Shovelhead, panhead, and knucklehead are terms used to refer to different types of Harley-Davidson V-twin engines that were used in motorcycles produced by the company. Here's a breakdown of the key differences between these three engine types:
Knucklehead: The Knucklehead engine was introduced by Harley-Davidson in 1936 and was produced until 1947. It earned its name due to the distinct shape of the rocker box covers, which resembled the knuckles of a clenched fist. The Knucklehead featured overhead valves, a 61-cubic-inch (1,000 cc) displacement, and a distinctive appearance. It was the first Harley-Davidson engine to incorporate overhead valves, which increased performance compared to previous models.
Panhead: The Panhead engine was introduced by Harley-Davidson in 1948 and remained in production until 1965. It derived its name from the distinctive shape of the rocker box covers, which resembled inverted pans. The Panhead was an improvement over the Knucklehead, featuring a redesigned cylinder head with better cooling, hydraulic valve lifters, and a 74-cubic-inch (1,200 cc) or 80-cubic-inch (1,340 cc) displacement. The Panhead engine was known for its iconic appearance and was the last Harley-Davidson engine to use the separate rocker box design.
Shovelhead: The Shovelhead engine was introduced by Harley-Davidson in 1966 and was produced until 1984. Its name originated from the shape of the rocker box covers, which resembled an upside-down coal shovel. The Shovelhead represented another improvement over previous models, featuring an updated top end design with improved cooling, increased displacement options of 74 cubic inches (1,200 cc) or 80 cubic inches (1,340 cc), and improved reliability compared to the Panhead. However, the Shovelhead had its share of issues related to oil leaks and overheating.
In summary, the main differences between these engine types are primarily related to their time of production, design improvements, and displacement options. The Knucklehead was the earliest, followed by the Panhead, and finally the Shovelhead. Each engine has its unique appearance and technical characteristics, contributing to the rich history and legacy of Harley-Davidson motorcycles.