How do I find the build date of my engine?
I often get inquiries asking me to date a particular engine. Unfortunately, there is little concrete
information that helps us absolutely date a Lauson engine. To date, no one has found Lauson records
that correlate serial numbers to build dates, however through observing a large number of engines,
and the serial numbers of those engines, certain corollaries can be drawn.
For engines with a serial number of the form x-yyyyy where ‘x’ and ‘yyyyy’ are one and five digit numbers respectively and a dash separates them, an apparently accurate (to date) method has been suggested by John Newman, Jr. of Saint Louis MO. John postulates that the ‘x’ in a serial number of this form will represent the year in the 1940’s that the engine was built; so for example, an engine with serial number of 5-12345 would have a build date in 1945; an engine with a serial number of 7-23456 would have a build date in 1947; etc. serial numbers of this form are found on RSC and TLC model types. A few have occasionally been observed on several other model types, such as the RLC.
Most RSH and RSH era engines (such as TLH, PAH, RSV, 55S, 55A, 55AB, V, R, etc) engine tags seem to have a serial number of seven consecutive digits. It has been speculated that the first digit represents the year in the 1950’s. If this is true, an engine with a serial number such as 5310243 would have a build date in 1955. I have observed that the first two digits also (usually but not always) affords an plausible build date of 19xx. Were this true, the above serial number might represent the year 1953.
I can not begin to tell you how to accurately date an over head valve Lauson or an engine from the 1st generation design period.
I have compiled a chart to assist you in dating your engine by supplying ‘reasonable’ build ranges for the different Lauson models that were built. This chart is compiled from research I’ve done and the information comes from a variety of resources. I do not claim the chart to be entirely accurate, from time to time I uncover information that may allow me to “tweak” these dates a bit. It really is a “best guess” based upon the current information at my disposal.