Tech - Cams Understood The single most misunderstood component in motors today is the camshaft. In the next two articles I'm going to try to unravel some of the mysteries of camshaft selection. What our objective is, is to select a cam that will provide the best possible hp/torque for the rpm range that we operate the motor at. Now I'm going to say this again listen carefully our objective is to select a cam the produces the best possible Hp and TORQUE at the RPM WE OPERATE THE MOTOR. Before we start lets get a couple of things out in the open. #1 the most common camshaft error is over caming the motor. #2 is selecting a cam that is not compatible for the RPM range that we plan to operate the motor. There are a number of things, which effect the cam. Cylinder head flow rates The cylinder heads must be able to flow enough air for the amount of time that the valves are open. Carburetors The carb must also flow enough air to support the cam. Exhaust pipes. The exhaust pipe must not only flow enough air they must be designed so that the sound wave reversion is compatible with camshaft timing. There is a little clue here for you sharpies and that is the word airflow. Airflow is everything and the camshaft is the controller of the airflow. It determines how much, when and how long. The result of all the cam shaft specifications is where in the rpm band the motor will make the best power. Now one more thing before we dive in to the mystery and that is we need to under stand our objective here. For the purposes of these articles I'm not interested in RACING motor but rather street motors and street motors need TORQUE and they need TORQUE in the 3000 to 5000 ranges this is the range we most often operate the motor (freeway cruising). There is a law of camshafts we need to keep in mind. -If you have at top you won`t at the bottom and if you have it at the bottom you won't at the top. We can't have it all. In a STREET motor we don't need it at the top, we do need some at the bottom but we really need mid range. So here is where we are going to look for our torque. Now we also have to look at the bike we ride. A dresser is going to need more bottom end than a FXR do to the weight and wind resistance. All right so now that we have all this behind us we cam move on to the cam its self. When we speak of cams we speed in a different language. We talk Duration, Lift, Timing, overlap, lobe centerline, and lobe center. All of these terms define how a given cam will operate and they all are important. More often than not people speak of duration and lift, and these are the two parameters that they use to choose a cam, however these two alone are nothing. We have to learn to look at ALL the numbers. Defining the terms. Theoretical valve lift. Theoretical vale lift is the theoretical maximum lift at the valve it does not take into consideration valve lash. Variations in rocker arm ratio or geometry or valve train deflections. Cam shift lift This is the number every one throws around when talking cam .its the number that the cam lifts the lifter. For example if the number is .495 it means the cam will lift the LIFTER .495 because the rocker arms don't have a 1:1 ratio this is not the amount that the valve lifts. Net valve lift Now this is what the motor actually sees when all things are brought in to play things like, lash (or hyd lifter compression) valve train deflection, rocker arm ratio and what ever else may effect the valve train. The way we determine this number is, after the motor is totally complete ready to run, we install a dial indicator on the valve and measure the lift as we turn the motor over by hand. Advertised duration Advertised duration is commonly printed in cam manufactures literature it does not take into consideration certain cam shaft ramp designs. It is measure in crankshaft degrees and represent how long a valve is off the seat .A more accurate duration measurement is taken at .050 lift .050 lift duration This measurement is taken when the lifter has risen .050 off the can shaft base circle and has closed with in .050 on the ramp. Here we have a more accurate figure that is better for comparison and usually closer to true duration. And at least eliminates concerns about ramp clearance. Experience has shown that airflow at this lift is not a consideration. Overlap Over lap is the period of time both valves are open at the same time and is measured from the beginning of the intake stroke and ends at the end of the exhaust stroke. Lobe center Lobe centerline is a measurement of degrees taken from the centerline of the intake lobe to the centerline of the exhaust stroke. To imagine this draw a line from the center of the cam out ward through the center of the intake lobe and then again from the center of the cam through the exhaust lobe center and then measure the angle in degrees between the two. Lobe center values will affect the cam shaft timing. A wider angle will decrease over lap and a narrow angle will increase the over lap. This is an important figure in camshaft selection be cause it effects where the power band will occur. Lobe centerline cannot be changed after the cam has been ground. Lobe centerline Lobe center is different than lobe center line and should not be confused. Lobe center is an imaginary line drawn through the lobe center from the cam center and can be changed by advancing or retarding the cam. What is doesn't do is combine the separation angles between the intake and exhaust lobe. Symmetrical cams This simply means that the cam lobe is the same on both sides. Which means that the valve opens and closes at the same rate. Asymmetrical cams Here the lobes differ from the opening side to the closing side. This allows the cam grinder to open the valve a one speed and close it at another. Here is wear some cams are quite and some noisy. If the grinder has chosen to set the valve down slowly on the seat it will be a quitter cam than if the grind lets the valve down to quickly. Single pattern cams In the case of single pattern cams both the intake and exhaust lobe are the same. A cam can be asymmetrical and single pattern or symmetrical and single pattern. Dual pattern cams Dual pattern cams have different profiles on the intake and exhaust lobes. A cam of this type can be any combination of