Locking threaded inserts for Kubota L4740

[Husaberger]

Some of the bolts attaching the engine to the frame on my Kubota have stripped out
I would like to use a locking threaded insert instead of a HeliCoil
They come thin and thick walled
Has anyone done a similar repair and did you use thick or thin walled inserts?

 

[etpm]

In my 45 plus year career as a machinist I have installed and used many different types of thread inserts, even ones I have made myself. If there is enough material in the part with the stripped threads then the thick walled inserts are best when considering the use of the type of insert you want to use. My conditional opinion. There is a tool made for driving in the locking pins. Make sure to use this tool. Though you can drive the locking pins in with a hammer and a punch, or even just a hammer, driving the pins successfully is almost guaranteed when using the tool. Without the tool, not so much. Especially since it sounds like you may not have much experience with these inserts.
All that said, I still prefer Heli-Coil type thread inserts. I prefer them because if the stripped hole has not been worn out too big a Heli-Coil type thread insert offers more strength than the original thread and removes the least amount of metal from the repaired part. I have installed over 15,000 Heli-Coil type thread inserts just for one customer. This customer uses them in aluminum castings for marine use because they are so much better than cast aluminum for fasteners that must be removed and replaced, such as some types of service hatches on boats. Installed correctly they have never failed.
I am curious about why the original threads failed. Do you know why? If so then make sure you correct the reason for the failure. If you don't know why the threads failed in the first place then you should not only figure this out but realize that when considering which insert to use the thick walled insert should not be used. This is because the type of insert you are wanting to use cannot be removed easily without damaging the thread in the parent material. This is mainly because of the locking pins, which have already damaged these threads. By the time you have worried the ruined insert out the hole will probably be a mess and will require drilling and tapping for the thick walled insert. Even though locking inserts use standard taps, unlike Heli-Coil type inserts, they do not use standard hole sizes for the tap. This hole is larger than would normally be used for the tap. This doesn't matter because of several reasons that I don't want to type about in this already too long post. But it does mean that if the pin locking type insert fails you have less material to work with when installing yet another insert.
Eric

 

[Husaberger]

Thanks Eric
Good post

In my 45 plus year career as a machinist I have installed and used many different types of thread inserts, even ones I have made myself. If there is enough material in the part with the stripped threads then the thick walled inserts are best when considering the use of the type of insert you want to use. My conditional opinion. There is a tool made for driving in the locking pins. Make sure to use this tool. Though you can drive the locking pins in with a hammer and a punch, or even just a hammer, driving the pins successfully is almost guaranteed when using the tool. Without the tool, not so much. Especially since it sounds like you may not have much experience with these inserts.
All that said, I still prefer Heli-Coil type thread inserts. I prefer them because if the stripped hole has not been worn out too big a Heli-Coil type thread insert offers more strength than the original thread and removes the least amount of metal from the repaired part. I have installed over 15,000 Heli-Coil type thread inserts just for one customer. This customer uses them in aluminum castings for marine use because they are so much better than cast aluminum for fasteners that must be removed and replaced, such as some types of service hatches on boats. Installed correctly they have never failed.
Good insight

I am curious about why the original threads failed. Do you know why?
Even though I bought the tractor new, and it has never been abused, it has been used to the limit of its capacity
I think I simply noticed it late and by that time repeated cycling had caused the threads in the block to strip

If so then make sure you correct the reason for the failure. If you don't know why the threads failed in the first place then you should not only figure this out but realize that when considering which insert to use the thick walled insert should not be used. This is because the type of insert you are wanting to use cannot be removed easily without damaging the thread in the parent material. This is mainly because of the locking pins, which have already damaged these threads. By the time you have worried the ruined insert out the hole will probably be a mess and will require drilling and tapping for the thick walled insert. Even though locking inserts use standard taps, unlike Heli-Coil type inserts, they do not use standard hole sizes for the tap. This hole is larger than would normally be used for the tap. This doesn't matter because of several reasons that I don't want to type about in this already too long post. But it does mean that if the pin locking type insert fails you have less material to work with when installing yet another insert.
Eric

