I have some holes that have lost their thread. I have other holes on there way out. Some in aluminum, some in steel. I need to start being the guy who actually fixes these properly.
Helicoil is the standard word for threaded inserts, but there appear to be quite a few of these spring type inserts. Are any better than others? There are also steel sleeves, some with shoulders. Are those even better? What do I need to know to do this well?
Material and thickness are the major considerations here. The types of inserts is dizzying. Check out mcmaster for threaded inserts and reas up on some of the infor provided to get the best for your application.
Post some details about the most important fixes if you want help getting a start.
In reply to stafford1500 :
The most critical fixes will be M6 engine case bolts in motorcycle engines. Often these are "save or scrap" type repairs.
Second most common are M6 repairs in steel or aluminum motorcycle frames. These are low torque bolts that generally hold plastics on and get used a LOT which is why they wear/strip out. Then a variety of M5-M8 repairs in bikes and cars.
I currently have one engine case bolt that I know I need to do. In the past I've used nut-serts in frame holes, but you need to take a LOT of material out to get those to fit, not my favorite option.
Edit: Also, thanks! I hadn't thought that I needed to look at things like the drill bit size needed and think about available material. Neat stuff.
Helicoils are the gold standard - but they can be fussy, especially for relatively small sizes like M6. There are different "levels" of install tool - the more expensive versions generally work better.
But I always budgeted 25-50% more inserts than I needed for each project at my previous job - you're going to break a few.
Another consideration - Helicoils need special Helicoil taps. For a homegamer, if you only have one or two sizes you're doing constantly, it is probably worth getting the Helicoil kits. Another option if you have a whole bunch of different sizes in small quantities is Keensert (key-locking inserts in McMasterworld). They use standard taps, and you can generally get away with no install tool or a homemade tool or bolt to install.
I wish I could be more definitive from my own experience, but all I've got is that I've picked up the impression that Timesert is something of a step up from Helicoil, though this could clearly be application-sensitive. They're solid pieces rather than wound wire.
And the hive seems to mostly think Helicoil is dandy in direct comparison.
Oh man, a "which threaded insert should I use" discussion can get almost as bad as a "which oil should I use" discussion...
I use Helicoils to repair damaged M8 and M6 threads in aluminum and I haven't had one fail me yet. They can be a little fussy to install if you're just using the cheapo install tool with a slot in the end. For the M6 size especially, the "prewinder" style install tool is a godsend. The part number for the M6 tool is 7751-6. The retail price is ridiculous, but you can find genuine ones on eBay for $30, which is where I got mine. Knockoffs abound as well, I haven't tried those, but it's not a very complex tool, so they're probably fine. Good luck.
In reply to obsolete :
That's fantastic advice. Thanks.
Spring type inserts require the least amount of material around the hole, are easy to source and are (if you discount the cost of the installation kit) generally the cheapest of the thread repair options. Pretty much any other option is a step up in strength and durability.
If I'm limited in realestate and/or repairing a thread that's damaged due to a ham fisted fastener installation where I'm confident that the original thread would have survived in normal usage I'll use a spring type insert. Otherwise I prefer to use one of the other options.
In reply to mazdeuce - Seth :
I hope it works for you. If the threads you're repairing are perpendicular to flat surfaces, and you're not going to be doing the work on a drill press, I'll also put in a good word for drill and tap guides.
Yeah I don't do helicoil anymore, been using time-serts for everything for the last several years. Huge fan. They are holding the exhaust manifold to the head in the rallycar (and half the rear subframe bolts iirc), at least a couple head bolts in various things, a motorcycle exh stud, etc etc..
Time-serts is the way to go
I have not done the testing myself, but helicoils are the industry standard for a reason.
When I put a timesert in, I feel like I have just spent a truckload of money, counterbored the hole and made less thread depth, spent way too much time, and all I accomplished was an added failure point. They're a sleeve with threads inside of threads. I realize that the taper in the insert "locks" against the substrate, but it is a solid sleeve. It feels like putting in an adapter. They can also be finicky about depth of the bolt.
A helicoil on the other hand is a coiled wire. The threads of the bolt mechanically pinch the entire length of the coil. Each individual coil along the entire depth is forced against the substrate under torque. Instead of a sleeve acting like a threaded adapter, you are physically replacing the threads with an actively-clamping steel locking mechanism along the entire length of the threads.
