YAMAHA KT100 CRANKCASE TYPES and SERIAL NUMBERS
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courtesy of Pete Muller - MULLER MACHINE People sometimes ask about the different types of crankcases on a Yamaha KT100 and the relationship to the serial numbers. Yamaha has used 3 different methods of manufacturing cases during the life of the KT100 :-
Sand cast cases are the oldest being used since about 1977 or so. Only the first few hundred KT100's produced had sand cast cases. They are generally characterised by a very dull, rough, sandblasted look. Permanent mould was used for all cases from around 1978 until about 1989 or so. These cases can be (and usually are) fairly shiny, with a bit of an "orange-peel" look to them. Pressure die-cast cases have been the only thing available since around 1989. They have a "slick" look to them, and are a bit lighter in weight than the earlier cases. Generally speaking, the permanent mould cases are the best. The material in these cases is denser and quite a bit more stable than sand cast or pressure die cast. Certain pressure die cast cases can be very porous. Be very careful with pressure die cast cases. Simply stamping a name or number in the top of a case can be enough to permanently distort a case. They are very soft, regardless of how they might look or machine. Make sure that the bottom of the cases are flat and that the top surface of your motor mount plate or adaptor is also very flat. Bolting a case to something that is not flat can result in some fairly significant distortion. Below, you will find a listing of the serial numbers that correspond to each type of case. Yamaha has sent cases to NZ with 3 different prefixes (787, 7U5, 7F6), and suffixes of either 5 or 6 digits. There may be cases around with other serial numbers such as "7MJ" prefix, but generally, the numbers listed below cover 99% of all the cases seen in NZ. SAND CAST 787-02xxx and 787-03xxx PERMANENT MOULD 787-04xxxx to 787-09xxx 787-100xxx to 787-103xxx 7F6-80xxx and 7F6-81xxx 7F6-080xxx, 7F6-081xxx 7F6-400xxx to 7F6-406xxx 7F6-500xxx 7U5-00xxx to 7U5-04xxx 7U5-050xxx to 7U5-056xxx 7U5-058xxx to 7U5-068xxx 7U5-100xxx 7U5-800xxx through 7U5-804xxx PRESSURE DIE CAST 7U5-805xxx through 7U5-813xxx 7U5-440xxx onward 7U5-500xxx to 7U5-519xxx 7MJ-000xxx onward
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