Engine Assembly Basics -- Cam, Valvetrain, Top-End
Cam, Valvetrain, and Top-End
From the February, 2009 issue of Popular Hot Rodding
By Steve Dulcich
In the last issue of Engine Masters, we set out to start a series of articles that gets right to the core of engine building by showing the tricks, techniques and tools required to successfully build an engine. The aim is to arm the reader who dreams about putting together a high performance powerplant with the information needed to get it done. How? The goal is to answer the question of "How to do it" as much as "What to do." We covered what goes into building a short-block, and how it is done, in the last issue. This time around, we turn our attention to the cam, valvetrain, and top-end.
Really, this is a pretty broad subject, and the details vary depending upon the caliber of the build, and the equipment being used. The idea is to focus on the ideas that are universal to any engine buildup. Some of the detail may be more than you need to know for a very basic assembly, but knowing more is never a bad thing. We encourage feedback from our readers, so if you have an area of engine building you'd like explored in detail, contact me at email@example.com.
Install and Degree the Cam
At the most basic level, only a few things need to be ensured while installing a camshaft. The camshaft must be clean and properly lubed, and once in, it must spin freely in the block. The lube used will depend on the type of cam. Flat-tappet camshafts require a special high-load break-in lube on the lobes, which is usually packaged with the camshaft. The bearing journals should be lubed with an assembly oil or regular motor oil. Roller camshafts, either mechanical or hydraulic, normally do not need special cam lube on the lobes, and can be installed with oil on the lobes and journals.
Installing the camshaft can be as simple as sliding the stick into the bore, and making sure the timing dots are in alignment at TDC when the timing set is bolted in place. Most mild to stock rebuilds, and a surprising number of high performance engines, are put together this way. Taking such an approach is like flying blind, since the camshaft's installed centerline will not be known unless it is actually checked by the process commonly referred to as "degreeing-in." Unfortunately, inaccurately degreeing-in the camshaft is one of the most common engine assembly blunders, often making matters worse than just lining up the dots. If the cam is going to be degreed-in, it has to be done with the utmost in accuracy. Tools for degreeing a cam are relatively inexpensive; degree wheels can be purchased from most cam manufacturers, while some such as COMP Cams offer kits with everything you'll need.
Degreeing-in begins with accurately...
Degreeing-in begins with accurately finding TDC, which serves as the key reference point for the cam phasing. TDC can be found with a piston stop, a deck bridge and dial indicator, or an indicator on a stand. Start by setting up a degree wheel and pointer at the crank, and set it up to indicate zero degrees at an eyeballed TDC. Next, use the dial indicator to fine tune the pointer. Since the exact TDC point is difficult to distinguish on the indicator, a checking height in the vicinity of TDC is used before and after TDC (the actual checking height isn't critical; I use both 0.025 and 0.050 inch). Zero the indicator at TDC, and then rotate the crank to the checking height before and after TDC, recording the degree wheel readings. Adjust the pointer so that the readings are the same value before and after TDC at the checking height. When the values are the same, the zero mark will be centered at TDC. When making the checks, the crank should be rotated in the normal direction of rotation.
Proper lube upon installation...
Proper lube upon installation is vital to a cam's survival, especially with a flat tappet. Apply the manufacturer's lube to the lobes, such as the moly-based paste supplied with this Lunati Voodoo cam, and apply oil to the journals. When installing the cam, use a cam handle tool, and guide the 'shaft carefully into the tunnel without banging-up the delicate cam bearings. The cam should slide into place easily and should rotate freely in the bore. If the cam binds, there is a problem that needs to be corrected before moving on. Possible causes of cam binding can be improperly machined or sized journals, a bent cam (run-out), as well as misaligned or damaged cam bearings. The bearings will show witness marks were the cam is binding.
Now that the degree wheel...
