Jeep Engines - Oljeep

180 MOPAR PERFORMANCE PARTSCAMSHAFT INSTALLATION TROUBLESHOOTINGFor a performance enthusiast and an engine builder,installing a camshaft is one of the most common operations.Camshafts are changed frequently and for many reasons.It’s just about the most popular thing to do to an engine.We have discussed how to centerline your camshaft formany years. We put the instructions on the back of ourdegree wheel (P4452990). We put the instructions on theback of every camshaft card that goes into every camshaftpackage we sell. We recommend that you use the camshaftcenterline method when installing the camshaft. We explainwhat this method is and how to do it. (You need two tools:and degree wheel and a dial indicator.) Getting the camshaftinto the block is NOT the problem. The problem comeswhen we attach it to the crankshaft. This is why we talkabout “centerline” (the relationship between the crankshaftand the camshaft).In the past few years we have learned that there are noproblems with the camshaft. There are no problems withthe instructions. Problems typically occur because theinstructions “were lost.” Another problem is using the “notools” approach (no degree wheel or dial indicator). Badplan! A degree wheel is very inexpensive and very easy toobtain. Dial indicators can be borrowed or rented.Here are some simple guidelines you should always followwhenever possible:1. Always centerline the camshaft.2. If you are not going to use a degree wheel and dialindicator, DO NOT use multi-keyed sprockets orsprockets with offset bushings. If you already have amulti-keyed sprocket or offset bushing camshaftsprocket, then get a new sprocket set.3.With a stock, single key sprocket, line up the dots asbest you can.4. If the engine runs poorly, DO NOT blame thecamshaft. Obtain a degree wheel and a dial indicatorand find the actual TDC and camshaft centerline. Formore information, refer to Cumshufi Centerline, laterin this section.SPECIAL CAMSHAFT THEORIESCamshaft DurationWe have all discussed camshaft duration at one time oranother. Duration is commonly used to describe any givencamshaft. “It’s a 280 degree camshaft,” is a typicalstatement. In the past, we have discussed duration relativeto using it as the method by which to choose a camshaft.The conclusion was that duration is the poorestspecification to use for selection purposes. Lift is the mostvaluable camshaft specification.Then we have “duration at 50.” This is commonly used inreference to race and other aftermarket camshafts.Production camshafts use an “advertised duration” to referto their camshafts. Advertised duration is also used by allthe aftermarket camshaft grinders for virtually allcamshafts with less than .600” to .650” lift (at the valve).This is beginning to get confusing! We have more durationsthan we know what to do with. So to this end, let’s see whatwe really know about duration. First, duration is measuredin degrees. Second, camshaft duration is generally anumber that’s greater than zero but less than 360. Third,there are two crank degrees for each camshaft degree. (Tosimplify, we’ll consider everything in crank degrees.)This duration topic isn’t as easy as you probably thought!With our camshaft selection hanging in the balance, let’sexamine a typical camshaft card and see if we can gathersome more data. An aftermarket camshaft card will listinformation similar to the following: lift, advertisedduration, duration at 50 (.050”), overlap, centerline, intakeopening, intake closing, exhaust opening, exhaust closing,and valve spring requirements.Intake and exhaust opening and closing points are givenin degrees. These four numbers are generally consideredthe events.Ovevlup is the relation between the intake and exhaustlobes, and centerline is the relation of the intake lobes toTDC (top dead center) or to the exhaust lobe. In either case,although they are both measured in degrees, neither overlapnor centerline is specifically “duration.”To help define duration, let’s focus on the intake lobe (wecould have selected the exhaust lobe). Looking only at theintake lobe, one of the unique features of duration becomesobvious; that is, the sum of the intake opening, the intakeclosing, plus 180, equals the duration. Therefore, if theintake opens at 30 degrees BTDC (before top dead center)and closes at 50 degrees ATDC (after top dead center), thenthe duration is 260 degrees (30 + 50 + 180 = 260).[IITIntake Duration = 1.0. + I.C. + 180The same basic equation also works for the exhaust side:Exhaust Duration = E.O. + E.C. + 180What’s different about the exhaust lobe is when the eventoccurs; for example, the exhaust opens BBDC (beforebottom dead center) and the exhaust closes ATDC. (Referto Figure 4-23.)r --Tn