Thread repair 101

[PGK]

I was doing some work on a bike this weekend and found that several of the valve cover bolts were missing thread. That is, I took the bolts out and their threads came with them. On a high-mileage bike this is not uncommon, in fact it is more often than not the case. But this is applicable to anything that has threads that gets tightened/loosened often, or anything that you broke 'cuz you don't know which way to turn a wrench.

I decided to use a heli-coil for this repair, because it is quick, easy, comes in a kit, is available at autozone, and is a very durable and dependable method of thread repair. Other methods I have used are time-serts and keen-serts, which I hope to cover at a later date. All are good and acceptable methods for repairing threads. They have strengths and weaknesses though. I would not use a heli-coil to repair a drainplug, for example, or any plug that hold a fluid, because they do not provide a great seal. Fluid can work its way through and around the coils. Time serts or Keen serts would be a better choice in that instance.


Step one is to keep your stuff organized. These things are small, and get lost easy. Not to mention it's a pain in the ass to have the inserts, but not the tool, or have the tool but not the inserts. The tools are size-specific, so keep them in the same container as the inserts they match.


Drill the hole. The helicoil tap has the correct drill size written on it. In this case, the correct drill size was 1/4". I am using the M6x1.0 helicoil kit. Generally, if your autoparts store has one metric helicoil in stock, this is it, as it is a very common size.


Start the tap with your fingers.


Continue with the wrench. If you are using an end wrench, as I am, be careful not to side-load the tap, this can make cutting the threads more difficult and can introduce 'wobble' to the tap, causing it to cut unevenly.


Be sure to lubricate the tap. Helps it last longer.


Don't forget to lubricate your brain.



These two pictures show the tool that is included in the kit. I hate it. The tool makes it much more difficult to use, and was the source of a lot of my frustration with using the kit. The solution? just use the threaded rod, not the plastic housing. It makes it a lot easier, you just have to be careful. screw the insert in slowly, applying even pressure.


The last step is to remove the tang at the inner end of the coil. Do this with a punch and a hammer.


Before you know it, you've got a functional threaded hole again. You can see the end of the helicoil at the bottom of the hole.


Re-install the cover and torque it. If this step had been done all along, odds are I wouldn't have had to re-thread it.

I also wanted to point out this:

Which is an example of a badly installed helicoil. Either it came out with the screw, or it wasn't installed all the way. Either way, teh suck.


It was easy to remove with pliers though.

You need not despair over damaged threads, they are quite easily repaired.

[ViPER1313]

Only time I have had to use a helicoil was on a brake caliper slide pin. M7 - go try and find that kit :wink:

[jongp3]

you failed to mention the price on those.. hehe

[PGK]

The kit was 29.98. It came with the tool, the tap, and 10 coils. Not a bad price, considering.