Sheared bolt/thread size for tap

[mobylette]

I decided to do a simple job this afternoon, of course things did not go smoothly. I wanted to replace the thermostat. The nuts came undone easily, but despite soaking in plus gas, the cover was stuck to the studs. Tried the two nuts trick to turn a stud, sheared it off flush with the ally housing . Decided to drill the cover and chisel open around the studs, success. Applied mole grips, gently and slowly turned the remains of the sheared stud, sheared off again flush with the head . Had a cup of tea. I have now managed to drill the stud out, and pick most of the threads clean. An old stud goes in reasonably easily, but I would like to clean it up properly. What size tap do I need please?

[les]

The thread in the head Is 5/16 unc. Go for the second tap.

[mobylette]

Thanks, this one : 5/16 X 18 UNC HSS SECOND TAP?

[les]

Sounds about right. When you get one just check it against one of the old studs.

[philthehill]

When fitting the thermostat housing give the studs including the stud threads (UNC & UNF) a good smear of 'Copper Ease' which will help stop the housing becoming seized again on the studs.

[mobylette]

Thanks, I was planning plenty of copaslip, don't want to go through that again. The thermostat that came out was a bit odd, it was marked "made in Taiwan" and stamped 195 which I assume is Fahrenheit (90C).

[paul 300358]

I'm always surprised that the studs aren't cadmium plated, cadmium is approximately halfway between aluminium and carbon steel on the galvanic scale so reduces corrosion.

[philthehill]

As the three thermostat studs fit into two blind holes and one through hole I would suggest that a 3rd or plug 5/16" UNC HSS tap is also obtained.

[Declan_Burns]

The studs are available in stainless steel.
http://www.minispares.com/product/Class ... o%20search
Regards
Declan

[mobylette]

Gaah!, too late, already ordered standard items from ESM, however I seem to recall that stainless and alloy don't sit well together electrolytically (is that a word?). Pity that they didn't make the housing out of brass.

[philthehill]

Some MG Midget/Sprite fitted with the cross flow radiator used a cast iron thermostat housing.
So long as the studs are given a good coating of Copper grease there should be no future problems with stud seizure or corrosion.
I personally would not use stainless studs or bolts for engine assy.
There are different qualities of stainless steel and unless you know the full specification I would give stainless a miss.

[mobylette]

When I fitted the new thermostat, I thought it looked sightly larger and it was a snugger fit in the housing. I measured them up. The old one was 52mm compared to the (correct) new one at 54mm. I reckon water was bypassing the old one to some extent. The heater is now definitely warmer although by no means hot. Next job: fitting a temperature gauge. What could possibly go wrong this time?

[pgp001]

Have you flushed out your heater core ?

My heater was absolute rubbish until I stuck a hosepipe on it from either end a few times, the amount of crud that came out was unbelievable, now the heater works really well and warms up very quickly indeed.

Phil

[mobylette]

Thanks, I have back flushed the heater. It is a 1961 model with the round heater. Took it for a spin today and the heater was quite warm, probably as good as a "fug stirrer" gets.

[mobylette]

Of course that wasn't the end of my problems. Checking the thermostat housing after a run, I found coolant escaping up the replaced stud , this being the stud hole open to the water way. I had some Loctite 55 (like posh PTFE tape, OK up to 130 C) in my plumbing bag, so removed the stud and wound the thread with the tape. Replaced everything, went for a good run and no leaks . Next job is to upgrade headlamps with some Wipac halogens so I can see where I am going on these dark winter nights. What will go wrong? I will let you know.