We tangled with my Son's 280 SE today. He had lost a water pump, and we pulled it when the new one came in. One of the longest bolts refused to come out, and sheared off flush.
We just thought it rusted tight, and parted on removal. When we tried to extract the broken part with an easy out, and noticed some sticky compound in the hole. Even the bolt top pieces wouldn't be free!
It looked like this:
The glue is not as strong as the steel, and forced a drift on the drill hole; when the steel broke through.
Here is the glue by itself:
My 8mm by 1.25 pitch tap couldn't clear this, and it clogged up as soon as it hit the glue. It's interesting to see that this obstruction is rotating with the removal attempts. The original threads had been damaged by cross threading, so there was little metal to use for securing this bolt!
My Son decided to do a thread repair:
First step is to drill out the hole oversize, to match the upsized tap in the thread repair set. Here is the first cut, not yet full sized; and you can see the glue beginning to come out.
The glue began to discolor from the heat:
Notice that the plug of glue has rotated again, and is mostly gone.
Here is the full diameter hole:
Drilling progressively larger holes allowed us to move the center of the hole back to the center of the original hole. If you just drill to fill size in one step, the hole would be wrong, and still have glue on it! This is optimal for the thread repair insert.
Most mechanics know the rest, but I'll run through it for those who don't. First, the oversized tap in the thread repair kit is used to thread the hope with a larger diameter thread; designed to accept the new thread insert.
The insert looks like a closed spring with a flat piece across the bottom center. This flat piece fits the provided insertion tool from the kit in the slot in this tool. This slot allows the insertion tool to twist the thread repair insert by this flat piece. Once it's screwed into the newly tapped hole, the tool is rotated a quarter turn and tapped down. The tapping breaks off the flat piece, which can be blown out using compressed air.
Once this done, the new thread is ready to use, and the rebuild can proceed.
The water pump is reinstalled now, and torqued up perfectly! One step closer to this beast being back on the road, it is beginning to look real nice.