Spark Plug Hole Repair 14mm KZ-Z1

Old Topic, been discussed before somewhere?
But! Opinions on the best long term solution?
Question is: Which insert to use???
Old nice head, had broken off plugs in for 20 years! Fused together! "NO" They is not coming out!!!!
Metal is going to be drilled out, matter of fact 3 are in there. So I am going to do all 4 holes.
Going to be done on a Brigeport mill, correct angles, jigged up correct, etc.!

With many options today, there are many inserts, kits to repair like the common Ford Triton V-8's 4.8, 5.6
Snap On, K-D
The old original Heli-coils, Time Serts, Thread Serts and probably more?
I prefer the ones with a lip to sit flush in the head after machining the spot in head.
Thanks. Don't want to invest in doing the head without the plug hole fix first.
Just looking for options and opinions. Here are some I see:

I'd use Timeserts if the threads are buggered. Before making that leap though I'd get the old plugs out and chase the threads with a proper 14mm thread chaser tap (not a regular tap because they remove too much metal). The thread chaser tap sort of smashes the metal back into place to keep the threads intact to the greatest extent possible.

Before you do anything that may damage the cylinder head check around at machine shops in your area to see if they have a Metal Disintegration Machine (MDM) or Electric Disintegration Machine ( EDM) machine. Either of those can be used to disintegrate the spark plugs without hurting the cylinder head. See link below for descriptions; there are many YouTube videos showing how they work. Ed

electroarc.com/

I use the timesert's like the one in the second to last pic.
The tap for it is a no drill tap that guide's off the old threads and cuts the hole and rethreads for the insert.
I'll get a pic at work tomorrow.

No issues in using the following and locally available at O'Reillys, Auto Zone etc....

I had a spark plug fire out once on a 550 , it was repaired with a helicoil - in situ, no dismantling, worked great for another 15 000 miles .

Once I had a parts 550 with a holed piston. Some muppet had tapped it out to the next size up using a car spark plug of the wrong heat range. Usually that sort of bodging is reserved for 50cc and 125cc learner bikes.

But given the choice now I'd go for an insert, as recommended above.

The one OMR posted is what I use grease the tap and no need to pull the head off.

Hey Guy's Thanks for the replies!
Merry Christmas To those who partake! And Happy Holidays!
OK, this engine was 1980 Smog Head Drive shaft bike that was sitting since the 90's ???
P O broke off this end plug. Then tried chiseling along outside to get it to move. It didn't!
So in 2016 it ends up on craigslist, Partner bought it for the Mark II cases and crank for drag bike extras, I took other parts.

I ended up with the head (bike had 14,400 miles only) sat for 20 years. I have drilled out the metal core to a decimal drill size of .447"
I ran a metal blade down to the aluminum threads. I'll get it out eventually!
I still might be able to save original threads, I am going to weld a piece of rod to it and try to it pull off. But want to mill the outside to clean it up. Looks like crap now!
That's why I was looking at an insert with a lip up top side. Want to do this first before I waste time re-doing the head.
My concerns also: were the small amount of area by the 2 valve faces & plug hole?
If I go through all the way, the insets are almost 5/8" .625" up from the original 14mm .550"?
Will the insert be in way of vale seats. I, myself know it will be ok to use, just wondering what someone else would think of this?
Plan is it just going to eBay for sale. Mark II smog head. Of course I would explain the work in future ad!
Thanks. couple of pics.

I repaired Toyota cylinder head bolts holes in engine block. Used inserts from some ebay seller. They worked fine.

z1kzonly wrote: Hey Guy's Thanks for the replies!
Merry Christmas To those who partake! And Happy Holidays!
OK, this engine was 1980 Smog Head Drive shaft bike that was sitting since the 90's ???
P O broke off this end plug. Then tried chiseling along outside to get it to move. It didn't!
So in 2016 it ends up on craigslist, Partner bought it for the Mark II cases and crank for drag bike extras, I took other parts.

I ended up with the head (bike had 14,400 miles only) sat for 20 years. I have drilled out the metal core to a decimal drill size of .447"
I ran a metal blade down to the aluminum threads. I'll get it out eventually!
I still might be able to save original threads, I am going to weld a piece of rod to it and try to it pull off. But want to mill the outside to clean it up. Looks like crap now!
That's why I was looking at an insert with a lip up top side. Want to do this first before I waste time re-doing the head.
My concerns also: were the small amount of area by the 2 valve faces & plug hole?
If I go through all the way, the insets are almost 5/8" .625" up from the original 14mm .550"?
Will the insert be in way of vale seats. I, myself know it will be ok to use, just wondering what someone else would think of this?
Plan is it just going to eBay for sale. Mark II smog head. Of course I would explain the work in future ad!
Thanks. couple of pics.

Jeff fill welded the hole then drilled and tapped it. Came out good as new.
Steve

I actually did get the metal out of the original threads! Cleaned with the 14mm tap. Ground the valves and seats. Gave it a little surface grind.
Nice smog head now. The newer style nitrated valves hold up really well over the years. This head sat for 15-20 years off of the engine.
Guides were tight! New seals, Springs measured great. Gonna give it some black paint. Cams will be shimmed ready to bolt on a short block! All the same matched valve train parts. Stuff only had 11,400 miles

A little Anti-seize compound on the threads of the plugs will go along way toward removing them on down the road.