| Hey everyone, I want to introduce an article I wrote in collaboration with Wiseco where I discuss piston wear and replacement. I think you'll find it useful because it will give you an idea when pistons should be replaced and how they wear. Check it out below! The piston in an internal combustion engine is arguably one of the most important components found in the engine. When it comes to high-performance engines used in powersports applications it is also a component that is regularly replaced and serviced. Knowing when your piston should be replaced and how it wears is key to maintaining a reliable engine. In this article we’re going to discuss replacement intervals, piston wear, why it’s important to replace the piston, and piston replacement options. |  |
Piston replacement intervals are typically outlined in your machine’s factory service manual. Using dirt bikes as an example, many manufacturers outline a piston and ring replacement schedule of every six races or 15 hours for a four-stroke powered machine. If you’re new to the sport or have never looked at your factory service manual these service intervals may seem shockingly short. The service intervals are based on the service schedules required to maintain a factory level racer’s machine. Unfortunately for the average rider more often than not the outlined service intervals end up being conservative. In reality, piston replacement intervals should be established based on how the individual owner rides and maintains their machine. Engine displacement, engine make, air filter maintenance, environmental conditions, riding style, and the type of riding the machine is used for will all have an effect on how long the engine should be operated before servicing it. Monitoring the engine’s health through periodic checks such as compression and leak down tests is the best way most riders can appropriately time major service tasks such as piston and ring replacement. Due to the number of variables that affect engine wear it is simply not possible to specify a replacement schedule that fits everyone’s needs other than a very conservative schedule.
Piston wear will typically occur in four key areas for both two and four-stroke engines which include the piston skirt, wrist pin bore, ring grooves, and piston crown. The next time you disassemble your top end keep an eye out for these wear points.
Piston Skirt Wear - The piston skirt is the portion of the piston that gives it its cylindrical shape. Nowadays on four-stroke engines, the piston skirt is very short and limited to the major and minor thrust faces of the piston. For reference, the thrust faces typically correspond with the intake and exhaust valve sides of the cylinder head. Two-stroke pistons use the same nomenclature but feature much longer more pronounced skirts.
Piston skirt wear occurs because of the thrust loading that results from the inherent geometry of the crank mechanism as the engine fires. Peak combustion pressure occurs slightly after top dead center which causes the piston to thrust into the cylinder wall.
Piston wear will typically occur in four key areas for both two and four-stroke engines which include the piston skirt, wrist pin bore, ring grooves, and piston crown. The next time you disassemble your top end keep an eye out for these wear points.
Piston Skirt Wear - The piston skirt is the portion of the piston that gives it its cylindrical shape. Nowadays on four-stroke engines, the piston skirt is very short and limited to the major and minor thrust faces of the piston. For reference, the thrust faces typically correspond with the intake and exhaust valve sides of the cylinder head. Two-stroke pistons use the same nomenclature but feature much longer more pronounced skirts.
Piston skirt wear occurs because of the thrust loading that results from the inherent geometry of the crank mechanism as the engine fires. Peak combustion pressure occurs slightly after top dead center which causes the piston to thrust into the cylinder wall.
