Here is the stock spring seat in a production head. This raised, stepped register serves t
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.
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.
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 for aftermarket dual springs, so the register needed to go
A spring cup should be used to keep the valvespring from dancing around on the cylinder he
If dual springs are used, the stock, umbrella-style valve-stem seal (right) will not fit w
Rather than floating on the valve stem like the stock umbrella seal, the P/C-style seal is
With high-lift cams, the amount of clearance between the retainer and guide becomes an iss
The cutting tool used to machine the guide boss for P/C seals also has a cutting edge for