well, my wife says i can't leave well enough alone, and she's mostly right. so i've been thinking about these little spacers, and wondering about just exactly how much force it really does take to move a rocker arm with a thackery washer on it.
like everybody else, i have bits and pieces of stuff lying around to mess with.
so here's some old rocker box i have with thackery washers in it, installed the way i mostly see them, against the rocker arm, with the flat washer on the other side against the rocker box:
notice how the washer is digging into the oil cutout on the rocker arm:
and here's another one, with the steel spacers installed, done before i got it. whoever he was, he also ground the casting flash away a little bit, but didn't polish anything:
he installed the spacer against the rocker arm, in the same spot as the thackery washers in the other rocker box. these rockers don't have the little cutout:
anyway, i lubed everything up as well as could through the hollow rocker shaft and from the outside with PB Blaster:
and then stuck an old pesola spring scale on them to see how much tension it would take to make the rockers of each type rock. i used to use the scale to weigh squirrels, but it works okay for rocker arms too:
in a dozen or so tries, the rocker arms with the thackery washers always took a minimum of 350 grams to start any kind of movement, and never swung fully at under 450 grams of tension. sometimes it took as much as 600 grams to make them move.
in contrast, the rocker arms with the spacers would fall under their own weight, either way, whenever i twisted the rocker box. i never bothered to hook up the spring scale to them at all.
so here are some thoughts and observations:
-- neither of the rocker shafts had any looseness or any apparent binding in their travel.
-- i didn't take anything apart to inspect the insides, but the box with the thackery washers didn't feel like it took any more or less force to move than they always do.
-- according to what i've learned about friction, sliding friction doesn't increase with velocity, so the 300-450 gram force needed to start the rocker moving at the top and bottom of its travel won't increase with rpm.
-- this only measured static friction, the force necessary to start the rocker rocking. as soon as it started to move, it moved too quickly for me to see what the spring scale might have been showing. so i don't know what the resistance of the moving parts might have been, after they started moving.
-- i didn't try to see whether it's harder to move a rocker from the absolute end of its travel than it might be from a little less than that. so in hindsight it's possible that the rockers might take less force to move if you start them closer to where they actually sit on top of the valve at zero lift. forgot to control for that . . .
-- this was done with cold parts, not warmed up, with no oil pressure inside (such as it is in a triumph), and with absolutely nothing else held constant.
-- the boxes are different kinds-- one is from a later head (hollowed out for the two-piece head bolts, and drilled for dowels), with the little oil cutout. the other is the earlier style, not milled out inside, and has the drilled rocker arms, which you can see from the holes in the pushrod ball ends.
and here are the guilty parts in question:
so it's clear that some friction exists, and that the friction is measurable at the point where the rocker arms stop moving, reverse direction, and start moving again. once they're moving, the force needed to keep them moving is way less.
but is this significant? i don't know. i suspect not, because with valve springs that might be pressing on these rocker shafts with way over 100 pounds of force, each, a few hundred grams of friction doesn't seem like a lot. but i'm not an engineer.
i have bikes with them, and bikes without them. i haven't ever noticed a difference, but i am not particularly sensitive and haven't pushed rpms to the limits, either.