RedSabre Mike If you go to a GM store we have a kit for motor repair. They are timecerts. Have used them for the last 3 years. If the repair is done right the repair is stronger and will last longer than the helicoil. I have had to replace helicoils in my shelby heads. They would back out under heat cycles. I replaced all 8 in the heads with timecerts and 2 in the main block. Raced the motor and have had no problems. IMO the timecerts are stronger than a helicoil. Lock into the hole, mount flush. They also come in a master kit for about $300.00 with all the metric sizes you would need. In the kit is the correct drill bit, bottom tap, reamer to make the timecert flush with the surface, and the installer. This is for each size. IMO if helicoils are so good, then why would GM (and only speaking from 25+years of GM experience) give us a kit with timecerts and not helicoils?
The is for both Aluminium and iron repairs. I think helicoils work great for quick repairs and will hold under low load torque settings, like spark plugs. But under heavy torque loads, and many heat cycles they weaken. Rick Lake Ps I have not tryed Keycerts but they work about the same as Timecerts. Installation is key.