It is my sincere desire to inform, not criticize anyone in particular, in the use of dynomometers and the numbers that come from them. It seems to be that who ever has the highest horsepower number on paper wins. In reality that couldn't be further from the truth. Dyno numbers are realitive. What I mean by that is the numbers only have real meaning to the shop and the operator doing the testing. Because of the wide range of testing parameters, for example, acceleration test versus steady state test, the rate of acceleration, RPM range of the test, length of time of the test, how quickly the throttle is applied and removed along with the state of tune, engine misfires and torque spikes all greatly effect the numbers on paper. Only the dyno operator knows how to compare all the results as he should be using similar technique's in his testing if he intends to compare any results. That's to say nothing about the calibration of the dyno and the inherent repeatability of the dyno itself. Dyno manufacturer's will have a + or - range of accuracy generally 1% or 2%. If your testing a 5HP engine the margine of error is minimal, but if your testing high HP engines that number may be sizable. 2% of 1000 HP is 20 HP. Add all of the above testing parameters to that and the numbers can be quite different than what I would call the engines actual HP. Manufacturer's generally use what we call "SAE Corrected Power". These are specific parameters and techniques to test by. Most dyno facilities are using "Standard Corrected Power". Why? Because the numbers are higher with those testing parameters. For that reason we choose not to publish specific dyno test results and refer power levels instead.



There is a fair amount to cover, so let’s get started. You will need a number of special tools to be able to maintain accuracy on this specialized Yamaha 4 cylinder double overhead cam engine. First is the double dial indicator cam position fixture. Next an indicator to locate the piston at TDC, then a degree wheel to mount on crankshaft and a pointer mounted to the top mag cover bolt behind the rotor.
It is important that the valve lash be adjusted BEFORE you begin the degree process as the lash will affect the opening and closing numbers especially at lower lifter rise numbers. I recommend .008 on intakes and .010 on exhaust. Do not exceed those lash numbers. Remove the small black plug from the mag side cover and align the timing marks with number 4 cylinder in firing position, both intake and exhaust valve closed, TDC Compression. This is the position where the dots on the cams align with lines on cam caps and the line on the rotor align with the mark inside the small hole in the mag side engine cover. Now remove spark plugs, cam cover and mag side engine cover along with the shaft and starter reduction gear.  Hold the rotor from turning and remove the 19mm large bolt that holds the rotor to the crankshaft. Torque is 94 ft.lbs. when reassembling.  Be careful not to lose the oil restrictor bent wire. Mount the degree wheel to rotor and snug up with the stock bolt and thick washer against the degree wheel. You may need a .040 thick washer behind degree wheel.
 The cam fixture should be placed on the top of head on the mag side, resting on cam cover surface and positioned so the indicators are touching the cam lifters and fixture is pushed up close to the camshafts. Place small hold down on top of fixture and insert 6mm X 12mm bolt in intake cam cover bolt hole and tighten lightly. Zero indicator dials by rotating the bezels on dials. If you need to make a larger adjustment, you can loosen the set screw at the base of indicator and slide indicator body up or down. Be careful not to over tighten the set screw as it could bind the indicator shaft and damage indicator. Light pressure is all that is needed to hold indicator. Install the piston TDC indicator in number 4 cylinder behind the cam fixture. You can zero the indicator now. Align the pointer and degree wheel at TDC.  Rotate engine 2 complete revolutions watching all indicators are moving freely and verify that all indicators return to zero at returning to TDC. Now you’re ready to find exact TDC. Rotate engine clockwise till piston indicator moves .050 and look at degree wheel. It should be about 15 degree’s before TDC if not you may set it at 15 by rotating the degree wheel on crankshaft or by moving the pointer. Then rotate the crankshaft counterclockwise watching the piston TDC indicator go to its maximum or “0” and then past it to the .050 after TDC.  It should read about 15 degree’s after TDC. Continue to rotate the crankshaft back and forth from .050 to .050 each side of TDC until the degree’s are EXACTLY the same on both sides. It may be 15 or 15 ½ but should be the same. The degree wheel is now set correctly at TDC. This is important; all the measurements depend on accurate TDC indication. Now rotate the engine around in the direction of rotation, counterclockwise, several times and verify that all the indicators read “0’’ on number 4 TDC compression stroke.
