Time-Sert Spark Plug Thread Repair On a Motorcycle Aluminum Cylinder Head

Aluminum motorcycle cylinder heads have fragile spark plug threads. Thread damage or wear is often remedied with a complete replacement cylinder head or head casting. A head casting or complete head is expensive. On high-end, multi-cylinder motorcycle engines, the parts plus labor to install a new cylinder head can reach thousands of dollars.

In this video, I walk you through my repair of worn spark plug threads—with the cylinder head still in place. The procedure actually makes spark plug threads better than new. For a permanent upgrade and repair solution, my solution is a Time-Sert® spark plug thread repair kit.

While wire coil type inserts sometimes have their place, I never use them for a spark plug thread repair. After watching the Time-Sert® repair procedure, I'm sure you will agree. I install a Time-Sert® at the first sign of loose spark plug threads. Race teams often install these inserts on a new engine. (See "Footnote" below.)

Footnote: A viewer expressed concern about cutting threads with the cylinder head in place. There are other Time-Sert spark plug thread insert installations at YouTube with the cylinder head in place. A popular Time-Sert® installation is the repair of Ford Triton engine aluminum spark plug threads with the aluminum head(s) still in place. According to Time Fastener Company (manufacturer of Time-Sert® kits), the tapping and insert installation can be done with the cylinder head in place. The instructions suggest use of heavy grease on the step tap flutes to capture chips, following up with a shop vacuum to draw out any remaining residue: https://www.timesert.com/html/faq.htm....

In this demonstration with the Honda XR650R aluminum head in place, the intake and exhaust valves are closed completely, which is noted in the steps. (Backing off the valve rocker adjusters will assure that the valves are seated.) The piston is positioned just low enough on the compression stroke for the tap to safely clear the piston. With the valves still closed and piston still in this position, a powerful shop vacuum with a tapered nozzle pulls aluminum tap chips and residue from the cylinder and combustion chamber area.

The Time-Sert® installation technician can decide whether to remove the cylinder head or whether to use heavy grease on the step tap flutes. When using heavy grease on the step tap flutes, it may be difficult to remove all grease and residue. With the softer aluminum thread material, I chose to run the tap dry and draw out aluminum debris from a dry cylinder and dry combustion chamber with the strong shop vacuum and tapered nozzle.

Although many do this procedure for cast iron spark plug threads with the head in place, iron chips or residue would be more abrasive than aluminum. As a precaution for a cast iron cylinder head, I would likely remove the head and install the Time-Sert® on the bench. Clean-up of all tap chips and residue would be done before reinstalling the iron head.

Note: After cutting/tapping the insert threads, be certain to remove all debris from the cylinder. I performed the tapping operation with the piston rising on its compression stroke and all valves closed. On this Honda motorcycle engine with a decompression mechanism, the valve lash adjusters must be backed off to provide full seating of the valves before performing this procedure. All valves are seated and the piston is down in the cylinder on the compression stroke, enough to clear the cutting and installation tools. After tapping, the strong shop vacuum with a tapered nozzle pulls debris through the spark plug hole. Make sure all debris is removed.

This channel features maintenance steps for motorcycles. Your subscription is appreciated!