Now that the degree wheel and pointer are set up to read exactly TDCNow that the degree wheel and pointer are set up to read exactly TDC, a lifter is installed on the No. 1 intake lobe, and a dial indicator or a special checking tool is set up to record the tappet rise. The object is to read from the degree wheel exactly how many degrees past TDC peak intake lift occurs. Begin by rotating the crank and zeroing the indicator at peak lift. Since the exact point of peak lift is difficult to distinguish, a checking height is used when reading the degree wheel. I use both 0.025 and 0.050 inch, recording the degree wheel readings at these points before and after the indicator goes over the nose of the lobe. The installed centerline is determined by averaging the degree wheel reading at a given checking height before and after peak lift. When making the checks, always rotate through the checking positions in the normal direction of engine rotation.
Lifters basically come in four types: flat-tappet and roller, available in solid or hydraulic versions depending on the camshaft type and design. Always use the appropriate lifters for the type of camshaft being used. Flat-tappet lifters must rotate in the bores, while rollers must maintain their alignment to keep the roller wheel in line with the lobe and avoid destruction. Typically, solid rollers and retrofit hydraulic rollers use a link bar arrangement to pair up the lifters and hold them in alignment. OEM hydraulic rollers will typically use alignment yokes and a spring-steel spider for alignment. The essentials for lifter installation are cleanliness, proper lubrication and free movement.
Solid roller lifters are often...
Solid roller lifters are often shipped with protective grease in the bearings, and require cleaning and soaking in synthetic oil to properly prepare them for use.
When installing the link bars...
When installing the link bars for a roller set-up, makes sure that the link bar is orientated properly. For some applications, a link bar installed in the wrong orientation will cause failure--typically the manufacturer will provide markings and instructions on the correct orientation. When the lifters are installed, set the cam at the base circle for that pair and work the lifters through their range of motion to feel for any binding.
In contrast to a roller, a...
In contrast to a roller, a flat tappet must rotate in the lifter bore for survival. Lube a flat tappet with cam lube on the base and engine oil on its sides and oil the lifter bores. The lifter must slide easily in the bore, without any binding or tight spots. Some block cleaning procedures using shot tumblers can create a burr at the top of the lifter bores, causing binding. Always prep and check the lifter bores during the mock-up stage of engine assembly.
With hydraulics, either flat-tappet...
With hydraulics, either flat-tappet or roller, the lifters should never be pre-filled or primed in their hydraulic mechanism. The lifters will fill with oil and self-adjust when the engine is pre-lubed and fired.
In a shaft rocker system,...
In a shaft rocker system, the pivot point and valve tip are in a fixed position, so the geometry is also fixed by the design of the system. Changes can be made to raise and lower the pivot point, or move the rockers forward and back relative to the valves, but these kinds of changes involve precision machining and modification normally in the realm of the most advanced engine builders.
In a stud-mounted system, two of these variables depend on pushrod length, since the actual pivot point of the rocker will change with the pushrod length. With stud-mounted rockers, the pushrod length will affect the position of the rocker pad or roller across the valve tip. In a shaft or fixed-pedestal system, the valve tip position, as well as the rocker's pivot point, is fixed. With these systems, the geometry is essentially set by the rocker design and the valve length. Pushrod length in these installations comes down to achieving the required range or position in the rocker's adjuster. In custom installations, the pushrod length will often need to be determined by mocking up the valvetrain with checking pushrods, available from Powerhouse Tools and others.
With a fixed fulcrum rocker...
With a fixed fulcrum rocker arrangement, the only variable is the pushrod length, and it should be set to position the rocker adjuster in the range of travel recommended by the rocker manufacturer, typically with about one thread of the adjuster showing below the rocker body. With some rocker designs, oiling is dependent on the adjuster falling within a narrow specified range.
The rocker's sweep across...
The rocker's sweep across the valve tip can be found by marking the tip with layout dye, and rotating engine through several lift cycles. A centered pattern with minimal sweep is ideal. With stud-mounted rockers, the sweep and position of the roller depends upon the pushrod length. Longer pushrods generally move the pattern out, while shorter ones move it in.
Rocker clearance is an important...
