First H-D OHV twin

What year did William S. Harley design the first OHV twin?

Not sure, but I think it was 1913. First OHV was the 8 valve introduced in late 1915 as a 1916 model.

Johnny,
I don't know when he designed it. The first attempt at producing the V-twin was in 1909. It had atmospheric valves and was a failure. The next V-Twins hit the market in 1911.

I was thinking of the patent drawing dated 1919 of the aluminum cylinder/aluminum pushrod OHV twin. Damn Curt, I didn't know about the 8-valve that early!

Johnny
William S. finally convinced the rest of the board of directors that a strong racing program was needed to spur retail sales. They finally agreed to his program in 1913 and hired William Ottaway to oversee the program. I think there is some controversy over when the 8-valve was introduced, but there is a photo floating around that shows a 8-valve at the starting line in a race that took place in 1915. Officially it was introduced in the 1916 model year. The 8-valve was available for retail sale to meet FAM regulations, but was priced at 1500.00 to discourage sales to privateers. According to my book on the subject, there were no sales of new 8-valves to individuals. They believe only 30-50 8-valves were built.

In my book the 8 Valve was absolutley the coolest bike ever ! Saw one at the AMC meet ,( York, PA. ) a couple weeks ago, and me without a camera

According to Harry Sucher's book "Harley Davidson the Milwaukee Wonder", Ottaway designed several prototype 8 valve engines, but they suffered from preignition, even though he had attempted to follow the design work that Harry Ricardo had been developing over in England. Ottaway finally convinced Walter Davidson to Pay Ricardo's steamship passage to the States and his design fees. After several weeks of experimentation, Ricardo got good results, getting the engines to turn out 55hp from 61inches. This was in 1915. The other catch was they had to pay royalty fees to Ricardo for every engine built, so Walter, who was apparently quite tight fisted, was reluctant to build any more than necessary of these machines. At least, this is Harry Sucher's spin on the story. It's an interesting book throughout. Also, some 30.50 singles were also made, not sure how many, and about 30 of the 61's according to him. He also says that a few were eventually sold to select privateer racers. No mention of the general public though.
This book also relates that Joe Petrali flew with Hughes on the only flight of the Spruce Goose.
Dr Dick