I personally prefer Helicoils, but again, not because of testing, because of doing. Right now, six 1/2" helicoils are holding the 6' brush hog blade spinning at 1800 rpm and whacking into rocks, cutting 1" brush, and otherwise being abused for the last 10 years behind a Ford 901. I think I can trust it for an M6.
I'm interested to hear the physics behind what makes a Timesert better, though.
Another thought is to simply upsize the bolt if there's enough material. You'll often find that a stripped out M6 is nearly the size of a M8, run a drill bit through to clean it up and then tap it to M8. A lot easier than an insert of any type, and that'll buy you another 20 years before you have to worry about it. And it still hasn't messed up the ability to put an insert in.
For example, a M6x1.0's drill size is 5mm. Stripped it will be a bit larger than 6mm, depending on how messed up it is. A M8x1.25 is drill size is 6.8mm, which is probably within .5mm of what you're already at, so just get the proper drill size to do the M8.
Other than that, I've only ever used Helicoils, and they work quite well.
In reply to mazdeuce - Seth :
Seth, for the engine case holes I would tend toward the Helicoil since it is likely there may not be much material at the hole boss. Also get the helicoil just under flush and that will help retain the insert better. It is designed to be oversize and the last thread edge digs in a little. Also use loctite on the insert to help retain it.
For the chassis/frame holes you may need to go with something like a rivnut since it is thin material and they will not require huge holes for install. Get the matching material rivnuts to reduce galvanic corrosion and if the need to be replaced down the road they can be drilled out easily.
The helicoil sizes you mention should probalby be purchased as the set with the install tool and several lengths of insert. I have a few in the same types of sizes and replenish just the inserts I use up on a regular basis. The rivnuts also require special install tools, but those can be anywhere from cheaper 10 use items to lifetime tools, or even homemade. Also replace the used rinuts with the lengths needed when you use them so you have them next time.
If your repairs were for materials that had lots of material around the holes the staked inserts would be my suggestion, since they are much less likey to come out under use. Now for thin metals, there is pressed is insert called a Pemsert that is great for low torque applications and only needs a hole drilled to size and device to press it into place. These are really easy to install/use on thin stuff.
Helicoils are the only approved repair here at work that isn't welding and drilling/tapping.
Helicoil inserts are fairly cheap, once you are set up for them.
I like to install them pre-emptively. Now, granted, I'm bad at DOING this 
All of the load bearing threads in my aluminum rearend housing have been Helicoiled for peace of mind.
I also had to Helicoil the ancient Control Tech stem on my bike, which required I buy a second tap to convert into a bottoming tap. Worth it.
I've always used helicoils with success. Heck, every bell housing bolt in the 350Z is helicoiled after I stripped one during one of the transmission installations. The LS's threads had seen better days and I knew the inserts were easier to install on an engine stand than in a paddock.
In my corner of the aerospace industry, we aren't allowed to use helicoils. The tang can become DOD, and they can back out. Locking threaded inserts or captive nuts are our options.
I understand they are the standard for most practical repairs.
In reply to stafford1500 :
Thanks for that write up (and everyone else too) I'm solid in the rivnut world with the better Astro Pneumatic tool and tons of inserts. I now have the Helicoil kit in M6 on the way and will expand with installation tools and what not as I use it. My eyes have also well and truly been opened to the world of threaded inserts and I have lots of options kicking around in my head for the future. I also feel like I should have known more about this sooner.
In reply to mazdeuce - Seth :
I was pretty sure I remembered you had a threaf about rivnuts, but figured better too much information/explanation was better than not enough.
Keep in mind the helicoils can be had in various lengths. The long ones can be cut down in a pinch... On the use of loctite with helicoils, you will have to let it cure before putting fasteners in. Do keep in mind if the hole is not blind, the tab that Matt Gent noted above, can get dropped into machinery. The stainless tab in suprisingly not good for machinery.
I've had helicoils try to unwind when I remove the bolt from them. If its something I install and remove often, I definitely don't use a helicoil. Something that's a one and done, I'll go to it.
In reply to Mr_Asa :
See my notes furter up about getting the last thread underflush and using loctite. That should make helicoil nearly bulletproof.
Mr_Asa said:I've had helicoils try to unwind when I remove the bolt from them. If its something I install and remove often, I definitely don't use a helicoil. Something that's a one and done, I'll go to it.
I've never installed a helicoil myself, but a number of the aluminum "big brake kit" caliper adapters I've bought over the years have had helicoils in them. And yes I've had this problem when doing brakes, the spring starts to unwind out of the bracket.
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