Upper Valvetrain Design

Words: Larry Shepard

This article is the second of two parts and should be looked at with the “Lower Valvetrain Design” Tech Insider story in the November/December 2010 issue of Mopar® Magazine. In the previous article I discussed the camshaft, tappets and pushrods. In this article I’ll start at the other end—the valves—and work toward the pushrod. With the various upper valvetrain parts and pieces, there are many, many part numbers so I’ll only list a few examples of each type of part. There are even more versions available from aftermarket manufactures. Some aftermarket manufacturers specialize in specific parts like valves, and others carry a wide range of valvetrain components.

The typical V-8 wedge or HEMI® engine has two valves per cylinder. These valves are largely defined by the cylinder head. Valves have a head diameter, a stem diameter and overall length along with grooves cut toward the end of the stem. The stem diameter is defined by the inside diameter of the valve guide that is cut/machined into the cylinder head. Note: aluminum heads use valve guide inserts that are pressed into the head. Most production wedge engines use 3/8" stems. The head also defines the valve’s length but the intake and exhaust valves on wedge engines tend to be slightly different in length. The A-engine uses a length of 4.97" while the B/RB engine uses a length of 4.87". The typical 340 (1972–73) and all 360s used 1.88" OD (head diameter) intake valves, P4876397. The 1968–71 340 used a larger 2.02" intake valve, P5249185. All of these valves are made of stainless steel and have high-flow performance characteristics. You can upgrade from the 1.88" intake valve to the 2.02" valve by grinding the valve seats in the cast-iron cylinder head. Note: aluminum heads use valve seat inserts pressed into the head and these inserts have to be changed to allow a large valve head size change. The typical 383 and 440 big block (B/RB engine) comes with 2.08" intake and 1.74" exhaust valves and it is common to upgrade these production cylinder heads to 2.14" intake valves P5249200 and 1.81" exhaust valves P5249202. The 426 HEMI (1964–71) uses 5/16" valve stems and different lengths on the intake and exhaust sides (4.86" exhaust, 5.40" intake). The 426 HEMI intake valve, P5249203, has a 2.25" head diameter while the exhaust is 1.94". Note: different stem diameters can be installed in a set of heads by drilling and honing the guides in the heads to the larger size, or by installed smaller inserts/guides. The W2 small-block heads have a long-valve race package that is based on a 5.29" length valves like P5249197 (1.60" exhaust). Longer valves must be used as a team or installed as a package because springs, rockers and pushrods are all affected. Longer valves allow for increased installed heights, which allow for bigger springs which allow for higher lift cams.

The valve seals ride on the stem of the valves. The typical production valve seal is made of a special rubber and is called an umbrella seal. They fit inside the valve spring. The 5/16-stem valve seals are P5249661 while the 3/8" stem seals are P4120492. These umbrella seals work fine in single valve spring applications but if you require a dual spring, then you will need a seal with a smaller outside diameter and the cylinder head will have to be machined for the new seals. P3690963 is a smaller outside diameter seal designed for a 3/8" valve stem and requires the top of the guide in the cylinder head to be machined to .530". Smaller 5/16" or 11/32" outside diameter valve stem seals are available from aftermarket suppliers. Valve seals should be replaced at every rebuild.

On the top end of the valve stem, the end away from the valve seat, there are groove(s) cut for the valve keepers (split locks). There can be a single groove, two grooves or a triple groove. The two- and three-groove designs tend to be used in production applications and the three-groove is common on production exhaust valves. Single-grooves are used in performance applications and racing. Because they fit around the stem of the valve, the stem’s diameter also defines the keepers (locks). The third design feature of the locks is its angle which fits into the retainer. There are generally two angles—7-degrees and 10-degrees. The 7-degree angle is used in production and the 10-degree is used in racing but there are many 7-degree racing applications (lots of overlap with this feature). A set of 7-degree, 3/8" stem, single-groove keepers is P4120618. A set of 10-degree, 3/8" stem, single groove keepers is P4286612. Note: The 426 HEMI single groove is a square-cut groove while the single-groove used on the Magnum® (5.2L and 5.9L) V-8s is a round groove. There are many other combinations of stem sizes and grooves and angles. These are only common examples.

The next part is the valve spring retainer. The keepers (locks) fit around the valve stem and fit inside the retainer, which holds them in place once assembled (locks them onto the valve). Therefore the first aspect of the retainer is the angle—7-degree or 10-degree—which is defined by the keepers. Somewhat related aspect is the valve stem size (5/16" or 3/8") because the larger stem size makes the basic hole larger. The third aspect is the basic design of the valve spring itself—single, dual or triple. The number of coils in the spring can change the number of seats (steps) in the under-side of the retainer or the inside diameter of these steps. This can get confusing so just select a retainer that works with the chosen valve spring. The final aspect of retainers is the material—steel, chrome-moly, aluminum and titanium are common. Typically only steel is used in production. The steel, 5/16" (426 HEMI), 7-degree retainer for use with single springs is P4452769. The chrome-moly version for use with dual springs is P4529288. The chrome-moly 3/8" 7-degree retainer for single springs is P4452033 while the 10-degree, dual spring design is P4120785 (made of titanium). There are many other variations.

