And the saga continues...
Yesterday I removed all the rockers, thrust washers and hydraulic compensators on the drivers side. I chose the drivers side because I was convinced that the tic was coming from that side.
I cleaned everything on that side... I even sprayed brake cleaner into the oil supply holes in the head for the compensators and then blew it out with compressed air. Thousands of tiny black particles smaller than a grain of sand came gushing out of the other oil supply holes. When I wiped the little black specs with a paper towel they appear to simply dissolve into black smears on the paper towel.
Then I used a football (or basketball, whichever you prefer) inflation needle pressed against the tiny oil hole in the compensators and blew compressed air into the compensators. I could feel the compensator ball expand out (couldn't detect the motion by eye but I could feel it) and oil leaked out of the place in the top of the compensator where the shaft with the balled (round top) leaves the compensator body.
I cleaned the inside and all around the holes in the heads where the compensators get screwed in and then I reinstalled all the compensators... at the same time I verified that the little hole in the compensator base and the oil supply hole in the head indeed do not line up. The compensators tighten down with the oil hole at random locations so it is important that what I called the "culvert" (the beveled edge around the top of the compensator mounting hole in the head) is clear of any obstructions.
One by one I reinstalled the thrust washers and rockers in the same positions that came from... stopping to use the go no-go gauge on each compensator. As would be expected, the go no-go gauge indicated on every compensator that a thicker thrust washer was needed. I assumed this was due to the fact that the compensators had not yet been cycled through by rotating the engine for the recommended 30 seconds.
When I finished reinstalling all the thrust washers and rockers, I used the remote start (with power disconnected from ignition and fuel pump) to engage the starter and crank the engine for 30 seconds. I then rechecked every valve using the go no-go gauge and every valve checked nominal. That's when I realized what the go no-go gauge is actually designed to check... pre-load and only pre-load.
So what is pre-load? Pre-load is a measurement of the distance from the top of the ball of the compensator to the top of the surface that the compensator screws into, but only after the pressure from the valve spring is applied. This is a known (nominal) distance and the length of the indicator on the go no-go gauge is set to visually show that distance falls within the 1.5mm range of the measuring slot on the go no-go gauge. Given sleight variations in the internals of the lifter, that distance (under the load of the valve springs) may deviate by some amount positive or negative. That's what the thrust washers are intended to compensate for... sleight variations in the loaded distance between the top of the compensator ball and the surface the compensator screws into. That's it! The go no-go gauge tells you nothing about anything else in the valve train other than the distance from the top of the ball to the surface of the head.
So sleight is the difference between the totality of the length of the valve stem above the seat of the valve, plus the thickness of the thrust washer, plus the dimensions of the rocker, that plus or minus deviations are accommodated by varying the thickness of the thrust washers in increments of .35mm... that's about .013" (13 thousandths of an inch). So much for eliminating annoying rocker tics by changing thrust washers... not gunna happen.
So what can cause an annoying rocker tic? The short answer is "any of the components in the valve train", but the more useful answer is a worn rocker or a collapsed hydraulic compensator. Of course a bent valve could do it or broken valve spring but we're looking for the more common cause, and that would be a worn rocker or collapsed (or partially collapsed) compensator. Setting the precise pre-load via the use of the go no-go gauge may make the anal-retentive among us feel better, but it is not likely to quiet down a noisy rocker.
bTw... Upon restart, the tic was still there, even though I had set the pre-load to nominal via the go no-go gauge on every valve on the drivers side. Today I'll do the same extensive cleaning and pre-load adjustment to the passenger side... just in case.