Hi!
Yesterday I was going to replace the thermostat on my 4.2 engine as preventive maintenance.
Of course it did not go as planned and 2 of the 3 bolts broke off.
Any advice on how to remove them properly?
I am not confident to drill out these bolts…
I think your best option it to pull off the houseing…you then have studs sticking out…they are obviously well siezed in…so apply heat to the stud and gently try to remove it…may take a few goes…let it cool apply heat again…dont be in a rush or you could damage the manifold…also possibly weld a nut on the end of the stud…it gives you something to grip on and applies heat at the same time
As Steve said, remove that thermostat housing, and then see if you can get a hold of the stubs with a vice grips. A lot of heat will be needed on them, and just beware not to melt the aluminum doing it. As Steve also pointed out, it takes patience and time.
What @Wiggles said. The housing will need to come off. You have a couple heating options.
Cheap, one of those small butane torches often seen used in kitchens and soldering.
More expensive, might be the time to invest in one of the magnetic induction heating stud removal tools.
If you decide you have to drill it out, it is vital that the hole is drilled down the center of the broken bolt. Here’s a tool that will make that easily done. These spring loaded pilot drills are normally used to drill pilot holes for the screws in hinges, but they work great for center drilling broken bolts. This one a Snappy brand and uses an 11/64 drill bit.
I would spray the bolts with PB Blaster - a very good penetrant. Let it soak in for a day and perhaps apply heat with a butane torch. Then drill the bolts and use an EZ Out to unscrew them. There are various sizes of them but I would try a 1/8 inch or 3/16 drill hole.
Those are an absolute must in your quiver!
Once again the forum throws up something I have never seen!
I found it was corroding aluminium jamming the bolt… at the very least the manifold must come off - best of luck!
If you remove the manifold you will still be facing the same issue — how to remove the bolts. I would say that unless you can’t access them in situ I would try to get them out before you resort to removing the manifold. See my previous post about using EZ Out extractors.
Thank you for your answers. Lot of great options.
I think I will first try heating the bolts with an electric tool I use to solder copper tubbing at home.
I’ll let you know how it goes!
let it heat & cool many times, as many as needed, never lose patience
similarly rap the stud to assist break bi-metallic corrosion
work the stud back & forth
as soon as it moves in the slightest, you have it all but beaten
never succumb to the temptation to use excessive twisting force
A little update.
Today I got SAE sockets in my mailbox.
Last bolt (or I should say the last that is not broken yet) rounded pretty much instantly.
First attempt with a 13mm socket was definitely a mistake.
Now I think I have to remove the intake manifold with the thermostat, and see what I can do.
Can you just remove the thermostat houseing…is there still studs protruding from the inlet manifold…if so then you may not have to remove the complete manifold…heat on the stud or weld on a nut will probably do it…Steve
Hello, here is a quick update.
Today I removed the carbs and air box as a single assembly. Obviously that was the easy part.
Next, because the last remaining thermostat housing bolt was rounded, I decided the remove the intake manifold
Note: finding non metric wrenches in a shop, here in France is an absolute challenge!
So I only had 1/2in flare nut wrench. Space between head and manifold is tight. It was a total nightmare but I ended up removed every nuts, except one due the wrench being too big.
Next step is ordering the right tool, intake manifold gasket and thermostat housing bolts.
Also, I’m considering switching to HS8 carbs. I just found I nice used 2" intake manifold for cheap, which would solve my problem with thermostat housing bolts.
Do toy think that it would be a smart move? Maybe a bit more GO and ability to install a manual choke (my car and with HIF7…).
I very much like HS8.
They can quite easily be adapted to manual choke operation, in fact you should do this as the AED is noted to be problematic
If I was you I would order a couple of Metwrinch sockets and spanners
These are high quality and made in Germany I believe
I would get 3 sizes 11,13,14mm, which covers 7/16, 1/2, 9/16 and Whitworth sizes, they are specially made for rounded fasteners, check the website
The spanner engages the flats not the corners
You can get the studs out if you follow what I said
You must use heat, I broke a stud and now my 100% record is shattered, 
and that was cause I was too stupid and lazy to get my torch, its next door neighbor came out easy
Thanks for the advice!
I did use the torch today, multiple times and I have to admit that it worked beautifully!
If you have any stud protrusion, you may have to resort to locking multigrips (which work well, sometimes in adjunct with a file)
with a tough job, there are few things to try, ideally you can warm the entire manifold, but most folk dont want to use the oven, so if not just concentrate on heat cycling the smaller area, rap the fastener head, and cool with penetrating lubricant
If the thread union is vertical, a good sign of impending success is observe if the penetrant is “boiling” at the junction, this means it is penetrating
its also important to work the fastener back & forth, not just anti-clockwise
be aware there is a good chance the female alloy threads will be toasted
I know of no better example of where anti-seize should be used
I bought a set of bgs imperial wrenches and a set of sockets off ebay. Dirt cheap, worth a lot.
I bought BGS sockets too! I really appreciate the quality, for such a low price !
I also bought whitworth wrenches yesterday, per @awg recommendations.
