Roughly five years ago, we ran a series on shaft rockers. That series explained why and how shaft work rockers work so well in race (and street-strip) applications. In that series we mentioned how Dan Jesel (www.jesel.com) pretty much invented the new breed of rockers: “In something like a small block Chevy application, the stock rocker has a relatively short pivot length. This means the arc it travels in is comparatively small, particularly in contrast to other pushrod engines (Jesel notes that a stock small block Chevy has a rocker pivot length of 1.45-inches. In comparison, a big block has a pivot length of 1.65-inches). What this all means is the stock small block rocker arm tip more or less scrubs across the tip of the valve as it opens. This isn’t much of an issue at lower gross valve lifts such as those experienced with stock or mild camshafts (such as those used in production engines). But when you increase the lift dramatically (as seen in today’s race engines) and simultaneously increase the spring pressure you’re soon faced with another quandary: An increase in friction.”
Essentially, the new Jesel shaft rockers were a means to improve upon the rocker geometry of a small block Chevy. The shaft rocker system wasn’t bound by the rocker stud location on the cylinder head, and it allowed Dan Jesel to move the rocker in a position on the head where it wasn’t scrubbing. Over the decades, that line of thinking expanded to function on all sorts of engines and all sorts of cylinder heads.
There was also a bit more to the equation: Replacing a conventional rocker setup/stud girdle combination saves a lot of work when you’re performing simple maintenance such as lashing the valves. Here’s an excerpt from that older series and it still holds true today: “Typically, the drill (valve lash) went like this: First you loosen the stud girdle, and then you lash the valves. The girdle is re-tightened and finally most folks check the valve lash once more. If the studs are the least bit out of alignment, tightening the stud girdle changes the valve lash. Not fun. But you also have to be extremely careful with clearances on some combinations – the rockers and girdle can touch, which obviously spells more (and bigger) trouble.”
Now that’s the backstory. Over the years, Jesel has refined their complete line of rockers considerably. They offer all sorts of combinations for an almost dizzying array of cylinder heads (as a sidenote, Jesel pretty much keeps in stock, a complete selection of sample heads from which they engineer and manufacture rockers). Many of those rocker combinations offer multiple options too. And one of the latest rocker combinations available from the folks at Jesel is the steel body Sportsman Rocker.
According to Jesel: “Jesel Engineers have combined all of the features of our Pro Aluminum Rockers with the durability of our Pro Steel Rockers. Jesel Sportsman Steel Rockers provide engine builders with the option of high strength steel rockers at an extremely affordable price and can be ordered separately or as an upgrade to certain Pro Aluminum rocker systems.”
“The Jesel Sportsman Steel Rockers are assembled with all of the proven components of our Pro Aluminum rockers. Featuring a 0.625" wide body with an ultralight slot to reduce weight and moment of inertia. They’re designed to be a direct replacement for the current Pro Aluminum bodies and will bolt to existing stands. Featuring a 0.360" wide non-needle valve tip roller and cup style tool steel adjuster, the rockers can be optioned with needle bearing nose rollers and ball style lash adjusters for high lift / high spring pressure applications. The rocker geometry is designed to minimize roller movement on the valve tip and each rocker body is manufactured from premium alloy steel. A through hardened heat treating process along with a black oxide coating will provide for years of dependable service and corrosion resistance.”
What didn’t change with the steel rocker option for the Sportsman rocker kits was the fact they allow for longer pivot length rockers, various rocker ratios, adjustable stand heights and they still incorporate easy to adjust valves that maintain lash adjustment, race-after-race.
Next issue, we’ll dig deeper into the Jesel Steel Sportsman Rockers. You’ll find the innovations are considerable. Watch for it and in the meantime, check out the accompanying slide show:
Click Here to Begin Slideshow
One of the major benefits found in the Jesel shaft rocker system is that design isn’t constrained by the rocker stud location. The stand locates the rocker, not the location of the rocker stud threads.
The way a rocker arm contacts (or scrubs across) the tip of the valve has a huge effect upon horsepower, efficiency and reliability.
The method to mount the rocker is important. Here, we’re setting up a shaft system on a Brodix big block Chevy cylinder head. We’ll dig deeper into this down the road.
The ultimate weight of the rocker arm is important, but there’s more to it than overall weight. Here you can see a 1.7:1 ratio Jesel Sportsman rocker for a big block tips the scale at 192 grams.
In comparison, a 1.7:1 ratio Jesel Steel Sportsman rocker weighs 246 grams. Mass Moment of Inertia (MMI) is likely more important, and we’ll look at that in the next issue.
