Editing Rocker arms

[[File:Rocker diagram.jpg|right]]

==Overview==
The rocker arm is a fulcrum. Its job is to turn the cam lobe's circular rotation into an up and down movement. This is able to be done because the rocker has a pivot point or fulcrum that allows the cam lobe to open the valve.

==Rocker arm ratio==
The rocker arm's pivot point is not in the center of the rocker; instead it is offset more towards the pushrod. The amount of offset is expressed as a ratio (1.5, 1.6, 1.7, etc.).

The rocker arm ratio multiplied by the cam lobe lift equals the net valve lift.

The stock small-block Chevy rocker arm has a 1.5:1 ratio. These rockers are called 1.5 ratio rockers or just 1.5 rockers for short. This means that the rocker arm tip at the valve end of the rocker moves 1.5 times the amount of movement seen at the pushrod end of the rocker- which is also the same amount as the camshaft's lobe lift.

Let's say your camshaft has 0.350" '''lobe''' lift. With a 1.5 rocker, the cam's lobe lift becomes 0.525" lift at the valve (0.350 x 1.5 = 0.525).

The same 0.350" cam lobe using 1.6 rockers would give you 0.560" lift (0.350 x 1.6 = 0.560), w/o having to remove and replace the cam. With the Chevy factory hydraulic roller cam and lifter set up, this will give you more lift before running into problems w/the dogbone retainers losing contact w/the stock lifters.

Changing the rocker ratio will also change the off-the-seat duration seen at the valve a small amount. However, seat-to-seat duration will not change.

==Types or rockers==
There are several different materials rocker arms may be made of: hardened steel, stainless steel, aluminum- both extruded and cast. There are several different designs: pedestal mount, stud mount, shaft mount. There are different pivot point: Ball and stud (like a SBC), shaft, or a roller trunnion. There are different tips: Self aligning, non self aligning, roller (also in SA and non SA designs).  

===Stamped steel===
A mainstay of OEM engines. They're cheap to produce and perform adequately, although in serious competition and high performance applications they leave a lot to be desired. The ratio is often less than advertised, the ball pivot like used by Chevy and Pontiac are prone to wear and friction.

===Roller tip===
The roller tip only rockers are mostly a gimmick. Their only real advantage comes not from the roller tip (which by one estimate would need to be a 2" diameter roller to duplicate a stamped steel rocker), but from the more accurate ratio; stock stamped steel rockers often have less than advertised ratios and this means less than advertised lift, and a good chance of less peak performance.

===Roller trunnion===
[[File:LS7 stock rocker arms.jpg|thumb|400px|Gen 3/4 Chevy rockers]]A roller trunnion is the best improvement that can be made to a rocker arm using a design that permits it. As an example, Chevy Gen 3 and 4 engines use a roller trunnion without a roller tip. These rockers are very efficient and represent the state of the art as far as OEM rocker arms go. These rockers can be upgraded with a replacement trunnion bearing assembly and are then good for high performance use beyond what the stock bearings could take. <br style="clear:both"/> 

===Full roller===
[[File:Jessel mohawk AFR ford windsor.jpg|thumb|400px|Jessel full roller rockers on a Ford Windsor engine]]Aftermarket rockers are available as full roller (tip ''and'' trunnion). The benefits are less friction and less oil needed to lubricate them. While these used to be considered high-end race-only parts, the price has dropped to the point where a set of decent full roller (tip and trunnion) can be had for not much more than a quality set of stamped steel rockers.
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===Self aligning vs. non self aligning===
[[File:SA vs non sa rockers.jpg]]

==Lewis tool==
[[File:Lewis tool in use.jpg|thumb|500px|Lewis tool being used on a SBC head]]A Lewis tool is used on SBC heads to lengthen the pushrod slot towards the rocker stud for use with increased ratio rocker arms. This can also be done by hand using a die grinder or even a rat tail file, but the Lewis tool makes short work of it by using the tool, a 5/16" drill bit and drill. <br style="clear:both"/>

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[[Category:Engine]]
[[Category:Cylinder head]]
[[Category:Undeveloped articles]]
[[Category:Undeveloped Engine articles]]
[[Category:Undeveloped Cylinder head articles]]