Скачать или смотреть This Tiny Engine Part Changed Everything - Flathead vs OHV vs OHC!

Combustion engine valvetrains have evolved over time. While flathead and overhead valve designs were more popular in the past, most modern engines run overhead cam designs.
Sponsored by Mobil 1 – https://www.mobil.com/en/lubricants/

Three common combustion engine valvetrain designs are flathead, overhead valve (OHV), and overhead cam (OHC). Many older cars have engines with flathead or overhead valves, and these designs also tend to more commonly used flat tappets for actuating the valves. Flat tappets place a unique demand on the engine and engine oil, as this is a high heat, high pressure, high shear stress location of the engine. Without an oil film, you’d have the quickly moving metal of the camshaft sliding against the relatively stationary tappet – a recipe for lots of wear. To combat this, oil additives like ZDDP can be used to minimize wear, by creating a sacrificial layer that wears instead of the cam and tappet. That’s why Mobil 1 Classic, formulated for classics and collectibles from 1951-1996, has more ZDDP than modern engine oils, to help avoid the unique wear challenges of older engines.

Modern engines take advantage of roller tappets, which allow for more aggressive cam profiles, and they require less ZDDP in the oil, because the rollers reduce friction between the cam and tappet. Check out the video for all the details on how engines and engine oil demands have evolved over time.

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