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1972 CB350
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Discussion Starter #1 (Edited)
Hey everyone, new to the forum and CB350 ownership. I was doing some initial work on my '72 CB350 and decided to pull the spark plugs. The left plug came out hard, and turned hard the whole way. The pictures below show aluminum threads stuck in the spark plug and the severely damaged threads in the plug hole. Looking back I probably should have applied some heat and more penetrating oil but too late now.



I did some research and many people recommended a time sert or Sav-A-Thread. I checked my toolbox and just happened to have the Sav-A-Thread kit with the right thread size and pitch (M14X1.25) I'd used previously to repair an aluminum oil pan. Many people say to not use a Heli-Coil. Note, this kit is made by the same company but is completely different than a standard heli-coil. These inserts are solid steel designed to repair stripped spark plug holes and hold pressure while a heli-coil is basically a spring that can separate and is not designed for this application.

Tools/materials needed:
Sav-A-Thread kit 5334-14 ~$30
Heavy grease (I used some bearing grease I had)
carb/brake cleaner
High Temp RTV gasket maker
3/8" ratchet/breaker bar
Flathead screwdriver




Before attempting the repair rotate your engine so the valves are retracted/seated and the piston is far down in the cylinder. The tap that comes with the kit protrudes far into the cylinder and WILL DAMAGE the piston and valves if the motor is not in the correct position.

Fill the flutes of the tap in the kit with grease, don't be shy. The grease here is used to trap the aluminum shavings and prevent them from entering the cylinder of the engine. It won't catch all of them but we'll take care of that later. Begin threading the tap into the spark plug hole making sure the tap is aligned perfectly with the hole the entire time. If the hole is tapped at an improper angle this fix will not work. Use a ratchet or breaker bar to thread the tap further. After about every full turn or two, back the tap out fully and clean the shavings and grease from the flutes. Replace with new grease. Continue this until the tap is fully threaded into the hole.

Shavings after process is finished-

Wipe grease and shavings from the cylinder head and hole. Rotate engine until piston is near TDC. You can use a long flathead screwdriver or pick with grease on the tip to pick up all the metal shavings that are on top of the piston. After this, use brake or carb cleaner to remove grease from the new threads in the hole. Put a light coat of RTV on the longest Sav-A-Thread insert, this will match the length of your spark plug threads. Notice the knurling on the insert, this needs to be at the end of the hole nearest you once threaded in.


Thread the insert onto the tap and then use the tap to thread the insert into the plug hole. The top of the insert needs to sit flush with the top of the plug hole so the spark plug makes a good seal. Once the insert is threaded in and flush with the surface, remove the tap and the insert should remain in the hole. Check again that the insert is flush. Wipe RTV away and use the expansion tool (punch) to expand the insert and hold it in place. Insert the narrow end of the expansion tool into the insert and give it a few solid hits with a hammer. You can now insert and torque the spark plug. Wait ~24 hrs for the RTV to cure before running the engine.

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