In the previous article on rocker stands, and as a general theme to the subject of pushrod valvetrains, the importance of stiffness was stressed. Also important though is that the mechanism is set up on the engine as intended when designed.

This means that the relationship between the tip of the valve, the roller tip and rocker pivot are as designed. Not only does a badly set-up mechanism deviate away from the designed valve lift profile, but the relationship of the Read more…

The previous rockers article in RET-Monitor looked at the important matter of component stiffness; with the advent of the now widely used Spintron testing, engineers began to see the value of increased rocker stiffness when considering the ability of the valvetrain to remain under control.

The same reasons that pushed people along the development path of increased pushrod stiffness also led Read more…

For those who have no interest in pushrod engines in racing, their criticism of categories such as NASCAR, and the engines used, revolves around a perceived lack of technology. The regulations for the Sprint Cup series in certain areas don’t help dispel this perception, mandating flat-faced lifters to be used in bespoke race engines when all modern pushrod production engines have turned to using roller lifters. In racing too, where choice of roller type isn’t restricted, the flat lifter is generally shunned in Read more…

The pushrod, or overhead valve (OHV), engine has a lot to recommend it in terms of packaging, although it achieves this at the expense of much valvetrain stiffness compared to an overhead cam (OHC) mechanism. One of the least stiff members in the pushrod valvetrain is the pushrod itself. Owing mainly to space constraints, but also possibly to mass targets in a smaller regard, the pushrod is a long slender component whose stiffness can dominate the dynamic behaviour of the whole valvetrain system. Read more…

The pushrod valvetrain, while having great advantages for engine packaging, has the distinct disadvantage of not having a very direct connection between cam and valve, as is the case with overhead cam (OHC) engines. Even in the case where finger followers with roller bearings are used, the stiffness of the system is higher than is typically the case with an overhead valve (pushrod) system. As has been stated in previous RET-Monitor articles on pushrods, efforts are always being made to enhance the stiffness of the components in Read more…

Rockers are a critical element in the valvetrain of any overhead-cam engine, and so we should not be surprised to find that their development continues to be the subject of much activity in racing circles. Much of the racing in the US, for example - including the incredibly popular NASCAR categories and their various ‘feeder’ series - is based on engines using the overhead-cam (pushrod) valvetrain.

In recent years, NASCAR has allowed the various Read more…

In the RET magazine Focus article on pushrod valvetrains (issue 45, March/April 2010), we looked at the effect of flat tappets in limiting the lift velocity of a direct-acting cam on a lifter. The limitation is exactly the same as that in direct-acting overhead camshaft engines. Textbooks on the subject tell us that the distance of the cam-to-lifter contact from the axis of a flat tappet is proportional to the lift velocity of the cam profile. The exact relationship is shown in mathematical form in the RET article. Read more…

When we look at the offerings from the major pushrod manufacturers, we see that there are many who offer assembled pushrods made from multiple pieces - usually three - with a typical race pushrod consisting of a long, slender central section combined with two ends which are assembled into the central section. Dieter van der Put, in his recent article looked at a method of producing a single-piece pushrod from three pieces, using the process of friction welding. Read more…

After having written in my previous article about process control issues, something occurred to me about the differences between engine applications. In general, RET-Monitor and Race Engine Technology magazine put an emphasis on high-performance engines. This often means also high-revving engines, due to the simple assumption that the easiest way to make power is make use of high rpms.

What came to mind is what this statement means in Read more…

In previous articles about pushrods, several designs have been discussed and explained. And although in these articles the developments, manufacturing and control processes are said to have matured over the years, there are still many race series worldwide where top-end pushrods are not used.

Often the reason is product cost. These race series rely on performance parts that are not as sophisticated as the high-level series, or not even production Read more…