MTFCA Forum

A proper size tap would be my first inclination, making sure I had it positioned straight. If the hole 'buggered up' in on the side where the hole can be accessed from the backside, the chance of cross-threading is minimized. If all else foils; heli-coils.

What are we working on? First, I would remove the radiator and then tap the head with a bottom end tap. Also, don't beat yourself up. We all do dumb stuff. It takes a real man to admit it. bobt

The difficulty with a tap or thread chaser is getting the correct start on the damaged thread. If you do manage it, you have done well. Otherwise, it may mean drilling and tapping to fit a helicoil, a good option anyway in aluminium. Square on access will mean removal of the radiator.

Others may have different ideas.

Allan from down under.

Jugster wrote: ↑

Sun Apr 09, 2023 11:09 pm

I did something dumb; something embarrassingly amateurish. While reinstalling the upper radiator hose fitting on the front of my aluminum high-compression head, I cross-threaded one of the two bolts into the soft aluminum and now the bolt won't screw more than halfway in, and at something of an odd angle, at that.
.
Do I need a tap or a thread-chaser or what?

FWIW somewhere on someones car a while back I remember seeing one of the bolts there were "through bolted" with a nut. Probly due to the same issue. It worked. That's all I can say. You gotta decide.

If you are unable to salvage the threads, I suggest using a Time-sert or Key-lock insert instead of a helicoil. While helicoils are good for use in steel or iron, they may not be the best in aluminum. Time-serts are a fully threaded "bushing" type of insert and will provide a better thread engagement with the aluminum and the bolt.

I agree, get the radiator out of the way OR if the head is not installed yet, secure it well to a bench and ensure you drill STRAIGHT.

Good Luck

Helicoils are outstanding in aluminum and used all of the time by every industry which uses aluminum in it's fabrication. As far as how they are used, they are installed by the 10's of thousands in new products, for every 1 time they are used for repairs. We see them as a repair, while industry sees them as part of new product manufacture.

I built the hand controllers for the last Space Shuttle, the Shuttle robotic arm controller in the cargo bay for all Shuttles, and all of the robotic arm controllers for the Japanese Module on the International Space Station and they were each chock-full of helicoils. I mention this so as to dispel any notion that it is only my armchair opinion that Helicoils are an excellent and widely used product; but rather, it is my experience.

Here's a trick I use which helps avoid cross-threading nuts, bolts and screws:

I turn the nut, bolt or screw counter-clockwise until I feel it "click" whereupon it is usually properly seated (for lack of a better term) and then I turn it clockwise.

Others on the forum probably do the same thing.

When I first made my aluminum adapter plate for mounting the Chevrolet head I drilled and tapped for 1/2" bolts as the plans called for. I found that I could not get the head lined up correctly so installed 7/16 thread serts (sp). While different from Helicoils, they have worked fine in the aluminum plate.

Helicoils are fine. But as with any thread insert, its imperative the hole be drilled and tapped straight. Not as easy as it sounds. I typiclly mount the piece on a mill table and guide the drill and tap with a chuck or fashion and attach a drill guide to the piece if
the dimension or location doesn't permit using a mill.
When we strip a thread, we're always in a hurry to fix it. Take the time and do it right and you'll do it only once .

Erik Johnson wrote: ↑

Mon Apr 10, 2023 11:48 am

Here's a trick I use which helps avoid cross-threading nuts, bolts and screws:

I turn the nut, bolt or screw counter-clockwise until I feel it "click" whereupon it is usually properly seated (for lack of a better term) and then I turn it clockwise.

Others on the forum probably do the same thing.

Excellent idea. I do this myself, and if when turning it clockwise, there is a lot of resistance, you need to check the male threads on the bolt and the female threads to make sure the threads are not the problem.

I would make a 1" or thicker plate (steel or Alum) with two on-size holes in a mill or on a drill press. Use one hole with a longer bolt in the "good" tapped hole and let the plate guide your tap into the bad hole (to keep the tap straight). If the tap doesn't clean up the threads you can use it to drill out the hole and install a bushing or heli-coil.

For such sins the Gods have provided Heli-coils... I have used them on T's when I have forgoten to clean out head bolt holes, and on VW's for the error of stripping manifold bolts... they really DO work, and for this, they are a God-send.....

One steel head I bought had the holes drilled slightly larger and tapped with a Metric size.

That has worked well in the past for the 14-24 screws in the Bendix cover too.

It might work elsewhere.