Jeep Engines - Oljeep

188 MOPAR PERFORMANCE PARTSProblems occurring with mechanical rockers can be muchmore complicated. Since there is no need to put spacersbetween the rocker shaft and the pedestal, a leak there wouldbe unusual. Rocker shaft installation is very critical. Bananagrooves are usually added to mechanical valve gear shafts toimprove oiling of the rocker itself. Bushed rockers are moretolerant of low oil conditions, but standard mechanicalrockers should be adequate for most applications. At thispoint, with oil to the rocker, it must be distributed to thevalve tip and the pushrod tip. Accomplishing this is verytricky. Exactly where and how these holes are located is verycritical, and each engine is unique.Valve Train GeometryThe valve train is everything that connects the valve to thetappet. Valve truin geometry involves knowing where allthese parts are located and how they fit together. Geometryitself is not easy to explain, even if you have taken mathcourses in college. Understanding geometry and applying itto an engine is even more difficult to explain. Although it isquite complicated to work out, DaimlerChrysler/Moparvalve trains are well sorted-out systems, as are mostproduction systems.Weight is very important to ultimate engine speed as arevalve spring loads. Geometry itself can yield rpms with thesame valve spring loads.Valve train geometry directly affects valve train oiling which,in the long run, is the most important consideration. If thevalve gear doesn’t oil properly, you may smoke-out or bumthe pushrod ends, valve tips, etc. Titanium valves or increasedvalve spring pressure will not solve these problems.To help you, we have come up with several valve traingeometry “tips.” However, these tips are only to help youbuild your engine, they are not blueprinting (inspection)standards. Blueprinting standards apply to one part and oneaspect of that part. As you begin to put various parts together,you have a problem that is called “stack-up of tolerances.”Predicting, keeping track of, and controlling stack-up oftolerances is what good engine building is all about.As stated earlier, valve train geometry is related to howparts fit together and where they are located; for example,the number of adjuster threads showing below the rockerarm, or the valve tip-to-rocker arm relationship. Althoughthis may sound relatively straightforward, everythingaffects these relationships: the cylinder head, block,camshaft, valves, valve job, etc. Yes, you can make itperfect for each set of parts, but that would cost thousandsof dollars. And you wouldn‘t go any faster! However, thereare ways to cut down this expense.You could hand select the block, head, etc., but the bestsolution is to use cut-to-length pushrods. Custom cut-tolengthpushrods solve all these problems without all theexpense. Pre-made pushrods work fine but, if you want anexact relationship (geometry) between the rocker arm andthe adjusting screw, you’ll need a cut-to-length pushrod kit.The valve tip-to-rocker arm relationship isn’t as easy.Usually the factory set-up is close. Valve lift is a big factor.Valve lengths and valve jobs also make a big difference.The cylinder head must also be considered. A littlecompromise is best used here. If the rocker arm pad is onthe valve tip with the valve closed, and is still on the valvetip at maximum lift, consider yourself lucky. We don’trecommend cutting the valve tip for any reason. It willremove the hardness on the valve tip and make it soft. Withvery mild camshafts and soft springs, the problem may notbe as obvious, but it’s there!DynamicsDynamics is defined as the engine speed (rpm) potential ofa given camshaft profile when used with a specific valvespring and valve gear set-up.A high performance hydraulic camshaft in a 2-Bbl. enginemight have an ultimate engine speed of 6,400 rpm, but witha high performance spring the engine speed becomes 6,900rpm. Obviously a 2-Bbl. engine with a stock camshaft isn’tgoing to go 6,400, which means the valve gear is better thanthe rest of the engine pieces. This is strictly a valve geartest. In many cases the ultimate speed may be 7,500, butfalse motion may occur at 6,000 or 6,500. The engine willnot achieve the ultimate speed. In any case, the camshaftdictates the engine’s output, and a valve spring must bechosen that will allow the camshaft to do its job.A Super Stock engine might run 6,000 rpm while a LateModel engine might run 7,500 rpm-the same valve springcan’t be used even if the camshaft is the same.Concentration on ultimate speed can lead to overkill results.Note: Titanium valves are usually used to obtain ultimateengine speed, but this would be overkill in most cases.VALVESThe 4.0L Power Tech engine standard production valves aremade of heat resistant steel and have chrome plated stems toprevent scuffing. All valves use a three bead lock keeper toretaining the valve spring and promote valve rotation.The important considerations when choosing valves arediameter, length, stem size, weight, number of lock grooves(Figure 4-25) and valve head shape or profile (Figure 4-26).