asymmetrical or symmetrical of profiles. By now your head is probably spinning don't feel bad so is mine but if you become familiar with all this next month in part II you will begin to understand how to pick the right cam for your individual needs. There are many factors that need to be considered when choosing a cam. The compression ratio of the motor, the weight of the bike the load its going to carry, the displacement, the rpm range it will be operated at the efficiency of the cylinder heads and so forth. For our discussion I am going to limit our scope to street bikes that are mostly used for highway cursing. We need to understand that the name of the game is " cylinder fill " we want to fill the cylinder as full as possible with air and fuel in the shortest possible time. Then we want to compress it as much as possible before the spark plug ignites the mixture. The cam is the master control valve for this operation. It will determine when the fuel is let in and how long and when the exhaust is let out and for how long .It will also determine how much pressure is built in the cylinder .The term is cranking compression this is the compression that the motor actually sees and is usually higher than the static compression ratio which is a mathematical formula based on volumes of the cylinder, combustion chamber, and head gasket. The more compression we can use the more HP the motor will make, but we are limited in the amount of compression buy the combustion chamber design octane of the fuel available, and if we exceed these limitations detonation will occur .The result of which is damaged to the engine. Now there are two ways to increase cylinder pressure (compression) #1 is to reduce the size of the combustion chamber thus raising the static compression ratio or #2 seal up the cylinder as soon a possible. And raise the cranking compression. Now here is where we have to decide what our engine needs. Lets say we have a stock 80 evo motor with 8.5: 1 compression the heads are flow restricted and the combustion chamber is not all that great, but we know that we can use more cranking compression without incurring detonation so we want to look at our cam specs and look for a cam that has less duration so that the valve overlap is short which seals up the cylinder sooner and raises cranking compression. This will increase low speed torque, which is just what we want. On the other hand if our motor had a 10:1 compression ratio and we increased the cranking compression it would be likely to detonate so we would want a cam with less duration to keep cranking compression to a reasonable level. Over camming a motor is the most common mistake people make and the most common error there is to much duration if you over do the duration the motor will be lazy have poor cranking compression will lack throttle response and have poor intake vacuum so the carburetor is nearly impossible to tune at low speed Since our goal is to increase the fuel /air mixture in the cylinder we need to look at other ways to accomplish this and one of these is increased valve lift. There are limitations as to what we can do here. We are limited by valve to piston clearance, valve spring strength, and valve clearance between the spring collars. When we increase lift it will also make the valve operate faster. We need stiffer springs to prevent the valves from bouncing on their seats when closing. Some cam grinders grind the exhaust side of the cam lobe different from the intake side so that when the valve closes it doesn't slam onto the seat this is called an asymmetrical cam, other grinders grind their cams the same on both sides. I personally don`t like this type of cam because they tend to be noisy. Back to our stock motor. The springs in the stock motor are weak and valve float occurs around 5500rpm, so installing a cam with a high lift and trying to rev it up will simply float the valves also. We may run into piston to valve clearance problems. In the case of a motor with the proper head work and piston modifications (where necessary) we will have stronger springs and more clearance to allow the higher lift with out adverse affects. Hopefully at this point you can begin to see the effects of duration and lift on a given motor. Unfortunately there is no way to say which cam is best for any given motor with out testing all the cams available. The most we can do is have some idea of what a given cam will do for us and be able to avoid cams that will hurt us. Below I have listed some guidelines for cam selection that may help you: Late closing intake poor compression will cause poor performance over the entire RPM range Semi-late closing intake here we will have very well mid range pretty good top end but not the best Early closing intake this is what we like for a heavy bike because it will give us excellent bottom end and good midrange Late closing exhaust here we end up with a narrow RPM band the low end will be good as well as the midrange but we will have an engine difficult to use. Semi-early opening exhaust This timing will give us good cylinder scavenging which results in a cleaner cylinder mixture at high rpm the low end will suffer some but the mid range will be very good. Early opening exhaust WE have reached a place we don't want to be. Here we loose our entire bottom end and our mid range will be lazy what it will do is run hard on the top. In conclusion, we want a cam that displays semi late closing intake with a semi late opening exhaust for the best over all performance in out street bike. We also would like a narrower lobe centerline and close centerline for the best possible torque. We want to run the most cranking compression the engine will allow and the highest lift practical for the best possible cylinder fill. Installing a cam is not a major job the requires vast amounts of knowledge and a lot of time . It does require paying attention to the task. I am going to help you . there are several ways to install a cam I'm going to tell you the easiest way it will take more but it is the easiest for a first time cam change . Personally I can change a cam without opening up any thing but the cam cover and push rod tubes , but this is not for a first timer . FIRST ! Obtain the service manual and for your model bike and read the section on cam