Harley-Davidson has been making motorcycles since 1903. There have been many major redesigns of everything from engines, suspension, frames and bearing designs. It’s very difficult to break that into common torque values. Besides, you don’t want to estimate the torque value on a critical fastener such as a head-bolt or axle. However, there are engineering guidelines that correspond to specific fasteners. General torque engineering specs can be referenced for any Harley-Davidson fastener, for the first models in 1903 to the latest V-Rod.
When in Doubt, Don’t Over Tighten!
A word of caution: it may seem like a good idea to err on the side of over-tightening an important fastener if you’re not sure of the torque value. It is not. Over-tightening can create the same likelihood of failure as under-tightening. Only with under-tightening you may have some warning in the form of vibration or noise; with over-tightening, if the bolt fails, it will just snap.
Baseline Torque Specs: Sizes and Threads
You don’t need factory torque specifications to work on a motorcycle. You need to know the diameter of the bolt and how many threads per inch it has. Then, you need a specifications matrix for that bolt.
Baseline torque specifications are for non-lubricated bolts with no plating. If you are using chrome-plated bolts, the torque value is the same for a non-lubricated, non-plated bolt. For a zinc-plated bolt, the torque value is 15 percent less than the baseline value. For a cadmium-plated bolt, the torque value is 25 percent less than the baseline value.
As with some plated bolts, lubricated bolts require less torque. Both lubrication and plating can make the binding surfaces smoother, so less torque is used to overcome friction and to seat the bolt to a given amount of pressure. If a bolt is lubricated with oil or assembly lubrication, the torque should be reduced by 15 to 25 percent. Teflon or Molybdenum dry film requires 50 percent less torque, as does Cetyl Alcohol.