jimivice

There are numerous thread repair methods, Heli-Coil, KeySerts, thread inserts. Heli-Coils will work for the majority of times and is synonymous with thread repair and although not fool proof is the most common method. If the threads pulled out and you get the proper thread depth for the Heli-Coil it will hold. The common problem I see with Heli-Coils is that the Heli-Coil is not put in deep enough to where the the first coil pulls out. The coil is to long,the insert extends beyond the thread. The tang can not be removed cleanly, it gets pushed aside or distorts the coils. This will either chew up the bolt or the coil will screw out of the bottom of the deck surface. Manley has the fixture to drill the hole square to the deck surface, when drilling by hand. The fixture accomates drill bushings and supplies the proper drill bushings for 7/16" or 1/2" threads. The fixture could also be used to drill for Keyserts or thread inserts with the purchase of the proper drill bushings available from any machine shop tool supplier (ie McMaster or MSC). In most cases threads will pull during the final torque of the final assy and the repair has to be done by hand on the motor. I have had after repairing one thread and after reinstalling the head another thread will pull out. This generally happens with old blocks and there is no way to tell if a thread will pull out. If you have run a tap through the threads (common practice) you unknowingly created the problem. In essence you have made the thread to loose or taken away from the root diameter of thread and do not have proper thread engagement. ARP makes "clean out taps" that do not remove material or thread restoring taps are available from tool suppliers. If,as was suggested, the milling machine can accomodate the block, it might not be cost effective to repair one thread.