Mopar Performance Valvetrain Parts - Mopar Muscle Magazine

Mopar Performance Valvetrain Parts - Valvetrain Variable
Mopp 0301 01 Z+mopar Engine Valvetrain+stock Spring Seat Here is the stock spring seat in a production head. This raised, stepped register serves to keep the stock single spring from floating excessively from side-to-side. With larger-diameter aftermarket single springs, quite a bit more misalignment can occur before the register restrains the spring's lateral motion. With dual springs, the register interferes with the inner spring, which often sits right on top of it, raising the spring load over the rated spec. With some spring combos, it opens the potential for coil binding the inner spring.

Build a stock-style or mild Mopar engine, and all you have to know about the valvetrain is how to tighten 10 rocker-shaft bolts. Delve into the exciting realm of high-performance, highly modified pavement pounders, and the valvetrain is one area you can't afford to neglect. If the world of high-lift cams, aftermarket heads, roller rockers, and high rpm is where you want to be, you'd have to know a lot more than how to tighten on those stock shaft rockers.

A true high-performance engine lives or dies by its valvetrain. Getting all the valvetrain hardware sorted out can be one of the most time-consuming aspects of assembling a true high-performance engine. The racier the combo, the more involved it becomes. But even in a relatively mild build, it pays to check the specs and do it right. Setting up a racy valvetrain may seem like a lot of hassle, but if going fast is the goal, no one ever said it would be easy.

Spring Seats
The spring seat, or pocket, is the flat area of the cylinder head on which the valvespring sits. Though there are no moving parts there, it is one of the most critical areas for valvespring performance. Getting this portion of the head in shape requires just two things: that the pad fits the type of valvespring being used, and that it securely locates the bottom of the spring. The stock pad in both big- and small-block heads have a 1.000-inch-diameter stepped register which locates a stock single spring by its inside diameter. Swap to larger-diameter single springs and there will be much more clearance to the register, along with more side-to-side slop possible at the bottom of the spring-not the ideal situation. If the combination calls for a dual valvespring, the raised center register will interfere with the inner spring. For dual springs, the register should be machined off.

Seal Deal
Valve seals keep the abundant oil around the valvetrain from finding its way between the valve stem and guide and down into the combustion chamber. Why the concern? Besides puffing blue smoke, oil has a low octane level and quickly reduces the detonation tolerance of an engine, and that can be destructive. Suck oil into the combustion chamber, and some of it will burn. The byproduct here is carbon-lots of carbon. In street use, an oil burner will have the valves, pistons, and ports caked heavy with carbon in relatively short order. There's no question that keeping excessive oil out of the chamber is a worthy goal; however, the guides do need a small amount for lubrication. Stock Mopar engines used umbrella seals, which ride up and down with the valve, shrouding the guide from direct oil exposure while allowing a light mist of lube to reach the stem. This is a simple arrangement, and one that works quite well.

In a high-performance engine packing serious camshaft, the springs are often replaced with dual-spring assemblies to provide the load necessary for valvetrain control. Unfortunately, the inner spring takes up the space required to fit an umbrella seal, so in these installations, a more compact seal arrangement is required. The most popular solution is to swap the stock seals for compact Teflon seals. The aftermarket seals mount positively to the top of the guide boss, requiring some minor machining of the guide. These aftermarket seals are effective at controlling oil entry into the guide. Some engine builders believe the Teflon seals work too well, and they leave the seals off the exhaust side in race-engine applications. Intake valves are much more likely to draw oil since the intake guide is a vacuum, while the exhaust mainly sees exhaust-gas pressure, which helps keep oil out.

Mopp 0301 08 Z+mopar Engine Valvetrain+plastic Sleeve The sealing lip of a Teflon seal can easily be damaged when it slides over the keeper grooves of the valve stem. To protect it, a thin plastic sleeve (usually available where valve seals are purchased) is slipped over the valve before the seal is installed. Some lube at the seal and valve stem helps the seal slide on with ease.

Pushrod Predicaments And Rocker Revelations
Pushrods in a high-performance engine build are always items that need to be considered. Most Mopar engines were equipped with heavy, solid-steel pushrods of 5⁄16-inch diameter-definitely not performance valvetrain stuff. Virtually all aftermarket adjustable valvetrains require aftermarket or custom pushrods. There are several factors to consider when choosing pushrods for a specific engine build, notably the length, diameter, tube material, and types and sizes of ends. The load capacity of the pushrod is determined by the material it's made of, the wall thickness, the diameter, and the overall length. If the pushrod material is not up to the load put against it, the result will be pushrod deflection and valvetrain instability. Increasing the wall thickness, diameter, or both, will increase the stiffness of the rod. All else being equal, longer pushrods have less capacity than shorter ones.

We spoke to the pushrod experts at Smith Brothers for some basic rule-of-thumb guidelines on pushrod material selection. The chart below gives some of the materials and general max spring loads recommended by Smith Brothers.