Perhaps the heart of the upper valvetrain is the valve spring itself. The two main design features are the valve lift and the installed height. The valve lift is mainly defined by the camshaft’s lift but is also affected by the rocker ratio. The installed height is generally defined by the cylinder head. For the popular V-8s, there are basically two installed heights used in production: the A-engine height which is around 1.67" to 1.70" and the B/RB/426 HEMI height of 1.83" to 1.86". The third height is generally referred to as the 2.00" height. This is only used in racing and most commonly known in the race-version of the W2, also called the long-valve version. To convert one of the standard installed heights to allow the use of the 2" hardware, typically you must use longer valves. The A-engine (1.67"/1.70") single spring for general high-performance use is P4120249 which can be used for cam/valve lifts up to .500". For lifts up to .535" use single spring P5249847. If you have more than .535" lift from the cam package, then you must use a dual spring like P3412068 or P3614542. For the B/RB/426 HEMI (1.83"/1.86") engines the general high-performance single spring is P3690933 (for lifts up to .510"). For lifts up to .540" use single spring P5249848. For higher lifts than this, the dual springs are P2806077 and P4876064. If the lift gets around .640" or higher, generally you will have to use a triple spring available from the aftermarket.

The next part of the upper valvetrain is the rocker arm. The rocker arm pushes on the valve stem and is pushed by the pushrod, from the tappet from the cam. First there are hydraulic rocker arms that are used in production—set P4529742 for the A engine—which are stamped rockers and are not adjustable. B/RB rockers are similar (stamped) but are unique in dimensions and shape details. Then there are adjustable rockers used on the 426 HEMI mechanical and hydraulic cams and the 1970 340 T/A 6BBL. Hydraulic cams do not need adjustable rockers but mechanical cams do require rocker adjustment. 
Note: mechanical rockers (adjustable) can be used on hydraulic cams but hydraulic rockers (stamped, non-adjustable) can’t be used with mechanical cams. Most of the production rocker ratios are around 1.5. For performance use there are higher ratios such as 1.6 and 1.7 in some cases. Always figure in your real rocker ratio with your cam’s lift when figuring out the total lift for valve spring selection. For performance and racing applications there are roller-tip rockers and aluminum roller rockers, and offset rockers for clearance around large intake ports such as the oval-port W2 and some of the large-port B-engine heads. Note: an offset is usually given in inches measured from the valve tip centerline.

The production-style rockers use a rocker shaft which holds/aligns the rockers over the valve tip. The A-engine production-style rocker shaft (hydraulic valve gear) is P4510636 and the B/RB version is P4529101. The 426 HEMI intake rocker shaft is P5249631 while the exhaust is P5249632. The most unique rocker shaft is the race W2 package which uses offset attaching screws, P4120589.

On the 426 HEMI the rocker shafts are attached to the head and held in place by rocker stands, P5249505 (aluminum). Most of the A and B/RB engines have the rocker stands cast into the heads but the race W2 engines, P5249049 (billet aluminum), and the early 413/426 Max Wedge engines (1962–63), P5007217, use rocker stands.

Most of these rocker shafts are hollow to allow oil to reach all of the valves, rockers and various valvetrain parts. To seal these hollow shafts, a plug is pressed into each end. If you want to clean your rocker shafts, these plugs must be removed and should not be re-used—new rocker shaft plugs, P5249633. Lesser known parts like the rocker shaft holddowns, like P5249712, help hold the shafts round and straight, and rocker arm spacers P3690896 help move the rocker along the shaft to align more exactly over the valve tips, along with rocker shaft springs P4452827 for the 426 HEMI are all part of the valvetrain and have specific duties.

Trick tip: with all these parts as discussed above and all the many, many variations of these parts and adding in cylinder head milling, block milling, cams, tappets and valve grinding and seat work, there are problems that pop-up. The most common or easiest solution is to use adjustable-length pushrods which are available from Smith Brothers, www.pushrods.net—this is more of a concern with hydraulic cams, which are also the most popular.

More Mopar upper valvetrain parts—valves, springs and rocker arms—are being added to Mopar’s lineup. For additional information, refer to the latest Mopar Performance catalog or visit www.mopar.com. Space limits my discussion; if you have specific questions, please call the Mopar Direct Connection Tech Line at 1-888-528-HEMI (4364).

Larry “Shep” Shepard is a retired Mopar Performance engineer, author of numerous Mopar Performance books and a Michigan Motor Sports Hall of Fame inductee.