Valve Head Gear
- CYLINDER HEAD ROCKERS & ROLLERS
One area of the power search that most of the enthusiasts tend to forget about are the rocker arms and their geometry. These are probably the best lessons anyone can learn. In most cases you simply purchase a new set of rocker arms and bolt them onto your cylinder heads. Unfortunately, the trouble with that plan and particularly with small and Big Chevrolet, FoMoCo (Ford), Windsor, Cleveland and 385 Mopars and a few others is that the factory rocker arms can often be way out in the ratio department. Using a small block Chevy engine as an example, the OEM or (original equipment manufacturer), specs call for a rocker ratio of 1.5:1. This in simple terms means that the rocker arms will multiply the camshaft lobe lift by 1.5 times. If the lobe lift on a small block camshaft is .400 of an inch on both the intake and exhaust lobes, you can multiply it by the rocker ratio of 1.5 and the gross valve lift should be .600 of an inch.
Unfortunately, a stamped steel rocker ratio might only check out at 1.43:1 or even less. As a result, the gross valve lift works out to .572 inch. The valve train effectively has lost about 5% of the total lift. This only gets worse as the lobe lift numbers increase (the camshaft becomes more radical).
What’s the answer to the problem at hand? There are several solutions, but if you can’t afford a trick set of aftermarket roller rockers, the answers start hiding themselves from you-rapidly. The most inexpensive option is to check a box full of rockers until you find all 16 of them that have the highest effective rocker ratio and are that close to one another. In order to accomplish this, you will have to get into action and install a solid lifter on one rocker arm to zero lash. Next is to install your dial indicator to read off the valve stem side of the rocker arm. Turn the engine through one complete revolution with a power bar fitted with an extension and socket.
Compare this gross (zero lash) to your camshaft specs. You might be surprised to see that the numbers do not correspond. To verify the figures, either verify the number with your camshaft specifications car or check the lift at the lifter and multiply the number by your rocker ratio. This number is the theoretical gross valve lift. In many situations, a factory rocker arm will have a ratio that is significantly less than you would of imagined.
As mentioned previously, most small block rockers ‘check’ at between 1.4:1 and 1.47:1, very few attain the advertised number of 1.5:1 in the ratio department. To correct the problem you can either rummage through boxes of new rockers until a ‘perfect’ set is found, or install a set of aftermarket rockers. If you install aftermarket rockers, be absolutely sure to verify the ratio. Performance aftermarket parts aren’t perfect either.
- LASHING THE VALVES
Is there a difference in lash procedure between an engine equipped with stock rockers and one equipped with roller rockers? There’s none in terms of lash numbers, but there is one thing you have to remember. When lashing valves with OEM rockers, you can sometimes slide the feeler guage in at a at bit of an angle. This isn’t possible with a roller tip rocker. If your engine is equipped with roller rockers, be certain that you slide the feeler guage in a straight line between the rocker tip and the top of the valve.
In any case, the idea is to use a ‘go-no-go’ system, keeping it as smooth as possible. In other words, if the cam company calls for .024 inch lash, then a .024 inch feeler guage will fit, but a .025 won’t. After some practice with your particular combination you’ll get a real feel for the correct lash. Some guys like a ‘tight’ pull on the feeler guage, others don’t it’s just a matter of a personal likes or dislikes of styles.
- CYLINDER HEAD LIGHT
When working with aluminium cylinder heads and/or aluminium cylinder blocks, cold lash numbers can vary greatly from the hot figures. So why does this happen? Simply because aluminium moves by expanding and contracting a great deal more than cast iron when heated up. Because of this you can understand why and how valve lash figures become decidedly different with ally combinations. Although it’s difficult to provide the hard and solid numbers for all camshaft and engine combo’s, Chevy offered this advice as a rule of thumb: ’Cold-lash all ally engines .010 inch tighter than the Hot-lash specs’.
Generally, you can use this as a good starting point and go on from there. Some ally head to iron block combinations are very close to an all iron engine in terms of cold lash. Others might be and well be anywhere from .005 inch to .010 inch tighter. Your best chance is to contact your guy who grinds camshafts for you and ask him for a specific cold-lash number for the particular combination you may have.
- SHARP SET TIMING SIGHTS
Eyeing the timing marks is always going to hinder any mechanic in a dark engine compartment and is never easy and to make matters worse, the timing marks become harder to read when unnatural or partial light is directed into the engine compartment. Even the addition of a degreed balancer or a timing tape can still make for some partial visual impairments. Most of the time the problem isn’t always the degreed markings on the balancer. Instead it’s the timing mark pointer that’s not accurately lining up and showing you the exact marking that can be exactly pin pointed. Trimming your standard pointer to a ‘V’ shape at the zero marking. The pointer is easier to read and eliminates confusion over the timing marks location.
