Repairing Threads (On The Cheap)

Getting you out of a hole.
At some point of working with bikes or cars, you'll be faced with a thread that's been damaged through over tightening, cross-threading, or simply full of corrosion/paint. A good set of taps and dies, or a thread chaser set, is invaluable for these times, but here's a neat trick that can get you out of that hole when you have neither.

But first, here's a few of the sets I use regularly. Well worth the investment, even it only saves you once.

Snap On Thread Chaser Set

M10x1.25 Chaser, Nut andTap

Beta Tap Set

Now the cheap method.
1) Take a bolt of the correct thread. 
In this case an M8x1.25 - this refers to the diameter of the bolt, not the size of the head (M8 = 8mm), and the pitch (distance between each raised point in millimetres).

 

2) Cover the thread in rag, and place the bolt in the vice. 

3) Take a square, triangular or flat file and start to cut a slot into the end of the bolt.

4) Once it starts to look like this, turn it 120º and cut another slot. 

5) Repeat one last time so you have three slots around the bolt. These are going to carry the swarf away from the problem thread, and prevent further damage. 

I use plenty of WD40 when clearing threads in aluminium, and take my time. If it tightens up, work it back and fore, and spray with lube until it frees. 

If you can't work out the correct angle the bolt should be screwed in (due to cross-threading damage), see if you can screw some other bolts in surrounding holes. This will give you a guide to follow when you're trying to get it back on track. Similarly, a spark plug will normally follow the same angle as the others in a multi-cylinder engine. 

Take your time to work out angles before screwing the chaser, or tap, into the hole or you'll cut a good thread at a crap angle!

The budget thread chaser. 
This can also be put to good use with old spark plugs if somebody's managed to cross-thread them or the holes are full of old carbon etc. Just slot an old plug in the same way. One thing to remember, your budget chaser isn't as hard as the correct tool, so don't expect it to keep clearing in the same way. This is more about getting you out of a jam on a Saturday afternoon when those vital stores have closed.

  

Vinegar - one week later.

I wasn't sure what to expect.  The vinegar was definitely doing something because the colour had turned dark brown (the rust magically dropping off?).

So, a quick wash off in water was in order.  The parts were coated in a grey/black residue which needed washing off and a quick rub with a wire brush.

The pliers will rust quickly after being in the vinegar so wash them, and WD40 them, straight after.

The next step was to tidy the threads up using a thread chaser kit.  A tap and die set would also be fine for this but I didn't have a large enough die.

This is a great kit - not that expensive either considering it's Snap On, and it has got me out of a lot of trouble over the years. 

It has slots placed within the thread of the "chaser" nut so that any swarf cleaned from the threads can stay away from the bolt, preventing further damage.

You can see the slots more clearly here on the tap version.

I'm pleased with the results.  Not all the bolts have come up to this standard but I'll perservere and replace only the parts that I need to.