Jeep Engines - Oljeep

4.0L POWER TECH IN-LINE 6 (CONNECTING RODS) 149SPECIAL CONNECTING ROD INSTALLATIONPROCEDURESRod RatioFor all-out modified race engines, it is recommended that arod ratio (length of the rod divided by the stroke) of 1.75 to1.85 be maintained if possible for best performance. (Thestock 4.0L engine has a rod ratio of 1.78 - this is consideredthe best overall choice.) Side clearance should be 0.25-0.48mm (0.010-0.019”).Measuring Side ClearanceSlide snug-fitting feeler gauge between the connecting rodand crankshaft journal flange. The correct clearance is0.25-0.48 mm (0.010-0.019”). DO NOT increaseconnecting rod side clearance (two rods) beyondspecifications. Replace the connecting rod if the sideclearance is not within specification.Note: Excessive side clearance increases the oil demand ofthe engine as a result of excessive oil leakage past theconnecting rods. Increasing oil demand reduces the oilavailable for lubrication and cooling at high engine speeds.Excessive side clearance also increases the amount of oilsprayed on the cylinder walls overloading the oil rings.The excessive oil then ends up in the combustionchamber and can cause pre-ignition. (By definition, oil isa very low octane fuel!)Cap AlignmentSometimes the simplest questions can be the hardest toanswer. In some cases you assume that everyone knows theanswer already. For example, someone asks the question,“Can you reverse the cap on a connecting rod?” The answeris, “No!” Although this is correct, the follow-up question(“why?”) is not so easy to answer. During engine assemblywe line up the numbers on the sides of the connecting rods.Therefore, if we reversed the caps, the numbers would notline up. Sounds good, but is it the complete answer?Since we (Mopar Performance Parts) are in the partsbusiness, we should have an answer to this question. Afterall, there are no numbers stamped on the side of serviceconnecting rods or Mopar Performance Parts connectingrods (or any aftermarket connecting rod for that matter).Therefore, the numbers can’t be used to tell us why. Doesthis mean that the caps can be reversed‘? How about on aservice connecting rod? The answer is still “No!” We’llhave to look deeper to find out why.Connecting rod cap tab slots are a feature that you maythink will lead to the “why?’ answer. There is a slot in thecap and one in the connecting rod that align the bearingshells. These two tabs (or slots) have to be together. Thiswould mean that the two slots would be next to the samebolt. Although this is true, it is NOT the complete answer.(It is only coincidence!)If you take the cap off the connecting rod assembly, youwill notice that there is a V-groove across the parting faceof the cap. You will note that the V-groove is on theopposite side from the bearing tab slot. There is also a smallV-notch in the bearing shell which should be installed toline up with the V-groove in the cap. This groove provideslubrication of the cylinder wall on the opposite bank. We’regetting warmer!In racing and other very high performance engines, theconnecting rod caps may not have a V-groove. Extremelyhigh rpm applications don’t need any more oil on thecylinder walls, so the V-groove may be omitted. Eventhough the V-groove isn’t always there, the fact that it isdesigned to oil the opposite wall leads us to the correctanswer. The groove-to-wall relationship means that how theconnecting rod fits into the crankcase is important.The key to all of this is to notice that the chamfer on the bigend of the connecting rod is not the same on both sides.There is a big chamfer on one side and a small chamfer onthe other. The big chamfer goes toward the crankshaft whilethe small chamfer goes toward the other connecting rod. Ifthe cap gets reversed, then there would be a small chamferon the connecting rod and a large chamfer on the cap. Thisis how you can tell that a cap had been reversed. DO NOTassume that a used engine did not have some of its capsreversed. The proper way to install the connecting rod intothe engine is that the right cylinder bank (#2, 4, 6) shouldhave the large chamfer toward the rear of the engine. Theconnecting rods on the left bank (#l, 3, 5) should have thelarge chamfer toward the front of the engine. The servicemanual ties the direction of the chamfer to the “notch” inthe top of the piston. In racing we may reverse the pistonsor have no offset and therefore no notch or arrow. Thereforeit is best to install connecting rods by chamfer and cylinderlocation. The service manual also says that you should fitall connecting rod and piston assemblies on one bank untilcomplete. This is important. DO NOT alternate from onebank to another.