In addition to this, aftermarket companies have designed bolt-on timing pointers with an adjustable pointer that can be easily set up to read ‘on-zero’ or from four degrees retard to 16 degrees advance. From this simple little addition of the adjustment, the pointer makes any timing checks easy and simple and also solves the timing-out, pointer problems that can sometimes plague engines and engine builders. Occasionally, the TDC mark on a factory harmonic balancer will be slightly out and so can the timing pointer. This is unacceptable to any standards and all adds up to an extremely inaccurate ignition timing numbers as well as valve lash figures that can be out.
- RELIEF VALVE SPRINGS
A valve springs life is always critical to any performance street rod engine. How can the valve’s spring life be considerably improved? The first step is to pre-stress new valve springs prior to their installation. In other words, the springs are squeezed to the limit by a soft-jaw vise and compressed several times before installing the valve spring to its place. The idea isn’t to damage the spring in the vise but instead, the spring should be compressed just nicely, without pushing the spring into a coil-bind, but just enough to push it to the limit a few times but not over. (Watch the spring carefully as you compress it together). Install the spring on the cylinder head and check the seat pressure. If the spring fails miserably, “tag” it or return to the selling dealer and install a new one. If you don’t have access to a soft-jawed vise something soft should be attached to either side of your vise jaws. The cushion you have now added saves the valve springs from being scarred by the course steel lining jaws of the vice.
Here’s another method you can try for improving the life of the spring:
Inspect the inner spring and dampener carefully. You might find that some valve springs have added “flashing” on the spring ends. (This is common on some types of dampers.) If that’s the case with your set of springs, use a small die grinder and very carefully smooth over the odd burrs and high spots that are present. Similarly, some dampers have very sharp edges on the “flats.” The life of the damper can be improved by gently de-burring and chamfering them, and it can be done in five minutes flat - if you have the right tools laid out and at your disposal.
It should be pointed out that damper failure is more common than we’d like to think (especially on high lift, radical profiled cams).
Occasionally, a damper will physically “unwind itself” and the lower portion of the assembly will work its way between two lower coils of the outer spring. Naturally, this stacks the spring into a coil bind. When this happens, all kinds of carnage can occur if you don’t nip the problem before this can happen. In most cases, selecting the correct length of damper will suffice, but if the problem hampers your application, you can solve it by shortening the damper a few mills. You might try this old racer trick (its been around for about 30 years or more). Sand blast the damper after it has been de burred and the edges chamfered.
- TENSION ON VALVES
When the time comes to installing the valve springs on the cylinder heads, have a close look at the relationship between the inner spring and the damper to both the cylinder head seat and the valve spring retainer. Because of the many different types of designs manufactured in springs, valve retainers and spring seats, there might be some coil-bind at these locations, but no coil-bind on the outer spring. Have a close look as the engine is turned through a cycle (manually), don’t use the starter to spin the engine over, it will be too fast and your eye wont be able to follow the springs exact motion, not to mention what can be damaged along the way.
In the case of a poorly selected spring (or spring retainer), don’t be surprised if you see coil bind on the inner spring(s). If that’s the case, you will have to pull everything to pieces and install an inner valve spring that suits both the application and the spring retainer. This exercise must be executed clinically or you will end up with catastrophic complications that will set you back thousands of rands and sleepless nights.
While you’re at it, regularly check the springs with a seat pressure tester (inexpensive models such as this Moroso unit are readily available). These testers simply slip over the rocker arm. Add a bit of muscle power and pull down on the tester. The number that appears on the beam scale (its like a beam torque wrench) will give you the spring seat pressure reading. If the seat pressure is down from the manufacturers specifications, you can bet your bottom dollar that the valve springs are tired and need to be replaced with new ones. Make it a practice to check the spring seat pressure every time the valves are lashed. The checking process adds about 15 minutes to the routine maintenance schedule and is always very rewarding once the above process is completed with dedicated accuracy.
- BUMP STARTER
Setting the valve lash on any solid lifter engine can get old in a hurry. Especially if you have to climb inside the car, tap the ignition switch and run around to the engine and check the balancer-timing tab location. Temporary remote starter leads are one answer, but who wants to burn their hands every time you hook it up? The solution is a permanent bump starter switch. Moroso and other companies offer state of the art waterproof switches that can be mounted somewhere in a convenient location.
Wiring the bump starter switch is simple. Wire one lead to the battery cable lead on the starter while the other lead is routed to the switched “Starter” or “S” terminal on the starter. When in operation, the ignition switch remains untouched. Simply press the bump starter and allow electrons to spin the engine over to the appropriate balancer location. When a “bump” starter switch is installed, it takes away most of the aggravation usually experienced, the down side is that you’ll still have to use a large half-inch drive bar to rotate the engine to the exact pointer location. In most cases, you can ‘bump’ the engine to a point, which is close enough to your mark, and then use the power bar to move the balancer and timing marks up to the exact position. This procedure eliminates the brute force required to turn over the engine. The final grunt work can place the timing marks in the ideal position. Fitting a ‘bump’ switch will relieve you from some tedious pressure when getting down to the basics and for the effort of fitting one you will never look back.
