Truck has been making noise for some time, but reallly started getting obnoxious a few weeks back. I was luckily enough to score a brand new in box GM replacement manifold off fleabay for $40 shipped like 6 months ago, but just really did not want to do the job...
And I was right. Found of course 2 cracks, and the rear most bolt had apparently broke off the head on it's own some time ago. There was a good 1/4" of the bolt exposed and protruding from the head however, but after grabbing onto it with a vise grip, it too broke off leaving a nice piece in the head. And of course, this is the one nearest the firewall - really not kind to get to.
Tried an easy out, but there was no budging that chunk. Ended up having to drill it out and then retap the hole a size larger (M10). An angle drill is a must here.
Got it all bolted back up and upon final tightening, one of the middle bolt heads also broke off. FUDGE! Had to pull everything back off and repeat the drilling/tapping process on this one. The good news is that the manifold bolt holes easily accepted the larger sizes hardware of the 2 replacements.
My guess is the constant temperature extremes that the bolts see eventually weakened the smallish M8 bolts to the point where even mild torquing might break them. If I had it to do over again I would have obtained at least a new bolts ( maybe even studs and nuts?) for the whole thing so it might not happen again.
