Head bolt thread repair

[Dave Young]

Just stripped a head bolt hole out on my block. What’s the correct heli-coil kit to use?

[DanTreace]

This type works well.

[mtntee20]

Dave, I prefer Key Lock inserts over Heli coil. I have used both. I've had Heli coil inserts fail but I have never had, seen, nor heard of a Key Lock insert failure. Someone with greater experience related to stripped head bolt holes might have a much better recommendation.

Good Luck

[Dave Young]

Thanks, guys.

[Dan Hatch]

Stevens made a tool set for this job. Many years ago I made some copies of it. Here is a link to that.
http://www.mtfca.com/discus/messages/506218/522248.html

I still use it on an engine in car. But on a rebuilding job I use Lock N Stitch inserts. Best made.

[Norman Kling]

I have never heard of Lock Key inserts. I have used many helicoils in Model T's and other engines without a problem. Only problem was on my 26 Touring. One of the bolts in the rear corner next to the firewall broke. I drilled it out and didn't want to go too deep for fear of going into the water jacket and then the water would come up and rust the bolt in place. it was down deep enough to completely insert the coil I blew 2 head gaskets right in the rear corner next to the manifold. I didn't see any water leaking because of the location, but on two different tours I blew the gasket right in that location. Unfortunately the torque wrench read 50 ft lbs so I thought it was tight enough but it blew. Anyway what was happening was the torque wrench was measuring the bolt which was bottoming out but not the torque against the head. It was so far down that the head of the bolt looked like it was tight against the head. The last time I replaced it I put a washer under the head of that bolt. No more problems and no more leaks. That fixed it and I didn't have to grind all the other bolts to shorten them.
Norm

[Allan]

The beauty of key lock/threadloc inserts is you can use standard size taps to fit the insert. There is no need to buy a whole kit to do the job. They also come in different outside diameters that allow fitting to oversized/wallowed holes.

Allan from down under.

[RGould1910]

There are a number of types of inserts available. Ive used most. They all worked well. The solid type with pink adhesive is sold locally. I've used the thin wall variety for high heat areas.The key to a good repair is getting a perpendicular to the deck alignment. Not as easy as it sounds. You can use a head to align things. I've used a junk head after enlarging the holes to accept a drill bit. I repaced all threads on an early block on a mill bed once to get square cuts and it came out right. For just a few threads using a head is relatively fast and simple. Im sure the subject has been addressed before.

[DanTreace]

Drill bit size is 29/64” for the Helicoil tap.

Recently used the cylinder head on my T as drill guide for this drill bit, as Ford cylinder head bolt holes are oversized for clearance of the head bolts, so the drill bit fit just fine. Easy to keep a vertical drill oversize hole in the block. Just measure carefully the depth needed for the insert.

[Craig Leach]

Hi David,
I'm in total agreement with Richard & Dan about using a old head. I keep cracked heads just for that reason. I also drill
the head out to use as a tap guide to be sure I get the threads straight in the hole. My BIL used the Key-Lock inserts in a
engine in the car using a mag drill on several misaligned & inserted head bolt holes. I have a junk low head that
someone tried to wallow out the holes to fit misaligned inserts to no avail.
Craig.

[Dave Young]

Thanks to all for some great tips

[RGould1910]

Had the same experience, Craig, on a valuable head where a former owner installed helicoils. Most all were misaligned. I had to use thicker solid inserts to correct the problem. I placed the block on mill bed to get vertical cuts but still used a head to locate the drill and tap.
I liked the fact that the inserts I used didnt require a fractional size drill bit and specialty tap. That was well over ten years ago and the inserts are holding up well so far as I can tell.

[Allan]

I rescued an early block which had been modified to take 1/2" head STUDS! I used Keyserts to repair all 15 holes. They come in three different wall thicknesses. They use standard size drills for tapping the holes in which they are to be fitted. They use a standard size tap to cut the threads used to fit them in the holes. An added bonus is the three tangs on the side of the insert, which when driven home, lock the insert in place.

Allan from down under.