Larry, I am not an expert here, just trying to learn. Wouldn’t adding two washers be a simple test to prove/disprove clearance issues?
If the pressure doesn’t increase, the relief valve strength is potentially higher than the 65 psi and look elsewhere.
If the pressure increases, you still might have wear issues but there is enough capability (pressure) in the current system to overcome those losses.
CT
Yes, adding washers to see if the pressures come up is a great idea and certainly not discouraging it. However, I speculate that it won't help that much in the mid RPM ranges, maybe at 2700. The low idle pressures, to me, indcates a sub-optimal oil system, as well as the progressive decline seen. Either the pump capacity is low or too little restrictoin exists in th oil system. 5 washers is a lot, assuming he has the right spring, further pushing me to speculate on low performance.
Nothing is currently dangerous or risky, just not at levels normally seen with these engines. The fact that it is not stable seems to indicate that this is a progessive problem. 400 hour ago he got 85 PSI with two washers. Now he gets 65 PSI with a new spring and 5 washers. Not a lot here to make me think that more washers will solve it. Further progression of this, IF it occurs, are likely to appear at the idle end. If this continues, at some point there won't be enough flow at idle.
Maybe others can chime in with their experience, but I have typically seen around 50 PSI at idle on Lyc's even with hot oil. To me, 35 stands out as sub-optimal and only marginally above the minimum. The regulator is fully closed at idle (why you see the ramp from idle to 1300), so more washers here is not going to help the low idle pressures.
To be clear, I am not recommending any type of action beyond continual monitoring. Pressures currently all above specified minimums. But at some point you have to ask why is performance declining. Given the recent removal of the regulator (presuming he checked for knicks or debris), additional washers and a new spring, it is hard to see this as a regulator fault causing the decline. No way to know whether it will be stable from here on or will continue to decline. That said, if there is a broken tooth floating around in the pump, bad things could happen fast. Pretty unlikely but you just don't know. I would want to know WHY pressures have declined as that can calibrate your "worry level."