It is sometimes easy to forget that after all the efforts a cam manufacturer makes in producing his products, the greatest cause of failure is not in the installation or its timing but in the first few seconds and minutes of its active life.
It’s a sobering thought but no matter how fine the surface finish or accurate the machining, inevitable imperfections - however slight - will lead to contact high spots at first run. Unless these are carefully ground Read more…
I don’t know about you but when I was young, my written command of the English language was, shall we say, a bit lacking. “Needs to pay more attention to his spelling,” was the end-of-year comment by one of my English teachers. But despite my best efforts - or possibly because of them - a future in the engineering professions seemed to beckon. I mention this because to me the best invention over the past 20 years or so has been the autocorrect option in wordprocessing software or the predictive text mode on my phone. Thus, when I Read more…
To be a good engineer, I have always maintained, in addition to an inquisitive mind and a grasp of the technology, you also need to be a student of history, for on many occasions the practices of the past give an insight into the possible problems of the future. And as all older engineers know, there is nothing like having been there the first time around to spot the problem when it next re-occurs, perhaps in another format. Read more…
The design of valve lift profiles can no longer be described as the sole province of the specialist engineer. Today we have many excellent software packages that will do just that without having to go anywhere near a polynominal equation or even think about things like ‘instantaneous radii of action’. Introduced to the precise geometry of the valvetrain, these will, with relative ease, output a profile within the constraints of jerk, acceleration and velocity. Once more, with the interactive nature of these programmes, all this can be achieved in a matter of hours rather than Read more…
As an engineer first, a motorsport enthusiast second and historian third, I welcome the recent upsurge in historic rallying. But whereas most journalists or writers would perhaps reflect on the sheer thrill of hearing the sound of a BDA reverberating through the forests, my particular recollection is listening to one particular example idling just before entering a service halt. To put it bluntly, it sounded like a bag full of hammers!
I’m used to listening to hot engines, and beneath the Read more…
High lifts or long durations are common features in high-performance camshafts, and when optimised can produce high engine torques over a useful but often limited range of engine speeds. The introduction of variable valve timing can widen this range of useful speeds, but at part load against a partially closed throttle, large valve lifts introduce pumping inefficiencies that are increasingly unacceptable in performance roadcar engines. Over the past decade, therefore, a multitude of variable valve lift concepts for spark-ignition engines have evolved. The simplest of these is the Read more…
The most common aspiration of just about all power unit engineers is that of greater engine performance. Better fuel economy, improved toxic emissions or simply better torque over a wider range of operating speeds - much of it but certainly not all - is down to the selection of the cam profile and its timing.
In the search for greater efficiency, compression ratios have increased in recent times, resulting in much smaller, Read more…
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. Read more…
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 later in the process or even years down the road. Read more…
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
