Updating oiling u ul ulh
On the downside, the flathead also requires the airflow to make at least a 90-degree turn to enter the cylinder, which makes it less efficient, colloquially called poorer "breathing".
The design was common on early engine designs, but has since fallen from use.
The VL had a single downtube frame and total loss oiling, culminating in an 80ci version (VLH) in 1935.
In 1937, that engine was redesigned to include a recirculating lubrication system, and designated the model U, and it went into the same frame and running gear configuration as the model E Knucklehead, which had originated in 1936.
The K series was replaced by the overhead valve Sportster series in the retail market in 1957.
However, racing versions of the 750 cc K model, designated KR, continued to be produced in very limited numbers for some time after, winning both roadraces and dirt track events against overhead valve bikes limited to 500 cc through 1969, when the American Motorcycle Association finally decided to change the rules and make the venerable flatheads uncompetitive.