Helicoil reliability

[lobo11]

Intake Manifold repair--I have the whole story in a different thread down a smidge. Thoughts on helicoils, they seem to do well when I have used them in the past, but I am still nervous. Below copied from other thread. Thanks.

It is done, and all went smooth until a faulty torque wrench made the day miserable. First rocker arm bolt that we tightened down stripped due to what appeared to be a broken torque wrench, if only we would have used the other (working) wrench istead. Went online and found many folks have used helicoil inserts for this problem, bought the right kit and inserted helicoil. This makes me nervous, even though the helicoil manufacturers clain the helicoil makes stronger threads than the soft metals and metal alloy threads, after all they are selling this stuff, right, what else would they say? After this set-back all goes smoothly with the properly operating torque wrench. The old girl seems to be running fine, actually better with the new plugs, wires, and cleaned injectors. I am hoping the helicoil is an acceptable fix, what say you all? I know aluminum threads are not the strongest to start with, but I am still nervous. I am hoping that the stress on the rocker arm bolt is low, and the pushrods travel is limited more by pressure than the rocker arm?? Other than the stripped thread the fix wasn't all that bad. The PermaDry gasket seemed of much better quality, only a UOA will tell me if I have helped and if the job was well done. At least there is no AF sitting under the valve covers that I can see. Disappointed in GM in regards to a few engineering set-ups. Oh well.

 

[Quest]

Helocoil has been widely used in the industry for decades, so their reputation for reliable fix is assured.

The only thing that I can think of that may have led to the failure of helicoil mainly has to do with the operator who may have used the wrong drill bit(1 size larger/small than the one spec'ed by the coil) and that would have caused more trouble down the road.

 

[XS650]

Heli-coils are generally agood fix, althougfh anything can be screwed up.

Aluminum thread fail from various causes. One is that the thead gets worn from the fastener being removed and reinstalled, particularly when there is some corrosion and dirt involved. Another is that the shear area of the aluminum in the threads is inadequate and the threads shear off.

A heli-coil helps solve both problems. The steel helicoil provided a steel surface for the screw to thread into, so no more aluminum wear.

The thread pitch diameter of the helicoil is larger that the pitch diameter of the screw thread pitch diameter, so it has a lot more resistance to shearing the aluminum.

 

[lobo11]

Found a published journal article online from some Czech University that basically concluded from their testing that the helicoil threads have at least as much holding strength as the original threaded parent material. I think the tested in steel and some aluminum alloy.

 

[Volvohead]

The helicoil is as strong as the base stock it's threaded into. For softer alloys, the casting will give way before the insert does.

I don't get the "wear" comment, unless you plan on taking this apart repeatedly. Perhaps you meant fatigue. Once it's torqued, you've adequately loaded the threads. If it later fails from fatigue, it will be from some additional, non-fastener related load in excess of design.

Helicoils have been around forever, and as stated, have a hard-earned good reputation among professionals.

I wouldn't worry about it further if it was properly installed and torqued to specification without incident.

 

[FowVay]

I work in the aviation industry. We repair everything from Jet Engines to reduction drive gearboxes with thread repair kits.

In low torque applications we use plain Heli-coil inserts. These work well in housings made of aluminum and magnesium.

In high torque applications or where excessive vibration is encountered we use a product called a Time-sert. This installs a sleeve with a shouldered and sunken cap on the surface which allows greater torque to be applied and also absorbs vibration and shock loads better.

For automotive use I believe that Heli-coils work well. For problematic and poor design applications such as Ford spark plug threads, I'd spend the money on a Time-Sert kit.

 

[mechtech]

If it was installed properly, you'll have no problems.
The outside thread of the coil is much larger than the inside, and will have greater surface area. Being steel, it won't strip internally as easily as aluminum.

 

[Clyde65]

Which Helicoil kit did you use? They have several kinds.

1) Did you use the recommended drill bit?

2) Did you use the recommended tap?

3) Did you oil the tap with cutting fluid?

4) Did you cut the threads correctly by backing up every quarter turn to clear the chips?

5) Did you clear the chips out before installing the Helicoil insert?

6) Did you use the correct installation tool?

7) Did you use the proper length insert that covers at least 90% of the hole?

Final comment: I don't trust micrometer type torque wrenches unless they are high quality and are calibrated regularly. The old fashion beam type torque wrench will never let you down.

 

[Quest]

Ans:
-yes
-yes
-yes
-yes
-yes
-yes
-yes

I use clicker type torque wrenches most of the time and have them calibrated on a 1~2yr basis. I have beam type torque wrench and they work just as well.

On the sideline,I'm a torque wrench buff and I do collect good, quality American and Japanese made torque wrenches, mostly beam type made in the 60s to 80s.

I think unless someome made a mistake or gross negligence, otherwise, micrometer torque wrench should be just as dependable as other forms of torque wrench.

I smiply don't buy the "my torque wrench" wrecked my day sort of saying---I have used all kinds of torque wrenches so far and most of them are dependable and trustworthy so far, so long as they have not been dropped on the floor. I used to have a micrometer-based torque wrench also (a mechanic friend borrowed it and never returned, it's been 4+yrs since *sob*).

 

[Shannow]

I'd trust a helicoil at least as much (and prolly more) than a thread into soft alloy.

As to failed torqu wrenches, I saw one once.

Neighbour couldn't budge the front pulley bolt on a Nissan that he was rebuilding. Put his torque wrench on it (only handle long enough), and nudged it with the starter.

Interestingly, next motor he rebuilt, he complained about "plasticine bolts".

 

[demarpaint]

I used one on an old Ford 200 inline 6 head bolt, back in the mid 70's. Held for years without any issues. They work.

Frank D

 

[Brett Miller]

A properly installed Helicoil will hold very well, NAPA used (they still may) to sell a steel thread repair insert called a Keen-sert. It used steel pins to anchor the insert. They worked very well and were stonger than the orignal part.

 

[lobo11]

I think the recommended drill bit was a really odd one, and I used one 1/64 smaller than recommended. I guess I should have went out and tried to find the odd size.

 

[Schmoe]

I know helicoils will not hold up for spark plugs when the 5.4 Fords spits them out. Only timeserts worka akin to what vow said.

 

[lobo11]

I am hoping not to see the level of stress a spark plug must see upon combustion.

 

[JetSnake]

quote:

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Originally posted by FowVay:
I work in the aviation industry.

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Same here. I work for Mesaba airlines. You?