A
Anonymous
Guest
I,ve been seeing, in various places recently, people advising the polishing of connecting rod beams. The idea is to remove those crossways grinding marks, left by the factory after they clean up the foundry flash, to eliminate stress-risers.
However, the way I learned it, many decades ago, was that a forging has a hard "skin" which adds to its fatigue-strength. To polish a rod, you start with a grindstone, then hit it with a sanding drum using progressively finer grit rolls, until you get to a surface finish you consider to be "polished". Of course, you are careful not to overheat the part at any time. But to work your way through those factory grind-marks, you also are removing much or all of that forged-in hard skin, and very likely shortening the fatigue-strength of the part. Therefore, as I learned it, don't polish rods or other forged parts unless you are willing to pay for the additional step of getting them shot-peened, which re-creates the hardened skin. And since the big-name shot-peeners in this town didn't inspire my confidence that they knew what the hell they were doing, I've never polished rods after that first experience. Anyway, for a street engine, magnafluxing, re-sizing, and good rod-bolts should suffice.
Or am I wrong? I keep seeing contrary advice.
However, the way I learned it, many decades ago, was that a forging has a hard "skin" which adds to its fatigue-strength. To polish a rod, you start with a grindstone, then hit it with a sanding drum using progressively finer grit rolls, until you get to a surface finish you consider to be "polished". Of course, you are careful not to overheat the part at any time. But to work your way through those factory grind-marks, you also are removing much or all of that forged-in hard skin, and very likely shortening the fatigue-strength of the part. Therefore, as I learned it, don't polish rods or other forged parts unless you are willing to pay for the additional step of getting them shot-peened, which re-creates the hardened skin. And since the big-name shot-peeners in this town didn't inspire my confidence that they knew what the hell they were doing, I've never polished rods after that first experience. Anyway, for a street engine, magnafluxing, re-sizing, and good rod-bolts should suffice.
Or am I wrong? I keep seeing contrary advice.
(he he)... is interesting and something I have been thinking about recently. I'm getting ready to start a rebuild and was wanting to balance the rotating assembly. Being I have never done this on a multi-cylinder engine and all the talk of balancing your rods to within a half gram. What is the correct method of shaving weight off of your rod? Would you shave the beam or where specifically do you like to grind or shave the rod? Shot peen... Then, Do you do the same thing with the pistons? Same question...Do you shave the piston skirt? I would think you would want to balance each recipricating unit or each rod,bolts, wrist pin and piston as a unit. Now, All that being done, do you then balance the crank? Maybe tungsten inserts? or are they fairly close? And then... As long as I'm going nuts with my grinder anyway, How about the trick where you take off the rough edges of the crank to reduce windages? Anything special I should look out for other then just using common sense in removing the rough edges? or should I just leave all this stuff up to common $$cents and the pros? I've just always liked going nuts on my two strokes and I have time. At least I have a lot more time than I do common $$cents. :roll: 
