From Moped Wiki
The head gasket is the gasket that goes between the cylinder block and the cylinder head. Head gaskets help this connection between cylinder and cylinder head seal. Thicker, or multiple head gaskets also serve to decrease compression.
Some moped engines, such as those found on Sachs mopeds, have cylinders permanently connected to the cylinder head. On these engines, there is no need for a head gasket.
Some mopeds are able to run without a head gasket. To run without a head gasket, the mating surfaces of the cylinder and cylinder head must be smooth and perfectly flat. Some tuners remove their head gaskets to increase the amount of compression on their engine.
Head gaskets can be made of metal, paper, or felt.
Head gaskets made of metals like aluminum or copper can be reused. Once removed, one technique for preparing these gaskets for reuse is to anneal them with direct heat. This softens them some, and allows them to compress again when re-installed between the cylinder and cylinder head.
NOTE: It is unclear if annealing is needed in all applications. There are no controlled tests to date that definitively proove the benefit of annealing. It is felt that annealing will allow copper to "deform" slightly to fill in the surface marks left by machining and to deform where a steel wire "O" ring has been placed around the cylinder bore. Annealing makes the copper soft. This may defeat your purpose if you are trying to optimize on head gasket streignth.
If our GWG P/5 gasket dressing is used we believe that annealing is not needed in most cases.
After the gasket has been worked to proper size it is ready for use. It may be necessary to re-anneal the gasket if it has work hardened. Annealing is a heat treatment that softens copper. The gasket may work harden somewhat if you have worked with it but it still should be soft enough for use.
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.