Repairing A Spark Plug Hole

Article By: Tyler Malinky

Originally Published In The February 2012 Issue Of Cycle Source Magazine


Especially when it comes to old motorcycles, you may find that threaded holes for fasteners or spark plugs may have been a bit abused. It doesn’t take much more than one ham-fisted mechanic cross-threading a spark plug in an aluminum head to turn the threads to junk. A quick and excellent way to repair threads are with the use of Time-Serts, which are available in a wide variety of sizes and lengths to fit any application. The following series of photos show Todd repairing a 14mm spark plug hole on a Triumph head.


The first step is to use the stepped tap and thread it into the hole to be repaired. The smaller, first step will chase the threads on the damaged hole and keep it going in nice and straight before it gets to the larger step that will cut threads for the Time-Sert. Cutting oil or a little lubricant like WD-40 helps the tool cut easier.



Slip the included T-handle over the stepped tap and run it all the way through the hole, cutting threads to accept the Time-Sert. You want to run the tap in until it is just below the top surface of the head, and then fit the 2nd cutter over the shaft of the tap.


The 2nd cutter will complete two operations. It will cut a slight step at the top of the threads for the lip on the Time- Sert, and then it will face the top of the head to accept the crush washer on your new spark plug.



Using the T-handle again, apply pressure and turn the tool. Stop after a couple of turns and check your progress. You want there to be a nice, even circle cut around the spark plug hole to give a nice sealing surface for your crush washer, as seen in the next photo.


Using compressed air, blow away any aluminum shavings and prepare to put the Time-Sert into the newly cut hole. By hand, thread it onto the end of the installation tap until it is a snug fit, and thread it into the hole.


Using the familiar T-handle, thread the insert in until it is snug and settled into the plug hole. You can now back the installation tap out with no problem, leaving the insert in place and ready to go. You will no longer have worries about compression leaks at your plug holes or blowing a plug out of the head, and a nice benefit of using Time-Serts is that they can be removed and replaced if you end up damaging one some point down the line.

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