Jeep Engines - Oljeep

~~INTRODUCTIONThe 4.0L engine uses a cast nodular iron crankshaft thatrotates within seven (7) main bearings and has a standardbore and stroke of 98.4 x 87.4 mm (3.88 x 3.44”).Crankshaft rotation is clockwise, when viewed from thefront of the engine.The crankshaft is a cross-shaped four throw design witheight counterweights for balancing purposes. Thecrankshaft is supported by seven select main bearings withNo. 3 serving as the thrust washer location. The mainjournals of the crankshaft are cross drilled to improve rodbearing lubrication. The select fit main bearing markingsare located on the crankshaft counter weights. Thecrankshaft rear oil seal is a two piece design. The front oilseal is one piece design retained in the timing chain cover.The crankshaft has a main bearing journal diameter of63.489-63.502 mm (2.4996-2.5001”), and main bearingjournal widths of (No. 1) 27.58-27.89 mm (1.086-1.098”),(No. 3) 32.28-32.33 mm (1.271-1.273”), and (Nos. 2,4, 5,6 and 7) 30.02-30.18 mm (1.182-1.188”).The crankshaft has a connecting rod journal diameter of53.17-53.23 mm (2.0934-2.0955“) and a connecting rodjournal width of 27.18-27.33 mm (1.070-1.076”).For high performance racing engines, Mopar PerformanceParts recommends a forged crankshaft. Forged crankshaftsallow you to specify to your grinder exactly what stroke youwant, and cost less to have finished than billet crankshafts.And for those of you who want an oversize bore engine, acustom ground forged crankshaft is the way to go.For more crankshaft specifications, refer to 4. OL EngineSpecz$cations, ‘Engine Assembly’ section of this chapter.~~ ~High Performance CrankshaftThis Mopar Performance Parts high performancecrankshaft has a 3.41“ stroke and has been carefullyinspected and Magna-fluxed. 4.0L engine only.P4529205High performance crankshaft.Balanced and Unbalanced CrankshaftsWhen describing crankshafts, we use words such as“balanced” and “unbalanced.” However, what is physicallydifferent about the crankshafts is not as obvious as thewords may imply.Since the unbalanced crankshaft is easier to understand,we’ll start with that one. Unbalanced crankshafts haveSOLID journals. That means there are no holes through thefirst and last crankshaft journals. Racers like this becausethey can offset grind the crankshafts if desired. Other racersC ran ks haf t4.0L POWER TECH IN-LINE 6 (CRANKSHAFT) 137who use superchargers and/or alcohol fuel like solidjournals because they see them as being stronger (becausethere are no holes in them). These are called “unbalanced’or “solid journal” crankshafts.To spin-balance a typical crankshaft that has solid journals,you have to add Mallory metal. This can be expensive.Therefore, production crankshafts have a machined holethrough the first and last journals. These are balance holes.Racers call them “balanced’ crankshafts, so we call thembalanced crankshafts. The name ONLY refers to the large1-1/16” hole (approximately) through the first and lastjournal. The crankshaft should still be balanced with itsspecific connecting rods and pistons like any other raceengine crankshaft. However, the big holes usually eliminateor cut down the use of Mallory metal.Crank BoltThe crank bolt is often used to turn the engine over by hand,but this is only a convenience item. Its real function is tohold the vibration damper on. That is why it is put on withso much torque. If the interference fit on the damper hub isnot there and the crank bolt is not torqued, the damper can’tdo its job. This will cause the crank to eventually fail.To hold the damper on properly there is a special large, hardwasher that is used. We have included this special washerin our damper attachment package (P4529677).BASIC PREPARATIONWhen preparing a crankshaft for racing applications, thefollowing steps should be performed:1. Crankshaft bearing journals should be checked forspecified diameter and clearance. If it is a hardenedcrankshaft, it shouldn’t be ground for clearance. Thesecrankshafts are hard only to a depth of .0003”. The mainbearing clearances should be 0.03-0.06 mm (0.001-0.0025I’). The best way to measure crankshaft journalsis with a micrometer. To measure main bearingclearances, the bearings can be installed, the boltstorqued to specification, and the inside diameter of thebearing measured 90 degrees to the parting line with aninside micrometer or snap-gauge. The differencebetween these two measurements is the bearingclearance. Plastigauge is accurate enough for most raceapplications (P4286819 - includes all 3 sizes).2. The bearing journals may be polished by hand, firstwith #400 and then with #600 paper. Any nicks, burrsor scratches should be polished out. Chamfer oil holesin journals and use a wet stone to break edges. Checkthe oil passages to each journal.l- -11