Timeserts or Helicoils

There have been some test comparisons between the two suggesting that Helicoils are approx 5%(?) stronger and I’ve always wondered why. So I compared the diameter of a 3/8”-16 Timesert to a Helicoil and got my answer. The OD of the timesert is .446” and the OD of the Helicoil is .464” Thats a 4% increase in diameter and thats where the extra strength comes from.

A 3/8”-16 big sert with a .552” OD is 18% bigger in diameter than the Helicoil so theoretically its much stronger that the Helicoil.

But you don’t want to remove more metal than you have to and for that reason you might want to use the Timesert. See the photo below of an engine case with timeserts to avoid pulling out threads with a high output race engine (as recommended by Ron Wood who’s 750 short stroke suffered this problem at 8000RPM). You can see that there is very little aluminum around the bolt hole and in this case you definitely want to use the timesert instead of a Helicoil.

The big sert is available when you’ve stripped out a regular size timesert or helicoil. Helicoils can come loose and unwind but Timeserts lock in place and rarely seem to fail – Ron Woods motor being a good example. More objective tests need to be made but it seems obvious that the bigger the OD the stronger. But most people will want to take out as little alum as possible and leave room for later repair. The Timesert requires less aluminum removal than the Helicoil. Helicoils are cheaper and more popular - but personally I prefer the professional look of the timeserts and also because I have had the helicoils unscrew on me.

Interesting! I have (I think) all Helicoils for Norton - not easy to achieve. What is a good source for Timeserts in the various sizes for Norton? Right now, I'm deciding about gearbox outer cover screw repair so this is timely - there's so little metal around them.

I'm with you on this one. Timeserts have been my favorite for a long time, although I do still use helical inserts occasionally. Timesersts are not available in some of the odd sizes I have encountered.

Also, I'm not sure using the OD as a criteria for pull-out strength is valid, considering that in one case you are just pulling out a single length of wire, and in the other a solid insert. Would be interesting to do a measurement.

Ken

Several years ago i drilled out and installed E-Z Lok inserts in the head studs of my 850 . They are a solid insert and have been great . No fear of torquing anymore .. Two days ago i just repaired the left spark plug hole using Save a Thread by Heli-coil .. Time will tell

Hard to argue against Helicoils. They have been around a long time, being used extensively in the aircraft, marine and space industry, as well as more pedestrian applications.

BUT...Any such insert is going to be MUCH stronger than the original aluminum threads. I wouldn't hesitate to use whichever one happened to be handy or most easily available in the size needed.

I used the timesert on drain plug , quick & easy plus when I got it home it felt like there for good , that 10+yrs ago no issue … used helicoil work always considered them a temp. fix …. until I could get pump into shop …

Didn't Comnoz do a test where helicoil ( maybe surprisingly ) was the most resistant to pulling?

I also used the timesert on a stripped oil drain plug.
I would be surprised if the helicoil was stronger, and I am not sure that just comparing the insert size is valid.
The final part of the timesert installation is to expand the inner end of the thread so that the insert can’t easily pull out.
Has to be stronger in my opinion.
But….. they are so expensive in the UK, so use helicoil for non critical parts like the seat knob.

SteveC said:

I also used the timesert on a stripped oil drain plug.
I would be surprised if the helicoil was stronger, and I am not sure that just comparing the insert size is valid.
The final part of the timesert installation is to expand the inner end of the thread so that the insert can’t easily pull out.
Has to be stronger in my opinion.
But….. they are so expensive in the UK, so use helicoil for non critical parts like the seat knob.

Click to expand...

I guess it's horses for courses. Each are probably better suited to a particular situation.

Project Farm tests thread repair methods.
Cheers

Steve W. said:

Project Farm tests thread repair methods.
Cheers

Click to expand...

See the video at 13:40 Timesert and Helicoil come out the same. Unfortunately time serts are more expensive.

jseng1 said:

See the video at 13:40 Timesert and Helicoil come out the same. Unfortunately time serts are more expensive.

Click to expand...

I don't think that showed any difference in the pull-out strength of the inserts. All three inserts held until the bolt broke, so all they were measuring was the tensile strength of the bolts.

Another consideration with the E-Z Lock insert is that it has a larger diameter external thread, which is great for strength, but might be an issue in tight locations, or where there isn't much wall thickness left after drilling for the insert. Good example is the threaded holes in the crankcase for the cylinder through bolts, when the case mouth has been bored out for 920 cylinders.

Ken

I have installed a helicoil insert in my 850 drain plug repair. No issues after 80 K that I have ridden.
I change my oil every 2 k or so. I drain the sump and replace the filter, every time I change oil.
The engine is out for rebuild but the helicoil stays.

jseng1 said:

There have been some test comparisons between the two suggesting that Helicoils are approx 5%(?) stronger and I’ve always wondered why. So I compared the diameter of a 3/8”-16 Timesert to a Helicoil and got my answer. The OD of the timesert is .446” and the OD of the Helicoil is .464” Thats a 4% increase in diameter and thats where the extra strength comes from.

