Rob Noth said:
Bob, don't start sleeping yet...
Dave - either you know something I don't, or it's the other way round
Rob, perhaps we are simply approaching the problem from a different direction. There certainly is nothing wrong with following the instructions to the letter. However, discarding all "instructions", some things remain:
Suppose for a moment that a rocker is being tightened down by hand. Regardless of the position of the cam or lifter, as soon as -0- clearance is reached, you will know because the bolt will encounter resistance. Again, disregarding the position of the cam, in ANY case, this resistance will be encountered BEFORE the pedestal is tight. This is because even when the valves are closed, there is preload on the lifter. We have to agree on this point.
What happens after that will vary. If the lifter is on the back of the cam and the valve is in the closed position, you will apply force to the bolt to either a) force preload on the lifter or b) force the valve open. In either case, whether you are collapsing the lifter or opening the valve, the torque required to turn the bolt is less than 10ftlbs. I have verified this.
In the case of a) you will find that from the point of increased resistance to the point where you feel a definate "stop" as the fulcrum bottoms, is 1/2 to 1 full turn of the wrench (if the valvetraim geometry is correct). You have just set the preload. Ford states that this process should be done with the valves closed, one at a time (or in pattern if you have it), rotating the motor as you go. This point will be achieved with no more than 10ftlbs as the manual suggests. Now that you have all the preloads set, you can simply go back in one batch and torque all bolts, valve open or not, to 20ftlbs. This is the Ford specified proceedure.
However, in the case of b) and the valves are being forced open due to the fact that you are not on the back side of the cam and did not rotate the motor and tighten in sequence, you cannot check preload but you can continue if you use caution. If you make sure that the fulcrums are seating correctly in their bosses, you will notice that the torque required to overcome the spring tension is still less than 10ftlbs. So with 10ftlbs of torque you are still able to get yourself to the same position as you were in scenario a), or in other words the fulcrums tight. Now remember that the Ford manual says final torque can be done with the valves in any position, and should be 20ftlbs. If that is the case, and we have taken the clearance out of the valvetrain and "set" the fulcrums with 10ftlbs, it only stands to reason that the final torquing of 20ftlbs will end in the same result whether you followed the exact letter of the instructions or not.
What IS important to realize is that it is very easy when tightening past the tension of the springs, for the fulcrums to become cocked and you not notice as you crank away. This can and does result in irreperable damage to the fulcrum bosses (as I said I've seen some cracked). It is ALSO worthwhile to note, that if you are tightening an open valve with a stiff aftermarket spring and only have maybe 1/2 of the normal threads engaged in the head, it is possible to pull the threads out as you tighten. In any case, after the fulcrums have been seated in their bosses, it remains only to torque the bolts to 20ftlbs and the position of the valve at that point is not relevant.
David