Quote Originally Posted by Tim Kurcz View Post
Most outboard rods are forged steel, copper plated (carburize mask), rough machined (removes copper plate from intended surfaces), assembled, carburized, then finish machined (ground/honed). Copper plated areas are soft, only the bearing/wearing surfaces are hardened. To prove this to yourself, clamp a spare rod in a vice, apply torsion with a pipe wrench, and watch it twist without shattering.

For the proto rod, copper will be removed from the cap, the extension blade tig welded in place with the rod assembled and fully torqued. Following, the journal bore will be honed round and to size, and the pivot bore will be machined.

After swing fitting, the proto rod and cap bearing surfaces will be Brinnell tested. If there is no significant difference, the 888 might be run with welded rods. If the difference is unacceptable, custom rod caps will be machined, and the bearing surface will be carburized, honed, etc.

Side note: It might surprise you to know that mod outboard racers have been honing .002" - .0025" from the big end bores for many years. This procedure followed Mercury's change from .880" to .882" crank pins. It allowed rods to survive race conditions without overheating (bluing).
While the outer surfaces of the rod are copper plated to mask the carburizing process (so that the rod isn't hard and brittle on the surfaces that are under tension) and only allow the bearing surfaces to be carburized, the rods aren't in the fully annealed condition. The rods are strong due to the forging process and subsequent heat treat, but not brittle, as they would be if they were carburized all over. Doing a Brinell test on a regular (unwelded) rod and comparing the hardness with the modified end cap is a good plan. If you knew the alloy you could heat treat the cap after welding and it would be as strong as it could be.

I'm well aware that these rods are commonly honed out to increase the bearing clearance. I had a set done when I built my 44 in motor to APBA stock specs. But when you hone these rods to take about .001 inches off of the surface (x 2 to open the diameter up by .002). That doesn't go through the carburized hard surface. I don't know how deep the carburization is taken in these rods. Since the purpose of carburizing is done to make the surface hard enough to be a bearing surface it most likely isn't deep. Deeper carburizing wouldn't serve any purpose so I doubt it's very deep. The only way to know is to grind the rod and then do a hardness test on it, or get a copy of the rod print where it is probably noted on the drawing. My point was that you don't want to grind off too much of the bearing surface or you will risk having a soft bearing surface and that will deteriorate quickly under the contact stress of a rolling element bearing. If you only have to take off .003 from a surface (3 x what you take off in the process of loosening up the rod clearance) you are probably fine.