Stripped thread, don't fret

This article builds on some tips and tricks from my Removing damaged fasteners  article.

Stripped threads are something that strikes fear in even the most seasoned mechanics.  Stripped threads will have the novice do-it-yourself-er nearly breaking down in tears.   Of course stripped threads seem to always crop up or happen at the most in-opportune times and places.  Its always that last fastener that is either a frequently inserted and removed (ie. drain/fill plug) or the last fastener required to finish the assembly.  A stripped thread stops you dead in your tracks, unless you have a plan.  In this article I will discuss a few methods for common thread repairs.

Causes: Stripped threads are caused by a few things but are most commonly caused by two issues.  Issue 1: Dissimilar metals being screwed together, in the example of the drain plug, usually the case is aluminum and the plug is steel.  The steel plug wears the aluminum threads out from repeated in-and-out over time as steel is harder than the soft  low grade aluminum used in engine cases.  Issue 2: Over torqued or tightening of the fastener thus tearing the threads out of the hole.

Remedies: The first one is obvious, tighten and torque the fastener to the proper spec outlined in the service or owners manual.  Next would be to use ant-seize compound regularly to help lubricate the threads going in and coming out.  This also prevents electrolysis and corrosion from the contact of dissimilar metals
Thread inserts:

Invariably the threads are stripped so you need to replace them with new.  There are several ways to do this, from drilling a larger hole and tapping it for a larger fastener, but in the case of a drain plug for example there may not be enough material left to do that or it is just impractical.  Here is where thread inserts come into play.  There are two major brands Heli-Coil and Time-Sert,  essentially both of the end results are the same-brand new threads the exact same size as the original.  Each type requires drilling out a slightly bigger hole (removing the existing threads) and tapping the “new” hole for the insert to thread into and lock in place.  Now you have instant new threads. 

Now to the first timer this will seem intimidating, but take your time and follow the directions.  Below are some tips for the first timer.

Tips: Use a thick grease on the drill bit and tap to collect most of the metal filings from falling into places you don’t want them.  Go slow with the drill to make sure you are as straight as possible.  Work the tap in and out until you create the new threads for the insert, trying to thread it one time all the way through can risk breaking the tap and then you have a real mess as it will be nearly impossible to remove.

Thread repari kits like this one are inexpensive and come with everything you need to do the job.

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