Jeep Engines - Oljeep

4.0L POWER TECH IN-LINE 6 (ENGINE ASSEMBLY) 257Crankshaft End Play . ......................Rod Side Clearance . ......................Deck Height: Above BelowCamshaft LiftAt Valve: Intake Exhaust ________At Camshaft: IntakeInstalled Camshaft CenterlineCamshaft I. D.Exhaust ________(or part number, if available) _________________At this point we’ll assume that we’re rebuilding the enginefor added power and that there was nothing wrong with iton its last pass; that is, it isn’t broken. So why are thesemeasurements important?Let’s look at each one individually. Crankshaft end play canindicate that the crankshaft is worn and needs to bereplaced. It may also indicate that you have anengine/drivetrain mount problem that needs to be fixedbefore you break the engine. If the connecting rod sideclearance is high, you may need connecting rods or thecrankshaft journal may be worn. Deck height affects thepiston selection and directly relates to the engine’scompression ratio.The easiest way to identify a camshaft by measuring the liftboth at the valve and at the camshaft lobe. This allows us tocalculate the rocker arm ratio. The camshaft centerlinecheck allows us to put the camshaft in the engine in theexact same location as before. If we don’t do this, we canlose some power/performance with the same pieces we had.The camshaft I.D. is sometimes stamped on the end of thecamshaft that goes into the engine. This is sometimeshelpful with aftermarket grinds. But, if it isn’t there, thenthe camshaft lift will get us what we need. One of the mostimportant items is to write this information down.Pari IdentificationCasting numbers can be used to identify new or usedcylinder heads and cylinder blocks, even new or used intakemanifolds. Forging numbers can be used to identifyconnecting rods. In either case, these numbers cannot beused to purchase the part from a dealer, speed shop, etc. Inmost cases, the service number (number used to obtain theitem) will be one or two digits different from the castingforgingnumber. This doesn’t usually cause a problem, onlyconfusion, except for production camshafts. Camshaftshave a casting number, but it’s of no use in identifying thecamshaft except to tell you which engine it came out of,which you usually already know.The problem is that all production cams (2 to 3 designs in agiven year) for a given engine are all ground from the samecasting. At this point, cam identification is best done bymeasuring the cam lift at the lifter. This is much morereliable than casting numbers.Otherwise, casting numbers and forging numbers are asvaluable for new parts as they are for old ones. Write bothin your notebook.INSPECTION AND PREPARATIONCylinder BlockThe basic block should be checked and reworked inaccordance with the following procedures:1. Before disassembling the block, the deck height of thepistons must be checked. Deck height is the distancefrom the top of the piston to the top of the deck surfaceof the block. This is an important dimension since ithas a direct influence on compression ratio. If thepiston is a flat top style, it will usually be below thedeck and this is the distance that must be measured. Adomed piston will stick up above the deck surface andthe distance is measured from the deck to the top of thedome. Mark this figure down for future reference andcompletely disassemble the block.Optional Step: Stress Relieving (refer to ‘Block’section of this chapter).2.3.4.All the head bolts should be screwed into the blockwithout the head. Visually inspect the rows of bolts forany that may be bent, drilled at any angle, or for holesthat are not drilled deep enough. When the head boltsare screwed in, the depth of thread engagement shouldbe checked and recorded.The main bearing bores must be checked for bothspecified diameter and alignment with each other. Ifeither is off, a Tobin-Arp align boring machine (or anysimilar type machine) must be used to align bore theblock. A crankshaft-turning tight spot indicates that thebores are out of alignment.Sonic Testing (refer to ‘Block’ section of this chapter).