Inexpensive thread chaser

While I was rebuilding my engine I sent the heads out to be reworked.  When the heads came back they had painted them with a high temp rust inhibiting paint.  This was all well and good, but part of the problem was that the threaded holes for the rockers, in addition to other mounting points were now gummed up with paint.

Regardless of whether the shop should have plugged the holes prior to painting, I found myself in a situation where cleaning the threads was needed.
I set about to remedy this by getting a proper sized bolt, a vice and my 4 inch angle grinder.

So first step is to find the proper bolt for your threaded hole.

Step 1 Prepare to grind

So, now that you have the proper sized bolt for your application.  Lock it down securely in a table vice.  Now grab your grinder.  In my case at the time I didn't have a dremel or other small hand held grinder so I used an angle grinder.  It was a lot more difficult  to get an exact grind but completely doable.  I suggest that if you have a small hand held precision grinding tool such as a dremel, you should definitely use that.

Start out by making a tapered grind along the length of the bolt on the threads.  The taper should be a fatter/wider grind at the bottom of the threads and thinner at the top.