Tuesday, September 23, 2014

Motorcycle Engine Power

 

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Motorcycle engines produce a lot of power for their weight. Part of the secret lies in high engine speeds.

A truck engine produces peak power at about 2,500 rpm and a car engine at about 6,000 rpm, but modern 4 stroke motorcycle engines develop peak power at up to 15,000 rpm or more. So the circulating oil comes under huge thermal stress as it transfers heat away from low mass components under high power conditions.

Compact multi-cylinder, multi-valve engines use complex oil circuitry with narrow oil ways. The oil needs to keep flowing hot or cold. High piston speeds and power out-put generate very high temperatures with not many places for that heat to go. So the oil plays a crucial cooling role, which demands oils with high thermal stability.

Deposits can build up on the pistons and rings. After a while these can cause increased wear and reduced compression. When the engine is working hard oil temperatures rise rapidly.

Poor quality oil can vaporise leading to a rapid rise in oil consumption and a fall in protection. And all the while the oil is carrying combustion by products and wear metals into the sump and filter. Over time this leads to the oil becoming increasingly contaminated and less effective.

Today's demand for extended service intervals means that the oil has to remain effective in the engine much longer, for up to a year between changes. That's critical because motorcycle engines contain less oil than trucks or cars and work it much harder.

Car engines have 3 separate zones -- the engine, the clutch and the gearbox. The clutch is dry, while the engine and gearbox use their own specific oils. But most 4 stroke motorcycle engines use a wet clutch and the lubrication system is combined so that all these zones -- engine, gearbox and clutch rely on the same oil.

One oil to do 3 different but equally important jobs.

 

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