In the early days of the motorcycle, performance increases were dramatic. As with any current or recent technology, the designers and engineers constantly look for improvements to their products. In the case of the early motorcycles, engine performance was extremely important and not just in out-and-out power, but also in reliability and economy.

For the most part, engine performance increases typically came about by trial and error.

Manufacturers would attempt to increase their engine's performance by increasing the compression ratio (for example), when the piston broke a new design would be incorporated to cope with the increased loads and heat generated. (Note: very early machines used steel pistons before aluminum items were developed to reduce the reciprocating mass and to better dissipate the heat generated.)

Leading the development of the early engines was the need to compete in competition events such as board track racing in the US, or reliability trials elsewhere. With the general public's lack of knowledge regarding motorized bicycles of early motorcycles, the manufacturers chose competition events to showcase their wares. When power equaled results (as seen in board track racing for the most part) engineers worked constantly to improve the engines, it could be argued that competition involvement was the R & D (research and development) of the early manufacturers.

Major Engine Changes

At the turn of the 1900s, two distinct types of engines were prevalent: 2-strokes with piston porting, and 4-strokes based on the Otto cycle design.

                                                                2-strokes

The first 2-stroke was invented by Sir Dugald Clark in 1881. The Clark design, however, called for valves and a compressor to force mixture into the engine, whereas the 2-stroke engine known today was invented by Englishman Joseph Day. The Day design had flap valves in the inlet port and one on top of the piston (side transfers were not initially used). Approximately 250 examples of this engine were made.

An employee of Day's, Fredrick Cock, modified the design by allowing the piston to control the opening and closing of the inlet and exhaust ports which, along with the introduction of transfer ports, gave us the design of 2-stroke common from the early 1900s onward.

Major design changes to the 2-stroke engine have included the following:

Piston porting (as detailed above)

Cross-flow scavenging

Heads and pistons reshaped to afford loop-scavenging

Carburetor mounting position changes (cylinder side, cylinder rear, cylinder front and crankcase)

Multiport cylinders

Expansion chamber exhaust added

Water cooling

Oil injection

Fully electronic ignition

Variable exhaust port timing

Read valving

Disc valve induction

Electronically controlled carburation jet settings

Electronically controlled variable exhaust port timing

                                                              4-Strokes

Nicolaus Otto is generally credited with inventing (in 1876) the 4-stroke engine. Even today, 4-stroke engines found in any automobile are said to be based on the Otto cycle design. But taking that rudimentary design and turning it into the fire breathing engines we have become so familiar with took many years of development.

Major design changes to the 4-stroke engine have included the following:

Piston material changed from steel to aluminum

Valve positioning changed from side valve, to inlet over exhaust, then to overhead

Camshaft position changed from crankcase, to cylinder to head positioning

Compression ratios increased from 5:1 (side valve Harley Davidson) to 14.5:1

Main bearings changed from ball type to shell

Rings changed from twin scraper to two compression and one (made up of three parts) oil control ring

Valve materials changed from steel, to stainless steel, to titanium with various coatings (ceramic, for example)

Air cooled, to water cooled, to a combination of oil, water and air cooling (Suzuki GSX, for example)

Single cylinder to eight cylinders (engines with eight or more cylinders have been produced but no sold commercially)

Straight pipe exhaust systems to megaphones, to canister mufflers with tunable baffles

The above list details most of the major design changes on the two main engine types, but in addition, all of the associated components on motorcycle engines have undergone development from the early designs. These include carburation systems and electrical systems.