These ten Harley-Davidson engines are just as legendary as the models they powered - and they will run forever with the right maintenance.

Read more: 12 Major Motorcycle Brands Ranked Worst To Best Arguably one of the most influential motorcycles in the brand's back catalog, the Harley-Davidson EL Knucklehead was introduced in 1936.

Harley-Davidson isn't the oldest American marque – that distinction goes to Hendee/Indian – but it's the only one that has been in continual operation since its inception in 1903 up through ...