The HGK 15R was a state-of-the-art 2.5 cc speed engine at the time of its introduction in 1974. It was made in Tokyo, Japan by a company calling itself (in Japanese) the Hashioka Technical Laboratory. It was the first commercial model engine to use the now-familiar aluminium-aluminium-chrome (AAC) piston/cylinder technology.
The HGK 15R was supplied as a complete package with pipe, pipe connector and all necessary Allen keys as well as a matching speed spinner. There was also an alternative version called the HGK 15N which was supplied without a spinner in two distinct variants timed for piped and un-piped operation, albeit without a pipe being supplied with the engine in the former case. That model was evidently intended for FAI free flight competition.
The HGK engines were manufactured to extremely high standards but suffered (at least in the earlier stages) from excessively loose piston fits. This was evidently due to the fact that HGK were first in the field with AAC technology at a time when that technology and the need for a tight piston fit at top dead centre were not well understood. It does not reflect at all upon the firm's manufacturing capabilities, which were of the highest order. Although the company's later models reflected a complete grasp of the requirements of AAC technology, the damage done to the company's reputation by the earlier problems with piston fits resulted in their only surviving in production for 12 years, being wound up in 1986.
For the full story of the HGK engines, see my separate article elsewhere on this web-site.