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Engine Assembly, Part 6: Completing the Assembly
By Wayne Scraba/
Printable version
Degree of DifficultyModerate
Estimated Time240 minutes
240 minutes
Rocker, Intake, and Carburetor Installation -
In our last segment, we buttoned up the top end of the engine (cylinder heads). Essentially, we constructed a complete "long block." This time around, we'll complete the assembly with rocker installation, intake, carburetor and so on. By the way, the homestretch is very simple. There are a few special tools you'll need, but there's nothing here that's extravagant. And like we've stated in the past, if you can tighten bolts and know how to operate a torque wrench, it's pretty much easy street. Take a look:
Completing an Engine Assembly
Lifter Installation
If you can apply lubricant to the body of a lifter you can install it. Essentially, you should apply motor oil (liberally) to the lifters. Slip the lifters into their respective bores. If the engine is equipped with roller tappets, install the lifter pairs with the associated connecting links. Today, most connecting links are permanently attached to the lifter body, and in most cases the lifters are positioned with the links facing the center of the lifter valley in the cylinder block.
Push Rod Installation
In most cases, the pushrods simply drop into a guide plate of some sort in the cylinder head, with the lower end fitting directly into the cup of the lifter. The top end fits into the matching rocker arm. It's a simple install.
On the other hand, if the engine is modified with items such as a small base circle camshaft, non-stock cylinder heads, non-stock rocker arm mounting positions, severely milled deck (or head) surfaces, longer-than-stock valves, the use of valve lash caps and other factors, you may need to establish the correct pushrod length.
Even in a normal situation (where the geometry hasn't changed due to the factors mentioned above), the tip of the rocker arm tends to sweep across the tip of the valve. If the geometry has changed, and the pushrod length is not optimized, the amount of movement the rocker sees across the valve tip is considerable.
In order to check the geometry and to establish correct pushrod length, you'll need a checking pushrod. There are several available. We have one from Crane Cams. First, turn the engine over until the rocker arm/pushrod combination you're checking is on the base circle of the cam (both valve closed). With the rocker removed, coat the tip of the valve with a black felt marker. Reinstall the rocker arm. Move the rocker so that a mark becomes visible on the tip of the valve. If the geometry is correct (and the pushrod length is correct) then the mark you see on the valve tip (made possible by rubbing away the felt marker "paint job" you made) should be located approximately 1/3 of the way across the tip, on the inboard side (towards the intake manifold). If the mark is in the center of the valve tip or if it is closer to the exhaust (header) side of the valve tip, the pushrod is too long. If the mark is closer than 1/3 the distance to the intake manifold, the pushrod is too short.
In order to establish the right pushrod length, you'll need the adjustable "checking" pushrods mentioned previously. Install the checking pushrod in place of the conventional model. The adjustment feature allows you to lengthen or shorten the pushrod as necessary. Repeat the "paint the tip" and check the scrub mark with a longer or shorter pushrod length. It's a matter of trial and error (shortening or lengthening the adjustable pushrod) until you arrive at the length where the scrub line on the valve tip is correct. At this point, measure the adjustable pushrods so you can determine the optimum length. You can now order the right pushrods (length) for your application. Once they arrive from the manufacturer, it's a good idea to double check the length (and the geometry) before slipping them into place.
Rocker Arm Installation
Conventional stud mount rocker arms simply install over the rocker studs and are most often held in place by way of a lock nut. When installing conventional rockers, you should double check the fulcrum. Most roller rockers are designed with a machined flat that mates with the rocker adjuster nut. Be sure the machined flat is correctly oriented. Apply a small amount of engine assembly lube to the pushrod tip. The engine will have to be rotated through a complete cycle so that all of the rockers are installed while the cam is on the base circle. All that remains is to install the rocker and to set the valve lash (refer to your cam manufacturer specification card for the valve lash figure and refer to the engine manufacturer specifications for the valve lash procedure).
When it comes to shaft mount rockers, the installation isn't much more difficult. With pushrod length verified, torque the stand bolts to specifications. Next, apply assembly lube to the pushrod tip and bolt the rocker to the rocker stand. Torque the rocker shaft bolts to specifications. Keep in mind the engine has to be rotated through the cycle so that the rockers are installed with the cam on the base circle. Set the lash, and you're done.
Intake Manifold Installation
There's no question an intake manifold is an important piece of the high performance puzzle. If installed improperly, they can definitely have a negative effect upon performance. The best plan is to test-fit the intake manifold to ensure that it will actually work on your engine (things like cylinder head and block milling have an effect upon manifold fit). Here's how it's done:
Place a dry intake gasket on each side of the heads and lower the manifold in place. In some applications, you use a light to peer down the port to check alignment. In other cases, you can feel the fit by using a piece of wire to probe the port alignment by way of the plenum (a stiff piece of mechanic's wire or a coat hanger will work). You should also check the end gaps at the front and rear of the manifold where the intake attaches to the block valley. There must also be a small gap at the front and the rear.
Remove the intake and carefully clean the gasket mating surfaces with brake cleaner (or solvent). Apply a bead of RTV silicone sealer along both of the ends of the lifter valley (the front and rear of the engine). Next, install the intake manifold gaskets on the cylinder heads. A small amount of gasket adhesive can be used to ensure the gaskets do not move as the intake is installed. Carefully lower the intake in place, setting it straight down the valley on the respective gaskets. Do not attempt to slide the manifold from side to side or from front to back. This can create gasket misalignment. By the way, this sounds more difficult than it really is. You simply have to line up the bolt holes in the intake with the threaded holes in the cylinder heads.
Hand-thread all of the intake bolts into the cylinder heads. Much like the cylinder heads, there's almost always a specific torque sequence used to tighten intake bolts. Typically it begins from the center and works outward. Consult a factory manual for specs on your specific powerplant. Much like the cylinder head torque sequence, begin the process with 1/3 (approximately) of the specified torque. Repeat the torque sequence three times (this is often necessary in order to get the manifold gaskets to compress fully).
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