Nokas: Verskil tussen weergawes

Afhangende van die ligging van die nokas, kan die nokke die kleppe direk aandryf of indirek deur verbindingstange. Direkte aandrywing behels 'n eenvoudiger meganisme met gevolglik minder bewegende dele wat minder falings tot gevolg het, maar dit vereis dat die nokas aan die bokant van die silinders gemonteer moet word. Die oorhoofse montering van die nokas is deesdae 'n algemene verskynsel in moderne enjins. Sommige enjins gebruik twee nokasse, een vir die inlaat- en een vir die uitlaatkleppe. So 'n rangskikking staan bekend as 'n ''[[Dubbele oorhoofse nokas]]'' {Engels: Dual overhead cam (DOHC)}. 'n [[V-enjin]] kan dus soveel as vier nokasse hê.

 

 

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Sliding [[friction]] between the surface of the cam and the cam follower which rides upon it is considerable. In order to reduce wear at this point, the cam and follower are both [[surface hardening|surface hardened]], and modern [[lubricant]] [[motor oil]]s contain additives specifically to reduce sliding friction. The lobes of the camshaft are usually slightly tapered, causing the cam followers or valve lifters to rotate slightly with each depression, and helping to distribute wear on the parts. The surfaces of the cam and follower are designed to "wear in" together, and therefore when either is replaced, the other should be as well to prevent excessive rapid wear. In some engines, the flat contact surfaces are replaced with rollers, which eliminate the sliding friction and wear but add mass to the valvetrain.