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Difference between revisions of "Harley-Davidson Flathead"
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==Advantages== | ==Advantages== | ||
Generally the flathead's valves are carried on one side of the cylinder. A chamber is recessed into the underside of the head to allow the poppet valves to alternately rise from their seats to admit the fuel-air mixture and for the exhaust gases to escape the combustion chamber. This has a number of advantages, primarily making the cylinder head much simpler, without the complex mechanism contained within the head of an overhead valve engine. The head of a flathead engine commonly consists of only a single piece of cast metal. | Generally the flathead's valves are carried on one side of the cylinder. A chamber is recessed into the underside of the head to allow the poppet valves to alternately rise from their seats to admit the fuel-air mixture and for the exhaust gases to escape the [[combustion chamber]]. This has a number of advantages, primarily making the cylinder head much simpler, without the complex mechanism contained within the head of an overhead valve engine. The head of a flathead engine commonly consists of only a single piece of cast metal. | ||
It also means a valve can be operated by pushing directly up on it, as opposed to needing some sort of mechanical arrangement to push it down or to drive overhead cams, as on a [[overhead valve|"valve-in-head"]] engine. It may also lead to slightly easier cooling, as the valves ([[pushrods]] are very seldom used, Indian motorcycles are an example) are out of the way of the cylinder, making a cooling jacket simpler to construct. (See limitation below.) The line of intakes along the side of the engine leads to the alternate name '''L-block''' (or '''L-head'''), due to the cylinders having the shape of an upside-down L. This configuration is also known as (Ford) sidevalve engine. | It also means a valve can be operated by pushing directly up on it, as opposed to needing some sort of mechanical arrangement to push it down or to drive overhead cams, as on a [[overhead valve|"valve-in-head"]] engine. It may also lead to slightly easier cooling, as the valves ([[pushrods]] are very seldom used, Indian motorcycles are an example) are out of the way of the cylinder, making a cooling jacket simpler to construct. (See limitation below.) The line of intakes along the side of the engine leads to the alternate name '''L-block''' (or '''L-head'''), due to the cylinders having the shape of an upside-down L. This configuration is also known as (Ford) sidevalve engine. | ||
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On the downside, the flathead also requires the airflow to make at least a 90-degree turn to enter the cylinder, which makes it less efficient, colloquially called poorer "breathing". Breathing was not greatly important for early production cars because engines could not run long and reliably at high speed, and most engines had poor combustion, so this was a minor concern given the benefits in simplicity. The maximum compression ratio is also low at only about 7:1, further reducing efficiency (although it means the engine can run on low-octane fuel). | On the downside, the flathead also requires the airflow to make at least a 90-degree turn to enter the cylinder, which makes it less efficient, colloquially called poorer "breathing". Breathing was not greatly important for early production cars because engines could not run long and reliably at high speed, and most engines had poor combustion, so this was a minor concern given the benefits in simplicity. The maximum compression ratio is also low at only about 7:1, further reducing efficiency (although it means the engine can run on low-octane fuel). | ||
The greatest advancements to flathead engine technology were developed in the 1920s through experimentation by Sir Harry Ricardo of Great Britain, who improved the performance and efficiency of flathead engines by intently studying their flow characteristics. He published his findings, and obtained patents, in 1927. Primarily, his '''Ricardo Head''' can be recognized on sight, because he moved the location of the exhaust valve farther from the center of the cylinder than the intake valve (they had previously been symmetrical). He also paid careful attention to the form of the intake and exhaust tracts cast into the cylinder block as regarded turbulence in the intake stream and within the combustion chamber. | The greatest advancements to flathead engine technology were developed in the 1920s through experimentation by Sir Harry Ricardo of Great Britain, who improved the performance and efficiency of flathead engines by intently studying their flow characteristics. He published his findings, and obtained patents, in 1927. Primarily, his '''Ricardo Head''' can be recognized on sight, because he moved the location of the exhaust valve farther from the center of the cylinder than the intake valve (they had previously been symmetrical). He also paid careful attention to the form of the intake and exhaust tracts cast into the cylinder block as regarded turbulence in the intake stream and within the [[combustion chamber]]. | ||
A more serious concern is exhaust, which often follows a more complicated path to leave the engine. This increases the tendency for the engine to overheat under sustained heavy use. It is sometimes possible to arrange the sidevalve engine layout so that the exhaust will be taken away through a valve and an exhaust tract located on the opposite side of the cylinder from the intake valve, in which case the layout is referred to as a '''T-block''' or '''T-head'''. American LaFrance famously powered their production fire engines with T-head motors from the 1920s to the 1950s. The [[Cleveland|Cleveland Motorcycle Company]] produced a four cylinder in-line motorcycle using the T-head configuration in the 1920s. | A more serious concern is exhaust, which often follows a more complicated path to leave the engine. This increases the tendency for the engine to overheat under sustained heavy use. It is sometimes possible to arrange the sidevalve engine layout so that the exhaust will be taken away through a valve and an exhaust tract located on the opposite side of the cylinder from the intake valve, in which case the layout is referred to as a '''T-block''' or '''T-head'''. American LaFrance famously powered their production fire engines with T-head motors from the 1920s to the 1950s. The [[Cleveland|Cleveland Motorcycle Company]] produced a four cylinder in-line motorcycle using the T-head configuration in the 1920s. | ||