Lauson Small Engines

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.

Overhead valve engines, cast iron block

ModelHPintroduction datewithdrawn dateComments
VA219291935Air cooled
VR219291935Like VA but water cooled with radiator
VW219291935Like VA but water cooled with tank, sold under 'alpha DeLaval" label
UA319331935Upgraded VA
UR319331935Like VA but different carburetor and head
UAS4 1/419331940Air cooled, upgraded UA
UW319331940Like UAS but warter cooled with pump
UWR419331940Like UA but water cooled with radiator
ZW5 1/219351937Water cooled with pump
ZWR?19351940Like ZW with radiator

1st generation design- L head engines, cast iron block

ModelHPintroduction datewithdrawn dateComments
RA1/219301933Air cooled washing machine
RAB1/219301933same as RA with battery ignition
RAU3/419301933Larger version of RA, suction carburetor standard, optional float carb
RAY119301941Larger version of RAU, float carb standard
LA1 1/219301935larger version of RAY
LW1 1/219331935Marine engine
LWR1 1/219331935Marine engine
LB219351945Replaced LA, air cooled
LBM219401945Air cooled marine version of LB, no governor
LF2 1/41935?Replaced LW, marine engine water cooled
LFR2 1/419351945Like LF but with radiator

2nd generation design- L head engines, cast iron block (with the exception of some millitary engines?)

ModelHPintroduction datewithdrawn dateComments
RLA3/419351945Air cooled, built for millitary?
RLB3/419351937Like RLA, washing machine
RLC3/419371951Civilian version of RLA? float or suction carb
RLE3/41937?Like RLA
RLM3/419401945Air cooled marine version of RLC
RSC1 - 1 1/219371951Larger version of RLC, suction carb or float carb
RSM1 1/219401951Air cooled marine version of RSC
RC1 1/219401951Water cooled version of RSC
RCM1 1/219401945Marine verison of RC, no governor
TLC2 1/419371951Larger verison of RSC, air cooled
TLM2 1/419441951Air cooled marine verison of TLC, no governor
PAC4 1/419441951Larger version of TLC, air cooled
PAX5 1/219441954Like PAC, external magneto
H24 1/419451957Oil test engine
PMM5 1/219481951Marine water cooled
LMC3/419481951Replaced RLC, air cooled
LMH119511958Upgraded LMC
LMV119511958Vertical shaft version of LMH
RSH219511960+Upgraded RSC, air cooled
RSV219511958Vertical shaft version of RSH
55S1 1/219511958Economy version RSH?, suction carburetor
55A219511958Economy version RSH?, float carburetor
55AB219511958Like 55A
PAH5 1/219511958Upgraded PAC
TLH319511960+Upgraded TLC
V1 - V15219511958Vertical shaft version of RSH, flush mount
P25 - P446 1/419531960+Upgraded PAX
TLV319551958Vertical shaft version TLH
R219561958Vertical shaft version of RSH, auxiliary horizontal PTO
CH171 3/419571958economy RSH, float carb, rectangular tank
CH20219571958like C17, cylinderical tank

3rd generation design- L head engines, alloy block

ModelHPintroduction datewithdrawn dateComments
SLV219541958air cooled vertical shaft
VA2 1/219561958SLV with larger bore

Chart of lauson Generations

The following chart is my attempt to show the linage of some of the more popular Lauson air cooled engines. It’s my best guess and is meant to give you a pictorial view of where your engine fits into the production period of the various air cooled engines Lauson produced.

Lauson Corp.--><--Lauson Company-><------ Lauson under Hart Carter control-----><-Tecumseh Power Div.->

- 1930 --------------------- 1940 ----------------1950 -------------------------------- 1960 ---->



              RLA ------------------|
  RA -------------- RLC ------------------- LMC -- LMH ------------------------------ Tecumseh H >
  RAB ---------/                                   \ LMV ---------------------------- Tecumseh V >
  RAU --------/


                                          /- RSC Goodall - RSH Goodall (RSH775) -|
  RAY ------------- RSC ------------------------- RSH ------------------------------- Tecumseh H >
                                                  55A -------------- CH20 ----------- Tecumseh H >
                                                  55AB ------------- CH20 ----------- Tecumseh H >
                                                  55S -------------- CH17 ----------- Tecumseh H >
                                                  RSV -------------- SLV ------------ Tecumseh V >
                                                                          \ VA(vert.) Tecumseh V >
                                                  V --------------------------------- Tecumseh V >
                                                  R --------------------------------|


  LA ----- LB ----- TLC ------------------------- TLH ------------------------------ Tecumseh H >
                                                  \ TLV ---------------------------- Tecumseh V >


VA --- UA --- UAS ----------|

                                           PAC - PAH ------ P-25 ------------------- Tecumseh HH>
                                           PAX -------------/
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