Jeep Engines - Oljeep

4.0L POWER TECH IN-LINE 6 (BLOCK) 135Deck HeightOnce the main bearing bores are known to be in alignment,the deck surface of the block should be checked to make sureit is parallel with the axis of the crankshaft. The distancefrom the centerline of the crankshaft to the deck surface ofthe block should be exactly the same at the front and rear. Ifnot, the deck surface will have to be milled. At this time thedeck height can be machined to the proper dimension.Note: Deck heights that are above the block surface will beincreased by milling the block. Check the engine’sblueprint specifications before milling. The resultingmachined surface of the deck must be on the rough side toproduce a good gasket seal and prevent the head gasketfrom moving.Notching the Cylinder Bore for Connecting RodClearanceIf you are attempting to install a crankshaft from a 4.2Lengine into a 4.0L engine, you may have to notch thebottom of the cylinder bores (as required) to obtain .100“clearance (Figure 4-4).There are many variables associated with this popularmodification (too numerous to go into detail here). Formore information, call the Mopar Performance PartsTechnical Assistance Hotline at 1-248-969- 1690, or faxthem at 1-248-969-3342. They’ll be glad to help you.Rod Notch at Bottom of Cylinder BoreDowel PinsEnsure that all dowel pins used for aligning purposes arethe proper height (not too high), and that the dowel pinslocate the head properly so that combustion chambers areproperly centered over cylinder bores. Check to be sure thatthe dowel pins don’t hold the head up off the block.Note: Check without a head gasket.Rear Main Bearing Oil SealThe rear main bearing oil seal machined groove should beroughed slightly with a center punch and the rope seal mustbe seated all the way in. The rubber rear main seal shouldbe held in place with Permatex (RTV) behind the seal.Camshaft BearingsvNotchCylinder Bore Notch forBig Rods or Long Strokes-TOP of BlockWhen installing camshaft bearings, make sure that the oilholes in the bearings line up with the oil holes in the block.DO NOT replace the camshaft bearings unless they are bador the block has been tank cleaned in acid.DeburringROat -$)EYf Bottom of Cylinder BoreUse a small, fine file to remove burrs and break all sharpedges in the main bearing bores and around the cylinderbore chamfers, as well as other sharp edges on the block.Tappet BoresThe tappet bores may be shined with #400 paper to removeany rough spots or burrs. A brake cylinder hone may alsobe used with care. Tappet bore clearance is very important.If it is too tight, the lifters will stick. Use .0015” for flattappets and over ,001 5” to .003” for rollers. High clearancecan cause low oil pressure if the tappet bores are “wet.”If a big, flat-tappet camshaft that requires .100” oversizemushroom lifters is going to be used, the bottom of thelifter bore should be spot-faced to a slightly larger diameterthan the diameter of the mushroom lifter bottom. A backspot-facing tool is required to do this.CC’ing the BlockFigure 4 - 4For complete information, refer to Measuring 1/2” DownFill Volume, ‘Pistons and Rings’ section of this chapter.ADDITIONAL CYLINDER BLOCK PREPARATIONAND ASSEMBLY TIPSBuilding a high performance engine requires a lot ofmachining and assembly. Getting the bores straight, round,and with no taper is very important to making horsepower.However, there are several little items that are oftenoverlooked in engine building until it’s too late.