Thermal expansion is indeed a factor to consider when designing cam chain tensioners for 4-stroke engines. The primary goal of a cam chain tensioner is to maintain proper tension in the cam chain throughout the operating temperature range of the engine.
To account for thermal expansion, both automatic and manual cam chain tensioners are designed with mechanisms that allow for compensation as the engine heats up. Here's a brief explanation of how each type of tensioner handles thermal expansion:
Automatic Tensioners: Automatic cam chain tensioners are equipped with a spring-loaded mechanism that applies tension to the chain. As the engine warms up and thermal expansion occurs, the tensioner compensates by automatically adjusting the tension to maintain the desired level. The tensioner is designed to respond to the changes in chain length caused by thermal expansion, ensuring optimal chain tension under varying temperatures.
Manual Tensioners: Manual cam chain tensioners require periodic adjustment by the user. When initially installed, the manual tensioner is typically set with some slack in the chain to allow for thermal expansion. As the engine heats up, the chain expands, and the user must manually adjust the tensioner to take up the slack and maintain the proper tension. This adjustment is typically done when the engine is at operating temperature to ensure that the tension is set correctly for the expanded chain length.
In both cases, it's crucial to consider the specific thermal expansion characteristics of the materials used in the engine components, including the cam chain itself, the tensioner mechanism, and the engine block. By accounting for the anticipated thermal expansion, engineers can design tensioners that maintain the appropriate chain tension throughout the engine's operating temperature range, thereby minimizing the risk of chain slack or excessive tension.