Camshaft Surface Temperatures in Fired-Gasoline Engines

The authors measured camshaft surface temperatures in two different gasoline engines: a Ford 2.3-liter overhead-camshaft engine with finger-follower and an Oldsmobile V-8 5.7-liter engine with rotating tappets and pushrods. Using unique surface thermocouples in the cam-lobes, we found that maximum cam-lobe temperatures occur at the cam-nose and increase linearly with speed and oil temperature. At high speed, the rotating tappet produced lower temperatures than the finger-follower. In addition, at maximum speed the cam-lobe temperatures in the ASTM Sequence V-D and MID tests were similar--200°C. The similarity in these surface temperatures explains why both engines require similar zinc dithiophosphates (ZnDTP) for wear control. The surface temperature controls the surface chemistry.