Numbers of cylinders Position of the engine Transmission Cooling of the engine Engine 2t or 4T.

• The optimum unit cubic capacity is approximately 250 cm ³

  If the cubic capacity decreases:
  Frictions increase compared to the provided power.
  Machinings become more delicate.

  If the cubic capacity increases:
  The filling becomes more problematic.
  Inertias limit the rise in mode.
  The sealing of the segments becomes more critical.

• The calculation of the number of cylinders becomes very simple:
  500/250 = 2 cylinders.
  750/250 = 3 cylinders.
  1000/250 = 4 cylinders.
  1250/250 = 5 cylinders.
  1500/250 = 6 cylinders.
  

• Why does one find twin-cylinders of 1200cm ³ and more?

  For certain marks (BMW, GUZZI, HD, Ducati), it is due to a tradition. For others it is related to a phenomenon of mode or copies of the preceding marks.
  The motor bike is in any event an irrational machine.
  We will note it by examining the following points.

Position of the axis of the engine

• Transversal(examples: Honda furnace, Triumph Bonneville, Ducati, Yamaha XJ, HD).

  It is the position currently most widespread.
  This solution is simplest for a drive chain or by belt.
  All the axes of rotation are parallel (engine, limps, wheel).
  That avoids the use of expensive gears with bevel gearbox: hypo ïof or conical.
  This solution is badly adapted to transmission shafting and cardan joint.
  In this case it requires the use of 2 bevel gearbox.

• Longitudinal(examples: Bmw, Guzzi, Honda St1100, Honda Gl).

  This provision is well adapted to a transmission shafting.
  It is the only practice for long engines.
  It has the disadvantage of causing a torque reaction at the time of the rapids assembled in mode.

• Why one finds engines transverse with transmission shaftings.

  Often it is about the evolution of a motor bike with chain towards a tree motor bike.
  Or the manufacturer does not have front-to-back engines in his range and it is necessary well to satisfy the " motards grandpas ".

Transmission (chain, tree, belt).

	Advantages.	Disadvantages.
Chain.	Good output. Economic design.	Expensive maintenance.
Tree.	Clean. No maintenance.	Expensive to manufacture. Rigid transmission.
Belt.	Flexible. Clean.	?

• Water

  It is the most rational system. It is also most complex, expensive and heaviest.
  It authorizes all the provisions of the engine without being concerned with flow of the air.
  The engine is less noisy.

• Oil.

  Let us not dream the radiators with oils cool only oil. If you want to test; make turn to the stop an engine " cooled " by oil.
  It is only one good complement of air cooling

• Air not forced.

  The air circulation around the cylinders imposes a provision on the engine.
  The twin-cylinders of the type BMW, GUZZI, put up well with this type of cooling. This can explain the survival of the twin-cylinders moreover 500cm ³
  The 4 cylinders pose problems for the cooling of the central cylinders.
  The twin-cylinders of the type HD have difficulties in ensure the thermal balance of the rear roll.
  This type of cooling is very simple, very light.

• Turbine.

  It is used little for the motor bikes. It equips or equipped scooters.
  I used a Lambretta scooter to climb the alpine collars without never overheating.
  I am unaware of why this solution is not used on our modern motor bikes. It is perhaps still a question of mode.

• 2 times.
  Today the engine 2 times is uses only for the small-engined cars and the motor bikes of cross-country race or trial.
  This engine is very simple and light. It requires a lubrication with lost oil.
  There is an explosion by rotation. What explains why with cubic capacity equalizes it is more powerful than an engine 4 times.
  The correct operation is dependent on a balance between the pressure of fresh gases and used gase.
  This balance is obtained by the bodies of admission and exhaust of the engine.
  Young friends when you arrange your pot and your carburetor you improve only the noise of your machine.
  The engine 2 times is pointed. It has only one good mode of operation.
  It consumes much gasoline (for the provided power) and oil.
  It consumes also candles.
  It is an attractive by its weak weight and its simplicity, but capricious engine to use.
  

• 4 times.
  

  More complex than the 2t with in more its distribution (valves, camshaft chains or belt of distribution). It is thus heavier, but also more reliable and better controllable.
  Oil remains under the combustion chamber. It is not burnt.
  The engine is more flexible.
  The noise is more pleasant.
  

• 2t 4t conclusion.

  From 125 cm ³ the engine 4 times is essential.