Here is the 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.
We were prepping these castings...
We were prepping these castings for aftermarket dual springs, so the register needed to go. Spring-seat machining tools are available in a variety of diameters, such as this 1.680-inch cutter from Powerhouse (PN POW351335). The spring-seat cutter can be used in an ordinary hand drill.
A spring cup should be used...
A spring cup should be used to keep the valvespring from dancing around on the cylinder head. Several styles of cups and locators are available, which register either to the outside of the spring or on the inside of a dual-spring assembly. We used a Comp Cams' cup (PN 4700) for these 906 heads, which locates a 1.550-inch spring by its outside diameter.
If dual springs are used,...
If dual springs are used, the stock, umbrella-style valve-stem seal (right) will not fit within the spring assembly. The common solution is to replace the seal with a compact positive seal such as the Teflon P/C-style seal to the left.
Rather than floating on the...
Rather than floating on the valve stem like the stock umbrella seal, the P/C-style seal is secured to the top of the guide boss, which must be machined to accept the seal. Aftermarket seals are commonly available with either .530- or .500-inch inside diameters; machine the top of the guide to match. For 3/8-inch-diameter valve stems, the .530-inch seal is preferred, since it maintains more thickness and strength in the guide boss than the .500-inch seal. We used a .530-inch cutter, PN POW351345 from Powerhouse, to machine our guide bosses for the .530-inch seals. Again, this operation can be performed with a hand drill.
With high-lift cams, the amount...
With high-lift cams, the amount of clearance between the retainer and guide becomes an issue. Most stock big-block heads provide .640-.660 inch clearance; easily checked, as shown, with the valve mocked-up using a checking spring. A dial indicator is used to measure travel until the retainer bottoms on the guide. Remember that a stock seal robs about .125 inch of this clearance, so cams delivering more than about .525-inch lift will run out of room with the stock guide and seal. The positive P/C-style seals rob even more clearance, typically around .200 inch, so the guide boss usually has to be machined lower to accommodate high valve lift.
The cutting tool used to machine...
The cutting tool used to machine the guide boss for P/C seals also has a cutting edge for cutting down the guide boss' height. Just keep on going when machining to the required depth. Washers stacked over the guide boss can serve as a positive stop to machine to a consistent depth. We lowered ours by .280 inch, allowing for more than .700 inch of lift without interference with the Teflon seal in place.