Aluminum Head Thread Repair

The use of helicoils or inserts, such as a Time-Sert is pretty straight forward.  For any size tapped hole you can buy any of the various solutions in a kit that includes all of the materials/tools required.

The bigger question is which solution is right for your application.  The quality of the repair is pretty much subjective. That is, all of the name brand solutions will provide a quality repair if properly installed.  The purpose of this tip is just to point out a couple of things that may sway you one way or another.

Some mechanics when working with aluminum make it a habit to install inserts in all aluminum threaded holes before any assembly.  This is a time intensive and expensive practice, but does lead to a more robust thread, particularly where you are expecting to do disassembly.  In this case, inserts, like the Time-Sert is a nice solution because there is no guessing about depth of engagement.  They also look nice in the finished piece.

Probably the biggest disadvantage to an insert is their use "in the field".  That is, repairing a hole on an assembled engine.  In some cases, where chips are not prone to falling into the engine, a helicoil can be installed right through the bolt clearance hole with no disassembly. This is often not possible with an insert because an insert requires a larger clearance hole as you can see in the illustrations below.

Specifically, when repairing the cylinder head intake manifold attaching bolt holes on a 302/351w or 385 series engine, there are a few holes that can cause a particular problem for inserts.  These are the holes that are drilled through the head intake face at a 45 degree angle.  See the illustrations below.

As shown in the illustration to the far right, the clearance hole required for an insert is larger than the countersink provided in the cylinder head.  In this case, you would need a milling machine, or some other way to fixture a cutter to cut the relief required.  It just so happens that the relief provided is "just" large enough to clear a helicoil tap as indicated in the center illustration.  This is a case where a helicoil may be the simpler solution as it can be installed using a hand held drill.


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