dmm144j said:Hi,
I've got a copper head gasket in my '69 Commando. It's got about 1500 miles on it since put it back together and I wondered if it is necessary to re- torque the head?
Thanks/Mitch
hobot said:Its always good idea to anneal the ever loving hotter than red hot into the orange hot zone as clamp force and low heat+ vibration work harden it.
Since there is oxygen within the copper it can only be annealed (using flame heat) a few times before it becomes somewhat brittle. I don't rec. reannealing more than three times.
OXY/ACETYLENE TORCHES may give TOO MUCH HEAT. We do NOT REC. this method.
Heat the metal until it appears just dark red while in a dark location. More red or orange is not necessary. Ideally, a temperature of about 900d F is optimal. Let air cool. Once cool (in about five - ten minutes) brush with the"Scotch-Bright" pad on a flat hard surface to clean and flatten. A flaky post annealing residue is normal after annealing in air. Bright annealing in an inert gas oven is optimal and prevents this oxidation.
concours said:The answer is yes. That being said, I did my copper gasket retorque three times, never perceived any movement before clicking off. JFWIW
hobot said:Dear L.A.B. I don't post blunt statement unless I've lived em and can assure you the hotter ya get the copper the softer it remains on cooling,
hobot said:Well its sort of like reading the Bible, you can find passages to support what ever you like and same here, some say no need to anneal and other warn against over heating copper.
Again please try a anneal at dull red to bright orange and keep the results to your self but will know that effect better than right now. BTW this orange level also helped me get head banjo's sealed when no Al washers handy.
hobot said:Manufactures have many reasons for their advice not all of it based on actual practice or function.
There's nothing to be gained by heating copper gaskets more than a dull red in my opinion.
Annealing
Annealing the copper eliminates the dislocations so that the copper is once again composed of nice perfect crystals. This allows the copper wire to be reused since it is now soft and easily bent. Generally annealing is done at greater than 1/2 of the melting point on the absolute temperature scale. Copper melts at 1083C = 1356K so the annealing is done at greater than 678K = 405C = 761F. However, it will take a fairly long time at the lower end of the range so it is more common to anneal at about 700 to 800C. The copper can be worked and annealled many, many times for the purposes of bonsai since we really don't need extremely tightly controlled properties. The properties will degrade with repeated cycles for various reasons - oxidation being the most obvious.
The copper will maintain it's soft crystal structure after annealing at any realistic cooling rate (from very slow like letting fire die down to fast like throwing it in a bucket of water). Generally, I would suggest water cooling to prevent excessive oxidation of the surface. Steel (iron + carbon) on the other hand will change it's properties dramatically upon rapid cooling . However, it is possible to cool copper fast enough to make it into a brittle material. This normally involves cooling rates of greater than 10 million degrees C per second which can only be obtained by spraying a very thin film on to a very cold surface (this equipment is very expensive).
Copper just above its melting point keeps its pink luster color when enough light outshines the orange incandescence color. Copper that is glowing cherry red is at the correct temperature for annealing purposes
That's a bit of a climb-down from: "hotter than red hot into the orange zone"!hobot said:Copper just above its melting point keeps its pink luster color when enough light outshines the orange incandescence color. Copper that is glowing cherry red is at the correct temperature for annealing purposes
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Dances with Shrapnel said:Looks like Baghdad Bob from ministry of misinformation has struck again. Go with LAB advice- dull red and do not quench in water but let air cool. Quenching is taking you backwards- no surprise considering the source of that advice.
Retorque head after cool down of each heat cycle. Do not loosen first. Typicaly one ore two heat cycles with retorque should do it. You will reach a point where the fasteners will not torque any more and that is it.
Good luck with it and let us know how it goes.