Difference between Unit Construction Engine, Cast Iron Engine and AVL LB

   
 

Difference Type

Cast Iron (CI)

AVL

Unit Construction Engine (UCE)

Notes

Engine Type

pre-unit construction engine

pre-unit construction engine

Unit Construction Engine

The CI and AVL engines came with a pre-construction unit which are actually three parts – The Engine, the gearbox and the Clutch cases. These are put together and connected to each other independently.

Maintenance

Disadvantage – Heavy

Disadvantage – Heavy

  

In the CI and AVL engines, we have to change oil in three places. Also the cost of gaskets which require replacement frequently.

Loss of power in transmission

High

High

Lower

Loss of power in transmission since this design is not as efficient as the modern engines. Loss of power is as high as 33% between crank shaft and rear wheel. For example – the CI and AVL engines were capable of producing 18 BHP at the crank but due to loss of power in transmission, this figure would go down to 12 BHP at the rear wheel. UCE engines on the other hand produce 19.8 BHP at crank and power is 16 BHP at rear wheel – hence the loss of transmission is close to 20%

Mileage

Low

Low

Higher

Due to high Loss of power in transmission, CI and AVL mileage is 30 to 35 kms per liter However due to the comparatively less loss of power in transmission, UCE can give 45 kms per liter.

Tappets

Solid Tappets

Solid Tappets

Hydraulic tappets

UCE Engine uses Hydraulic Valves.
Pressured oil drives the pushrods in the engine. Since the oil pressure remains constant for longer periods of time, the pushrods don’t cause the valve clearance to change. This results in consistent performance. When we ride hard, the valves in UCE can stand at least 18000 to 20000 kilometers before requiring any attention. The valves would not become loose. However in CI and AVL the solid tappets  would often become loose and require adjustment.

Oil Pump

Piston Type oil pump 1.2 Liters per minute @ 5500 rpm Bad Engine Cooling

Gear Driven Oil Pump 2.42 liters per minute @ 5500 rpm

Rotary Oil pump 9.5 liters per minute @ 5500 rpm

In the CI engine (with design dating from 1955) piston type oil pumps were used.
These oil pumps circulated about 1 liter of oil per minute at 5500 rpm. (This is almost half of the bullets oil capacity)
At 5500 rpm when the engine is reviving at it’s top, just one liter of oil was circulating to cool down the engine. This is termed as bad engine cooling. Due to this reason, older bullets were not considered for riding hard and fast however are considered as a steady 60 kmphs motor cycle. The CI engine came with floating bush big end. This would only work well as long as it immersed in oil. However 1 liter of oil per minute at the top was not good enough
In 1990s, Enfield approached the Austrian engine design firm AVL to made modifications to the existing CI Engines – the AVL engine was born. Advantage of AVL over CI
Better Oil Pump and Roller type Big End Bearing. The AVL engine uses a gear driven oil pump – capable of pumping double the oil per minute than the CI engine at 5500 rpm. – better engine cooling. Also the roller type big end bearing worked better than the floating brush. The UCE engine is the most advanced engine as of yet. Capable of pumping 9.5 liters of oil per minute. The UCE engine has a piston ring designs which eliminates blow by. A lower blow by means lessor oil getting wasted or lower crank case pressures.

Material

Cast Iron Barrel

Aluminum Barrel

Aluminum Barrel

The AVL engine was introduced as an aluminum block. This could do better heat dissipation. However was prone to train clatter as it muffled less sound. The AVL killed the soul of the Bullet – The THUMP. AVL engine was first launched with the bullet machismo, however people who loved the THUMP did not accept the Machismo. Even though AVL was a better engine than the CI.

De-compressor

Manual

Manual

Automatic

The UCE engine also has an auto de-compressor that sits on the ECU engines exhaust cam that makes starting easier

Cam spindle

Adjustable Cam spindle

Adjustable Cam spindle

Automatic Cam backlash prevention

UCE has an anti backlash system engineered into the cams, making sure that the cam backlash is kept to the bare minimum. This results in increased cam life as well as maintaining consistent engine performance even under hard riding. 

Primary Chain Tensioner

Missing

Missing

Automatic

The UCE engine has an auto primary chain tensioner that makes sure the primary chain has just enough tension to ensure best performance and less maintenance.

         

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