1928 Blackburne 173cc

Blackburne was a trade name of Burney and Blackburne Limited a British manufacturer of motorcycles from 1913 to 1922 at Tongham near Farnham, Surrey. They were also a major supplier of engines to other motorcycle and light car makers and continued to make these until 1937. Burney and Blackburne also made small aircraft engines.

https://en.wikipedia.org/wiki/Blackburne_(motorcycles)

As Found

The core engine was acquired in the United Kingdom. The parts needed to make it a complete engine came from Austria, Australia, Belgium, Canada, France, the UK, and the USA. Other miscellaneous parts were sourced in countries not mentioned above.

Blackburne Engines
The Role of Blackburne Engines in Road and Air Propulsion
1930 Blackburne Hints & Tips
1924-27 Blackburne Hints & Tips