Ordering custom pushrods requires that you know or can find out a few basic specs. First is the required length, best measured by installing an adjustable checking pushrod and directly determining the length requirement. Most adjustable rockers work best with the adjuster set nearly all the way up-that is, with only about one thread showing out the bottom of the rocker. Some rockers, such as Comp Cams' Pro Magnums, require the length to be set so the oiling hole to the pushrod is in the range of the oiling band in the rocker adjuster. The checking pushrod allows the pushrod length to be adjusted until the perfect length is determined. With that done, all that's required is to measure it and give the length spec to the pushrod supplier. The overall length measured from end-to-end of the pushrod is not an accurate way to measure a typical Mopar ball or cup pushrod as the design of the pushrod cup can vary considerably. The preferred method is to measure the length from the ball end to inside the bottom of the cup. This is the true, effective length. Measure the overall length, then subtract the distance from the cup's top to the bottom of the cup.

The type of end required also needs to be identified. There are two possibilities here: ball or cup end, and two sizes, 5⁄16 or 3⁄8 inch. Whether a ball or cup is required is fairly obvious, but the size is often not considered. It has nothing to do with the tube size of the pushrod. Some lifters are machined for a 3⁄8-inch ball, while others are machined for 5⁄16 inch. The only way to know which one you need is to measure it. Likewise, determining the size at the rocker end is a matter of taking out the calipers and checking the diameter at the rocker adjuster.

Pushrod Max Recommended Load*Tube MaterialHeat
Treat
Maximum
Recommended
Load**
5⁄16"-dia./.049"-thick wallNo400 lbs.5⁄16"-dia./.049"-thick wallYes500 lbs.5⁄16"-dia./.083"-thick wallYes750 lbs.3⁄8"-dia./.049"-thick wallNo400+ lbs.3⁄8"-dia./.049"-thick wallYes500+ lbs.3⁄8"-dia./.065"-thick wallYes750 lbs.3⁄8"-dia./.083"-thick wallYes{{{900}}} lbs.

*General recommended max open-valve spring load for a 9-inch pushrod. Subtract 100 pounds capacity for every inch over 9 inches effective length. Add 100 pounds capacity for every 1 inch shorter than 9 inches.
**Maximum valvespring open load.

Mopp 0301 15 Z+mopar Engine Valvetrain+pushrod Clearance To Head Checking the pushrod clearance to the head should be part of the mock-up assembly of any performance engine. These 1.6:1 rockers, combined with 3/8-inch pushrods, resulted in a clearance problem at the outside tops of the pushrod holes. The area was clearanced with a carbide bit before final assembly.

Springs And Things
As the serious performance increases, valvesprings become more critical. In lower-rpm performance engines, which may never see more than 5,500 rpm, the most basic level of care in valvespring selection and installation generally gets you by. As rpm increase, springs become one of the most critical factors in wringing the performance potential from a combination. Become familiar with the seat load and installed height, open load, spring rate, and coil bind clearance. Let's take them one at a time.

Seat load is the amount of force the spring exerts with the valve closed. This affects the valve's potential to bounce on closing, which can cost serious power at high rpm. Springs are rated for load at a given height, referred to as the installed height. The more a spring is compressed, the greater the force, so the installed height directly affects the seat load. It's critical to know the installed height to have a known amount of seat load.

Open load is the amount of force exerted by the spring when the cam is at peak lift, which is the point when the spring is compressed the farthest. The open load is necessarily greater than the seat load, since the spring is compressed. The open load has to be enough to keep the lifter in contact with the cam as it goes "over the nose," yet not so high that it is beyond what the cam, lifters, and valvetrain can withstand for acceptable wear.

Spring rate is a rating on how "stiff" the spring is, or how much load is gained as the spring compresses, normally given in pounds per inch (lb/in). A spring rated at 350 lb/in gains 175 pounds with a cam delivering .500-inch valve lift, or half the rated lb/inch for 1/2 inch of lift. How much the spring gains for any amount of valve lift can be calculated by multiplying the lift by the spring rate. A .700-inch lift cam with a 600-lb/in rate spring will gain .700 inch times 600 lb/in for a gain of 420 pounds. Add the amount gained to the seat load, and the open load for any cam is the result. For instance, if the seat load was 200 pounds, gaining 420 pounds in opening will give 620 pounds open. Most spring suppliers publish specs of spring rates.

The coil-bind height of a spring is the height of the spring when it's compressed solid, and most spring manufacturers give specs on coil bind height. By measuring the actual installed height of a spring on a cylinder head and subtracting the amount of valve lift, the compressed height of the spring at full lift can be calculated. Comparing this figure to the published coil-bind height gives the clearance to coil bind. For example, let's say we have a spring with an installed height of 1.800 inches. If the valve lift is .600, the spring is compressed to 1.200 inches at full lift (1.800 - .600 = 1.200). If the manufacturer's catalog lists the coil-bind height at 1.100, it's safe to say there is .100 inch coil bind clearance left (1.200 - 1.100 = .100).

How much spring load is the right amount? It depends on the cam profile; type of a cam-solid, hydraulic, or roller; the valvetrain weight; and the engine's rpm range. Experienced engine builders typically spec their own springs, but for the average enthusiast, it's best left to the cam manufacturer.