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Hydraulic tappets

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In the OE roadcar business, where noise and cost of ownership are major barriers to many prospective buyers, the hydraulic tappet has much to recommend it. But in the world of motorsports, where lightweight and efficient valvetrains are most desirable, their use is generally viewed with disdain - or so I thought until recently when, via the industry bush telegraph, I heard of a particular race team owner actually specifying hydraulic tappets in his latest engine. To recap, a hydraulic...

The domed tappet

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For anyone starting out on a clean-sheet engine design it is always worth remembering the notice at the entrance to the Sahara desert. The notice, or so I am reliably informed, says something like, "Choose your rut very carefully…. you will be in it for the next 500 miles!" And for those who have had the good fortune to design a totally new engine, such a warning can never be taken too lightly, because design decisions made in the early stages can often bite back on you much...

Split cams

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A few months ago, in May I believe, we looked at a variable duration cam made in two pieces. While this was a novel approach to optimising the airflow into an engine over a range of conditions, reader Reine Gustafson of AGAP in Sweden contacted me recently about another cam design idea. This too consists of more than one piece and, as you will see, is simplicity itself. Now there can't be a cam designer or engine builder who hasn't been confronted with this problem at times and who...

Hertzian stresses

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The surface of a camshaft or its associated follower can fail in a number of ways. Adhesive wear leading to abrasive wear, and corrosive wear, are perhaps the most common but another type of wear - surface fatigue - is sometimes perhaps harder to understand. Adhesive/abrasive wear tend to be lubricant-based issues. Poor lubrication or an incorrectly specified lubricant - it amounts to the same thing - will cause the oil film to break down under extreme loads, producing metal-to-metal...

Camshaft surface finish

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The complex interaction of components that represents the valvetrain operates in some of the most difficult tribological circumstances. With rapid changes in instantaneous direction between adjacent parts, and high contact stresses, the challenge of maximising the output of the engine while maintaining an acceptable level of reliability has never been more onerous. While it is true that the vast majority of camshaft wear takes place during cold start and warm-up, when the temperature of...