Matthew Lockwood writes:
Helicoil vs. time serts: Had to remove the top case studs due to completely corroded studs. Helicoil is what you recommend. What about time serts?
Thanks for the question. In the photo below, you have time sert tools on the extreme left, and the other three packages are popular variations on the helicoil concept.
I have used all of them over the years. They will all work, and any of them will hold in the case the full strength of the stud, if the stud is installed with Loctite 620 upon assembly. Given a preference, I would pick a time sert, but it is just a style point, not a major issue. The time sert stuff is a lot more expensive than helicoils. If you look closely, the thread on the Recoil box says 5/16-18; this is for other places on the engine, I just had it handy for the photo I shot a few minutes ago. The thread for case studs is 3/8″-16. This type of repair is something that we demonstrate at every College. They are not difficult to do if an experienced guy shows you once. I have put literally several hundred of these in Corvairs that have gone on to fly for many years. My own personal engine has about 30 of them in it. When done correctly they are stronger than the original threads.