shaft replacement. Also look it the book at the front of the engine section , and you will find a spec. for the cam shaft end play . This spec. is .001 to .050 for evo motors . right here is the first tip I'm going to give you . forget this spec. Your spec is going to be .002 to .005 to eliminate cam noise . also you will see when you read your manual that there is a method of measuring the cam shaft gear diameters to obtain the proper gear lash . Here again for this procedure as well I am going to give you a short cut. When you install your new cam install the largest HD pinion gear ( orange code). At this point I want to explains something to you. Cam shaft noise is partly from cam shaft ramp design and partly mechanical noise from end play and excess gear lash. If you set the end play to what I recommend and the pinion gear size is correct when you start the motor cold, the cam gears will have a slight wine that goes away when the motor warms up. If the whine does not go away the pinion is to large and a smaller one must be installed , if it does not whine a larger pinion should be used .In the event you have the largest pinion installed them you can go to an oversize cam gear . The manuals method of measuring is supposed to eliminate this trail and error method , however the problem is these measurements are based on a given cam shaft to crank shaft center line measurement, in the real world the measurements are never what they are supposed to be, so you can forget what the book says . BEFORE you start you will need the following things cam cover gasket, pushrod O ring set Rocker box gasket set for your motor, lifter block gaskets , cam bearing , cam shaft oil seal and a cam shaft shim selection cam and push rods also you will need in addition to the normal tools a timing light and a dial indicator Now we are ready to begin . First unhook the battery , then drain the gas from the gas tank and remove the gas tank . While the gas is draining you will need to remove the front exhaust pipe and running board if you have them . If you bike is stock drill out the sensor plate cover rivets and remove the cover . Next remove the screw which retains the ignition rotor and remove the sensor plate . Back to the top of the motor remove the gas tank and spark plugs also remove the rocker box tops and rocker arms and take out the push rods ( refer to your manual for instructions on removing the rocker arms ) . Around back to the other side of the motor we want to remove the cam cover . when the cover is removed if you don't put a pan under the motor your going to have a nice mess . in side the cover is a little plastic shim for the breather don't loose it or for get to reinstall it . Now look at the timing marks. Jack up the rear wheel and place the bike in 5th gear , rotate the wheel until the timing marks are lined up . Remove the cam and look for the cam shaft thrust Washer . Here is where it gets complicated you MUST remove and replace the cam bearing failure to do this is a guaranteed cam shaft failure. There are a couple of ways to remove the bearing one is to take the bike to your local HD shop and ask then to do it for you . or borrow or rent their tools to do it . The third way is to buy the tools from Jim's * and then you will have the tools to do your buddies bikes or rent them out your self . OK after the cam bearing is replaced install the cam and its thrust washer and reinstall the cam cover with the gasket . Here your going to have to get clever, because you want to rig up the dial indicator so that it is against the end of the cam. Oh did I forget to tell you to remove on of the lifter blocks ? well do it now we need access to the cam here . Move the cam back and forth so that you can read the end play on the dial indicator . measure the shims with a micrometer to determine which shim to use. There may not be a shim the right size and you may have to have a machine shop grind one for you , they can easily take a thicker shim and grind it down . Remember .002 to .005 end play . After you have the shim you think is right installed go back and recheck often you will not be quiet right and have to make further adjustments. When your satisfied with the end play , remove the old pinion gear and install the new one ( the pinion nut is a left hand thread) ( orange code) . be sure the timing marks are aligned and replace the breather gear shim and button up the cam case . Reinstall the lifter block. Replace all the push rod tube seals . Take you new adjustable push rods and shorten them up all the way . Take a close look at them, some are short and some are long ,the long ones are the exhaust push rods. Insert the push rods into the motor Be SURE you have ALL push rod tube seals in place and reinstall the rocker arms and rocker box covers . It's time for the next crucial stage . Adjusting the push rods . Different push rods require different numbers of turns of the adjusting screw for the proper adjustment . Determine how many turns yours require. For sake of this article we are going to assume we have Crane push rods that require 3 turns . turn the motor over until one of the front lifters is all the way down and one is up . one of the push rods will be loose and one will be tight . Tighten the loose one to take out the slack . Use a flash light and look down on top of the lifter and make sure you have not depressed the piston away form the snap ring that holds the lifter together . Turn the adjuster 3 complete turns and lock it down . WALK AWAY , do something else for a while let the push rod set , put the gas tank back on or something . When you can turn the push rod with your fingers you can turn the motor over until the other lifter is up and repeat the procedure until all the push rods are adjusted . When you adjust the push rod you will lift the valve off its seat and you must give the lifer time to bleed down .If you don't and you turn the motor over the valve spring will compress so much that the top spring collar will strike the valve seal damaging it and your motor will smoke . From here its just a mater of reassembling what ever you have not already assembled and setting the timing as its described in the manual . I set my timing at 35degrees at 3500 rpm.

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