CAM DIAL-IN

Okay ... now you've got your cam, and you've read up on how a cam works, you've installed it according to the directions that came with it, and now all you have to do is dial it in so as to get the best use from all that cash sitting on the rolling stand. Now is not the time to get careless 'cos you want to be cruizin'. Just a little more time spent an' you'll have it.

Degreeing the cam is a reasonably simple procedure. This will first tell you if the cam is ground properly or if it should be going back to the maker. After that should all be well, you can tweak the cam timing and lock the cam in the block.

In degreeing a cam you must find TDC (Top Dead Center) on the #1 piston. There are a variety of ways to do this, ranging from simple to precise. A quick and easy method is to use a piece of wire (if you don't have a piston height "T" guage), resting it on top of the #1 piston as you crank the engine. When the piston starts to move back down the cylinder bore, the wire will mark the position of TDC. However, since the piston remains at TDC for several degrees, this method is not very precise.

A better way to find TDC is by using a dial indicator. With the indicator on the #1 piston top (usually using indicator probe extensions), crank the engine until the piston moves a predetermined distance, (0.050 on the indicator for example) from estimated TDC on the intake stroke and mark the crank damper, flywheel or degree wheel. Repeat the procedure for the exaust stroke. The point halfway will be exactly TDC. Your damper may already have a TDC mark onit, but since the point of degreeing a cam is to double check accuracy, you should check TDC this way as well. Once TDC is determined, set the degree whellto zero at TDC.

Look at the "dots" in the crank and cam sprockets. These are designed to align when the #1 piston is at TDC in it's bore. Many manufacturers reccomend installing a cam by these marks, although you may find (through trial and error) that your engine runs better with the ignition advanced or retarded.

Is to locate the intake centerline on the #1 intake lobe. This is reffered to by a number of terms including, "The Maximum Lift Point", or "Maximum Intake Lift", and is the point at which the lifer is at the nose of the lifter lobe. In other words, this is the point when the intake valve is opened the widest. The manufacturer will usually indicate what this specification should be. Don't confuse this with lobe centerline, dicussed later here.

Finding intake centerline can be done in much the same way as finding TDC, by installing a pair of solid lifters in the #1 cylinder valve bores. Place a dial indicator on the #1 intake lifter edge, the pushrod or the cam lobe itself, and rotate the engine until max lift is reached. Zero the dia indicator a this point.
Move the cam until the dial indicator reaches a predetermined amount, such as 0.050 or 0.100 inch on both sides of maxiumu lift, marking the degree wheel at each point, and split the difference. This number, is the #1 intake centerline. Repeat this procedure on the #1 exaust lobe to determine #1 exaust centerline.

Is to average the intake and exaust centerlines by adding them together and deviding by two. The resuling number is the cam Lobe Center Separation , which is the distance in cam degrees between the point of maximum lift on the intake lobe and exaust lobe for the same cylinder.

Is to compare the intake centerline and the lobe center separation, If the intake centerline is larger than the lobe center separation, the cam timing is retarded by that many degrees. If the intake centerline is smaller than the lobe center separation, the cam is advanced by that many degrees. If the numbers are equal, the cam is at split overlap.

Overlap is th epoint in the exaust stroke where the piston approaches TDC, the intake valve begins to open, and the exaust valve is not fully closed. Split overlap means that both valves are open the same amount at TDC. Factory cams are often timed for split overlap.

Now you've determined piston TDC and intake centerline. The relationship between the two is what determines cam timing. The cam card will tell you what this should be. Degree your cam to the specs on that card. If the cam is way off, it can go back to the manufacurer. If it's off only a couple of degrees, it may not de critical and there are ways to compensate, such as off-set keys and bushing. In competition precise timing could possible be the determining factor in winning a race. For daily drivers, timing is still important, but the degree of precision is less critical. If your cam is degreed to within two or three degrees of the manufacturers specs. you will probably not discern any diffenece in the performancec on the street. But, for max performance you should degree the cam to make sure it is correct.

TIP: When degreeing in your cam, you need to position the dial indicator plunger in a stable spot so that it will read acurately and repeatedly. Aquire a used-but-still-good hydraulic lifter for youe engine, remove the snap ring and pushrod cup. Invert the cup and glue it into the lifter body. The bottom of the inverted cup has an oil hole in the center that makes for a great place to seat the dial indicator plunger, making your dial-in procedure easier. After use, find a clean snug place in your toolbox untill the next time.