Engine problem
2000 BMW 323 Two Wheel Drive Automatic 100000 miles
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This is the first BMW engine I've worked on and first question asked on the computer so here goes. The car overheated so I took it down for inspection. Three very clean cylinders and a thin head gasket was all I found. We had the head milled .007 in. The block and bolt hole were clean.I used a standard thickness head gasket and new head bolts. I torqued them to 40NM with a quality torqe wrench.I used a beam type torqe wrench to watch as I Turn the 90 degree turns. On the first bolt in the pattern, at the start of the second 90 turn,(about 65 ft/lbs) the threads turned loose. I trying to decide: Do Heli-coil all 14 bolt holes.Do I use another set of bolts( they are still obviously shorter than the oringinal), Should I use the .3mm thicker head gasket. Any advise would be greatly appreciated

BMW recommends replacement of the block if the threads pull out. Helicoils are a possibility, I have personally never trusted them for high load areas. If you milled the head .007" you may have exceeded the amount of material the head can be machined, the minimum head thickness is 139.7mm. The heads on the M-52 motors are prone to cracking, be sure to pressure test. What is obviously shorter?