Here’s a mystery engine with a very familiar look! Despite that, I couldn't place it initially.
The engine came from an English source, where it had apparently spent many years. It has very much the look and feel of the closely-related Alag X-03 and Yin Yan 2.5 cc diesels from Hungary and China respectively - it even has the same mounting hole spacing. However, it lacks a serial number as well as any identification markings on the case, unlike both of the others. It also has a neat steel backing washer behind the prop driver to avoid the undesirable alloy-on-alloy rubbing situation which the use of an all-alloy prop driver creates. This spacer is not an add-on - it is very accurately fitted to the shaft taper to provide just the right amount of shaft end-float.
The neat spring-type needle valve assembly turned out to be a red herring. Maris Dislers suspected right away that it may have come from a Taifun Orkan - the "B" on the end is an indicator of this. Maris also believed that the engine may be a very early Yin Yan made in 1962 as a "proof of tooling" example prior to the addition of model identification characters to the crankcase die and also prior to the commencement of the serial numberng sequence. If so, it would be a previously-unreported and very rare variant of that engine. I must admit that if it wasn’t for the absence of any cast-on identification or serial number along with the composite prop driver, I’d have put this down as an early Yin Yan myself.
Bore and stroke are the usual 15 mm x 14 mm for a displacement of 2.47 cc. Porting is Alag and Yin Yan style all the way, with a healthy period of sub-piston induction. The cooling jacket is anodized gold, now somewhat faded from heat cycles. The piston has a conical crown. Overall, the engine is extremely well made – all fits are superb despite the fact that it has clearly seen a fair bit of use.
IDENTIFICATION MADE!! Further research has confirmed Maris's suggestion that this engine is indeed a very early Yin Yan 2.47 cc diesel from Shangai, China, probably one of the very first batch made in 1962. We've confirmed the previously-unreported fact that the very first examples of this well-known engine did not feature either cast-on model identification or a serial number. It seems that those identification markings were only added after the initial unidentified batch had proved itself and the manufacturers were getting set to hit the international market
The needle valve assembly as received was indeed a Taifun component. I've now fitted a genuine Yin Yan assembly along with an original; Yin Yan prop washer, so the engine is now completely original. It must surely be the rarest Yin Yan/Silver Swallow variant of them all! I've updated the Yin Yan/Silver Swallow article to include this variant.