I'll probably take your advice and start with the Heli-Coils and keep checking them a keep my fingers crossed
Agree that the locking thread inserts require a bigger hole so I'll keep that option as a backup

 

[etpm]

Thanks Eric
Good post

In my 45 plus year career as a machinist I have installed and used many different types of thread inserts, even ones I have made myself. If there is enough material in the part with the stripped threads then the thick walled inserts are best when considering the use of the type of insert you want to use. My conditional opinion. There is a tool made for driving in the locking pins. Make sure to use this tool. Though you can drive the locking pins in with a hammer and a punch, or even just a hammer, driving the pins successfully is almost guaranteed when using the tool. Without the tool, not so much. Especially since it sounds like you may not have much experience with these inserts.
All that said, I still prefer Heli-Coil type thread inserts. I prefer them because if the stripped hole has not been worn out too big a Heli-Coil type thread insert offers more strength than the original thread and removes the least amount of metal from the repaired part. I have installed over 15,000 Heli-Coil type thread inserts just for one customer. This customer uses them in aluminum castings for marine use because they are so much better than cast aluminum for fasteners that must be removed and replaced, such as some types of service hatches on boats. Installed correctly they have never failed.
Good insight

I am curious about why the original threads failed. Do you know why?
Even though I bought the tractor new, and it has never been abused, it has been used to the limit of its capacity
I think I simply noticed it late and by that time repeated cycling had caused the threads in the block to strip

If so then make sure you correct the reason for the failure. If you don't know why the threads failed in the first place then you should not only figure this out but realize that when considering which insert to use the thick walled insert should not be used. This is because the type of insert you are wanting to use cannot be removed easily without damaging the thread in the parent material. This is mainly because of the locking pins, which have already damaged these threads. By the time you have worried the ruined insert out the hole will probably be a mess and will require drilling and tapping for the thick walled insert. Even though locking inserts use standard taps, unlike Heli-Coil type inserts, they do not use standard hole sizes for the tap. This hole is larger than would normally be used for the tap. This doesn't matter because of several reasons that I don't want to type about in this already too long post. But it does mean that if the pin locking type insert fails you have less material to work with when installing yet another insert.
Eric

I'll probably take your advice and start with the Heli-Coils and keep checking them a keep my fingers crossed
Agree that the locking thread inserts require a bigger hole so I'll keep that option as a backup

There are available mechanically locking HeliCoil inserts. These inserts have a different thread form than standard. Because the locking action is supplied by the shape of the wire that the screw thread insert is made from and not from nylon or some sort of adhesive the fastener can be removed and replaced without loss of the locking feature. One advantage of the locking insert is that it is good at preventing the fastener from coming loose due to vibration. And if the fastener does start to loosen the locking action continues so this can help keep the fastener in the threaded hole for much longer. Here, I found a link that explains it better than me: HeliCoil Inserts - Helicoils and Heli Coil Products . Anyway, good luck and I'm glad I could help.
Eric
P.S. I'm so embarrased, I have been misspelling HeliCoil and have done so for a long time. There is no dash. I guess I got that dash fixed in my mind years ago. I hate it when I do that.

 

[newbury]

I don't want to type about in this already too long post.

Feel free to expound if your typing is up to it. You are becoming a valuable resource.

 

[etpm]

In writing about HeliCoils I forgot to mention a couple things. HeliCoils are made to a standard that other manufacturers also follow. They are technically called a Screw Thread Insert, AKA STI. They require a special tap. The taps are also made to a standard. Machinery's Handbook has all the data for standard Screw Thread Inserts but I don't know about the locking inserts. In any case, it is not necessary to buy a HeliCoil brand tap to get good results. It is necessary to buy high quality taps though for consistent good results, such as the threads being the proper dimensions. Any good machine shop supply house will have good taps. Buying a tap from Amazon for the lowest price may be a mistake. Even though I have used regular Screw Thread Inserts from several manufacturers, with mixed results, the only locking STIs I have used were genuine HeliCoil brand.
Eric

 

[etpm]

Feel free to expound if your typing is up to it. You are becoming a valuable resource.

