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Old 01-13-2016, 03:02 PM   #1
FrankWest
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Default helicoil vs replace screw with larger and retap

Never helicoiled before, does it work or is it just a crummy repair.
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Old 01-13-2016, 03:04 PM   #2
flatheadmurre
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Default Re: helicoil vs replace screw with larger and retap

Helicoil is an excellent thread repair.
If you need it to be solid thread inserts are available.
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Old 01-13-2016, 03:06 PM   #3
Bill Batson
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Default Re: helicoil vs replace screw with larger and retap

Helicoil is an excellent repair if done properly. Its good enough that its approved for aircraft repairs.

Only drawback is each size requires a seperate set of installation tools.
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Old 01-13-2016, 03:06 PM   #4
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Default Re: helicoil vs replace screw with larger and retap

Helicoil is a proven way to repair things. You do have to have enough wall to tap it out bigger for the helicoil.
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Old 01-13-2016, 03:36 PM   #5
FrankWest
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Default Re: helicoil vs replace screw with larger and retap

This may be a difficult question to answer generally, but try.
I want to know if I will have to drill out the existing stripped threads.
Will the helicoil tap be able to be screwed into the existing oversized hole..Or usually does the original hole have to be enlarged before the helicoil tap can cut the new thread?
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Old 01-13-2016, 03:39 PM   #6
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Default Re: helicoil vs replace screw with larger and retap

Helicoil is a good repair IF done correctly and you cannot go to a bigger fastener ie drill and re-tap the hole. BUT if you have the option of going to a larger diameter fastener with no other problems, drilling a hole bigger and taping it for the next larger fastener is always a win/win over a helicoil.
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Old 01-13-2016, 03:45 PM   #7
flatheadmurre
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Default Re: helicoil vs replace screw with larger and retap

Quote:
Originally Posted by FrankWest View Post
This may be a difficult question to answer generally, but try.
I want to know if I will have to drill out the existing stripped threads.
Will the helicoil tap be able to be screwed into the existing oversized hole..Or usually does the original hole have to be enlarged before the helicoil tap can cut the new thread?
Any tap helicoil or regular is designed for a specific diameter trying to drive it into hole the wrong size is abusing the tap.
An in some applications such as aluminum the helicoil can be stronger then a regular tapped thread in the base material.
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Old 01-13-2016, 03:48 PM   #8
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Default Re: helicoil vs replace screw with larger and retap

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Originally Posted by flatheadmurre View Post
Any tap helicoil or regular is designed for a specific diameter trying to drive it into hole the wrong size is abusing the tap.
An in some applications such as aluminum the helicoil can be stronger then a regular tapped thread in the base material.
All true, but I much prefer inserts to helicoils.
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Old 01-13-2016, 03:57 PM   #9
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Default Re: helicoil vs replace screw with larger and retap

A "Helicoil set" will usually come with the proper sized drill, a special tap, and several inserts. Drill out the hole, tap it, and install the Helicoil insert. I have saved several 94 carbs by using Helicoils in stripped threads on the top of the carb body. Since the Helicoils are steel and the carb body is pot metal, they are robust enough for this use. I usually set them with red Loctite and let them sit overnite before assembly. If repairing something where strength is important, I would check out "Timeserts". As to tapping to a larger size and re-drilling, that works, but the next time it has to come apart it can lead to confusion. And when it comes to "Concourse Restorations", well...
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Old 01-13-2016, 04:07 PM   #10
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Default Re: helicoil vs replace screw with larger and retap

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Originally Posted by JSeery View Post
All true, but I much prefer inserts to helicoils.
Inserts get my vote! Also check out an item called a keysert. Try Google to find it or go to www.youtube.com/watch?v=UTdJUMIcrPI
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Old 01-13-2016, 04:24 PM   #11
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Default Re: helicoil vs replace screw with larger and retap

If it is your latch screws, that is a heavy gauge sheet metal. Take them out, weld up the hole a little and re-drill and tap for machine screws, done.
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Old 01-13-2016, 04:40 PM   #12
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Default Re: helicoil vs replace screw with larger and retap

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Originally Posted by FrankWest View Post
Never helicoiled before, does it work or is it just a crummy repair.
Hi Frank, the heli-coil repair method is not an issue generally speaking.

Also mentioned here above is the 1-pc insert method, also not an issue, but usually requires a larger "footprint", in other words it takes a larger drill than the one associated with the heli-coil insert.

