Another Helicoil test

Trav

Trav

Joined
Nov 20, 2006
Messages
31,304
Location
MA, Mittelfranken.de
I just saw this on the TTC, it pretty much mirrors what Project farm found and what I have believed to be the case for decades. If you want strong threads coils are the way to go. I do a lot of M6 especially on VW/Audi 2.0T lower middle intake bolts, I do these as a precaution on every one I have removed the intake on, quite often the threads pull just removing the bolts.
I use an M6 Hertel or OCS STI tap and 6.3mm drill bit with a pre winder and tangless coils, ditto M8.

 
Helicoil for low stress. Time sert for high stress, or where the fastener will be repeatedly removed.

I am genuinely shocked by the Timesert result in the video.

For example - I had a subframe bolt break while doing a bushing replacement on the Volvo XC90. That model is notorious for corrosion in the frame above that bolt. This caused galling, and, well, while there was overnight soaking with penetrant, working, and care, there ended up being breaking, and ultimately, it had to be drilled out and the threads repaired.

Big bolt. M14. Critical strength requirement. Torqued to 90NM + 120 degrees. A non-reusable bolt* that gets stretched on installation. Huge load.

The Timesert worked perfectly. Also, Timesert was the only one that had an insert as long as, or longer than, the original thread depth.

That is an important point in my use decision. Helicoil and others offered only a 14mm depth for a 14mm bolt. With Timesert, I was able to get a 28mm insert - for twice the thread depth. Twice the bolt engagement and twice the engagement in the frame itself.

That was the clincher for this application.

The broken bolt in the frame. Can’t really get to it easily.
IMG_1983.jpeg


Timesert installed.

IMG_2017.jpeg


Fixed.

IMG_2020.jpeg



*I don’t re-use them. The torque is huge. I need a big cheater bar to get to the 120 degrees, and you can feel the bolt stretch. I have a 14x1.5 mm thread chaser, made from a new bolt (because the old ones are stretched) to clean those threads before pressing in the bushing and installing the bolt. There are four subframe bushings. They hold the subframe to the frame, so they really are critical components. New bolts are about $5 each. This isn’t an area to save a few bucks by re-using bolts.
 
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I would say coils for high load stress and serts for stuff that needs to be repeatedly removed. As far as length goes it is a full strength thread if it is 1.5 times the bolt diameter. The available coils are 21mm long for M14 which would provide full strength. The time serts were a bit disappointing under load.
I do use aluminum serts for spark plugs in aluminum heads because the aluminum insert does not change the heating characteristics of the plug.
 
I’ll check my inserts for depth when I’m back at the shop later today. Going off memory here.

As I recall, the threads in the frame were more than 1.5 diameters deep. Perhaps that is to allow the bolt to engage and tighten things up before seating and getting torqued to ludicrous tight.

Regardless, the Timesert worked in that application. I don’t mind the extra expense of a Timesert when a critical component like a frame bolt gets repaired.

The car itself is up in Boston, it’s my daughter’s now.

I do have a new respect for helicoil, though. I’ve used them for things like manifold bolts - infrequent disassembly and modest load.

But I will consider them in high load applications going forward.
 

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My 2002 F350 6.8L V10 had a heli-coil installed by the prior owner in cylinder three. I purchased the time sert kit with the plan to remove the heli-coil and replace with a time sert in cylinder number 3. That was spring of 2019. Have not got around to yet.... maybe I don't need to.
 
GON said:
My 2002 F350 6.8L V10 had a heli-coil installed by the prior owner in cylinder three. I purchased the time sert kit with the plan to remove the heli-coil and replace with a time sert in cylinder number 3. That was spring of 2019. Have not got around to yet.... maybe I don't need to.
Click to expand...
If its held up that long I wouldn't make more work for myself. The hole size may not tap properly going from a coil to a sert, it already had a STI oversize tap run down the hole for a coil, the different styles are not the same external size. You may open a can of worms you didnt bargain for.
 
Yeah my understanding was that "serts" are not necessarily stronger but more closely approximate the original hole for repeated removal and installation of a fastener. Coils can get temperamental if a fastener is removed and reinstalled a lot.

Also he's killing me trying to free-hand all those taps square. I understand this is how most mechanics will do it (esp for parts in the vehicle) but I feel it would be a more consistent, professional test if he used a spring loaded tap guide in a mill or DP. Would it actually affect the results? Almost surely not but as a machinist I still can't help the involuntary twitching as he starts those taps..... he's got a freaking drill press RIGHT there!!
 
