Harley-Davidson Shovelhead engine

With the adoption of unleaded fuels in the American market, the non-hardened valve seats of the vintage Shovelhead could wear excessively and require service.

[4] With Harley-Davidson trying to fix the engine rather than research and develop, they fell far behind the competition of the cheaper and more reliable Japanese bikes taking control over the market.

With the United States involved in the 1973 oil crisis, gasoline had a much lower octane and consistency that severely hurt the engine's performance.

Engine knock became a large problem; causing overheating that led to blown gaskets and damaged head bolts.

[5] After realizing they would need some serious improvement to fix their current situation, they produced some updates in 1978 to the engine that consisted of a larger displacement, and steel struts cast into the pistons to prevent them from expanding from the heat.

With many Shovelhead owners having to turn towards aftermarket parts to keep the bike running properly, Harley-Davidson realized they would have to start developing a new engine.

Belt drive was added to their motorcycles in 1980 to prevent the oil leakage from the enclosed chain, along with a 5-speed transmission and rubber motor mounts to help reduce vibration.

To bring more models into production, the FX Super Glide was released in 1971 with a "chopper" look that was ultimately an FLH with a Sportster front.

Because of the added weight of the larger engine on motorcycles with the Electra-glide package, the bikes were faster and more powerful at the tradeoff of being much harder to maneuver.