This Husqvarna excam system looks very much like the much later invented LITO excam system. (See: “Semi-Desmodromic Systems“). Only the first link in the distribution chain again is desmodromic.
It is conceivable to combine the first link with a BMG/Velocette like second distribution chain (see: “True Desmodromic Systems“) to get a complete desmodromic system.
Hereunder some citations from the WWW:
“One 250 cc machine was specially fitted with experimental valve gear. This was based on a rocking, rather than revolving, cam actuated by a long conrod connected to an eccentric on a half-speed shaft. This was one of Folke Mannerstedt’s pet ideas, which had earlier been tried on a single-cylinder 350 ridden by Arthur Ohlsson.
The new 250 was built as half a 500 with the rear cylinder blanked off, and was ridden in 1934 and 1935 by Ove Lambert-Meuller. It was called an ohc model and looked like one from the outside, but the vertical tower tube contained a long conrod, not a vertical drive shaft. It was later planned to introduce this mechanism (later called “ExCam”) in a new series of 500s.
A kit of parts for this conversion has been preserved, but no complete twin-cylinder engine was ever built.”
Source: http://w1.331.telia.com/~u33106502/hq/hq-artic.htm#Husqvarna´s fighting V-twins
“During the period of professor Hubendick, the department was very active and had many thesis workers conducting research. Among them was Folke Mannerstedt, a well known engineer in the field of racing engines and his thesis work of 1927 was the famous Excam, a variable camshaft system. Mannerstedt was also behind the outstanding success of Husqvarna Motorcycle Company in the TT-series (later Roadracing) in the 30’s.
“The 1935 Husqvarna was an advanced design for its time with a very high performance. Its main drawback was perhaps the pushrod valve gear, but Mannerstedt already had a clever way around it in his ExCam system, which could be adapted to any existing ohv design without radical modifications. If the Husqvarna had been developed as Folke Mannerstedt intended, it might have challenged more strongly the British singles and Continental multis.”
Source: http://w1.331.telia.com/~u33106502/hq/hq-artic.htm#1934 – Husqvarna´s year of destiny