Rocker clearance is an important consideration to be aware of. The rocker body needs to physically clear the spring and retainer throughout the range of travel. This is something that should not be taken for granted, especially with large springs and deeply dished or large diameter retainers. Springs such as COMP's Beehive design seen on this LS1 offer the greatest clearance.
With brutal race cam profiles,...
With brutal race cam profiles, the valve tips and rocker rollers take a severe beating. Lash caps top the valves with a very hard precision-ground flat surface, which provides a broader surface of contact between the rocker and valve, helping deal with the severe loads involved. Lash caps are typically .080-inch thick, and can also be used to correct minor rocker geometry problems by effectively lengthening the valve.
When ordering custom pushrods,...
When ordering custom pushrods, the best method is to use a checking pushrod and physically measure the required length with a 12-inch caliper. Note whether the pushrod tip has an oil hole, which introduces error in the effective length. If the pushrod features a cup end configuration, measure the overall length minus the cup depth to determine the effective length. Inform the pushrod supplier of the measurement, and the method of measuring. Choose a pushrod wall material suitable for the spring loads, and make certain to specify the correct tip size to match the rockers and lifters being used.
The amount of load a spring...
The amount of load a spring delivers is as much a function of its designed spring rate as its installed height. When ordering springs, a measurement of the available installed height is a key piece of information in selecting the proper springs. These Mopar big-block heads had 2.060-inch installed height. With the required spring cup, the installed height will be 2.00 inches. Simply ordering and installing a spring designed for a Chrysler big-block, which typically has an installed height of 1.880 inches will result in way too little seat load. A COMP PN 924 spring for a big-block Mopar delivers 125 lbs load at 1.880 inches, while at 2.000 inches, the load drops to 87 lbs, too weak for even a stock cam. Measuring and noting the installed height is the only way to determine if a spring will deliver the load required. Powerhouse has these handy height micrometers (PN POW101200), which make measuring installed height a breeze.
Some Things About Springs
As the seriousness of the performance effort increases, the more critical valvesprings become. In lower rpm performance engines, which may never see over 5,500 rpm, the most basic level of care in valvespring selection and installation will generally get you by. As rpms increase, springs become one of the most critical factors in wringing the performance potential from a combination. Things to become familiar with are the seat load, installed height, open load, spring rate, and coil bind clearance. Let's take them one at a time.The 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 rpms. 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 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 furthest. 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. A spring rated at 350 lbs/inch will gain 350 lbs for a theoretical inch of compression. How much the spring will gain for any amount of valve lift can be calculated by multiplying the lift by the spring rate. A 0.700-inch lift cam with a 600-lbs/inch rate spring will gain 0.700-in x 600 lbs/inch for a gain of 420 lbs. Add the amount gained to the seat load, and the open load is the result. For instance, if in our example the seat load was 200 lbs, gaining 420 lbs in opening will give 620 lbs open. Most spring suppliers publish spring rate specs. The coil bind height is the height of the spring when it's compressed down solid. 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 will give the clearance to coil bind. As an example, let's say we have a spring with an installed height of 1.800 inches. If the valve lift is .600 inch, the spring is compressed to 1.200 inches at full lift (1.800 in. - 0.600 in. = 1.200 in.). If the manufacturer's catalog lists the coil bind height at 1.100 inches, it's safe to say there is 0.100-inch coil bind clearance left (1.200 in. - 1.100 in. = 0.100 in.).
How much spring load is the right amount? It depends upon the radicalness of the cam profile; the type of cam - solid, hydraulic, or roller; the valvetrain weight; and the engine's rpm range. Typically, top experienced engine builders spec their own springs, but for the average enthusiast, it's best left to the cam manufacturer.
Although spring loads can...
Although spring loads can usually be found via the manufacturer's catalog, a spring tester such as the digital Moroso unit we are using here will provide all of the information needed. The spring can be checked directly for closed and open load just by compressing to the installed height and then compressing to that number minus the amount of valve lift.
