Water Pump Thread Repair

When I was disassembling the engine, there is one water pump bolt which snapped off in the block.  I left it there intending to deal with it later.  I needed to sort it out before I start putting the engine back together.

I tried using an Ezy-Out on the weekend with no success…not even a hint of movement.  It was in there to stay.  The only other way to solve the problem is to insert a new thread, so I bought a Screw Thread Insert kit this week.

For anyone who has never heard of a Screw Thread Insert, they are also known as a Heli-Coil.  They are a coiled piece of wire which is wound to match the original bolt thread on the inside and also have a corresponding thread on the outside which is screwed into a tapped thread.  Some pictures might explain it better…

Here is a picture of the kit.  You can see it contains a drill, tap, insertion tool, break off tool and 15 coils.


The first step is to drill out the old thread…


You then tap the new larger thread for the coil…


After cleaning out the swarf in the hole, you take a coil and put it on the inserting tool…


Then you simply screw it in the thread until it is just below the surface…


The last step is to break off the tang at the bottom of the coil, and you are done!


The best part of the coil is that it is stronger than the original thread.  They can also be used for other applications like stripped spark plug threads.


2 thoughts on “Water Pump Thread Repair

  1. Great story! Years ago I had a heli-coil fitted to a stripped plug thread on a Honda 500/4 which I had just bought. The mechanic gave me an option to do it with the head on, using grease on the tap to hopefully catch the swarf, then hopefully blow any residual swarf out the exhaust valve when the motor is started. If something got stuck under a valve seat, the head would need to come off. The option worked like a treat and for the years I rode the bike, that plug thread felt better than all the other alloy threads. You could thread the plug in by fingers, all the way and just nip it up with the socket.


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