Now we are now ready to get some opening and closing degrees. The question now is at what lifter rise do you want to take your readings?  Automotive cam grinders use .050, motorcycle engine builders generally use .040 or 1mm. SAE, Society of Automotive Engineers, use .006 or what is called Advertized Duration. All these lifter rise numbers will give you different duration numbers in crankshaft degrees that the valves are open. If you are trying to compare cams from different grinders, engine’s or engine builder’s you need to use the same lifter rise numbers to get a comparison. If you would like to get a good picture of the opening and closing ramps along with duration numbers to save for future reference, I use .001 .004 .006 .010 .020 .040 .050 They can all be gotten with 2 rotations if you go slow. NEVER BACK UP IF YOU MISS YOUR NUMBER, you will have to start over. I’ve made a spread sheet with all these opening and closing events in columns left to right to keep things in perspective. Being a motorcycle based engine let’s use .040 lifter rise. Start by rotating in the direction of rotation, counterclockwise, watching the exhaust cam indicator and stop when the indicator reads .040 and write down the number in degree’s BBDC on the degree wheel, stock RX1’s should be about 38 degrees BBDC, Apex’s about 51 BBDC.  This will be exhaust opening Before Bottom Dead Center. If you advance exhaust cam this number will get larger, opening the valve sooner. Now, continue to rotate crankshaft to find exhaust centerline. To do this we need to find the point in degree’s, similar to finding piston exact TDC, where the cam indicator is at .050 before Max cam lift and .050 after Max cam lift. Continue to rotate crank and stop at .050 before Max cam lift and write down the number in degree’s that the pointer is on the degree wheel. Continue rotating past Max cam lift and back to .050 on cam indicator and write that degree wheel number down also. Save those numbers for now, we will get back to them later. Continue rotating crankshaft until you get back to .040 lifter rise on indicator, the first number you wrote down, and write down that number on the degree wheel, should be about 18 degrees ATDC for RX 1 and 20 for Apex. Now you can add the number of degrees BBDC to the number of degrees ATDC and add 180 degrees to that and you have the exhaust duration at .040 lifter rise, about 236 degrees for RX 1 and 251 degrees for Apex. There is about 3 rotations up and 3 rotations down on cam indicators, at .300 lift. Exhaust will be a little more; intake will be a little less on RX1’s, Apex’s are over .300 lift on both exhaust and intake. Now we can calculate exhaust centerline. Take the 2 numbers in degrees we got at the .050 before max cam lift and the .050 after max cam lift, subtract the smaller from the larger, divide that number by 2 and add it to the original smaller number. That will be your exhaust centerline in degrees in relation to the crankshaft. Stock Rx1’s should be about 102 degree’s; Apex’s will be about 106 degree’s if all is right. Now continue to rotate crankshaft around to TDC, and you should be back to number 4 TDC compression stroke and all indicators should read “0”.   Do the same now for the intake. Start rotation counterclockwise. The exhaust will open first and after almost 1 complete crankshaft revolution just about 10 degrees BTDC for RX1 and 11 degrees for Apex the intake indicator should be at .040 lifter rise.  Write that number down on the degree wheel as this is intake opening Before Top Dead Center. Continue rotating crankshaft. Again we need to watch intake cam dial indicator and stop at .050 before max lift and write the number down that’s on the degree wheel and save for intake centerline calculations. Continue to max intake cam lift and past it down to the .050 on indicator and again write that degree wheel number down. Continue rotation and watch indicator stopping at .040 lifter rise, should be about 41 degrees ABDC for RX 1 and 56 degrees for Apex. Add this number to the opening number and add 180 to it and we should have 231 degrees of intake duration for RX 1 and 247 for Apex. Now once again take the 2 numbers we saved for our intake centerline calculation, subtract the smaller from the larger, divide by 2 and add it to the smaller and we should have intake centerline of about 103 degrees for RX 1, Apex’s are about 112.  It’s the same procedure for intake as the exhaust except the intake valve will be opening BTDC and closing ABDC.  When you retard the intake cam, this number will get larger, closing the valve latter, and cranking compression numbers will decrease. When you get familiar with this procedure, you can do both exhaust and intake simultaneously. Overlap is also available from your calculations. Simply add the number of degrees the exhaust closed after TDC to the number of degrees the intake opened before TDC, about 28 degrees for RX 1 and 31 for Apex’s. Notice that overlap numbers are very close for both RX 1 and Apex’s even though the Apex cams are much larger. Why? Look at the intake and exhaust centerline numbers and you will see Apex’s have spread the lobe centers, retarding intake advancing exhaust, thus decreasing overlap. Cylinder pressures are, however, very close on both RX 1 and Apex because Yamaha used a thinner head gasket on Apex’s to maintain cylinder pressure. Make sense?
