273 Rocker Arm to Shaft Clearance

gzig5 said
Chrome plating was suggested not for wear resistance, though it significantly enhances that, but because a slightly under-size shaft can be built up to size or built up and ground to size very accurately, and the cost isn't crazy.

Typically for a hydrodynamic plain bearing the desired clearance is about .001" per inch of shaft diameter. In the case of the rocker arms, they work differently than say a crank main bearing because they don't fully rotate and the oil supply is intermittent, not constant. The stock stamped rockers aren't even enclosed and have significantly less bearing surface on the rocker shaft than a 273 type would. How much clearance do you think are on them? They seem to rattle around a lot and it doesn't cause any issues. The spring pressure is going to be the deciding factor IMO. I think the OP could get away with .003" on the suggested build, but it would be a good idea to get feedback from RAU

Your comments about clearance in relationship to shaft diameter are partially why I posted, and, to be clear from my end understanding you weren't responding to me, I understood your suggestion of chroming to tighten the tolerance. The rocker shaft is a similar diameter as a piston wrist pin, and the wrist pin gets splashed oiling compared to the rocker assembly's pressurized. While I understand a wrist pin/piston dynamic functions differently than a rocker arm and the piston is aluminum--such as you don't want a piston flopping around or rotating in the hole due to excessive wrist-pin clearance--my concern with excessive rocker arm clearance is that the rocker arm will have more freedom to push back and forth perpendicular to the shaft and "rock" in and "X" pattern on the shaft as the forces of the pushrod and spring work on it, thus changing the fulcrum point and the rocker ratio and changing the sweep on the valve stem through the "X" pattern movement. As you have said, I doubt the .003" clearance will impact performance much on this build, but to me it's worth the discussion. FYI, spring pressure is rather mild on this build: 120 seat, 333 at .480" lift.

RustyRatRod said
Remember too, these rockers were skewed all over the map as far as being consistent with ratio. Gary at RAU will fix all that in one shot when he bushes them. He will correct for proper geometry and even change them to 1.6 if you want. There's just no down side. Course there's the cost. I guess it all depends on how far you're going with the build. Plenty of builds have run them as is with no problems at all.

Proper geometry is my central concern with the .003" clearance. The lack of wear proves to me that the assembly will hold up just fine if I run it as is. However, as I describe in my response above, the excessive clearance will allow the rocker arm's fulcrum to shift and its tip trajectory on the valve stem to change which in turn will change the ratio. Your point about the forged rocker arms being inconsistent in ratio is well taken, and the compounding change in ratio from the excessive clearance isn't desirable. The harm to performance remains unknown. If we were talking about a $1,000 investment, it would be worth dynoing the engine with the factory assembly and again with the reconditioned, but in this case the dyno cost would almost pay for the reconditioned assembly.