A 3/8”-16 big sert with a .552” OD is 18% bigger in diameter than the Helicoil so theoretically its much stronger that the Helicoil.

But you don’t want to remove more metal than you have to and for that reason you might want to use the Timesert. See the photo below of an engine case with timeserts to avoid pulling out threads with a high output race engine (as recommended by Ron Wood who’s 750 short stroke suffered this problem at 8000RPM). You can see that there is very little aluminum around the bolt hole and in this case you definitely want to use the timesert instead of a Helicoil.

The big sert is available when you’ve stripped out a regular size timesert or helicoil. Helicoils can come loose and unwind but Timeserts lock in place and rarely seem to fail – Ron Woods motor being a good example. More objective tests need to be made but it seems obvious that the bigger the OD the stronger. But most people will want to take out as little alum as possible and leave room for later repair. The Timesert requires less aluminum removal than the Helicoil. Helicoils are cheaper and more popular - but personally I prefer the professional look of the timeserts and also because I have had the helicoils unscrew on me.

Click to expand...

There is also the fact that helicoils don't have the "top hat" which gives them even more working thread than the timesert.

cliffa said:

Didn't Comnoz do a test where helicoil ( maybe surprisingly ) was the most resistant to pulling?

Click to expand...

robs ss said:

There is also the fact that helicoils don't have the "top hat" which gives them even more working thread than the timesert.

Click to expand...

As long as you ensure there are at least 6 turns of thread, the presence of a top hat at Time -Sert inserts does'nt matter.
On the other hand, a top hat does'nt contribute to pull-out strength if pulling load is opposite to direction of installation, as shown in the last video sequence.
If pulling load is _in_ the direction of installation, the top hat will form a restraint.

Please note that due to expansion of the aluminum, testing results at RT and at 400 'F are not comparable.

- Knut

mdt-son said:

As long as you ensure there are at least 6 turns of thread, the presence of a top hat at Time -Sert inserts does'nt matter.
On the other hand, a top hat does'nt contribute to pull-out strength if pulling load is opposite to direction of installation, as shown in the last video sequence.
If pulling load is _in_ the direction of installation, the top hat will form a restraint.

Please note that due to expansion of the aluminum, testing results at RT and at 400 'F are not comparable.

- Knut

Click to expand...

Yes I agree.
There is also the fact (IMHO) that Jim's test, although commendable, did not replicate the actual failure mechanism.
Failure of head studs occurs due to failure in tension, not torque.
His tests are indicative but not necessarily a true model of what happens.

gortnipper said:

Thread inserts in the Norton head (2019)

Here I have tested 4 common inserts used in the Norton head. These inserts were all 1/2 inch long. They all fit a 3/8-16 stud.

www.accessnorton.com

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I'd forgotten what a thorough job Jim Comstock had done on that subject. In practical terms, there doesn't seem to be that much to choose from between the different inserts, unless you go with some of the larger OD inserts for a little extra pull-out resistance. Still, I'll probably stick with the Timeserts and Bigserts most of the time, just because they look like a better design to me, even if they aren't. Or, as Jim S. said at the start of this thread, they look more professional. And, as he also pointed out at the start of this thread, helical wire inserts have been known to unscrew when removing the fastener. I've had that happen more than once, but I've never heard of it happening with a Timesert.

Ken

The Comstock test seems contradictory because at the end of the vid he says that the larger diameter inserts offer more strength. So it seems wrong that a big sert would have less strength than a smaller regular time sert. Maybe there were soft spots in that used head. I think another test needs to be made on uniformly made 6061 Aluminum plate to compare the strength of a larger diameter bigsert against a smaller diameter timesert. The larger diameter bigsert should be stronger in proportion to the OD because there is more aluminum engagement. To prove the point - make a 3/8" steel insert with a 1" OD and I guarrentee it will be way stronger than anything smaller.

Something else that should be factored into the test. Most bolts don't bottom out in the threads. The helicoil is a spring or a wire and you only pull on the aluminum section as deeply as the bolt extends. But a timesert is one solid piece and if the bolt only goes half way into the insert the steel insert still pulls on the entire depth of the aluminum. The deeper the aluminum thread engagement the stronger the insert.

jseng1 said:

Something else that should be factored into the test. Most bolts don't bottom out in the threads. The helicoil is a spring or a wire and you only pull on the aluminum section as deeply as the bolt extends. But a timesert is one solid piece and if the bolt only goes half way into the insert the steel insert still pulls on the entire depth of the aluminum. The deeper the aluminum thread engagement the stronger the insert.

Click to expand...

Unfortunately there is no linear dependency between thread (insert) length and load transfer. The reason is simply that bolt, thread insert, and the aluminum block stretches and the stretches are not in concert. The net result is a load distribution which follows a negative power function. In practice only a small fraction of the tensile load is transferred past the 6th interacting turn. This is true for the insert as well. As there is no compressive load acting upon it past interacting bolt thread depth, the internal stresses will successively relax. I plan to perform a nonlinear FE analysis soon to look at this effect in detail.

- Knut