Understand that all these numbers, EXCEPT CENTERLINE NUMBERS, will change if you change the checking number, lifter rise, for example using .006 instead of .040 lifter rise. Try it just for fun. With some practice you should be able to repeat the numbers within a degree or so.
 Now for the last calculation, we will find LOBE CENTER SEPERATION. Take your exhaust lobe centerline number of, let’s say 106 for Apex and the intake lobe centerline number of 112 and add together, and divide by 2. This is 109 degree’s or 109 degree lobe center separation as it’s called.  This relation is in cam degrees, not crank degrees
If after this process you find it necessary to move cams, I have bushings to insert in the cam sprockets that will move cam timing without slotting the holes or replacing sprockets.
Congratulations, you should have a better understanding of cam timing, hopefull




For engine builders cam timing is an everyday routine, but for those who are exploring inner operating characteristics of their engine for the first time, it can be a real challenge. The most popular method for adjusting cam timing is slotting the mounting holes in the cam sprocket. However, there is always a risk that engine harmonics could possibly loosen the bolt enough to allow the chain to pull the sprocket in the slot. With our cam bushings, you have a positive stop and the sprockets cannot move. The bushings and large holes in the sprocket also provide us with a systematic method for moving cam timing. The relationship between the number of teeth and the number of large holes gives us a unique 2 degree change for every hole moved regardless of whether you move in a clockwise direction for Advancing timing or a counterclockwise direction for retarding timing from the reference DOT on the sprocket. Please understand that this dot has no significance to timing the cams under normal circumstances.
It should be noted when cam timing changes are made, the dot on the cam lobe and the line on the cam cap on the head will no longer line up EXACTLY as per Yamaha shop manual.
   Take a sprocket in your hand and look closely at the dot next to one of the stock mounting holes. Place the dot at a 12 o’clock position looking straight at it. You will notice that there is a tooth exactly centered in relation to the hole. Now rotate the sprocket counterclockwise so the first large hole is at 12 o’clock. If you look very carefully at the tooth that is also at 12 o’clock you will notice that it is ALMOST centered in the hole The tooth is however, slightly off. This is what gives us the ability to change cam timing. Go further now, rotate the sprocket to the next hole counterclockwise and look at that tooth , you will see it’s off a little more than the previous one. The same goes for the holes on the other side of our reference dot but the tooth is off on the opposite side of the hole. The farther you move around the sprocket, the more the tooth by the hole you are installing the bushing in, is off as far as alignment with the hole is concerned. That’s the geometry of it all.
Now, the best way I find to get it correct, is by installing the bushings in the first or second hole left or right, depending on whether you are advancing or retarding, and install the cams in the stock position the same way you would normally install the cams as Yamaha instructs you to do so. Keep the reference Dot on the sprockets at the top so you can always see it. Align the dot on the cam lobe with the line on the cam cap, again, just as Yamaha instructs you to do so. Be sure that the flywheel reference mark is exactly lined up also. Only install 1 bolt for now in the cam sprocket and tighten lightly. Release tensioner and rotate the engine as you normally would to be sure that everything is properly installed and in alignment. Normally, for turbo applications, we are retarding the intake cam and advancing the exhaust cam. With all reference points aligned at TDC, release tension on chain, remove the bolt on the cam sprocket and rotate the sprocket jumping only enough chain links to get the bushing close to alignment with the bolt hole in the cam. It should not be Exactly lined up but very close. Now bump the cam lobe with a plastic hammer just enough to align the bushing hole and the bolt hole in cam and install cam bolt with a drop of locktite on the thread only. Be sure NOT to get any locktite on the bushing and shoulder of bolt. You should have it now. I recommend you do one cam at a time until you are comfortable with the procedure. When chain tensioner is released you can rotate cams around and install the second cam bolt.
This is a delicate procedure and I highly recommend you purchase my double dial indicator cam timing fixture. This fixture, along with a TDC indicator and a degree wheel, will give you the ability to know exactly where the cams are installed. Without the ability to degree the cams you’re guessing at the cam timing.
Hope this helps!


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