The well-known Sugden Special from 1950's England was a 2.5 cc crankshaft front rotary valve (FRV) plain bearing diesel which was specifically designed for home construction by professional dentist and skilled machinist Dave Sugden of St. Albans (who later relocated to Canada). This iconic design dates back to December 1954, when a series of construction articles written by Dave Sugden was launched in "Aeromodeller" magazine and the relevant plan was published. Arrangements were also put in place at the time to make crankcase sand-castings available to home constructors.
The series of articles in "Aeromodeller" later formed several chapters in the 1958 "Model Aero Engine Encyclopedia" from the same publisher. Much later still, the engine became the subject of a most informative article written by Ron Chernich and still available on MEN. That article includes a link to Ron's construction article detailing his own experiences in building an example of the engine. There's plenty of construction guidance available!
Being both light and powerful by the standards of the mid 1950's, the Special was widely seen as an excellent subject both for home construction and for use as a model powerplant. I'd guess that many hundreds of examples must have been constructed in the 65 years since the initial publication of this design! Many of them doubtless saw considerable use in the field.
The one problem for today's constructors is the fact that the supply of the required crankcase castings is highly problematic at the present time. The illustrated example was constructed in 2018 by my fellow Canadian Andrew Coholic from one of his own castings. I hope to publish a test of that example on this website in due course. In the meantime, Andrew's video of the engine running may be found here.
I've had a number of inquiries from people wishing to obtain a copy of the plans. Thanks to the kindness of my good mate Ken Croft, I've been able to provide access both to the plan and to the original construction article elsewhere on this website. Hopefully a new source of supply for the crankcases will emerge in due course.