The helicoil drawer.
IMG_2329.jpeg


The Timesert collection. Shown with it is one of the subframe bolts, that I converted to a thread chaser. The bolt is about 5 inches long. Additional inserts (where I wanted a different depth, or just plain needed more) are in the plastic bags. There is a substantial investment in this photo. But it sure beats replacing big parts with thread damage.

Also, I used M14x24mm inserts. Just over 1.5 times diameter. Not quite as long as I remembered, but I did match the depth of the original threads.

IMG_2331.jpeg
 
D60 said:
Yeah my understanding was that "serts" are not necessarily stronger but more closely approximate the original hole for repeated removal and installation of a fastener. Coils can get temperamental if a fastener is removed and reinstalled a lot.

Also he's killing me trying to free-hand all those taps square. I understand this is how most mechanics will do it (esp for parts in the vehicle) but I feel it would be a more consistent, professional test if he used a spring loaded tap guide in a mill or DP. Would it actually affect the results? Almost surely not but as a machinist I still can't help the involuntary twitching as he starts those taps..... he's got a freaking drill press RIGHT there!!
Click to expand...

I get that but he is duplicating the conditions most mechanics face when using these things. I try to use a guide block for drilling and tapping if at all possible even if I have to make one, it really helps. I also make guide bolts on the press for drilling broken bolts that have broken off deeper in the hole, most of the repairs I have to do are on the car so that is about as good as it gets and the results are good.
It is nice to have it clamped in a press and use an optical punch on the broken bolt but that is usually not happening on the car.
On blind holes I always start with a taper STI and finish with a bottoming STI.

The only places I like and do use Time Serts is in aluminum oil pan drain plugs and aluminum cylinder heads for different reasons, otherwise I prefer coils. In an iron head tangless coils or steel serts both work well. When I was working full time, this was a routine thing so lots of practice helps.
 
Machinist might look at the tap exercise and wince. But honestly, when the part is on the car, what choice would one have? I have a drill guide, but it sits new in the box because I’ve never had a chance to use it.

I’ve tapped a lot of things by hand, I’ve drilled a lot of things by hand.

In almost every instance, I’m dead on. But, even if I were off by say two or 3°, and and I can clearly see an error of lesser magnitude, but let’s say that I really screw up.

Every single one of the threads that I’ve had to fix was to hold on another part. So, does a 2° alignment variation in that fastener make a difference in the clamping force it generates over the held part?

I’m humbling suggesting that it does not. I am not a machinist. I do work with precision, at least as best I can. I am careful. But of all the things that I’ve had to repair, not one of them has leaked, come loose, or broken.

That includes the subframe bolt, which is on a car getting driven in Boston.

Time will tell if I did a good job on that one.
 
Astro14 said:
Machinist might look at the tap exercise and wince. But honestly, when the part is on the car, what choice would one have?
Click to expand...
I specifically stated that.

Merely pointing out that in a TEST the point is to reduce variables and tapping square is mostly practice with a bit of luck.

Same reason you wanna test battery impacts with a fully charged battery and same amp hours etc etc etc

Here the test is not a test of one's ability to tap square but rather the strength of each method if installed properly under ideal conditions with minimal or no variables.

As I said, I doubt it would have affected the results. And again I specifically said you have little choice when the part is in the vehicle
 
I agree, for the test to be fair across the different brands and types, you have to eliminate the angular variable, that hand, drilling and hand tapping could cause.

I am still genuinely surprised by how easily that Timesert pulled out.

Just, instinctively, you would think the thicker, more robust, insert would survive better.

At least, I did.

So, this test, many other tests, changed my mind on this particular topic. I won’t look down on helicoils anymore. For most cases, I think they’re better. Just based on this.
 
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Trav said:
The car will go to the bone yard years from now with that in there, no doubt about it.
Click to expand...
Well, at the risk of going off topic, she had it three weeks, took it up to Vermont to go hiking, and was in a very minor collision. Another vehicle decided to stop, and then reverse, on a state highway. It caught her by surprise, and she did her best to stop. The sum total of damage is 4 little holes in the back end of that Toyota RAV4 from the XC 90 license plate bolts.

So, my sincere hope is that it goes to the boneyard, many many years from now, but the reality of Boston traffic, and crazy people on the roads, might not let that happen.

I put a lot into the car so that she would be safe.

Doesn’t look its age…

IMG_2043.jpeg
 
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