You do not need the piston on tdc fire/compression stroke to tighten the rockers.
Mike, can you explain your reasoning for this?
Well I certainly can try, and that's a great question and it's a bit complicated for me to explain and some others could explain it better.
First of all, you can never go wrong following the instructions in the manual, and imo, it is a must have item for people that don't build engines on a regular basis, however, there are some things that can be done slightly differently than the manual suggests which will cause no harm, such as tightening the rocker nuts irregardless of the position of the lifters on the cam . I have done it that way on stock and mild builds that have moderate lift cams and/or moderate spring pressures for over 40 years and never had a problem and never had a rocker nut come loose . An engine shop I worked also did it this way and all my engine builder friends also do it this way also and have never had a problem, so based on that combined experience, we have found that it wont cause a problem, and we all do it that way to just to save time.
If the engine has a high lift cam like around .550 or more and fairly high spring pressures, I and others I know will do it with the lifters on the heel of the cam, which in most cases is at TDC fire/compression stroke.
At least one of the reasons the bolts won't come loose is because the force applied to the bolt by the spring is pressure which puts tension on the bolt and this type of tension is different than torque and this is where it becomes complicated for me to explain, however, it is explained in engineering manuals.
Two examples I can make which aren't great ones are the following. When a typical valve spring on a moderate performance engine is compressed to the point at which the valve is fully open, which might be around .550", it will be applying around 300 lbs of force/pressure on the valve side of the rocker tip . Since the rocker stud is located closer to the center of the rocker it will have a different amount of force applied due to the leverage ratio of the rocker, however for this example I will use 300 lbs of force on the rocker nut or bolt.
As you screw the rocker bolt or nut down with the lifter on the highest part of the lobe, the force of the spring on the valve side of the rocker will reach 300 lbs, however, you can easily screw the bolt or nut down to that point with just one hand and maybe a 6" long wrench because torque and tension/resistance etc are two different forces and are measured in different ways.
If you think of the system that uses a swedged nut to keep the nut from loosening on the rocker stud, the swedge only applies a light "pinching" force which is easily overcome when the nut is screwed down, and this nut does not use torque to tighten it and it has an enormous amount of force applied to it by the spring yet it doesn't loosen.
VALVE ADJUSTMENT
Below is from the link you posted and the first description has been a common and effective method for adjusting valves on most mild to moderate cams since I started building engines . The problem with using this method is that on cams with a lot of duration, you can get very close to, or even on the ramp of the cam lobe which will cause the adjustment to be somewhat less than it should be.
It is actually possible to calculate the point of crank rotation that the lifter will be on the heel of the cam, and if one does this, they can determine if using the TDC method will work for them or not . The amount the cam is advanced also needs to be factored in when doing this and most cam companies use 4 degrees as the built in advance, meaning the cam will be advanced 4 degrees when the cam timing gear marks are aligned at zero and this information "should" be on the cam card.
" In the past we were often instructed by the auto shop teacher or service manual to position each cylinder at TDC (piston at Top Dead Center), and then adjust both valves for that cylinder. However, we often find that this is not the correct procedure to obtain the proper lash setting, especially on modern engines or agressive camshaft profiles. The image at right shows the required position of the cam lobe relationship to the lifter that ensures correct valve lash adjustment."
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Odmark, I forgot to mention, if your rocker arm fulcrums are aluminum, I would consider installing the steel type used on the 4V heads because the aluminum ones have been known to occasionally fail with higher than stock spring pressures, unfortunately I don't know at what spring pressure they are likely to fail and yours may be perfectly fine with the springs you are using . It's just one of those things where if you replace them, they definitely won't fail but they might be very hard to find in your area although it is possible that Pioneer or another OEM parts supplier might be able to get them for you if you want to use them . At the very least I would closely check your fulcrums and rockers for wear, and high quality oil with around 1150 to 1600 ppm of ZDDP or ZDDB is a safeguard against premature wear.
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