Wrench Tips #6 – Re-Using Copper Washers

Wrench tips - annealing used copper washers

Wrench Tips
Tip #6: Re-Using Copper Washers

Its not that I'm cheap… Ok, let me re-phrase that. Its not JUST that I'm cheap, it's that I'm lazy and don't plan well.

Copper crush washers really shouldn't be re-used. To seal effectively the copper must be soft, as it is in an annealed state. The very act of crushing it under a bolt work hardens the metal, and years of being bolted to, say, your turbo, can have a tendency to age harden it as well. There is a decent chance a used, crushed, aged copper washer might seal again, but the only way to be sure is to try. In my experience, copper crush washers are not used anywhere you can afford to be wrong.

Common sense says buy new crush washers before assembling anything important. Reality says I didn't remember to and now its 10:30 on a Sunday night and I'm not stopping now just to wait for the copper washer store to open.

So, if you can't plan either, here's how you refurbish a copper washer.

First, get your propane torch out and heat them unti they are glowing like toilet seats in hell. If you're using Propane, you'll probably have to fashion a little oven from scrap brackets and aluminum tape, like the one pictured above, to contain the heat of the torch. Otherwise you won't be able to get them hot enough to really glow this well. Don't worry, you can't melt copper with propane. (You can melt copper with MAPP gas, though, so be careful!)

Wrench Tips sand the copper washers flat

Now, let the washers air cool slowly. Once you can touch them, you need to get rid of the ridges left from the last time you crushed them. Get some fine sand paper (at least 300 grit) and something flat. If your garage is too messy to find a flat horizontal surface, tape the paper to a window (of your house, not your car!) Glass that's less than 70 years old is usually very flat.

Now gently press down with your finger and sand simultaneously sand the washer and exfoliate your fingertip.

The washers will have turned black with oxidation as they cooled. You'll know you're done sanding when the whole face of the washer is shiny copper again.

 -Dave Coleman


Got any tips of your own? email them to dave@motoiq.com!


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1 comment

  1. First of all, great article. In regards to reusing crush washers, most people only focus on the flatness of a washer as the primary concern. But as stated, copper has a unique property of work hardening (when bent, hammered, rolled, or crushed). Fortunately, it is quite easy to anneal. However, while what you shared would would, I do have some suggestions for improvement.

    Two things:
    1) Copper does not need to be heated to the fiery glow of satan’s toilet. It only needs the dullest red you can just barely see in low lighting. Going hotter than this results in excessive scale, oxidation, porosity, and material loss from post process cleanup. It also takes more time and fuel. Save money, time, and improve quality. Just barely dull red.
    2) It doesn’t need to be cooled slowly. You can actually quench it immediately. This not only speeds up production, but the thermal shock can help flake off some of the scale that formed during heating. There’ not a benefit either way here. It simply doesn’t matter from a metallurgical point of view. (the grain structure that was under strain from work hardening was allowed to relax when heated, but there is no new crystal growth that happens during cooling like there is with steel). Google “does quenching harden copper”. It can harden some alloys, but crush washers are pure copper.

    As quality control, both before and after annealing, I would inspect for cracks or deep fissures and scrap the part if found. The part should definitely be resurfaced (finger on sandpaper) as a final step. No need to do this first, as annealing is important and will need cleanup regardless.

    That was a lot of words. In practice I could grab a washer, get it the dullest red in 30seconds with my MAPP, drop in a cup of water, and give a few licks on my glass plate with some 3M micro and be done in under 5min instead of waiting for the store to reopen tomorrow.

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