Spark Plug Inserts
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Tuned
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Spark Plug Inserts
You'd think something so basic would be sooooooo easy! Pulling my hair out. I need Spark Plug Inserts 5/8"-18 on the OUTSIDE Threads, and 14 x 1.25 Park Plug Threads on the INSIDE by 1/2" Long. I've been on so !any sites now, its ridiculous. All these vendors want you to buy a complete, overpriced kit, that MAY have 3 inserts in the kit, and I come to find, MOST suppliers don't tell you the size of the threads that you will be cutting. I already have the tool ! The Cutter has already cut for 5/8"-18 Inserts. Why is something so damn simple, so damn difficult ? Any help appreciated. P.S. Fixing Edelbrock Aluminum Heads, '49 to 53 8BA. Ya'all have a safe and good Easter ! 😊
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From: NM
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Tuned
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This looks right: https://www.oreillyauto.com/detail/c.../hel0/r532614n
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Tuned
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No, never been a Tapered Seat. These are Edelbrock Aluminum Heads for a Flathead Ford. The threads get a bit ugly after decades of use and a abuse. You'd think I'm looking for parts for a Russian Nuclear Submarine. Well, tomorrow, I can at least call a couple places. Happy motoring !
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From: Western NY
It seems that one is in search of a helicoil, parmacoil, timesert, or similar insert only kit - but usually an external thread is not specified and may not be standard, but system specific due to the geometries and so it would make sense to stay within the brand for which one has the tooling for and order the corresponding insert only kit.
Last edited by bmoran4; Apr 5, 2026 at 07:15 PM.
Fleet Owner
Joined: Jul 2004
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From: NM
It seems that one is in search of a helicoil, parmacoil, timesert, or similar insert only kit - but usually an external thread is not specified and may not be standard, but system specific due to the geometries and so it would make sense to stay within the brand for which one has the tooling for and order the corresponding insert only kit.
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Tuned
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It seems that one is in search of a helicoil, parmacoil, timesert, or similar insert only kit - but usually an external thread is not specified and may not be standard, but system specific due to the geometries and so it would make sense to stay within the brand for which one has the tooling for and order the corresponding insert only kit.
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Parts Nerd Extraordinaire
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From: Western NY
The part numbers provided appear to be for Carisle tools. Was the initial insert system used on the heads Carisle? What brand insert system was used on the head originally? That is what you will need to use. As we stated, 5/8-18 is unlikely to be correct for an insert, but maybe it was close to the appropriate STI tapped thread. One exception I found was the E-Z LOK system ( https://www.ezlok.com/assets/documen...Automotive.pdf ), but they only have the 5/8-18 external for a M12 internal spark plug. If a 5/8-18 tap was used in error to chase the insert threads, your repair options could possibly be very limited and get to the point where it could be more economical to replace the heads.
I would also be asking, why did the former insert system fail? Can you share any photos of a failed insert? Someone maybe able to identify it.
I would also be asking, why did the former insert system fail? Can you share any photos of a failed insert? Someone maybe able to identify it.
Hotshot
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From: Burbank, WA
I'm sorry you're having to go through this, Larry, I always hate having to deal with seemingly simple things that are made overly complicated and frustrating. I'm beginning to wonder, though, if perhaps you're a victim of some bad intel. As I do the math, the difference between 14mm and 5/8 inch is about .070", which seems a bit skinny to me to be threaded on both sides and still be functional. Would it be possible to drill and tap to 3/4-16 and use these inserts from McMaster-Carr (or similar)? 3/4 or 18mm seems to be the standard from what I've seen.
https://www.mcmaster.com/products/sp...e~standard-un/
https://www.mcmaster.com/products/sp...e~standard-un/
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From: Minnesota
Fleet Mechanic
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From: Minnesota
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Tuned
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Tuned
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I would like to thank all who got involved and tried to help. I got ahold of Timesert, they DO NOT offer a direct replacement insert for a 5/8"-18 Thread. Of course, I can purchase an oversize kit, for the measly sum of $432.00. I don't think so ! Ya know, the more time goes on, the more ****ty these companies get, and Customer Service is definitely a thing of the past. These are used heads I'm trying to repair, now I will continue my search, this time for Helicoils Wish me luck ! Thanks again. 😎