sweet, i will go to napa tomorrow if i get my frigging car back from the brake shop today.....taking forever!! just today it took them all day to put in a new brake line....still not done.....

 

I will have to agree with Glen on this one. Helicoils are a repair kit for stripped threads. I don't think you did a very good job explaining your reasoning behind why helicoils are better. Give a reference to where someone uses a helicoil where it is not in a repair application.

 

I was in the military, and in fact I was the truck driver NCO in charge of keeping up the trucks in our motor pool. I hear where you are coming from, and I totally rejected the aftermarket fixes such as the heli coil temporary fixes. My trucks never broke down after I and my crew fixed them. We always drilled and tapped. Not to say you guys have had good luck with the heli coils or anything, but the correct way is to drill and tap new threads.

 

Here you go!

http://www.emhart.com/pdf/62699_Emhart3.pdf

 

Im definitely with Scott on this one. Simply changing up a bolt size is not sound engineering practice, especially in millitary applications, where bolt grades are specified and must be adhered to, and field tools may be specified for a particular bolt size. You may have done this as a field mechanic "fix" however from an engineering perspectice this is frought with danger. See Scott's link for info of Helicoils being specified in Aircraft design, and their advantages with respect to galvanic corrosion.
Now, back into the real world of Classic Mustangs, the disadvantages I see of simply going up a bolt size are the following:
1 - The potential of the head being to large to fit in recesses or foul with adjoining parts.
2 - Not leaving sufficient area around the head to fit spanners or sockets because of the above.
3 - Where you have multiple bolts, its nice to able to use the same spanner/socket for them all, as apposed to needing different ones for your different bolt sizes. (particularly when working unnder the car or where visability is not great)
5 - The pain in the but it is to have to get the new larger bolts that are the right grade and length.
6 - having bolts that are not to standard does not fit with the concourse guys ( not that I fit fit into that category)

 

I think a brochure from the manufacturer is a biased reference, of course they are going to say heli-coils are superior. It does have some good information though. It would be interesting to know if NASCAR and IHRA top fuel dragsters use Heli-Coils on all of there engines where dissimilar materials are being mated together. I think it would depend on the application to determine which method is best, for example, spark plugs = heli-coil, there aren't many sizes of plugs to choose from. If it were an exaust manifold, drill and tap. I can see your point of keeping bolts the same size. Also, I don't think concours guys would like Heli-coils or bastard size bolts.

 

You asked me to show where they are being used in manufacturing. There you go. Hard to get any bigger than Boeing and NASA. Also hard to argue against the the top level engineers who designed components to use thread inserts. Over 250,000 thread inserts engineered as the fastening device in a 747, or a space shuttle. Remember Helicoil is a brand name. It also doesn't mean all 250,000 of the thread inserts were manufactured or sold by Emhart, that go into a space shuttle or 747. There are other brands of thread inserts out there. The key is that engineers design parts to be fastened together utilizing thread inserts. And that was what you asked me to show.

Most people think of thread inserts only for repair. They have actually never used them or even researched them. That is where the myths, rumors and negativity comes from.
I've used them quite a bit in design and fabrication. I've also used them for repair.
Next time you are at a race. Talk to any crew chief. I think you'll find they agree, and in fact use them. I'd be very suprised to hear from any professional who didn't know their value.
Right part for the right application.

Scott

 

Scott.....correct me if I am wrong, but don't you have to drill out the old boogered threads with a larger drill bit, then tap new threads, THEN insert the heli-coil insert? Heli-Coil claims the new primer free inserts are stronger than the original threads. If so, then I can see your point.

 

That's it exactly Glen.

 

They also mention problems with mating certain metals with the heli-coil. For instance aluminum and stainless steel. Seems it causes corrosion. I guess we don't do a lot of fancy metal repairs though, so is a moot point for us. Just plain old steel to steel.