Spark Plugs do not fit

PatMat · May 17, 2026

I am having a problem with fitting new spark plugs. It seems that the plugs I just removed have some added collar on them. I removed them only to find that the new plugs are too narrow for the holes. Both the old and the new are Champion N9YC. I feel like I'm losing my mind. I've ordered comparable spark plugs only to have the same issue. I have an old pair which I removed a while ago and even they don't fit in.
I did have the bike serviced a couple of months ago.

Carl H · May 17, 2026

Is there a thread insert stuck on the old sparkplug. Helicoil or Timesert? My guess is a thread repair that came out on the plug. Find out what brand it is and how it should be inserted so it stays put.

PatMat · May 17, 2026

Both spark plugs seem to have them. If that is the case, where do I go from here? Can I remove them from the old spark plugs without damaging the threads or can I find replacements?

BERT · May 17, 2026

Can you post a picture of the plugs

PatMat · May 17, 2026

johnm · May 17, 2026

PatMat said:
View attachment 124885

Yup. Like Carl said the left one has an insert stuck on the threads

Carl H · May 17, 2026

Those plugs are very sooty. Are you running with the chokes on? And if they are Champions the 9s are a hotter plug than standard N7Y.

I have only used helicoils, But the ones on your plugs doesn't look like one. Try to use a padded jaws on pliers and try to turn if off Gently. Maybe clean all the soot off with brake cleaner and see if it spins off easily..

The inserts could be bonded with "Loctite" so heat might be needed to break the bond.

Take a picture from the other side/top so I / we can see the insert end s. You really need to figure out the brand of the insert to replace them if the old ones get damaged.

kommando · Monday at 1:51 AM

It looks like a Timesert or similar, installed incorrectly so not held in the head and the sparkplug not installed with hi temp grease on thread. Ask DPO (Dumb Previous Owner) what thread repair insert was used or the workshop that fitted them. Removing the insert from the current plugs will destroy them so for now leave them.

Fast Eddie · Monday at 3:19 AM

How about cleaning the thread on the OD of the insert and the ID of the head, and refitting it into the head with Loctite and letting it cure.

With a bit of luck the Loctitie will hold it, allowing you to remove the plug and leave the insert in situ.

Nowt to lose by giving it a go…

Triton Thrasher · Monday at 3:21 AM

Carl H said:
Are you running with the chokes on?

Many are confused by the direction of the air laver (choke).

robs ss · Monday at 3:24 AM

Fast Eddie said:
How about cleaning the thread on the OD of the insert and the ID of the head, and refitting it into the head with Loctite and letting it cure.

With a bit of luck the Loctitie will hold it, allowing you to remove the plug and leave the insert in situ.

Nowt to lose by giving it a

Yes, good idea BUT... if you're tempted to use the spark plug as a fitting tool, very lightly grease the threads on the plug. Otherwise, hope that the plugs last a fair while!

Fast Eddie · Monday at 3:28 AM

robs ss said:
Yes, good idea BUT... if you're tempted to use the spark plug as a fitting tool, very lightly grease the threads on the plug. Otherwise, hope that the plugs last a fair while!

For future plugs yes.

But the challenge our hero faces currently is it appears the plugs are kinda stuck in the inserts. As Kommando said, trying to remove them from the inserts as they are will almost certainly ruin the inserts.

robs ss · Monday at 4:31 AM

Fast Eddie said:
For future plugs yes.

But the challenge our hero faces currently is it appears the plugs are kinda stuck in the inserts. As Kommando said, trying to remove them from the inserts as they are will almost certainly ruin the inserts.

Aaahhhh - I see where you're coming from!
You'd have to be sparing with the Loctite or the outcome could be the same as I outlined above.
Cheers

BERT · Monday at 5:28 AM

I'd have a close look at the insert compared to a new one and make sure a piece didn't break off the end and potentially drop into the cylinder. Have a good look with a borescope too.

PatMat · Monday at 5:41 AM

Thank you all!
This all started with the "Mystery of the Fouled Plugs". (Backfiring, rough idling) Now that episode will have to wait until the first challenge is completed. I did a search on line to see if I could possible find who made the inserts. There were a few which looked similar. It may be impossible to solve that way without buying up each similar kit and seeing if they fit.
The bike has been through a few owners before me. I'll start the inquiry with the the one from whom I purchased it. Regarding the choke, I don't use it when starting the bike. It usually starts up with the first kick. Just for clarity, when the choke handle is pointed towards me, sitting on the bike, it is closed. If I'm wrong, the mystery of the fouled plugs may be solved. The one from the kick start side is the fouled plug. The other side seems fine. The photo I posted, the right spark plug at the right is an old one and not part of this problem. I put them side by side before I was aware that the other had a collar on it.
I will try to come up with a plan to remove the collars.

baz · Monday at 6:00 AM

PatMat said:
Thank you all!
This all started with the "Mystery of the Fouled Plugs". (Backfiring, rough idling) Now that episode will have to wait until the first challenge is completed. I did a search on line to see if I could possible find who made the inserts. There were a few which looked similar. It may be impossible to solve that way without buying up each similar kit and seeing if they fit.
The bike has been through a few owners before me. I'll start the inquiry with the the one from whom I purchased it. Regarding the choke, I don't use it when starting the bike. It usually starts up with the first kick. Just for clarity, when the choke handle is pointed towards me, sitting on the bike, it is closed. If I'm wrong, the mystery of the fouled plugs may be solved. The one from the kick start side is the fouled plug. The other side seems fine. The photo I posted, the right spark plug at the right is an old one and not part of this problem. I put them side by side before I was aware that the other had a collar on it.
I will try to come up with a plan to remove the collars.

Tight wire choke off
Slack wire on

Onder · Monday at 6:33 AM

You might want to consider removing the head, sending it to a Norton head guy and having both holes
repaired . Obviously the last fix wasn't up to snuff. At this point doing it properly will save you
a lot of heartache and money down the road.

PatMat · Monday at 6:46 AM

Onder said:
You might want to consider removing the head, sending it to a Norton head guy and having both holes
repaired . Obviously the last fix wasn't up to snuff. At this point doing it properly will save you
a lot of heartache and money down the road.

I think you're correct on that point. If anyone out there knows of a place that does this type of work please forward me some names. I live in Brooklyn, NY.
Thank you!

Onder · Monday at 6:59 AM

NYC Norton. Member here....

speirmoor · Monday at 7:08 AM

Helicoil looks like. Good for single use but not repeated. Timesert much better.

Spark Plugs do not fit

Similar threads