In a direct acting mechanical bucket tappet type valvetrain, the cam and tappet contact is responsible for most of the frictional losses. Since this contact operates primarily in mixed lubrication regime, it offers an opportunity for friction reduction tthrough hrough surface engineering among other things. Recently, there has been considerable interest in exploring friction reduction opportunities with laser textured surfaces. The implementation of friction reduction opportunities is important to achieve futu future re emission commitments and to meet regulatory requirements. In this investigation, tappet shims from a 3.0L cylinder head were laser textured. Mainly two types of textures were produced, (a) regular array of dimples of various sizes and spacing, and (b) discontinuous lines. The area density of laser texture varied from less than 1% to 21%. The friction characteristics of these surfaces were evaluated in a motored valvetrain rig using the current North American factory fill GF-4 engine oil. The result resultss showed very little, if any friction benefits over the production shims with dimpled surfaces whereas the discontinuous lines showed significant benefit over a wide camshaft speed range.
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