What do roller rocker arms do

This also explains why larger or stiffer pushrods that weigh more than stock pushrods have minimal effect on valvetrain momentum. You want stiffer and stronger pushrods for reliability and valvetrain stability, especially with higher valve spring pressures in a highly modified high revving engine. Steel can safely handle a lot of valve spring pressure, up to pounds or higher say the people who make such rockers.

By comparison, the typical economy diecast aluminum rockers should not be used with more than to pounds of open spring pressure depending on the brand of rocker.

Extruded aluminum rockers can usually handle up to pounds of open spring pressure, with some rated for as much as pound springs. Always go by what the rocker arm manufacturer says their arms can safely handle.

Something else to pay close attention to when choosing rockers is the design of the rollers and needle bearings. More needles in the center bearing is better because it spreads the load over a larger surface for improved durability.

The rollers on the tips of many rocker arms do not have needle bearings, but some do — which helps reduce friction and valve stem wear.

The type of rocker arms that are permitted may be restricted by the rules in some racing applications. And even if rules are not a limiting factor, stamped steel rockers can usually handle engine speeds up to 6, rpm and valve lifts of up to. The same goes for cast steel rockers on Ford and Chrysler engines that use some type of shaft mounted rocker setup.

For engine applications that demand a step up, replacing the stock stamped or cast steel rockers with aluminum roller rockers will typically produce a gain of 10 to 15 hp with the same lift ratio, and even more of a power gain with a higher lift ratio. The extra power comes from the reduction in friction provided by the roller rockers — which also helps keep the oil cooler, too.

Depending on the design of the rockers, changing rocker arms often requires changing pushrod lengths. With stud mounted rockers, the rocker arm location on the stud determines the geometry of the valvetrain.

When the pushrod is the correct length for the application, the tip of the rocker arm will be centered on the tip of the valve stem when the cam is at 50 percent lift. If the pushrod is too long or too short, the tip of the rocker will be offset towards the outside or inside of the valve stem rather than centered over it. This can create side loads on the valve stem that increases friction, stem and guide wear.

Used in an incorrect application, these needle bearings may wear—and cause wear on the rocker shaft—faster than standard bushings. The roller tip, on the other hand, makes good sense. At a standard ratio, the tip of a rocker arm slides across the top of the valve. To aid the sliding, this tip is rounded and contoured to maintain consistent contact with the valve.

However, as the rocker arm ratio increases, angles get sharper, lift gets higher, and the tip has a harder time maintaining the right geometry to last as long. Replacing the contoured tip with a roller compensates for this problem at the cost of more complexity and weight. The additional weight is often compensated by a switch from steel or cast iron to aluminum, but this comes at a cost as well—usually financial.

If so, they work. Adjusting a rocker arm ratio is really similar to playing with camshaft specifications. And this is where you can get into trouble. Most of the engines in our classics are already designed with pretty aggressive cams and rocker arm ratios. To put this in perspective, we made two sets of tests on the A-series BMC engine we built for our Modern Midget project car. This cc engine ran a We made the first set of tests with a stock cylinder head and the second with a highly modified head that had received extensive porting and larger valves.

The results were predictable—in each case, the engine made more power at high rpm and lost some power in the lower ranges. For our first set of tests with the stock head, we compared stock rocker arms with a The ratios increased the 0.

The high-ratio rocker arms did well at the peaks, picking up about 5 percent more torque and power. However, we suffered in the midrange, losing more than 5 percent. This is a prime example or robbing Peter to pay Paul. For our second set of tests, we used our trick cylinder head with three rocker arm setups: stock We had similar results when fitting roller rockers to our modified head: We gained nicely at the top end while giving up power and torque in the midrange.

Understanding the role of the engine rocker arm in automobiles The rocker arm is the part responsible for transmitting the movement of the camshaft towards the intake and exhaust valves of the engine, a process that occurs through the direct contact of these parts with the tappets and according to the movement of the shaft.

Flat x roller rocker arm: know the variations We have already seen that the engine rocker arm is a component of the mechanical distribution system on the valve assembly and makes itself present in most internal combustion engines. Blog Original products All Posts. Technical Tips All Posts.

Technical Tips Management All Posts. You are part of RIO Did you know that several of our products were developed specifically based on your comments? Explore the site and contact us. They still use the stud from the trunnion pivot but they don't use the nut. They have a very short shaft with bearings on each end inside the rocker and the shaft is bolted securely in place and the bearings allow the rocker to pivot. They have a shaft that goes through the rocker arms.

Sometimes the shaft only goes through 2 rocker arms and sometimes the shaft will go through all of the rocker arms depending on how the head was manufactured. The reason for using a shaft is for rigidity. Putting a shaft through the rocker arms is much more rigid than just using a stud from the head. The more rigid the valve train, the less the valve train deflection and the less chance for uncontrolled valve train motion at higher RPM.