Thread: Helicoil in V8 block

Ok - I have been through this and I share your mechs concern on helicoils.

The first thing is that standard helicoils are too short and the number of threads interacting with the aluminium block is no where near the number that there is in an undamaged interface - you can get longer ones but i dont trust them.

When my block was being worked on the engine builder put in a helicoil and when I was assembling my engine that one stud just pulled out at about 2/3rds of the required torque.

I called the mobile thread repair guy and he recommended the way threads were repaired before helicoils, that is with a threaded insert. A lump of solid metal with a thread on the outside and the required thread on the inside - is not a "spring" like helicoils. I have used threaded inserts previously and they have always worked - and it worked on my engine where the helicoil failed - noting the threaded insert was long enough to be inserted all the way down so all stud threads matched the insert and likewise the outside threads ran the full depth of the hole in the block.

The downside of the threaded insert is they require a bit of metal around the hole for them to bite into where a helicoil does not require all that much metal to be drilled out.

Some will say that helicoils are strong enough but in my experience on a few engines they are a bit hit and miss where threaded inserts work well as long as there is a bit of meat around the hole as a larger diameter hole than is required for a helicoil is required.

Garry