Darkhorse Crankworks | 10629 Highway 42 | Newton, Wisconsin 53063 | (920) 726-9999
We have decades of experience building, blueprinting and balancing Harley Davidson crankshafts. This knowledge in balance factors, allows us to tailor a crankshaft for your riding style, engine design and its intended RPM range.
Dynamic Balance is defined as, "The state of equilibrium in which centrifugal forces, due to a rotating mass, do not produce force in the shaft and so vibration is reduced."
All Darkhorse Crankworks' flywheel assemblies are both static and dynamically balanced. Each individual part is balanced which equates to our flywheels in their assembled form dynamically balanced, pure physics and simple.
The illustration to the right, shows Darkhorse Crankworks' corrected and dynamically balanced flywheel. Each individual part has been balanced using the exact same ratios, which moves center of gravity in parallel with flywheel center and the sums of all parts are then
dynamically balanced. We do not use the automotive method, (spinning at 500-750RPM) that is reconfigured and loosely adapted to achieve balance in your crankshaft. At Darkhorse, our procedure insures that each flywheel is balanced to < .5 ounce/inches for all street bike versions. We guarantee this because we are balancing each individual flywheel, not an assembly that can get a varying input caused by inconsistent crankshaft trueness between the balancing procedures and final assembly. An automotive crankshaft’s total indicated run-out will not change from balancing to assembly. While a Harley-Davidson cycle will change almost every time - especially in a shop where main bearing tolerances are not strictly held under .0015".
Automotive-based equipment balances long one-piece crankshafts with multiple rod journals that cannot be disassembled. You are not able to balance of each individual rod journal, shaft and associated counter weight. Whereas a spin balancer achieves a dynamically balanced automotive crankshafts in large volume. Spin balancing an assembled Harley Davidson crankshaft with a bob weight to achieve a dynamically balanced flywheel is not the best available option to balance your Harley Davidson crankshaft assembly.
The illustration to the right, shows a dynamically imbalanced flywheel. This flywheel may be static balanced as a unit, but not dynamically balanced. This means neither end would fall due to gravity, but having the weight in opposing areas would make it want to shake since the center of gravity is not parallel with the flywheels. Using automotive-style balancing means that the connecting rods must be removed. The crank is then reassembled without rods, trued to within given specs, spin balanced with a bob-weight, disassembled once again, rods and bearings replaced and then it must be reassembled. It then must be trued to the same identical spec it was spin balanced which can throw the whole process out.
Darkhorse Crankworks' research on crankshaft balancing and vibration analysis also leads us to an often-debated topic in direct regards to Harley-Davidson crankshafts. What is the amount of acceptable run-out and where to measure? Our stance on this issue has not changed or wavered since 1980. The most important unit of measurement is at each main bearing race. This is where one primary source of vibration is introduced from what may very well be a properly balanced crankshaft if not true.
We true all crankshafts to within .0015” total indicated run-out at each main bearing race held on centers and guarantee them to stay within .0005” for two years and unlimited miles.
To only look at the end of the pinion shaft for your overall tolerances is unacceptable and irresponsible to the crankshaft and the entire engine and drive train. The run-out measurement at the END of EACH shaft is extremely important, but is typically a by-product of run-outs at each main bearing race.
At Darkhorse Crankworks, we continue to focus on perfecting our processes which equates to the smoothest crankshafts in the country.
Physics - Pure and Simple.