Please help - Any ideas welcome

I don't have anything useful to add, but would bring up the fact that brazing melts at around 1800F while aluminium melts at only 1400F. I had a friend (professional jack leg mechanic) tried to rebuild one of those engines. He overtorqued the manifold bolts and about 100 miles later, the crankshaft galled. Those engines are not suitable for real repairs. The bearings get out of true because the block twists so easy. Be careful. . .

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If you are down to looking for a hail Mary pass, this might work, at least for a while. It's called a manifold repair flange. The pointed end digs into the casting while the threaded end supplies clamping force. Could work since you are only contending with radiator level pressure. Man, that original tapped hole was sure close to the edge which is why it probably failed in the first place. I agree with the group that the only permanent repair is pulling it out and repair/replacement. Good luck.clamp1.jpg
 
Advisual said:
I was working on my 2007 Buick Rendevous changing out the thermostat and I accidentally stripped out the mounting thread with the wrong bolt. I am trying to figure out a way to repair it. I had a person come over who had an arc welding setup who tried to weld a bolt to the back side of the tread but it kept welding the nut with the bolt we were using to hold the nut in place. Also the nut was not welding to the cast iron block.
I have uploaded several pics to show what a before and after look like. I also show how I was trying to mount a bolt with a nut on the back side.
Can anyone suggest a way to fix my issue?

Thanks
Click to expand...
If the broken casting is indeed part of the block, this could be difficult. Rather than trying to build up the missing piece, I would try this. Clean up the remaining threads to be able to cradle a stud. Place an aluminum stud in the threads and tap in to seat in the remaining thread. TIG weld the stud to the casting. Not as good as a proper repair but with care, could last the life of the engine. The particular application is not a demanding one. You just have to create enough clamping force to seal the thermostat gasket. I would use a stainless steel nut on the stud and use anti-seize compound on the thread. Use care in tightening.
 
It's a Chevy 3.5, which is 0.1 better(???) than it's predecessor the 3.4. The thermostat is in the lower intake manifold. The manifold is aluminum. Crap American pot-casting aluminum, not easily welded. The day may have been saved with a heli-coil or better a timesert, before the ear was broken off the manifold. At this point the only option is to change the manifold. It's a 6.5 hr job, book time.
My question is why was the thermostat being changed? Random preventative maintenance? Or a hail mary trying to cure overheating? These motors are VERY prone to headgasket failures.
 
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