Jeep Engines - Oljeep

4.0L POWER TECH IN-LINE 6 (CAMSHAFT AND VALVE GEAR) 203Hydraulic PushrodsSince 1964, most Chrysler-Plymouth-Dodge-Jeep engineshave been built using hydraulic camshafts. This means thetappets are hydraulic. It also means the rocker arms arenon-adjustable. (There are a couple exceptions to thisgeneral rule, but it holds true for the majority.) Thehydraulic camshaft, tappet, and non-adjustable rockerrequire a special pushrod. The hydraulic pushrod has twomale ends. Length isn’t critical here as long as the lifter canadjust for the change.Hydraulic camshafts use a zero valve lash setting. Theactual adjustment is done by the hydraulic tappet. If thepushrod doesn’t bend, it does its job without problems andthe engine runs fine.As long as the engine remains “stock,” this holds true. Thatis because the hydraulic tappet has a lot of adjustment builtin.This adjustment takes care of production variations, withsome adjustment room to spare. The total adjustment isapproximately .180“ and it operates normally in the middleof its travel. You’ll have trouble if you get too close to theend of travel (up or down), so the last .010” isn’t usable.Production tolerances will take another .030”, which leavesapproximately ,050’’ in either direction or .loo“ total. This ismore than enough cushion for a stock engine. However, itmay not be enough for modified engines.“Modified engine” really means rebuilt or non-stock, notnecessarily “race.” The modification could be a biggercamshaft, milled or straightened head or deck surface,different tappets from those recommended, different valves,different head, or a change to the rocker stand or itsattachment. This assumes that “broken” pieces such as bentpushrods, scuffed valve tips, bent rocker shafts, wornpushrod socket in the rocker, scuffed rocker tips, etc., arefound and corrected. This is quite a list and obviously noteasy to check out. Do not despair. The pushrod lengthrequired for your “modified” engine can be checked fairlyeasily. The hydraulic tappet must be disassembled anddrained of oil to check the tappet’s collapsed height asinstalled. From this basic measurement you can determineyour “free lash” (too much or not enough) and know howlong your pushrod needs to be and if a stock (production)one will work.Realistically, most racers don’t do this. They quickly putthe engine together and worry about it when they find aproblem trying to start the engine. At this point they’llprobably blame the camshaft or the lifters. Assuming thatthe lifters get oil pressure and they’re recommended MoparPerformance Parts lifters, these pieces aren’t likely to be atfault. Assuming the camshaft choice is up a step or twofrom stock and that it is either a production unit or MoparPerformance Parts design, the camshaft isn’t the problemeither. In truth, the “why” can be very difficult to determine.This sounds like a problem, but it really isn’t. The reason isthat no matter why there’s a “free lash’ problem, thecheapest and easiest solution is adjustable hydraulicpushrods. Using these pushrods can solve all kinds ofproblems with mismatched parts.LlFTERSmAPPETSThere are three types of lifters: hydraulic, mechanical-flattappet, and roller. Their use is dictated by the camshaft. Thereare two types of mechanical tappets: standard and mushroom.The Jeep 4.0L standard production engine valve lash iscontrolled by hydraulic tappets located inside the cylinderblock, in tappet bores above the camshaft. The tappets havea hole in the tappet body. Oil from the cylinder block mainbore enters and flows through the tappet exiting the top ofthe tappet. Oil that exits the tappet enters the hollowpushrod, travels up the pushrod and exits through a smallhole in the rocker arm where it enters the cylinder head andreturns to the oil pan.Hydraulic TappetMopar Performance Parts hydraulic tappets are for usewith general purpose, high performance hydrauliccamshafts. Can be used as production replacement. (Soldindividually.)P4529220Hydraulic tappet.Hydraulic LiftersnappetsHydraulic tappets are standard in all 4.0L Power Tech engines.1. Preliminary Checka. Before disassembling any part of the engine tocorrect tappet noise, read the oil pressure at thegauge (install a reliable gauge at pressure sendingunit). The pressure should be between 255-5 17kPa (37-75 psi) at 1,600 rpm and higher. If vehiclehas no oil pressure gauge, check the oil level in theoil pan.