Whats in a name?
(or, What do all those letters mean?)
The letters and numbers used to name the
Single Cylinder Engines Originally, these all started with the letter A (AB, AE, etc). The second letter told the bore the AA had a 2-1/2 bore, AB 2-3/4, AK 2-7/8, AD 2-3/4 (but different stroke), AE - 3, AF 3-1/4, AG 3-1/2, AH 3-5/8. Some motors had a third letter S added, to mean High Speed, and therefore higher horsepower (AKS). The S was later dropped and all the motors were sold as high-speed versions.
A third letter H was added to the larger engines (AD, AE, AF, AG, & AH) when the governor was changed to an internal flyweight type making them AEH, etc. Similarly, when the smaller motors were upgraded for higher compression, a third letter N was added ABN, AKN.
new series of motors was introduced in the late 1950s, they retained the final
N, presumably because they ran higher compression (ACN, BKN, AEN, AGN). The second letter still indicated the bore of
the engine. Note the B in BKN
On any of these, the letter D might be added to the end, meaning stellite (heavy-duty) exhaust valves and sometimes exhaust valve rotors (AENLD). A leading M (MAENLD) meant a military version, with radio-shielded spark plugs and other changes to make it acceptable to the Armed Forces. A trailing M (AEM) meant a marine (boat) version. These typically had a spark arrestor on the carb, a shielded exhaust, and a forward-neutral-reverse transmission. A leading H was a vertical-shaft engine (HACN). Motors with a long enough production run had numbers added to signify minor upgrades like dry (paper element) air cleaners and recoil starters (AENL3).
The next round of designs went to a completely different style of names S-7D, S-8D, S-10D, S-12D, S-14D, TRA-10, etc. The S was the standard engine, while the TR was an engine set up for use on a tractor (a small tractor, one presumes). There was no difference in the basic engine that I could tell, only in air cleaner set ups, accessories and such. The number indicates the approximate horsepower of the engine (S-7D = 7 hp). The D still meant stellite exhaust valves.
Two Cylinder Engines These engines started with the TE & TF. The T meant twin cylinder, the second letter represented the bore (again, E meant 3 and F meant 3-1/4). Later, the THD came along, with the same bore & stroke as the TF but with different bearings and different head/jug design in line with the VH4. I can only guess what the H stood for heavy duty, perhaps? Later still came the TJD with the same bore & stroke, but different firing order & almost all different parts. In this case, the J seems to simply have been the next letter after H. On all four of these models, the D meant stellite exhaust valves. These too came in military versions (MTHD) and marine (boat) versions (THM).
In-line Four Cylinder Engines These all started with the letter A. The second letter was the bore size, and was followed by the number 4 (AC4). These too came in a military version (MAC4). Some were built with iron pistons instead of aluminum, and were labeled with a trailing I (AC4I). There may have been D versions (with stellite exhaust valves) of these as well, I am not sure.
V-4 Engines All of these engine names start with the letter V, representing the cylinder configuration. Early models used the same series of letters to represent the bore as the single cylinder engines did (VE4 had a 3 bore, VF4 had a 3-1/4 bore, etc.). The third character was a 4, for 4-cylinder. The introduction of the engines that replaced the original V4s but had the same bore resulted in the names VM4, VP4, etc. The middle letters in these seem to be simply a matter of expedience the new models needed new names, and these letters had not been used in the past (this is purely conjecture on my part). The introduction of overhead valve V4 engines signaled a new series of names, incorporating the letters V4, and a number suggesting the horsepower rating of the motor (V461). The trailing D again meant stellite exhaust valves, and the leading M means military (MVH4D).
about the WI engines? My understanding is that these were built in