By 1937, all Harley-Davidson's flathead engines were equipped with dry-sump oil recirculation systems similar to the one introduced in the "Knucklehead" OHV engine. The revised 74 cubic inches (1,210 cc) V and VL models were renamed U and UL, the 80 cubic inches (1,300 cc) VH and VLH to be renamed UH and ULH. The 80 cubic inches (1,300 cc) flathead UH and ULH models were discontinued after 1941. 
- Mitchel, D. (1997). Harley-Davidson Chronicle - An American Original. Publications International Limited. pp. 94-95. ISBN 0-7853-2514-X.