilling it myself if I had the head off and used my drill press to keep it all square. Already I've caused damage using a hand held drill.

If you have oil leaks to fix then perhaps best to live with your temporary repair until you have time to pull the engine for the oil leaks and then you can tackle this repair at the same time.

^And this. If I had no leaks I'd continue drilling.

So, then.. what I need to do is go on a run with the clamp and see how it holds out. I need to get the temperature up in order to stress the joint a bit (with pressure) and if it carries on holding I can be more confident. I'm going to get a Cometic gasket too, that's a good idea!

[JonB]

JonB, you've had almost every suggestion possible apart from doing a dance round it and praying to a pile of chicken bones!

I do have chickens in my garden... I hate the stupid creatures. Hmmm, I wonder if Mrs JonB allow a little "sacrificial ceremony" to the Lotus gods?

Well done and thanks BBB for adding a touch of comedy to the proceedings. It all gets very serious sometimes!

[alan.barker]

Jon,
go for a drive and make peace with the Lotus Spirit and return to being zen
That's what i am trying to do while i'm fighting Vapour Lock on my TVR 3000S
Alan

[JonB]

No sooner said than done.

At the Shepherd and Dog, Fulking.

Alas, it wasn't long before Mrs JonB mentioned she'd felt a drip of water on her ankle... ..but we had a nice meal, and the repair held.

[JonB]

Right then, some good news at last.

You probably know I am refreshing the engine seals and have the cylinder head out. I decided to try and drill the remnants of the bolt and drill bit out of the threaded hole, using a pillar drill fixed in an appropriate position. Took a few tries with various drill bits but in the end I have it drilled and tapped for an M8 bolt.

Looks much better than the clamped bodge I built.

That odd looking small bolt is the one. It's M8 thread with a 10mm head, but I could just as easily replace it with something that looks like the other bolt (the correct thread size). However, I think I may leave it as it is different looking enough to remind me not to try and put an Imperial bolt into the metric threaded hole.

So the other thing - as there's a bit of the original bolt still lodged in there, my M8 threaded hole is slightly off centre, requiring some easing of the cover hole.

You can see the cover hole is slightly slotted.

Reassembly entails use of a very thin paper gasket. I think this gets wet and the bolt threads end up getting wet, too; when I took the (less than a year old) bolt I'd previously installed in the healthy hole, it was rusted. So I am thinking of using one of those Ajusa composite reusable gaskets or putting two paper gaskets in there, smeared with Wellseal. Either way I will be trying to seal off the bolt threads (grease or Wellseal?).

[2cams70]

Permatex high performance thread sealant would work well on these bolts. I used it for my Burton water pump cartridge bolts. It doesn't lock the threads - just seals them. I would not trust the bolts being protected by just some sealant on the gasket.

[MarkDa]

I've always used blue Hylomar both sides of gasket on all thermostat housings.
Also Copaslip on threads - at the risk of jinxing this car, I've never had seized bolts