The 0.81 cc E.D. Pep diesel was a rather hurried and ill-considered response on the part of the E.D. management to the 1959 appearance of a rash of British-made 1/2A (.049 cuin.) glow-plug motors. They seem to have reasoned that if a viable diesel alternative could be placed on the market, the presumably die-hard British diesel users would stick with what they knew.
Unfortunately, they overlooked the fact that the 0.8 cc diesel market was already well served by such well-established models as the D-C Merlin, the FROG 80 and the Mills .75. Accordingly, their sales expectations were not fulfilled, resulting in the Pep never achieving any real prominence in the marketplace. All that it really did was make a further contribution to the over-saturation of the British market with small engines, the demand for which was shrinking in any case.
Still, the often-maligned Pep was a better engine than its reputation might suggest. For a great deal more information on the E.D. Pep story, see my in-depth article on Ron Chernich's "Model Engine News" (MEN) web-site. The full story of the E.D. range in general may be found in my E.D. article which appears elsewhere on this web-site.