RE: The Complete Saito Notes by Bill Robison
Old and new cams
"...this engine has not been run in ten years." This could mean the engine was new ten years ago, or it could have been an older engine even then. The point here is that it could have an early or late type cam shaft in it.
The older one responds very well to a valve clearance setting of 0.0005" while the later should be set at 0.0015" lash.
If the engine's real age is at least fifteen years try the half thousandth setting. If it runs fine there keep it set there. If it doesn't run well or if you're not sure of the age then use one and one half thousandths clearance. In either case you wont hurt the engine with the tighter setting.
In any case the engine will run fine with the 0.0015" setting, even as much as 0.002" lash is OK, but you get better power with the tighter setting.
Feeler strip for valve adjust
Most feeler "Sets" other than the basic ones have a 0.0015" strip included. As you can see in the attached picture this is also 0.038 mm, just 0.002 mm under the desired minimum clearance for the late cam grind.
If you set the clearance to 0.0015" and then tighten the lock nut, there will be enough distortion of the adjuster screw threads to get you the 0.04 mm clearance.
TDC Again
If you are at TDC either of two conditions will hold, assuming the valve adjustment is reasonably close.
1) Both valves will be slightly open, this is TDC between exhaust and intake strokes, the cam is in the "Overlap" position.
2) Both valves will be fully shut, with clearance in the pushrod/rocker gear. This is TDC between compression and power strokes, and is the correct position for adjusting the valves. Both rockers should be free to wiggle a little bit at this point, and the free clearance between the rocker end and the top of the valve stem should be no more than 0.002" - as I said, this is where I use the 0.0005" setting.
Hope this makes it more clear.
More on ½ thousandth clearance
Decreasing the valve clearance increases the valve open time, similar to putting a hot cam in your car. It allows the engine to breathe more freely and develop more power, but the idle does sometimes get a little lumpy. So don't be surprised by a slight increase in idle roughness. Closing the lash doesn't give you that hot a cam, but it's hotter than it is with loose valves.
Now go down to 1/2 thousandth clearance and you'll get even more, the idle still wont be bad.
As I said, the folks who have tried my 1/2T lash don't want to go back.
Quieting ramps
Since my post of 4/11/04 I have profiled several different Saito cams. See attached chart. While I did it out of curiosity about the actual valve timing, the dial indicator showed me that some of the Saito cams also have "Quieting ramps" in their grind. It is a "Lump" in the lobe intended to take up the clearance in the valve train, it eliminates the hammering of the parts when the lash is adjusted correctly. The correct adjustment is the height of the quieting ramp. If the lash is too great the ramp wont take up all the clearance, if too tight the valve will open too soon.
Attached graph is typical quieting ramp, degrees of rotation to the right, amount of lobe lift is vertical.
The 1/2 thousandth lash adjustment is still the best for engines without the quieting ramp, engines with the quieting ramp will work best at 0.0015" to 0.002" clearance.
Mike:
It is very hard to maintain engine heat to check the difference in the valve lash between ambient and running temperatures, but the crude measurements I've been able to make indicate the Saito engine's clearance opens about 0.0005" while running. That's why I can use 0.0015" clearance with the 0.002" ramp height.
Finally, having found no consistency in later checks concerning the quieting ramps I no longer recommend the 0.0005" clearance setting. You (I) have to check each cam individually to see if it does or does not have the ramp. Without the ramp the best running is with the tight adjustment, but the 0.002" is safe with either. If you don't know, stay at 0.002" lash.