Harley Terminology: Explained

Most riders will choose a cam based on their budget. In Harley terminology, a “bolt in” or “drop in” cam is always less expensive because the valve train will typically not need to be addressed. Some riders will opt for a high lift cam but will end up changing their minds when the shop explains the added cost to accommodate the cam(s). Other riders pay thousands of dollars for a performance package but have no idea what they are paying for.

In this video, Mike takes the time to explain Harley terminology and demonstrate parts and procedures pertaining to the Harley Davidson valve train. Hopefully clarifying some of the confusing questions, Harley terminology, or procedures that come up after talking with your service manager or mechanic.

Performance cams have a larger base circle with a higher lift and duration. They require performance valve springs, adjustable pushrods, and sometimes, premium tappets. Converting to performance valve springs is not as simple as swapping springs. Performance valves come with a valve spring sheet that specifies measurements and your objective for valve seat pressure.

Mike demonstrates measuring valve tip height. If valve stem protrusion is too much, you will exceed the allowable rocker arm geometry. Mike demonstrates two ways to measure retainer to seal clearance. If this distance is incorrect, the valve seal will be damaged or the valve guide can become cracked.

Mike also demonstrates seat pressure vs installed height (open seat) pressure. Mike demonstrates seat pressure differences between performance and stock springs. He also demonstrates coil bind which is when too large of a valve is used with too light of a spring. Every Harley Davidson manual specifies valve protrusion, tip heights, spring heights, spring lengths, installed seat pressure, valve open pressure, etc.

We hope that Mike’s demonstrations help you to have a better understanding of your manual and the Harley terminology you may hear at your shop or with fellow riders.

Related Videos:
Harley Davidson Motor Review – Shovel to M8
M8 Adjustable Rocker Arms
Twin Cam Top End R&R