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1970 Triumph Bonneville T120
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Discussion Starter · #1 ·
Hello Everyone. Long time lurker, first time poster here.

I recently acquired a 1970 T120 and have been working my way through changing fluids, rebuilding carbs, etc. I'm new to working on older bikes and discovering "creative solutions" that previous owners may have used. :)

I was trying to change the spark plugs tonight. I found that the right plug hole takes a 16 mm wide thread, and my new plugs have a 14 mm wide thread.

The old plug had some type of jacket threaded onto it that made it fit in the 16 mm wide hole. I was able to heat up the plug and take the jacket off.

I'd like to order more of these jackets but I don't know what they're called. Does anyone know what these things are called and where I can find more of them? I always feel like a schmuck when I wander into my local auto parts store, sheepishly hold up a part, and ask them for a new "one of these things."

Better yet, is there a way to restore my right spark plug hole to accept the normal 14 mm threads?

Thanks in advance for any guidance you can offer. I have already benefited tremendously by reading through all the posts on this site!
 

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I'll wager you have a "Keensert" or other repair insert on that plug.

At one point someone stripped the spark plug hole thread and a Keensert or Helicoil would be the appropriate repair.

More than likely the same mechanically challenged person who stripped the plug threads installed the Keensert.

Installed correctly a Keensert should be permanently installed in the head and not come out with the spark plug. These repair inserts are NOT reusable and should be locked into the plug hole as a permanent repair

Since the plug hole was re-tapped larger for the insert you need to identify EXACTLY what insert was used and you'll need a skilled tech or a machine shop to correctly replace and lock the insert in the head. A competent tech can repair with the head on the bike, but a machine shop will require the head be removed.

After the head is repaired it's always a good idea to put a small shmeer of anti-seize on spark plug threads.
 

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I'd like to order more of these jackets but I don't know what they're called. Does anyone know what these things are called and where I can find more of them? I always feel like a schmuck when I wander into my local auto parts store, sheepishly hold up a part, and ask them for a new "one of these things."
Welcome to the Forum,

No reason to feel like a schmuck and no reason to feel sheepish. Any DECENT parts guy will be of assistance. If you run into a smart asp turn around and leave. There are plenty of other stores that would love to have your business.

K 😷
 

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A picture would help. If a solid tube threaded inside and out then probably a Time-sert or KD Tools spark plug repair insert.
 

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I see that anti sieze grease is mentioned to put on the plug threads. I have done this for many years on every vehicle i have that has plugs. Copper coloured often used on brake parts inside drums. Everyone should use this grease on plugs and they will never the head and, hopefully, no stripped cylinder head thread. never had a plug thread strip on any vehicle when using this grease.
 

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I see that anti sieze grease is mentioned to put on the plug threads. I have done this for many years on every vehicle i have that has plugs. Copper coloured often used on brake parts inside drums. Everyone should use this grease on plugs and they will never the head and, hopefully, no stripped cylinder head thread. never had a plug thread strip on any vehicle when using this grease.
I like the silver Permatex Anti-Seize. Bought a can in the 70's and still have some left.

A little dab will do ya then spin the plug in till it seats then a 1/4 turn to crush the plug gasket.

Some plugs don't use gaskets and have a conical seat... anti-seize is still the right move.
 

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Most will used silver anti seize on spark plugs also fine to use copper anti seize (3m #8945). The copper has a higher heat rating and is also used on ox sensor threads. Copper is a bit more expensive than the silver stuff.

K 😷
 

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Hi,
A nice blob of copper grease on the spark plug electrode gives you hours of fun looking for the misfire, be careful with it.
The timesert is very cheap, the tools to install them are extortionately expensive. If you don’t have the tools then it is often cheaper to have an engineering shop that already them to repair the threads.
It might be important to replace like for like due to engineering differences between brands, It also might not but it is worth taking this into consideration. Also there must have been a reason why the original inserts came out, they are supposed to be a permanent repair. It is probably worth carefully checking the first repair drillings for size and condition.
If you are able to post photos of the head (close up of the spark plug holes) and the inserts that came out would be very useful, this forum is awash with brilliant and experienced engineers all happy to help if they can.

Regards
Peg
 
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1970 Triumph Bonneville T120
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Discussion Starter · #11 ·
Wow! You all really are a helpful bunch of people. Thank you for taking the time to try to help me!

Here are a few pics of the spark plug hole and one of the insert that came out. I tried to show the threads from all angles. Happy to take more pics if need be.
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Wow! You all really are a helpful bunch of people. Thank you for taking the time to try to help me!

Here are a few pics of the spark plug hole and one of the insert that came out. I tried to show the threads from all angles. Happy to take more pics if need be.
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Yup... exactly what I thought.

Do you have a local Triumph dealer or an independent shop with a good reputation that you trust?

A hack can cost you a new cylinder head.
 

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Cal-Van Spark Plug Insert 880-5, not KD Tools. The tap reamer kit 880 is about $20. Inserts $3.50 pr. Time-sert is better in that the kit uses a roll form tap to expand the bottom threads into the head but much more expensive. The Cal-Van is better than a Heli-coil in that it is a solid tube.
If the insert is still a good fit in the head you can use Loctite QuickMetal. It works to hold a Lotus axle carrier on the axle so it will hold a spark plug insert.
 

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Discussion Starter · #14 ·
Well, I ended up pulling the head and bringing it to Richter Machining in Marne, Iowa. The shop is attached to Baxter Cycle.

AJ Richter examined the head and advised that he wanted to try chasing the threads and putting in a new insert with high heat thread locking fluid. He did the work while I was there. While he worked, we chatted about old British bikes and I learned SO MUCH.

Removing and reinstalling the head was easier than I thought it would be. The worst part was the 3 hours of scraping the old gasket material off of the head and rocker box covers.

The bike is now running pretty decently. I think I can improve things by syncing and adjusting the carbs.

Thanks again everyone for your advice! If this isn't a cautionary tale about ALWAYS using anti-seize on spark plug threads and not over-torquing, I don't know what is! :)
 
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