The classic Harley-Davidson engines are two-cylinder, V-twin engines with the pistons placed at a 45 degree angle. The crankshaft has a single pin, and both pistons are connected to this pin through their connecting rods. This design causes the pistons to fire at uneven intervals. On the V-twin, the sequence is as follows: the first piston fires (this is the 0° position) the other piston fires at 315° into the stroke there is a 405° gap (as both cylinders go through their exhaust stroke) until the first piston fires again This design, which is covered under several United States patents, gives the Harley-Davidson V-twin its unique "potato-potato" sound. On 1 February 1994, the company filed a trademark application for the distinctive sound of a Harley-Davidson motorcycle engine: "The mark consists of the exhaust sound of applicant's motorcycles, produced by V-twin, common crankpin motorcycle engines when the goods are in use". Nine of Harley-Davidson's competitors filed comments opposing the application, arguing that cruiser-style motorcycles of various brands use a single-crankpin V-twin engine which produce a similar sound. These objections were followed by litigation. After six years, Harley-Davidson withdrew their trademark application.
Harley model designations are a sequence of letters and numbers, combined in limited ways. The sequences can be long, as in the 2006 model designation FLHTCUSE.The first letter may be one of the following:E, F, J, U, V (Big Twin), D, G, R, W (Small Twin), X (Sportster), or V (VRSC) Letters are appended singly or in pairs, as follows:B (Belt Drive), C (Classic or Custom), D (Dyna Glide), DG (Disk Glide), E (Electric start), F (Fat Boy (1990-present) or Foot-shift (1972 and prior)), H (High compression), L (Hydra Glide forks), LR (Low Rider), P (Police), R (Race or Rubber-mount), S (Sport or Springer), SB (Single belt final drive), ST (Softail), T (Touring), WG (Wide Glide), I (Fuel injection), SE (Screamin’ Eagle), U (Ultra) Custom Vehicle Operations models can also have a number (2,3,4) added.Note that these conventions for model designations are broken regularly by the company.