For instance, the drill size for the 7/16-14 heli-coil is 29/64" while the size for the 1-pc repair is 17/32". Difference is on the 1-pc insert it would get tapped with a "standard" type tap, 5/8-11. This method doesn't require purchasing a complete kit like the heli-coil setup, just the drill and the tap, probably from a any hardware store.

The MOST important aspect of EITHER repair is to both "drill & tap" the hole perfectly straight and "square". Whichever method you choose once you round up the tools you can use them to make a simple "jig" from these very same tools to keep it all straight. A small piece of aluminum (or steel) is all that's necessary.

(Add) This method is ONLY for "straight" (90*) holes, different method if the threads are at any angles like intake bolt holes on BBC head, etc?

Thanks, Gary in N.Y.

P.S. Here's a shot of the tooling for the 1-pc repair, fairly straight-forward. It WILL take some type drill press to fabricate the tool.
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File Type: jpg Thread Repair Tools B.JPG (74.0 KB, 88 views)
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Old 01-13-2016, 05:16 PM   #13
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Default Re: helicoil vs replace screw with larger and retap

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Originally Posted by ReggieK View Post
Inserts get my vote! Also check out an item called a keysert. Try Google to find it or go to www.youtube.com/watch?v=UTdJUMIcrPI
ReggieK
WOW, Inserts are the way to go! Helicoil looks like junk compared to the inserts.
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Old 01-13-2016, 05:25 PM   #14
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Default Re: helicoil vs replace screw with larger and retap

Helicoils are not junk. Both the helicoil and the inserts have their place. For example the hole for the tap for the helicoil is much smaller than the hole and tap for the insert. If your repair is near the side of the piece helicoil, if lots of material around the hole inserts. Helicoils are best inserted and held in place with a permanent locktite so they do not move. What are you repairing???? What is the size of the thread???
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Old 01-13-2016, 05:32 PM   #15
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Default Re: helicoil vs replace screw with larger and retap

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WOW, Inserts are the way to go! Helicoil looks like junk compared to the inserts.

You should make that statement to Pratt And Whitney and Boeing as heli coil is a mil spec repair. You should quit flying as aircraft and engines have 100's of heli coils.Nuff said.

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Old 01-13-2016, 05:38 PM   #16
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Default Re: helicoil vs replace screw with larger and retap

I am a retired Tool & Die Maker and have used both helicoils and threaded inserts my whole career. As indicated by more than one person in this discussion helicoils or solid inserts are both approved methods of repairing threads and are required in many applications as standard requirement in many designs in the aircraft industry, aerospace industry, and many mil-spec applications. Helicoils are not junk and not only are a precision repair but in many applications are considered prefered to the solid insert where the drill size is a limiting factor. Here is a big tip, when using either if the base metal is dissimilar to the helicoil or insert you need to use a galvanic corrosion barrier between the helicoil or insert and the base metal ( zinc chromate is a good barrier ). I.e., SS helicoil in aluminum, or pot metal will cause galvanic corrosion in the base metal.
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Old 01-13-2016, 06:04 PM   #17
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Default Re: helicoil vs replace screw with larger and retap

Nice informative reply from another qualified poster. ^^^^

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Old 01-13-2016, 06:07 PM   #18
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Default Re: helicoil vs replace screw with larger and retap

If you are repairing a threaded hole in a carburetor, use the helicoil. You don't want to drill out much material in pot metal carbs. Have used belicoils numerous times on Strombergs and Holleys. Even used one in a holley fuel inlet.
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Old 01-13-2016, 06:29 PM   #19
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Default Re: helicoil vs replace screw with larger and retap

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Originally Posted by AnthonyG View Post
... Here is a big tip, when using either if the base metal is dissimilar to the helicoil or insert you need to use a galvanic corrosion barrier between the helicoil or insert and the base metal ( zinc chromate is a good barrier ). I.e., SS helicoil in aluminum, or pot metal will cause galvanic corrosion in the base metal.
I've never used inserts, but on helicoils you are supposed to use a threadlocker on the coil. Is that adequate for preventing galvanic corrosion?
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Old 01-13-2016, 07:01 PM   #20
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Default Re: helicoil vs replace screw with larger and retap

I worked for Boeing (46 years) in both tool and die and later as an engineer and that is where I learned to dislike helicoils! LOL There is nothing wrong with helicoils, I have installed hundreds of them (maybe thousands, who knows) I just don't like dealing with them and much prefer inserts where they can be used. Seems to me helicoils can be a little more difficult to install if you are not experienced with do it.
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