A 20mm round is typically fired from a high-powered military weapon such as an anti-materiel rifle or an aircraft-mounted cannon. These rounds are designed to penetrate armored targets and are extremely powerful.
While a Harley-Davidson motorcycle engine is made of solid metal and is designed to be durable, it is highly unlikely that it would be able to withstand a direct hit from a 20mm round. The engine casing may provide some initial resistance, but the force and velocity of the round would likely be sufficient to penetrate it.
It's important to note that firing a 20mm round at any object, including a motorcycle engine, is extremely dangerous and highly illegal in most jurisdictions. This response is purely hypothetical and is not intended to condone or promote any illegal or harmful activities.