Mustang and Ford Performance Forums banner
1 - 3 of 3 Posts

·
Registered
Joined
·
402 Posts
Discussion Starter · #1 ·
just wanted to share some pics and discuss a lock-n-stitch spark plug thread repair i made this past winter to my AG heads. i bought the repair kit several years ago from when my other cobra spit a plug. modularfords thread about that here:
lock n stitch spark plug thread repair... pull heads...

it is definitely an effective repair, but like any other spark plug thread kit (i assume), it alters the combustion chamber. to me it looks like it removes an awful lot of material, and then leaves the new hole with many exposed sharp, threaded edges. i am wondering how that might affect combustion or compression ratio (if at all).

before insert:
Photograph Automotive tire Light Rim Wood


after insert:
Automotive tire Light Wheel Black Synthetic rubber


with plug:
Photograph Automotive tire Light Product Black

Cookware and bakeware Cuisine Dish Gas Cooking


compared to a stock AG head:
Automotive lighting Audio equipment Tableware Dish Wood



lock-n-stitch utilizes aluminum inserts for heat transfer and a locking pin to mechanically keep it from coming back out. it is the only kit that ford authorizes their dealers to use for out-of-warranty repairs (TSB #07-21-2). http://www.terminator-cobra.com/Ford_TSB07-21-2.pdf

if you notice though, the TSB only includes 2-valve engines. it does not list 4-valve engines, and i am wondering if that is due to the way the repair alters the combustion chamber. spark plug holes in the 2-valve heads are not as recessed or angled as in the 4-valve, so therefore they would not have nearly as much exposed theaded area.

you can see this difference between both in this video from modularheadshop in florida.

they offer the upgrade to 9 threads, but use timesert kits.

anyway, just food for thought and discussion. since these engines are getting older and there aren't any aftermarket offerings, upgrading the spark plug threads on AF, AG, and DA castings will probably continue to become more necessary.
 

·
Administrator
Joined
·
9,775 Posts
Chris,

I used the Lock-N-Stitch fix for a brand new set of 4 thread castings about 15 years ago. Because of the way the combustion chamber is positioned and the angle the spark plug enters at, the tap for the insert leaves a number of threads exposed in the combustion chamber. I originally began to blend these down to the thread root with a small Dremel tool and a sanding drum so no sharp edges remained. If you ever saw me with a Dremel tool it looks a lot like a monkey with a machine gun. I was just all over the place and most importantly not where I wanted to be.

The fix for me was to put the head in a Bridgeport and use, I think, either a ⅝ inch or 11/16 inch reamer to remove the exposed and unused threads protruding into the chamber. It worked much better than the monkey with the Dremel tool. A quick once over with a deburring tool removed the sharp edge and the job looked like it came from Ford instead of me. I would show you pictures except I was too slow on the draw to document in those days and today the heads are on the engine. When you do the job this way, you need to look carefully to be able to tell the spark plug holes have been repaired.

The difference in compression ratio is so small it doesn't matter. Although aluminum will not glow in the combustion chamber like cast iron does, I still wanted the sharp edges left from tapping the hole for the inserts to be gone. In the bigger picture it probably didn't matter but I wanted the right look in the chamber, so ...

With respect to the Ford TSB's on the repair, I thought I had a Ford 4V TSB on the Lock-N-Stitch fix but I can't find it anymore. I did find a Lock-N-Stitch write up on the 4V fix and I have attached it, if that is of any value.

With respect to the exposed intermittent threads from the insert tap I suspect, but can not say with certainty, they will not matter. The cleaned up plug wells after removing the threads look just like original OEM heads. If you elect to remove the threads just go to the root of the thread adequate to make the threads disappear. Depending on your skills with a Dremel tool you may or may not want to use a Bridgeport.
 

Attachments

·
Registered
Joined
·
402 Posts
Discussion Starter · #3 ·
Chris,

I used the Lock-N-Stitch fix for a brand new set of 4 thread castings about ten years ago. Because of the way the combustion chamber is positioned and the angle the spark plug enters at, the tap for the insert leaves a number of threads exposed in the combustion chamber. I originally began to blend these down to the thread root with a small Dremel tool and a sanding drum so no sharp edges remained. If you ever saw me with a Dremel tool it looks a lot like a monkey with a machine gun. I was just all over the place and most importantly not where I wanted to be.

The fix for me was to put the head in a Bridgeport and use, I think, either a ⅝ inch or 11/16 inch reamer to remove the exposed and unused threads protruding into the chamber. It worked much better than the monkey with the Dremel tool. A quick once over with a deburring tool removed the sharp edge and the job looked like it came from Ford instead of me. I would show you pictures except I was too slow on the draw to document in those days and today the heads are on the engine. When you do the job this way, you need to look carefully to be able to tell the spark plug holes have been repaired.

The difference in compression ratio is so small it doesn't matter. Although aluminum will not glow in the combustion chamber like cast iron does, I still wanted the sharp edges left from tapping the hole for the inserts to be gone. In the bigger picture it probably didn't matter but I wanted the right look in the chamber, so ...

With respect to the Ford TSB's on the repair, I thought I had a Ford 4V TSB on the Lock-N-Stitch fix but I can't find it anymore. I did find a Lock-N-Stitch write up on the 4V fix and I have attached it, if that is of any value.

With respect to the exposed intermittent threads from the insert tap I suspect, but can not say with certainty, they will not matter. The cleaned up plug wells after removing the threads look just like original OEM heads. If you elect to remove the threads just go to the root of the thread adequate to make the threads disappear. Depending on your skills with a Dremel tool you may or may not want to use a Bridgeport.
i think i would be all over the place with a dremel too, ed, and i would probably end up messing up a valve seat etc - a la monkey with a machine gun lol

anyway that's good to know about the compression ratio and sharp edges. i won't over think it. and that's probably why the over-the-fender repair i did back in 2014 on one hole on my other car hasn't had any problems since and has always run strong.

recently i also had a spark plug blow out on my 4.6 2v f-150 (only 4 threads). fortunately i was able to use this same kit to repair it, because both engines happened to be "type 2" in LNS-speak, so the same kit worked for both. the only difference in the kit between 4V and 2V kit is an extension for the reamer drill (for the long 4V plug well). next winter when i pull the heads off that 2V engine i'll be interested to see how that repair looks from inside. then i will do inserts for the remaining 7 holes.
 
1 - 3 of 3 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top