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My lightweight restoration hit a snag, the drive flange retaining bolt wouldn't torque up.

The thread had been stripped at some stage.

One option was to take off the hub and replace it, but I was keen to just repair the damage, rather than swap over seals, bearings and the extended wheel studs.

So I decided to use a thread repair kit.

This isn't a bodge, some applications require the use of thread inserts in order to allow repeated undoing.

I ordered a V coil kit from eBay, which arrived in time.


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The hub was masked up, and the hole cleaned out.

The first job is to drill out the damaged threads.

I guesstimated how deep I needed to drill and marked the bit with a Sharpie.

Drilling was the hardest part of the job, as my drill kept grabbing the threads and locking, I'm not sure the drill is entirely right, it's fine for wood, but in metal it just either locks or torques out.

Might be time for a new drill.




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I would say that is a perfectly acceptable method of repair. Folk have been using Helicoils and similar for many, many years.

Running a drill into a hole where there is not much of an increase in diameter often results in the drill snatching. The fact that you're using a pistol drill, rather than a drill press makes this situation even more likely. You just have to hold things as steady as you can and go carefully to avoid a wrenched wrist.

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Once drilled and cleaned with brake cleaner I blew out the chaff with the air line.

The next task is to tap the hole for the stainless steel spring insert.

The key thing on this is to get the tap perpendicular for the first five or so turns.

Start slowly. Really slowly and check the tap is at right angles, then go around 90 degrees and check again.



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The next stage is to tap the new, wider thread. Starting the tap is key to getting this right.

Slow and slower. By eye judge that the tap is perpendicular, and twist a quarter turn or so.

It should bite. Once it does, stop and check that it is at right angles, then do it again at 90 degrees. Do a half turn and check again, of its out, a gentle tap with the fist will straighten it. 

When I was taught how to do this I was taught to wind the tap back by a third to break the chaff. This does work, and makes the thread feel cleaner

Once you've five turns then it's all good. You might like to fully unwind the tap and see the chaff.




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Tap the hole until you run out of hole, just. Don't get the tap stuck! Blow out the chaff with an airline.

Time to wind in the insert spring.

Be careful with this.

Slot the spring into the tool with the sprue last, so that when you offer the spring to the hole, the sprue is going in first.




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Offer up to the tapped hole and turn the the twist tool until the spring engages with the thread.

Don't push!

The tool will wind the spring in, a little lube helps, but if you push the spring can jump threads, which is bad.

Just keep twisting until the spring is in the centre of where the bolt thread will be.


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Finally, tap off the sprue with the punch.

Job done.

A good solid repair. Torque to spec and forget.

This can be done in less than 10 minutes. I ended up doing all six, as I was unhappy with the level of engagement when I tightened the rest up. Took 40 minutes, I think.




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Great little write up for those not familiar with this type of repair. I'd just add that the collar on the insertion tool should be moved down so the helicoil/v-coil sits against it. It makes it a hell of a lot easier to get it started as you can apply a bit of pressure without stretching the coil or starting it wrong. I'd also add that don't be shy when you break the tang off, a quick, hard, sharp hit is better as if you go too gently you can just bend over the end of the insert.

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