So I saw a thread regarding a possible exhaust leak and it prompted me to post how to repair a boogered exhaust manifold thread. Imagine working on your box all day, you're tired, but almost done, just a few more bolts to put in before cranking it up. While installing the exhaust manifolds, the first manifold goes in without issue, as does the second except for that last bolt. That one refuses the grab the lead thread, removing the other bolts isn't helping, rotating the bolt backwards to find the lead thread is inconclusive, but it's time to press on. Finally, after all the jiggering around the bolt seems to grab the lead thread, finally. Being careful rotating it by had a turn or so it seems to confirm wishful thinking that it must have caught the lead thread, it must have! The next mistake is picking up a wrench and giving the bolt a twist, and after half a turn reality makes itself plain, you're the proud owner of a boogered head bolt thread. Steel bolt, aluminum head, guess where the boogered thread is. So after coming to the conclusion that this is a job for tomorrow, how to proceed? Well, this happened to a friend of a friend (FOAF) of mine. There are plenty of recovery options. one is to remove the head, take it to a machine shop, and have them put a helicoil in the offending bolt hole re-assemble the engine and give it another shot. Another is to put in a helicoil yourself, and as this is a DIY...
First buy a helicoil kit from a nearby auto parts store for the size bolt you'll be using
Second make a drill jig to drill a hole 90 degrees into the hole you'll be re threading. FOAF used a very square 2X2 piece of pine, a drill press, and the helicoil drill to make a pilot hole for drilling the head. Note the drill stop which is critical to drill to the correct depth and no more.
The jig was carefully positioned onto the head using the drill bit to center over the threads to be drilled, and held into position with a floor jack.
Drilling the end hole resulted in the following
Then the same jig was used to guide the tap for the helicoil, again using the floor jack to hold the jig in place.
After starting threading (several turns) using the vice grips for control, a square bit, extension, depth gauge, and breaker bar were used to complete the threading.
After that, the helicoil kit was used to install a helicoil so the exhaust manifold can be bolted up tightly without leaks.
The nice thing about helicoils is the repaired thread is stronger than the original. So next time a friend of a friend of yours boogers a thread, take a day off, make a jig and pick up some helicoils to make it right.