Ok, I guess I can expound a bit. Typical threads are about 75% of the theoretical 100% thread size. When similar materials are used for both the fastener and the tapped part and if the fastener is threaded into the tapped part at least 1 1/2 times the diameter of the fastener, then the tensile strength of the fastener will be less than the force required to pull the fastener straight out of the tapped hole. So the fastener will break if pulled straight out.
But it gets better. If only 50% of the theoretical 100% thread exists the fastener will still fail before the threads. Of course these figures apply to properly cut threads, not torn threads. If the threads are formed then the strength goes up. There are taps that form the thread and they have different colloquial names, such as roll taps or form taps.
Some materials, especially materials that tend to tear when a cutting tap is used, such as mild steel, are best for thread forming taps. Generally, stainless steels are good for formed threads. Brass and cast aluminum are usually lousy for form tapping, most cast iron alloys too. These material can be great for cutting taps because they make nice and small tightly curled chips. This feature means that the material doesn't form easily because of low ductility, so the formed thread will have lots of tiny cracks in it, which of course weakens the thread.
The type of insert the OP wanted to use in the first post only has about 50% thread. This doesn't matter because of the aforementioned reasons and is an advantage because it makes the minor diameter larger, strengthening the insert. And since the insert is in a tapped hole that is much larger than the fastener but only needs to be as strong as the original tapped hole there is another advantage because the much larger area of the insert outside diameter spreads the load over that larger area. And even though I don't know for sure it is very likely that the insert is made by forming the thread, not cutting it.
Besides the advantage of formed threads being stronger they are also easier to make because no chips are made during threading. So if the material can be formed it usually is. If you go to the hardware store and look at some grade 8 socket head cap screws, Allen head screws, you will see rolled threads. These formed threads are pretty easy to spot. Where the thread ends and there is an un-threaded portion of the screw, you can see that there is a reduction of the shank diameter just before the threads start. This reduction is not abrupt, like a machined relief, but gradual, at maybe a 10 degree slope. This is because the screw has two diameters before threading. The formed thread needs the smaller diameter because it forms the thread into peaks and valleys without removing any material. The thread will also usually have a better finish than a cut thread. Now I've had enough typing.
Cheers,
Eric

 

[ruffdog]

I agree with Eric. I would also start with the helicoil. If done correctly, they will be fine. The inserts the OP is showing works great in a softer base metal but must have a quality drilled and tapped hole.

 

[etpm]

I agree with Eric. I would also start with the helicoil. If done correctly, they will be fine. The inserts the OP is showing works great in a softer base metal but must have a quality drilled and tapped hole.

A HeliCoil must also have a properly tapped hole. In fact, I would say it is even more important for a HeliCoil to have a properly tapped hole. Which really isn't hard to do.
Eric

 

[Husaberger]

There are available mechanically locking HeliCoil inserts. These inserts have a different thread form than standard. Because the locking action is supplied by the shape of the wire that the screw thread insert is made from and not from nylon or some sort of adhesive the fastener can be removed and replaced without loss of the locking feature. One advantage of the locking insert is that it is good at preventing the fastener from coming loose due to vibration. And if the fastener does start to loosen the locking action continues so this can help keep the fastener in the threaded hole for much longer. Here, I found a link that explains it better than me: HeliCoil Inserts - Helicoils and Heli Coil Products . Anyway, good luck and I'm glad I could help.
Eric
P.S. I'm so embarrased, I have been misspelling HeliCoil and have done so for a long time. There is no dash. I guess I got that dash fixed in my mind years ago. I hate it when I do that.

Had no idea
Sounds like I should be using the screw-locking type