Nine weeks later, the automobile is running great. To bring closure to this repair and to post what I learned through the process, here are some things from the "what it's worth dept."

Note to self; Head bolts are M12x1.75x160mm. Second note to self; Be sure to check the thread pitch of the tap.

It was recommended to use a mag drill to be sure the drill and tap were on centerline, however not having such equipment, I bought a 1/2" drill with a side handle and used 3 different size drills so as not to lose the hole centerline and to step up to the size necessary for the heli-coil tap (as recommended by the local machinist). I also used a large socket over the bit to keep it at the proper depth. The challenge was keeping the drill straight while it was cutting. I checked the tap several times from the front and sides to be sure it was on centerline as I cut the new threads. If the threads ended up off centerline, there was very little variation, because the bolts screwed in without much resistance.

Others were emphatic about taking the manifolds off with the head, however, having the luxury (if you can call it that) of doing the job twice, I can tell you it is easier to remove the manifolds separately. Though you don't have to remove the intake, you should remove it after the head is off to access the little hoses under the manifold and to clean the egr tube, plus the water pump is a whole lot easier to replace (if it needs it). The second time, I removed the exhaust manifolds, unbolted the intake and removed everything necessary and was able to lift the head off by myself.

Then, using the old head bolts (with the bolt heads cut off and a slot cut in the top for a screwdriver) as dowel guides, the reinstallation of the head went a whole lot smoother because there was no chance of damaging the head gasket because the head slid down straight and flush. What I had to do though was remove some of the plastic firewall stuff to allow room for the head to slide straight down. Once the head was in place, I unscrewed the home-made dowel pins, installed the head bolts and torqued the head to spec. Also, this time around I used Copper Spray-A-Gasket as additional insurance.

I didn't know this, but when the head bolts failed, the exhaust system must have filled with coolant and oil. This made for a very interesting evening as I filled the neighborhood with smoke for about an hour. No one called the fire department, which was a good thing. The smoke from the tailpipe didn't seem to want to go away after an hour of running and in fact this morning I was a bit worried because it was still putting out some significant puffs. The oil level wasn't diminishing nor was the coolant level, so my wife and I decided to take a country drive and after about 40 miles, the smoke diminished and then finally stopped. Hooray!

The saga has ended. Praise God.

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1992 300CE - 157kMi (my white beauty)
1992 300CE - 220kMi (sold)
1990 300E - 189kMi (sold)
1990 300SL - 102kMi (salvaged parts available)
1986 300E - 230kMi (salvaged parts available)

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