MTFCA Forum

Guys: Has any one here ever drilled out the bolt holes in a Z head for 1/2" head bolt? If so what problems did you run into. I have test drilled a Ford iron head and works fine. Thanks for any info. Dan

Curiosity Dan,

Why are you going to 1/2", high compression? Their is enough casting in those for oversize.

All the Best,

Hank in Tin-A-See

Hank: I am fixing a stripped bolt in an engine with a Z head. Had to go to a bigger head bolt. Dan

Dan: Using a heli-coil insert, the standard head bolt can be used. No need to drill head.

Bob J.

Dan sent you a PM.

Hank

or thread insert.
https://www.zoro.com/e-z-lok-threaded-i ... lsrc=aw.ds

These are what I used in my aluminum adapter head. I was going to use the Chevrolet 1/2" head bolts, but after I went to put it together saw why the plans called for 7/16".

If you have a stripped head bolt hole in your block, use a helicoil to repair it. Using a solid type thread repair insert like an ez-lock removes too much material from the original area around the hole. Except for a few head bolt holes, there is only a cast boss around each hole under the deck and you really want to maintain as much material as possible in those areas. Ford was very thrifty with his cast iron so there is not much extra around those holes.

I read it as he already has drilled and tapped the hole for a 1/2" bolt. If that is the case how would you go from 1/2-13 to 7/16-14 with a Helicoil?
"Had to go to a bigger head bolt"

For what it's worth, I came across a 1913 engine in which all the original head bolt holes were drilled out and tapped to take 1/2" bolts. I still have the head that came off it. I used solid inserts called Keyserts to bring the block back to standard. These are available in at least two thicknesses, so you can tailor the insert to your application. From memory, I used the thinner ones. The beauty of the application was the minimal amount of extra material I had to remove, and the fact that the tap used to thread the holes in the block was a standard size. They are kept from backing out by driving down some little pins which are part of the insert.

Allan from down under.

As Allan mentioned the Keyserts work very well. They use standard tap sizes for the outer thread & have 2 thicknesses for the insert. The thin wall 7/16 insert has a 9/16 outer thread so the 1/2" hole could be drilled out to make it work. The key in using these is to follow the instructions carefully, once installed they will not come loose.