Thermostat stripped threads

[Loope]

I removed the thermostat housing to put in a new thermostat, and realized that a PO had messed it up. One of the bolts had broken off, and an attempt was made to drill it out. Part of the bolt was drilled out, but the drill had wandered and wallowed out the hole a lot, slipping off to one side. Then a helicoil was installed incorrectly... the hole was too big, and oblong shaped from wallowing the drill, there was hardly any trace of thread, only a few partial threads towards the bottom of the hole. The engine is a mid 1980's Chevy 305.

Would you think the intake manifold is salvagable? The hole is too messed up to install a heli-coil properly. I wondered about cleaning the hole and filling it with a thread-forming epoxy, or drilling/tapping for a plug and then drill/tap a new bolt hole in the plug. Does anyone have experience with these thread forming epoxies... would they work and hold up at the temperatures of the cooling water? Or do I need to break down and put on a new intake manifold? Or other ideas?

Thanks,

[Mikel]

I'm not familiar with that part, but I'm assuming it's aluminum?

I bet any machineshop could drill all of that out, reweld the hole, drill and tap.

[Loope]

Yes, it is an aluminum intake manifold. I did have another thought. PO left part of the broken bolt in. If I can drill it and use an EZ out to extract what is left, maybe a longer bolt would reach threads that are not damaged.

[tomb]

thread insert it has a self taping outer thread with sae threads inside,

[Mikel]

thread insert it has a self taping outer thread with sae threads inside,

Excellent idea

[glenn]

Yes, it is an aluminum intake manifold. I did have another thought. PO left part of the broken bolt in. If I can drill it and use an EZ out to extract what is left, maybe a longer bolt would reach threads that are not damaged.

Instead of a bolt use a stud if possible. It will go all the way to the bottom of the hole and use every last bit of thread possible.

[brute4c]

Is today your lucky day?
I have a stock 230 intake out in the shop...thermostat housing is bolted on...hasnt been removed in years...kinda dirty but hey its serviceable used...presently has the long studs for a governor setup...you can pull those and change to the shorter stuff if you dont need...your intake will have whatever you need there and elsewhere.

If YOU want it, pay the shipping and have a Merry Christmas...just let me know...

[Loope]

Thanks for the offer Brute4c, but my truck is a Chevy V8 engine. Guys, I like your ideas and appreciate the input. It will be a few days before I can work on the truck again, but I am going to try to get the rest of the old broken bolt out. If I can do that, I like the idea of using a stud, and will also consider the insert idea. I guess the direction will be determined by how much success I have in removing the remainder of the broken bolt.

Thanks and Merry Christmas to you all.

[kwai]

A good take-off chevy SBC intake as a replacement is likely cheaper and faster than trying to fix the old one.