The installed height can be...
The installed height can be adjusted downward by adding shims, typically available in 0.015, 0.030, and 0.060-inch thickness, and a wide range of inside and outside diameters. Spring cups and locators are usually .060-inch thick, and take away installed height.
There are a variety of retainers...
There are a variety of retainers and locks available having different degrees of strength and lightness. Selecting retainers begins with getting one that fits the spring. Retainer choice can also significantly affect the installed height, since retainers vary in the amount of "dish" in their profile, which alters their height. If more installed height is needed, specialty locks can be had which raise the retainer's position. Locks also vary from cheap stamped units to heavy-duty machined pieces heat-treated to carry extreme spring loads. Though most standard retainers and locks mate at a 7-degree angle, some aftermarket manufactures like COMP offer extreme-duty 10-degree pieces, drastically reducing the possibility of a lock pulling through a retainer. The 7- or 10-degree locks and retainers must always be used as a set.
Just as the retainer must...
Just as the retainer must match the spring at the top to properly secure and locate it, a spring cup should be used at the bottom to keep the valvespring from dancing around on the cylinder head side. 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 COMP PN 4700 cups for this iron Mopar head, which locates a 1.550-inch spring by its outside diameter. As is often the case, spring seat machining is required on these production heads to fit the locator.
Critical Clearance: V-To-P
One of the most important checks to make when building an engine is the valve-to-piston clearance. As cam duration and compression ratios go up, this figure becomes more critical. Some make the mistake of presuming that the valve-to-piston clearance is a function of the cam's lift specification, but in reality it is more related to the duration and lobe separation angle. The piston is well out of reach of the valve by the time the valve reaches maximum lift, usually at around 102-112 degrees after TDC. The critical factor is what's happening during overlap, when the piston is very near TDC, the exhaust valve is closing, and the intake valve is opening. The exhaust valve will normally get closest to the piston somewhere in the vicinity of 15 to 5 degrees before TDC, while the intake valve will be closest in about the same range after TDC.The most common methods of checking valve-to-piston clearance are directly reading the travel to contact with a dial indicator or making a check using clay on the piston tops. Both will provide a good indication. The dial indicator system will give a more precise number, but does not reveal potential radial clearance problems of the valve's edge to the position of the valve pocket machining. The clay system will show exactly where the valve is in relation to the piston and valve notches, but it is more difficult to get an exact clearance number.
To check valve-to-piston clearance...
To check valve-to-piston clearance via the clay method, a lump of clay is laid into the valve notch area of the piston while the cylinder head is off. The head is then installed, along with the complete valvetrain, and the crank is rolled over through the overlap event. The head is then removed, and the valves' impression in the clay is examined and the thickness measured with a caliper to determine clearance. The clay may be sectioned with a razor blade for a full view.
An alternative means of measuring...
An alternative means of measuring valve-to-piston is to rig the valves with light checking springs, and then installing the head and valvetrain with a dial indicator reading off the retainer. Start at 20 degrees BTDC, set the indicator to zero, and then work the exhaust rocker by hand until the valve hits the piston, and read the indicator travel. Repeatedly adjust the crank position 2 degrees forward, re-zero the indicator, and check again. The reading will diminish to the minimum V-to-P value, and then open up again. Next, perform the same procedure on the intake valve, moving from TDC to about 20 degrees after.
Bolting It Together
By now the short-block should have the cam installed and degreed, and the cylinder heads should be standing by fully assembled, with the compatibility and clearance of all of the valvetrain components verified. The piston-to-head clearance should have been verified during the short-block mock-up stage, and the appropriate head gaskets sourced for the desired quench clearance. All that is left is to bolt together the final long block by installing the cylinder heads, valvetrain, and intake manifold. These procedures are relatively straightforward if all of the checks have been made beforehand.
The cylinder head gaskets...
