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Discussion Starter · #1 ·
I'm rebuilding my CB360T, the PO had a helio-coil insert for the left plug that comes out easily. I want to weld the hole shut and drill/re-tap new threads for the plug. The bike had 6k miles on it and the inside of this head looks brand new. It would be a shame to replace it with another used part without having tried everything. The bike is sitting in my friend's fabrication shop, I think we're just in need of some guidance for the procedure and a list of tools that we might not have.

Also looking preemptively on where I might have better luck sourcing a replacement if all does not go well. I've already gotten shafted with a CB350 cylinder head labeled as CB360 on ebay... :(
 

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Replace the helicoil with the spark plug specific "Time Sert" repair insert as it is an easy solution and a much better and permanent repair that won't wind back out like a helicoil. Look up the Time Sert for yourself to see the quality of the design vs helicoil. A kit will cost you $100 plus, so for a one time repair a machine shop will put one in your head for much less I would expect.
The threads are already cut from the helicoil repair and the Time Sert will use those threads, yet you need the special tool in the kit that locks the new "Sert" insert into the bottom of the hole permanently. So I would look at a machine shop as an option since they will only need to thread and lock a new insert into the existing hole. Should be quick and pretty inexpensive for you to have it done

I have used them for years and never had one wind back out or fail, as they are made of a high carbon steel insert in most cases, or a special copper alloy in the case of the spark plug insert material.
 

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Discussion Starter · #3 ·
Replace the helicoil with the spark plug specific "Time Sert" repair insert as it is an easy solution and a much better and permanent repair that won't wind back out like a helicoil. Look up the Time Sert for yourself to see the quality of the design vs helicoil. A kit will cost you $100 plus, so for a one time repair a machine shop will put one in your head for much less I would expect.
The threads are already cut from the helicoil repair and the Time Sert will use those threads, yet you need the special tool in the kit that locks the new "Sert" insert into the bottom of the hole permanently. So I would look at a machine shop as an option since they will only need to thread and lock a new insert into the existing hole. Should be quick and pretty inexpensive for you to have it done

I have used them for years and never had one wind back out or fail, as they are made of a high carbon steel insert in most cases, or a special copper alloy in the case of the spark plug insert material.
Apologies that I haven't been active to respond sooner. Thank you for your advice! I will definitely check this out as an option!
 

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In my experience the inserts take a larger tap than the helicoils do and you have to cut the proper threads for an insert.

I just did a head that the helicoil backed out of. The insert thread cutting tool has a 14mm thread that is supposed to help guide and pull the cutter in. The original 14 mm threads were of course cut out by the helicoil tool.

I simply wrapped electricians tape around the 14mm threads until it was a snug fit in the enlarged from the helicoil spark plug hole. I did this with the engine assembled and it does carry the risk of getting swarf into the cylinder. I took two small sections off of a Swiffer duster and put them down into the cylinder. This material is fluffy, is made to grab and hold material and is easy to put in and most importantly pull out.

I put a dab of grease on top of the swiffer pile and grease in the flutes of the threader ... but ... I make sure to use a proper cutting fluid on the cutting threads.

The cutter and threading tool went in easier than I expected probably due to the hole being already enlarged. I made sure to apply lots of pressure to start the thread cutting but after a few threads were established it went very easy. Lots of in and out to keep cleaning out the flutes and adding clean grease then pulling out the swiffer pieces. I also used a vacuum with a small diameter hose to help clean up.

The insert I used had the direction to use high temp silicone and to let it set before running the engine. I make sure the newly cut threads are clean and free of grease and debris so the silicone has no issues with adhesion. The cleaning up and making as sure as possible nothing ended up inside the engine takes far longer than the actual thread cutting.
 

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In my experience the inserts take a larger tap than the helicoils do and you have to cut the proper threads for an insert.

I just did a head that the helicoil backed out of. The insert thread cutting tool has a 14mm thread that is supposed to help guide and pull the cutter in. The original 14 mm threads were of course cut out by the helicoil tool.

I simply wrapped electricians tape around the 14mm threads until it was a snug fit in the enlarged from the helicoil spark plug hole. I did this with the engine assembled and it does carry the risk of getting swarf into the cylinder. I took two small sections off of a Swiffer duster and put them down into the cylinder. This material is fluffy, is made to grab and hold material and is easy to put in and most importantly pull out.

I put a dab of grease on top of the swiffer pile and grease in the flutes of the threader ... but ... I make sure to use a proper cutting fluid on the cutting threads.

The cutter and threading tool went in easier than I expected probably due to the hole being already enlarged. I made sure to apply lots of pressure to start the thread cutting but after a few threads were established it went very easy. Lots of in and out to keep cleaning out the flutes and adding clean grease then pulling out the swiffer pieces. I also used a vacuum with a small diameter hose to help clean up.

The insert I used had the direction to use high temp silicone and to let it set before running the engine. I make sure the newly cut threads are clean and free of grease and debris so the silicone has no issues with adhesion. The cleaning up and making as sure as possible nothing ended up inside the engine takes far longer than the actual thread cutting.
 
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