Shaft Rockers Series Part II


Last issue we took a long hard look at how the modern shaft rocker for the little Chevy was born.  Originally, gaining rocker ratio was a big part of the plan.  But a side benefit was the reduction in valve train friction.  Fair enough – the reduction in friction is huge, but that too isn’t the end of it.  As it turns out, shaft rocker systems also offer a considerable amount of stability at high engine speeds.  Again, using the familiar small block Chevy as the example, the pushrod, the rocker stud and the valve are not always in line.  This isn’t much of an issue with stock stamped rockers and low valve lifts.  The reason is the stock stamped rocker can more or less compensate.   A conventional stud mount roller rocker replacement cannot “fix” the misalignment.  The geometry can be (and regularly is) adjusted with a shaft setup.  That’s the reason why shaft rockers prove more stable at higher engine speeds.

It’s no secret that today’s engine speeds are on the rise, and much of today’s research is performed in conjunction with SpinTron equipment (basically, a high tech valve train “dyno”).  According to the folks at SpinTron, here’s the basics on how it works:  “The SpinTron employs a high-powered AC electric motor to spin the crankshaft and valve train of the test engine while an advanced laser camera is used to track the valve motion and pushrod behavior. The data is transmitted to a computer in the form of a bell graph. Unlike other test systems, the SpinTron gives you “live” results on your screen, plus comprehensive reports you can print immediately or store for later analysis.

“The valve train is arguably the most critical and sensitive portion of the engine. That’s why we developed our Laser Valve Tracking System (LVTS). With the LVTS, you can precisely identify, document and record crucial characteristics of the valve train such as valve bounce, lofting, spring harmonics, and pushrod deflection.

To use the LVTS, first create a baseline valve trace by tracking the valve at a stable engine speed (typically 2,000 – 3,000 RPM). Then increase the engine speed to the next RPM you’ve preset in the test set-up screen. The SpinTron will record and graph each new valve trace over the baseline trace. This will allow you to compare valve-train stability at various RPM, which is an ideal way to prove or disprove new products, theories and materials. The SpinTron will perform these tests at speeds from 500 to 20,000 RPM.”

This equipment allows companies such as Jesel to trace valve train movement at high RPM.  And with SpinTron’s LVTS (Laser Valve Train Tracking System), they can precisely identify, document and record crucial characteristics of the valve train such as valve bounce, lofting, spring harmonics, and pushrod deflection.

Today, engine speeds have increased, sometimes dramatically (no secret).  With the increase in engine speed, Jesel has had to re-think rocker technology, particularly for very serious engine combinations.  For example, the latest Jesel MoHawk setups are the benchmark when it comes to building a lightweight design rocker. Heavy rocker arms hinder high rpm levels but cutting calories on the rocker weight isn’t the complete answer. Jesel’s MoHawk Shaft Rockers are based upon careful engineering advances that actually stiffen the rocker while simultaneously reducing weight. The MoHawk is CNC-machined from 7068 alloy, incorporating an extremely rigid center beam layout. They’re available with Jesel’s proprietary J-Ball adjuster, which eliminates the need for a traditional adjuster cup in the body of the rocker. This arrangement provides for more adjuster thread, along with a thicker rocker body strap area under the shaft. Jesel offers several versions of the MoHawk:  For example, the MaxiHawk is designed with a big-bore shaft while the J2K LiteHawk incorporates a smaller shaft as well as a narrow 0.760-inch rocker body, that effectively reduces the weight to only 95 grams. All MoHawk rockers are fitted with Torrington shaft needle bearings, tool steel lash adjusters, clipped-pin nose rollers and billet steel stands. That’s not the end of it either:  Jesel offers options including shot-peened rocker bodies; there are several different lash adjuster variations available, you can specify a heavy duty 3/8-inch nose roller with needle bearing or a light 1/4-inch nose roller with needle bearing. Finally, Jesel’s MoHawk Shaft Rockers are available in a wide range of pivot lengths, ratios and offsets.

As you can see, rockers have come a long way since yesteryear, but we’re not done yet. Next issue, we’ll dig deep into “mass moment of intertia” as it applies to rocker arms.  There’s more here than you might think.  Watch for it.

Today’s rapid valve train development would not be possible (or at least as easy) if it wasn’t for this device. It’s a SpinTron. Basically, it allows a manufacturer to spin and electronically trace valve train components to high RPM (repeatedly).
SpinTron development has allowed companies like Jesel to create radical shaft rocker arm designs such as their very successful MoHawk series. See the text for more info.


Another place where high-speed development was a big help was in the case of rockers with considerable offsets (such as those found with many aftermarket symmetrical port heads). These offsets place extreme side loads on shaft rockers. Jesel solved this dilemma with their “Zero Thrust” upgrade.

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