I always thought that the hammers were the hardest on the machine. That was up until I was invited to the Cat proving grounds, in Peoria, IL, to test out the prototype "D" model backhoes. I posed the same question to the man in charge of backhoe development (the head engineer for backhoes at Cat). His answer suprised me. He said that compaction wheels are the worst. He went on to explain that the hammer is really not that hard on the machine (unless the oil return line is not big enough). He went on to say that they found the wheel is worst because most operators will extend and retract, the dipper and boom, to the full extent of the travel of the respective cylinders. The momentum, of the boom and stick, in conjunction with the lack of resistance that the wheel affords (to the extension and contraction) allows great stresses to the cylinder when the piston bottoms out at the cylinder base or, especially, at the head gland. That's what he said anyway. He has the credentials so I figured he's right. I would think that it would be the same for excavators too since the work in such a similar way.
