1953 - 1956
Series BN1 and BN2
This is of course the original Austin-Healey. It was built 1953-56, and although a big straight six-cylinder engine is usually associated with big Healeys, this model is the exception since it had a four-cylinder engine. The 100 - spoken as "Hundred" - came in two variants: the early BN1 Series cars (10,030 built) with a three-speed transmission, and the later BN2 Series cars (4,604 built) with a four-speed transmission, both with overdrive. After that there are not any significant differences within this model.
The transmission, whether three- or four-speed, is not a significant consideration for the occasional driver or show car. However, the three-speed transmission of the BN1 is somewhat weak and spare parts are rare. For these reasons many owners have either retrofitted a four-speed transmission from a BN2, or they have modified the original three-speed transmission by removing a shift linkage-blocking device, installed by the factory, and thereby obtained four forward speeds. Avoid a BN1 with a retrofitted four-speed transmission if you are looking for a car that is strictly original, and avoid one with an original three-speed transmission that has been modified to provide four speeds since these transmissions will often be the weakest and most in need of attention.
Therefore, the later, BN2 Series car is generally preferred for its reliable four-speed transmission. The BN2 also enjoys other advantages such as improved front wheel bearings, wheel hubs and brakes, all of which enhance reliability and maintainability relative to the BN1.
We should also mention here two special models made during the period in question: the 100S and 100M. The 100S is a racing model and is exceptionally rare (just 50 made) and expensive. It is not typically considered a beginner's first choice, and unless your budget is into six figures and you have very knowledgeable and experienced advice on the model readily available, do not even consider one for your first Austin-Healey. The 100M is a variant of the standard 100 with increased performance. It is a very desirable model, but due to much confusion and misinformation over what constitutes an authentic 100M, it is best that novices either not consider it, or get the advice of someone with much experience and knowledge of this model. There are many pitfalls here and many cars out there are promoted as being 100M models when in fact they are not. Caveat Emptor! (See also the discussion of the 100S and 100M in the Austin-Healey Resource Book.)
Upside: The beautiful clean lines of Gerry Coker's original design; the folding windscreen which, while not really very practical, still looks smashing on the show field when lowered into the "racing" position; the torquey low-end power of that big four banger; the raw sports car appeal of this simple, pure, initial example of the marque. Additionally, many professional dealers consider this to be the model with the most potential for increased future value.
Downside: No creature comforts to speak of; the side curtains flap and leak (just leave them off) and overall weather protection is not the best; some parts are hard to find due to age and relative rareness of this model.
Bottom line: This is the real and the original Austin-Healey, designed and produced as intended and unadulterated by corporate design committees or the whims of the marketing department. It takes perhaps some higher level of commitment to run a Hundred, but for those who seek a defining 1950s sports car it would be difficult to do much better.