The cylinder head gaskets are an important part of the assembly. The gaskets must be capable of sealing at the power and pressure levels the engine will encounter, and be of the correct configuration for the engine. The gasket's thickness should provide the desired piston-to-head clearance, particularly when setting the engine up for a useful quench effect. These Cometics for a big-bore 572 Mopar were custom ordered for the bore size, and give 0.040-inch clearance to the narrow quench band of the custom dished pistons.
Cylinder head fasteners should...
Cylinder head fasteners should not be neglected. Studs provide greater clamping load than bolts, but make head removal more difficult, particularly in the vehicle. Make sure that the fastener's engagement in the block is sufficient, and use sealant if the fastener goes into the water jacket. Torque the fastener to its manufacturer's specs, using the engine manufacturer's pattern. Cylinder heads are torqued in steps. Unless the fastener manufacturer specifies otherwise, I usually torque by first seating the fasteners, then work the pattern to 50 percent of the rated torque, then 75 percent torque, and finally, full torque. Be sure to lube the thread with the lube specified by the fastener manufacturer. ARP can supply new studs or bolts of very high strength material for most popular engines.
The valvetrain is typically...
The valvetrain is typically more easily assembled with the intake manifold off. If the homework has been done ahead of time, the valvetrain will come together with no unforeseen surprises. Usually the valve covers wait until the intake has been installed, though they should be checked for adequate clearance by laying them in place without the gaskets, and rolling the engine over two full rotations and checking for contact with the assembled valvetrain.
Installing the intake manifold...
Installing the intake manifold shouldn't pose an undue headache, if the alignment was verified during the mock assembly. It is common practice to use a bead of silicone sealant on the end-rails where the factory used a separate end-rail gasket segment. Quality flange gaskets typically need no further sealant. Secure the intake manifold according to the intake manufacturer's specs.
Livin' For Lash
What separates a hydraulic lifter from a solid is the addition of an internal hydraulically operated plunger within the hydraulic lifter's body. The way the valvetrain is set up will depend upon whether the lifters are hydraulic or solid. Hydraulics generally run with pre-load, while solids must be set up with lash. Let's first consider a hydraulic. It's helpful to understand how the hydraulic mechanism works and what it does. Oil pressure enters the lifter through an orifice in the lifter body, and flows through another orifice into the hollow body of the lifter plunger. A one way check valve at the bottom of the plunger allows oil to fill the cavity below until all the valvetrain clearance is gone, effectuating the hydraulic self-adjustment to zero lash. When the cam rotates into the lift cycle, the check valve at the base of the plunger closes under the pressure imparted by the valve spring, preventing the oil from being squeezed back out as the valve opens. At the top of some hydraulic lifter plungers is a metering valve or plate, which supplies oil to the pushrods for valvetrain oiling.With the valvetrain installed (or adjusted), the pushrod compresses the plunger within its range of travel, and the hydraulic mechanism automatically zeros the lash. How far down the lifter plunger has been displaced at its base setting is called the lifter pre-load. The recommended pre-load with hydraulic lifters is usually in the range of 0.020 to 0.040 inch. Many stock valve-trains are non-adjustable, although many parts and processes involved in an engine build can alter the factory pre-load. In these cases, the solution is custom-length pushrods, or making the change to adjustable rockers.With adjustable rockers, setting the pre-load is simply a matter of setting the lobe being adjusted to the base circle, and tightening the adjuster until the clearance in the valvetrain is just taken out (zero clearance). Then turn the adjuster in 1/2 to 3/4 of a turn and lock the adjuster down.Solid lifters have no self-adjusting hydraulic mechanism, and need to run with clearance in the valvetrain. The lash specification is given on the cam card for a solid cam. The adjustment is made with the lobe being adjusted set on the base circle. A feeler gauge of a thickness matching the lash spec is inserted between the rocker and the valve tip, and then the adjuster is taken to zero lash and locked down. When the feeler gauge is removed, the lash will be set at the thickness of the feeler gauge. Lash is usually set cold when the engine is built, and then re-adjusted once the cam is run-in with the engine hot. The hot setting will be more true to the engine conditions in operation.