Motorcycles with 4-stroke engines are known for their reliability, effectiveness, and smooth running. However, motorcyclists may occasionally see smoke coming from the exhaust, raising questions regarding engine health and performance. In this article, we will try to find out the reasons why a 4-stroke motorcycle engine gives smoke.
Before finding the causes of smoke in 4-stroke motorcycles, let’s take a quick look at how these engines work. In one cycle, a 4-stroke engine completes four different phases: intake, compression, power, and exhaust. The piston travels downward during the intake stroke, sucking in a combination of air and fuel. The compression stroke that follows boosts the pressure of this mixture, which is subsequently ignited during the power stroke. Finally, the combustion byproducts are expelled through the exhaust valve during the exhaust stroke. Typically the followings are the most common reasons why a 4-stroke motorcycle engine smokes.
Burning Engine Oil
Worn Piston Rings
Valve Seals & Seats
Rich Fuel Mixture or a bad air filter
Burning Engine Oil:
The burning of engine oil is one of the leading causes of smoke in 4-stroke bikes. Engine oil is essential for lubricating and decreasing friction in the engine’s moving components. If the oil leaks into the combustion chamber, it might combine with the air-fuel combination and burn during the power stroke. As a result, smoke is released from the exhaust, which is frequently blue in color.
Worn Piston Rings:
Piston rings create a seal between the piston and the cylinder wall, keeping combustion gases from escaping from the combustion chamber. These rings can wear out or get broken over time, enabling oil to enter the chamber. During the combustion process, this oil burns with the air-fuel combination, resulting in smoke emissions. Usually, this occurs due to heat up or excessive pressure on an engine that rings may get broken and oil may enter the chamber. Fake Engine Oils are the biggest culprits of engine heat-up.
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Valves Seals & Seats:
Valve seals are in charge of keeping oil out of the combustion chamber via the intake and exhaust valves. When these seals weaken, oil can seep through, causing smoke to be produced. If the valve seats are not up to the mark, they can also cause this issue. Usually, if a cold engine smokes then it is caused due to valve seals and seat issues.
Rich Fuel Mixture or A Bad Air Filter:
A rich fuel mixture has a more fuel-to-air ratio than the ideal proper ratio. While a richer mixture may provide greater power, it may also result in incomplete combustion, resulting in unburned fuel particles exiting the exhaust as smoke. The color of unburnt fuel is black and they are the unburnt carbon deposits. If the air filter is not cleaned for a long time, it also causes smoke issues. Black smoke is also caused due to a choked air filter.
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Riders should do routine servicing and follow the manufacturer’s suggested service intervals to address smoke concerns with 4-stroke motorcycles. Checking the engine for oil leaks, worn piston rings, and broken valve seals on a regular basis will help avoid smoke issues in Four-stroke motorcycles.