One of my spark plugs is too wide

[69fiat124]

Hello everyone,
I just recently purchased a 1969 Fiat 124 Spider and when I went to change the spark plugs for the first time I realized that the third spark plug from the front of the engine has a completely different width to it. I think that someone broke a plug in the past and tapped a whole that was too big. What should I do? Should I try and match the size of the spark plug or should I completely remove the cylinder head to get it repaired or replaced?

[Daddio]

I have an 1800 head that has a repaired thread- drilled/tapped larger and a threaded sleeve with standard plug thread inside installed; more substantial than a helicoil, I suspect it's what they did before they came along.

Could yours have something similar that came out with the spark plug? Because they only come in a (very) few thread sizes. Is that plug different than the others?

[18Fiatsandcounting]

Should I try and match the size of the spark plug or should I completely remove the cylinder head to get it repaired or replaced?

Congrats on acquiring a '69 spider! One of my favorite model years, but I may be biased. To answer your question, I think it depends on how much effort and money you want to spend. If the engine runs well enough, you could simply replace the #3 sparkplug with a size that fits the oversized hole. Not ideal, but if you get a good seal, it's the cheapest and easiest route. On the other hand, pulling the cylinder head would allow you see what's really going on with the cylinder #3 combustion chamber, as there could be more damage from a past "event". This might be opening a can of worms, but it's something that you'd eventually need to address with a 50 year old engine.

If you do just replace the #3 spark plug, make sure it's the right length, in addition to the right diameter.

-Bryan

[SteinOnkel]

Having worked in a shop rebuilding cylinder heads, I can tell you that the helicoil/insert method is how 90% of these damages are repaired. If it's done right, it will perform exactly the same as original.

In your case I would let sleeping dogs lie and simply purchase one oversized spark plug. Make sure you rotate the engine by hand once or twice after installation to make sure it doesn't bind.

Cheers
Steiny

[18Fiatsandcounting]

Steiny, you're back! I was worried about you, what with all the fires in the North Bay... Hope all's OK.

-Bryan

[SteinOnkel]

Steiny, you're back! I was worried about you, what with all the fires in the North Bay... Hope all's OK.

-Bryan

Everything's good, thanks for asking. Even the air isn't too bad today, so I took the spider. It runs like a brand new car

[18Fiatsandcounting]

Awesome! If it weren't for you and Wetminkey, who would I have to argue about---I mean politely discuss---Weber carburetors?

So as not to hijack the OP's original thought too far, I'll leave it at that.

-Bryan

[69fiat124]

UPDATE:
Alright so I looked over the spark plug thoroughly and it would appear that there is a thin sleeve on the plug with threads on both sides. I tried to remove it but it is really stuck in there. I have not been able to look over the cylinder head to see what the threads look like yet. Should I try to remove the sleeve from the spark plug and lock tight it to the cylinder head or buy an over sized plug. Thank you to all that responded. You all have been of great help!

[blazingspider]

Sounds like someone installed a time sert threaded bushing to repair damaged threads in the original spark plug hole. Similar to a heli coil, you drill and tap the spark plug hole to accept the bushing. Then the bushing is usally staked in place at the top and/or some type of thread locker is applied to the outside threads as well to keep the time sert in the head and not have it come out when you remove the spark plug as happened in your case. I doubt you will be able to remove the time sert bushing from the spark plug with out damaging the outside threads but you can get replacement bushings, so I would go that route.

One other note. The thread pitch and size on the outside of the bushing is not going to be the standard plug size thread and pitch so finding a spark plug to fit is more likely than not out of the question. You don't want to go down that road anyway.

Google time sert for spark plug repair.

[18Fiatsandcounting]

The above are good suggestions as to an approach to fixing this. In the meantime, could you replace the other 3 spark plugs, clean up and gap the one with the insert, get the car running, and then deal with the issue later? My thinking is that, while the spark plug issue probably needs to be dealt with at some point, there may still be some life to the plug and it would buy you some time to be able to assess what else the car might need.

-Bryan

[blazingspider]

My thinking is that, while the spark plug issue probably needs to be dealt with at some point, there may still be some life to the plug and it would buy you some time to be able to assess what else the car might need.

Good point!!