Chapter Fourteen - Frame Repair
I was not going to include this chapter with this book because of the lack of pictures. I have, however, decided to rework what I wrote in 1993 without pictures. There is a lot of frame repair information here and someone is bound to benefit from it in text form.
Before attempting any frame repairs, it is of the utmost importance to inform the customer that any frame repairs you do may nullify the factory warranty that came with the bike. Always advise the customer to check with his or her retail dealer where the bike was purchased before doing any cutting of metal and burning of paint. Also, performing some frame repairs may open up the possibility of lawsuits from the customer. With those things in mind, let's proceed.
Frame repair can be divided into two major categories:
HOT: Those repairs that require the use of the torch to disassemble and/or reassemble the damaged portions of the bicycle frame. Hot repairs will usually require that the frame be touched up or repainted.
COLD: Those repairs that can be done to the frame without the use of the torch. This means mostly realigning, coldsetting, and cutting, facing, and tapping. Cold repairs can nearly always be done without touch up or repainting.
With only a couple of exceptions, this chapter will cover primarily hot repairs. Most cold frame repairs can be done with the information provided in earlier chapters of this book. Another good information source for cold frame repairs is the frame and fork section of the Park Tool Manual.
Before proceeding, it has always been a policy of mine to take apart a joint COLD whenever possible. Too many novices rush to grab the torch to disassemble a joint on a frame. Using a torch to disassemble joints on brass brazed frames raises real problems; the remelt temperature of brass is always higher than the original melting temperature. There is a delicate balance of alloys in brazing alloys called the eutectic. When the brazing alloy is at the eutectic, it has the lowest possible melting temperature for that alloy. During brazing, trace elements precipitate out of the brazing alloy, so the brass that is added to the joint is different from the brass that is in the rod. Basically, the brass in the joint is more pure, because important impurities that were added at the factory are gone. EXAMPLE: The inverse would be: Pure water has a melting temperature of zero degrees centigrade. Add an impurity like salt and the melting temperature is lowered. This is why we throw salt on hiways in northern climates in the winter.
When a brass brazed joint is originally brazed, the experienced technician can stay just below the critical temperature of many steel alloys. Unfortunately, the novice often tends to exceed that critical temperature even on the initial braze because the critical temperature is not much higher than the melting temperature of bronze rod. (Brazing rod is actually bronze and only called brass by many people from habit.) The remelt temperature is slightly higher than the original melting temperature and even the experienced technician will exceed the critical temperature of the steel during the remelt.
Silver brazed joints can be taken apart HOT and put together repeatedly with no problem. That is because the melting and remelt temperatures of Silver solder are hundreds of degrees below the critical temperature of the steel.
TIG welded joints MUST be disassembled COLD in all instances because the parent metal and the weld bead are one and the same piece after the welding process.
Taking joints apart COLD means using cutoff wheels, die grinders, files, sandpaper, and other high-speed steel or carbide cutters to removed damaged metal. When these are used to disassemble joints, there is almost never a possibility of reaching the critical temperature of the steel. (In some instances, the edge of a saw kerf can get red briefly which could hit the critical temperature in a very localized area.)
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