Yamaha KT100 - Serial numbers relating to case type

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Occasionally the question comes up about which Yamaha KT-100 cases are considered good ones and which are not.
Yamaha has used 3 different methods of manufacturing cases during the life of the KT-100. I call these:

Sand cast cases are very old... I'd guess them to be circa 1977 or so. Only the first few hundred KT100's that came into the U.S. had sand cast cases. They are generally characterized by a very dull, rough, sandblasted look.

Permanent mold (aka: gravity cast permanent mold) was what all cases were from around 1978 until about 1989 or so (I could be off a year or two). 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, satin-finish look, and are a bit lighter (in weight) than the earlier cases.

Generally speaking, the permanent mold cases are the most desirable. The material in these cases is denser and quite a bit more stable than sand cast or pressure die cast. (Click here to see a side by side weight comparison: newer die-cast on the left, permanent mold on the right)

Certain pressure die cast cases can be very porous. I've seen some pressure die cast cases that are almost "sponge like".
Be very careful with pressure die cast cases... they are simply not very strong. 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. Make certain that the bottom of the case is very flat, and that the top surface of your motor mount plate or adapter is also very flat. Bolting one of these newer cases to something that is NOT flat will result in some fairly significant distortion.

Below, you will find a listing of the serial numbers that correspond to each type of case. Please note that the "x" is a place holders. Yamaha has sent cases to the USA with 3 different prefixes (787, 7U5 & 7F6), and suffixes of either 5 or 6 digits. There may be cases around with other serial numbers, but the numbers listed below cover 99.9% of the many thousands of cases that have passed through my shop over the years.


 787-02xxx and 787-03xxx
 787-04xxx to 787-09xxx
 787-100xxx to 787-103xxx

 7F6-80xxx and 7F6-81xxx
 7F6-080xxx, 7F6-081xxx
 7F6-400xxx to 7F6-406xxx

 7U5-00xxx to 7U5-04xxx
 7U5-050xxx to 7U5-056xxx
 7U5-058xxx to 7U5-068xxx
 7U5-800xxx through 7U5-804xxx (and a few of the first 7U5-805xxx cases)
 7U5-805xxx to 7U5-813xxx
 7U5-440xxx to 7U5-458xxx 
 7U5-500xxx to 7U5-519xxx
 7U5-200xxx to 7U5-201xxx (current production is 201xxx as of November 2011)