Light aircraft engines with power ratings under 100hp could receive type certificates in the US with single-ignition systems before August 1, 1941. After that date, all engines and aircraft had to receive certification with dual-ignition systems. However, aircraft and engines built prior to that date remained legal and are still legal today. Many other countries, especially in Europe, required all approved aircraft to have dual-ignition engines. The first development of dual-ignition versions of the smaller US engines, therefore, was for export. For the early HOAE developers, the ignition type is given explicitly in the following compilations. If the ignition type is not given, it can be assumed to be dual ignition, to the best of my knowledge. For the "Big Three", the only engines known to have single-ignition (as well as dual-ignition) versions are the Continental O-110 (A-40) and O-170 (A-50 and A-65 only); the Franklin O-150 (4AC-150) and O-170 (4AC-171); and the Lycoming O-145. This is described more fully in each compilation. In later years, engines for unmanned military applications (drones, etc.) were built with single-ignition systems with an M prefix in their designation; e.g., the Lycoming IMO-360. Modern engines for light and ultralight aircraft licensed in the Experimental category offer single-ignition versions in many cases. However, neither these engines, nor the aircraft, are eligible for standard US type certificates.
Generally, an engine designation for a specific version will have suffixes after the displacement. An example is the Lycoming O-235, which has or had versions such as O-235-C, O-235-C1, O-235-C1A, etc. on into the O-235-P series. Each of these suffixes denotes a different version, which may have specific applications (e.g. tractor or pusher); different equipment and accessories (e.g. starter types, propeller shaft configurations, controllable-pitch propeller configurations and manufacturers, tachometer types, carburetor types, ignition details, fuel requirements, fuel and vacuum pumps, etc.); and different drive mechanisms for each of these accessories. Reporting of these suffixes is beyond the scope of this compilation. The FAA type certificate data sheets (TCDS) at the FAA Web Site are a source of data for certified aircraft and engines. After entering the web site, select and click on "Type Certificate Data Sheets", and proceed from there to find what you are seeking.
The horsepower ranges and dates of production that are listed in the compilation are very broad and, for the dates, are somewhat approximate because they cover the many versions of a single engine series under a given type certificate. Moreover, cessation of production is rarely reported in the reference material. No attempt will be made to provide photographs of the engines. Photos are available in the references, on Websites, and in present-day magazines, if they are desired.
The prefixes and suffixes to O on versions of the basic engines are very fundamental and important. They are listed below as obtained from various reference sources. Many of them are defined in the Jane's All the World's Aircraft (e.g., the 1981-82 Edition). They can be combined in various ways, as appropriate, and are as follows: