Re: Trouble - broken manifold bolt.

Posted by Fish'n Jim On 2018/6/14 20:49:31

A lot of different techniques for this common problem that varies in degree of difficulty.
The dilemma is to know ahead of time what you're dealing with and that is not so tractable looking from the stub end. That would require Xray to know for sure.
Although I understand the "burn it out" technique, I don't recommend that to the average garage and on a classic engine block. This is probably one of those, "war time" techniques that one employs when they're shooting at you. Plus if you heat only on the fastener you're stressing the block as fastener will enlarge faster than the cast and could cause a crack. Better to grow the hole or shrink the fastener than jam it tighter. I've encountered rust welded old cast pipe threads that won't respond to heat, and of course more heat is better, but in this case, the high carbon content will catch fire and actually burn and melt iron down to nothingness. An engine block is not that high in carbon, but the grain structure is important for strength, and if you go above red heat, the metal re-crystalizes on cooling and makes a brittle structure. So be sensible with heating and oxy-acetylene on cast. Better to not use the flame wrench, if possible.
Prevention is the better approach, and that means changing the stud or bolt material. Make sure the threads are good, lubricated, and deep enough for the length fastener. Plus using torque wrench stepwise for tightening, and ditch the impact and cheater/breakers. Know your own strength for hand wrench work.