Rocker arms
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===Stamped steel=== | ===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. | 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. | ||
| + | *http://www.cranecams.com/313.pdf | ||
===Roller tip=== | ===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. | 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. | ||
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| + | That said, the 1.52:1 advertised roller tip rockers are a lot more uniform and they can increase performance, primarily due to the increase in ratio- NOT because of the roller tip. | ||
===Roller trunnion=== | ===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"/> | + | [[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 GM 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=== | ===Full roller=== | ||
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[[File:SA vs non sa rockers.jpg]] | [[File:SA vs non sa rockers.jpg]] | ||
| + | ==Installing screw in rocker arm studs== | ||
| + | [[File:POW351300.jpg|thumb|400px|left|Stud puller/tap guide for SBC]] <br style="clear:both"/> | ||
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| + | When screw in studs are going to be installed, the stud boss will usually need to be machined shorter to make up for the thickness of the guide plate (if used) and for the hex portion of the stud and the radius between the hex and the stud. In the case of the early style SBC, 0.400" is usually a safe amount to remove, but this can vary some depending on the exact parts used. | ||
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| + | ==Rocker arm adjustment nuts== | ||
| + | Polylocs are the preferred method to hold the rocker arm adjustment. The stud needs to have a flat or even surface for the center locking allen nut to tighten against. | ||
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| + | [[File:Images.jpg|thumb|350px|right|Arrows show where self locking nut was "pinched" to disrupt threads to make the nut lock to the stud threads]] | ||
| + | If you're using stock lock nuts, they use a disrupted thread on the top side of the nut (arrows, right), so getting the nut to start on the stud is nearly- if not completely- impossible, unless the nut is correctly orientated on the stud (flat side down, as said). Replace these lock nuts if they've been used much; the self locking function loosens w/use. | ||
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| + | Self locking rocker nuts can do a number on aftermarket studs, so use polylocs when possible. In some cases polylocs cause clearance problems w/the valve cover so check first. Using a thick or doubled gasket will sometimes give enough clearance. Using polylocs on stock studs will not always work- the polylocs need an even surface for the set screw to register on, often stock studs are uneven on the top. | ||
| + | <br style="clear:both"/> | ||
==Converting a non-adjustable valve train== | ==Converting a non-adjustable valve train== | ||
Old and new engines have both used net lash or non adjustable rocker arm arrangements. The latest Chevy engines are now among these; for years the Chevy V8 enjoyed the benefits of an adjustable stud-and-rocker setup but unfortunately that's gone by the wayside. | Old and new engines have both used net lash or non adjustable rocker arm arrangements. The latest Chevy engines are now among these; for years the Chevy V8 enjoyed the benefits of an adjustable stud-and-rocker setup but unfortunately that's gone by the wayside. | ||
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