The E.O.I.C method for valve tappet clearance can be used on almost any single cam engine. E.O.I.C. stands for Exhaust Opening, Intake Closing. Setting the cam in a position where the valve is closed and the rocker is completely loose is one of the critical steps in setting your valves properly.
To simply explain the premise of the E.O.I.C. method: When the exhaust valve just begins to open, the intake will be closed (on the back side of the cam lobe) and when the intake just begins to close, the exhaust valve will be closed (on the back side of the cam lobe).
In order to set your valve clearance properly, the engine must be completely cold. If the engine has run at all and is still slightly warm, the metal rockers and valves are larger due to thermal expansion. This causes the gap between the tappet and the valve stem surface to diminish. Thermal expansion is the reason there is a gap in the first place. This is why you will notice that a cam has street specifications and race specifications for setting valve tappet clearance. An engine used for racing will see higher temperatures, therefore, more expansion. This in turn requires a larger clearance. When you are running your engine on the street, you can keep the clearance tighter because of the lower heat in the engine. This allows the cam to open the valve as far as possible without keeping the valve from seating when the rocker comes back up to close the port.
To show you the step by step process to set your valves this way, I am going to set the valves on B.V., my old long bike. The engine is modified and I'm running a Yosh Daytona race cam. This cam calls for .004" for both intake and exhaust. Typically the intake clearance is smaller because this port actually runs cooler due to the cold intake charge moving through and cooling the surfaces. The exhaust port runs hot of course. A stock CB750 valve clearance is .002" intake and .003" exhaust.
To begin, you'll need some toolin'. For the CB750 you'll need a set of feeler gauges that go down to .002", a 10 mm wrench, a flathead screwdriver, and an 18 mm deep socket and ratchet. First remove the spark plugs so when you rotate the engine you're not fighting the compression. If your rings are toast you don't have to worry about this.
Next, you'll want to set the bike up so the rear wheel is off the ground and set the transmission in 5th gear. This is one method that allows you to roll the rear wheel to move the engine. Another method is to use a wrench on the advancer mechanism nut in the center of the points plate. I prefer to use the rear wheel method so as to not risk over stressing the advancer mechanism and breaking something. Another note, be sure you're wearing the proper attire. Steel toe flip flops are a must.
Remove the tappet covers. I usually start on the number one cylinder and work my way across. You can use any pattern you want, but I find it easiest to do one cylinder at a time. There are matching lobes on the cam so when you set one valve for clearancing, there is a valve on another cylinder that can be set as well. This is another method of setting the valves, but it can be combined with this method to speed things up.
To move the engine, simply pull the tire in the driving direction. When you get to the point where the valve is near the proper position, you can roll the wheel backward and then forward again to check or refine the valve position. I have to use this method since I am running a Magneto and do not have any other way of moving the crank.
Now that the exhaust valve is ready to be set, take the feeler gauge that is appropriate for the clearance required. In my case, this is .004", but in the case of a stock engine it is .003". For valve clearance, .001" can change the performance of an engine significantly. In the picture below, the .004" feeler gauge slides under the tappet with minimal force.
When you push the feeler gauge between the tappet and the top of the valve stem, you will feel the gauge slip into a pocket before it slides under the tappet. This is because the tappet edge is filleted. Since the .004" feeler gauge fit, you want to check if the clearance is too large. Next, try to slide the .005" gauge under the tappet. You will feel it slide under the fillet, but if it fits under the tappet completely, the clearance is too big. In this case, it does not. The exhuast valve is set properly.
Next, prepare the intake valve for clearancing. Since I am using the rear tire method for movement, I need some way of seeing the exhaust valve. I use a mirror set on a stand and watch the rocker as I turn the tire. To prepare the intake valve, roll the engine forward and watch the exhaust valve until it begins to drop (open). Remember to only allow 1/32" of movement.
Grab your feeler gauge and check the clearance. The intake valve for this cam needs to be set at .004" so begin with this gauge. This one checks out at .004".
Move on to the .005" gauge. This time, the valve is too loose, because the .005" feeler gauge fits under the tappet.
To adjust the valve, place the 10 mm wrench over the nut and the flathead screwdriver into the tappet. Loosen the nut without moving the tappet position. Now gently turn the tappet clockwise to decrease the clearance (counter-clockwise to increase clearance if clearance was too small). Only a slight turn is necessary since you typically only need to change the clearance by a few thousandths of an inch. Once you have the tappet where you think it needs to be, hold that position with the screwdriver and tighten the nut. You do not have to lock down the nut incredibly tight, just snug.
Recheck your clearance and repeat the adjustment steps if you need to. This one is now set properly.
Recheck with the .004" and the .005" to ensure the .004" fits (to be sure it's not too tight) and the .005 does not.
Continue the procedure of E.O.I.C for the other three cylinders. If you have a low gas tank, you may need a 90 degree screwdriver to adjust your tappets.
When you press the feeler gauge into the clearance area between the tappet and the valve, be sure that you are not pushing very hard. It should only be snug. If you are pushing the feeler gauge in too hard, you will damage your gauge set and the tappet clearance will end up being too tight. Below is a gauge that has been damaged. The tappet has cut grooves into the metal. Some people bend the tips of their gauges so that they slip into the clearance area easier. If you do this, just make sure you push the gauge past the bend so you can test the clearance pressure (how snug it is) with the flat spot of the gauge.
Some marks on the feeler gauge can be expected, but this looks a lot better than the previous gauge.
Some gauge sets are made from softer metals. These gauges are going to be more suseptable to gouging so keep an eye on the condition of your gauges and don't force anything.
When you're finished, put your tappet covers back on, and you might as well clean and check the gap on your plugs while you have them out with the feeler gauges in hand. Reassemble everything, and then treat yourself to a delicious international meal of turkey tacos, asparagus, and Japanese rice beer.
For a quick recap: E.O.I.C.
Exhaust Opening: (<1/32")>
Exhaust Opening: (<1/32")>
Intake Closing: (<1/32")>
Set valves when engine is cold.
Remove spark plugs.
Rotate engine using rear wheel in 5th gear or using advancer mechanism nut.
Set valves when engine is cold.
Remove spark plugs.
Rotate engine using rear wheel in 5th gear or using advancer mechanism nut.
Confirm your clearances with your vehicle's manual.
Do not force feeler gauges into clearance area.
Finish with well balanced, international meal.
No comments:
Post a Comment