Jeep Engines - Oljeep

4.0L POWER TECH IN-LINE 6 (ENGINE ASSEMBLY) 261Cylinder Head and Intake ManifoldWith the short block ready to be assembled, the cylinderhead and intake manifold can be checked in the preliminarystages of assembly.The intake manifold should be checked for port alignment.The intake manifold’s angle should be the same as thecylinder head and it should fit such that with the gasketinstalled the intake manifold bolt holes line up.For more intake manifold information, refer to ‘InductionSystem’ section of this chapter.Camshaft and Valve GearChoosing the camshaft is the last of the three major enginebuilding decisions (the three being carburetion,compression ratio, and cumshaf), and it is easier to makeonce the other two decisions have been finalized. Thecamshaft directly affects the pistons, block, head, andcomplete valve gear, so it should not be taken lightly.Camshaft choice is often difficult because of the vastnumber of options available. However, once carburetionand compression ratio decisions are made (along with whatthe engine is going to be used for), the total number ofchoices will be narrowed down to a handful or less, whichis a lot easier to select from than hundreds.With head, valves, and springs initially assembled, the headassembly can be bolted to the block and preliminary checkson camshaft and valve gear can be made.1. General Camshaft SelectionThere are literally thousands of camshaft designs tochoose from. Picking the correct one for you and yourengine without spending too much money is a verytough job. Selecting the type of camshaft (hydraulic,mechanical, roller) is usually the hardest job. MoparPerformance Parts has specific recommendations forvarious engines. However, you must still decide on thetype that best suits your application. Once you havedecided to go hydraulic, solid, or roller, MoparPerformance Parts can make recommends that willwork best in your application. The easiest way toidentify the type of camshaft is by lift. Each categoryhas a lift range in which it works best. For completeinformation and performance applicationrecommendations, refer to ‘Camshaft and Valve Gear’section of this chapter.2. Valves and Valve Springsa. Valves should be measured (to be sure they are theproper size) and inspected for flaws or otherdamage. Measure the actual outside diameter ofthe valves to be used and record the measurement.b. Valve springs should be load checked. Weaksprings will have to be replaced. Record loads andheight checked at. The biggest advantage of loadchecking is to see if the springs have “gone away”or to see if a second set of the same spring is as“strong” as the first which worked well.c.d.e.Note: Not all spring testers are the same. Manyare not maintained and calibrated on a frequentbasis. This makes the absolute value of springloads quite unreliable. However it is a very goodcomparative tool; that is, measuring all springs onthe same tester or measuring the same spring newand used.With the valves, keepers, and retainers installed,check the valve spring height. This should becompared to the spring load information (#2b) andthe correct thickness shim chosen to get the sameinstalled spring load on each valve. Valve springinstalled height must be carefully controlled toavoid “coil bind” by providing at least .loo“ moreheight at maximum valve lift than the solid heightof the spring.Caution: DO NOT check solid height with aspring that you intend to use in the engine.Compressing a valve spring to solid height willoverstress it and cause premature load loss orspring breakage.With the same spring height setup as #2c, measurethe outer valve spring height, the inner valvespring height, and the keeper-to-valve guideclearance. The camshaft lift (lift of the camshaftmeasured at the lobe or lifter) multiplied by therocker arm ratio plus .050” should be less than thekeeper-to-guide clearance in the valve closedposition or the guide will have to be shortened.Measure the “solid height” of both the inner andouter springs. This solid height plus .loo“ plus thevalve lift (camshaft lift multiplied by the rockerarm ratio) should be equal to or less than theinstalled height for each spring.The valve spring installed height can be increasedwithout installing longer valves. Usually, specialretainers are used to do this. The increasedinstalled height stresses the spring less so that itlasts longer. It also allows for higher lift camshaftswith the same basic parts.Note: DO NOT sink the valve or machine theouter spring seat down into the head to increasethe installed height. This would result in decreasedperformance.