England's 1/2-A Enigma—

The A-M .049

by Adrian Duncan

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Click on images to view larger picture, hover over the images for a description.

In our companion article on the Frog .049 glow-plug motor from England, we detailed the circumstances surrounding the British 1/2-A glow motor "revolution" which began in mid 1959. We've already covered three of the participants in this particular contest between British manufacturers—the Cobra .049, Frog .049, and D-C Bantam. To complete our review of this interesting and in retrospect significant episode in British model engine history, it's now time for us to turn our attention to one of the less successful contestants in that particular competition between British manufacturers—the Allen-Mercury (A-M) .049. This intriguing little motor was presented as a product of the well-established firm of DJ Allen Engineering and was marketed by Mercury Models under the Allen-Mercury banner.

The production facilities of DJ Allen Engineering were located at 28 Angel Factory Colony, Angel Road, Edmonton, North London. Angel Road is now the North Circular Road and has greatly changed since the A-M factory was located there. The former Angel Factory Colony is now known as the Lea Valley Trading Estate.

The A-M .049 was to all intents and purposes a clone of the well-known Wen-Mac .049 glow motor which had been in production in the USA since 1952 and had passed through a significant number of variants by 1959 when the AM .049 appeared. The real question which has always surrounded the latter engine is the extent to which it actually was a British production? At the time, its claim to British manufacture was unchallenged, but looking back today we can see plenty of room for doubt.

Following the initial publication of this article, these doubts were confirmed through the receipt of additional first-hand information from reader Michael Clarke. Michael worked at Allen Engineering during the entire period in which the AM .049 was marketed, entering the company's employ as a sixteen year old apprentice in May 1957, concurrently with the firm's move into its new premises at Angel Factory Colony. He remained with the company until September 1962, shortly before it was re-organized under new ownership.

On the basis of his own first-hand knowledge, Michael was able to confirm a number of matters on which we were only able to speculate in the original text of this article. He also added some extremely interesting points of clarification regarding both the engine's origins and its production history. Such insights from one who was "there" at the time have a value that cannot be overstated, and our very sincere thanks go out to Michael for his kindness in helping us to present as complete a history of the A-M .049 as possible.

With that said, we are now in a position to get on with our story, but first, it's necessary to set the scene by paying a visit to America.

Background

The 1/2-A (.049 cuin) glow motor revolution had begun in the USA during the late 1940's. By the early '50's, 1/2-A engines constituted a significant proportion of the total model engine market in North America. The sheer size of that market encouraged extremely large production volumes and the economies of mass production at such a large scale allowed these little engines to be sold at remarkably low prices by world standards. Since free flight and control-line modelling predominated at the time in question, this brought power modelling within the financial reach of anyone having an interest and a few dollars to spend—no need to invest in R/C gear, complex control hardware, powerful throttle-equipped engines and large airframes. The hobby was both far simpler and more challenging back then—it required time and skill as opposed to mere money!

An additional facet of the US model manufacturing industry which gained impetus from the ready availability of inexpensive small engines was the Ready-To-Fly (RTF) market. This was by no means restricted to model aircraft but included boats and cars as well. The majority of these models were of the moulded plastic variety and were powered by 1/2-A engines.

One of the American companies which entered the RTF market during the early 1950's was the Wen-Mac Corporation of Culver City, California (in effect, a west-side suburb of Los Angeles). This company was established in 1950 by the brothers Len and Jack McRoskey in partnership with Adolph Wenland, hence the Wen-Mac name. Their main product line was a range of plastic RTF models which initially used engines obtained from outside manufacturers.

The Wen-Mac venture was an immediate success. By 1952 sales had grown to the point where the company was obtaining engines from no less than three different manufacturers (OK, Atwood, and Anderson), yet was still facing a shortfall in supply. The answer was obvious—make their own engines. They took this step in 1952 with the involvement of the legendary Bill Atwood. Bill, who had designed the engines used by Wen-Mac from other manufacturers, now became the designer of their basic in-house engine model.

Atwood had previously marketed a line of highly-regarded larger engines under his own name and had also been associated with the post-war North American marketing efforts of the Japanese OS company. Indeed, until 1958 Atwood continued to produce a line of basically similar small engines under his own name in competition with the Wen-Mac units before moving into an ill-fated and short-lived live steam venture and then going to work for Cox.

The Wen-Mac model empire was built around a compact .049 cubic inch glow-plug motor which was sold by the hundreds of thousands in a bewildering number of different guises. Some of these were sold over the counter as normal "hobby" engines for owners to fit in power models of their own choosing, while many others were used to power ready-to-use plastic models of all descriptions, of which Wen-Mac was a major producer on a world scale. Wen-Mac also mixed and packaged fuel for use in their engines.

By 1959, when the A-M .049 story begins, the Wen-Mac .049 had appeared in no fewer than twelve distinct variants. The three original models were simply designated as Wen-Mac .049's, but in 1955 a slightly modified variant appeared which was designated the Mk II Wen-Mac .049. As of 1959 this Mk II version had appeared in no fewer than nine distinct variants of its own, all identified on the case as Mk II's. Readers may at this point be coming to the realization that sorting out the various Wen-Mac models is no easy task. You'd be right, and our very sincere thanks go to Tim Dannels for doing just that in his invaluable and highly recommended "American Model Engine Encyclopaedia".

Production figures for Wen-Mac were quite astonishing, especially when looked at from a British viewpoint. At one point in the early 1960's, production of the Wen-Mac .049 reached 6,000 units per day! Reportedly, 15% of these were randomly selected for inspection and testing, and if a problem showed up the production line was halted until the cause was identified and corrected. To put this into perspective, it's highly doubtful that 6,000 examples of the A-M .049 were made in total during the two years or so that it was on offer.

The Wen-Mac company continued to manufacture models and engines in its own right until 1968 when it was acquired by the Testor Corporation, the owners of the McCoy trade name. Testors continued production of updated versions of the Wen-Mac engines under the McCoy banner.

While all this was going on in America, modellers from Great Britain had indulged in a brief flirtation with glow-plug motors for general-purpose use in the late 1940's and early 1950's but since then had remained steadfastly true to the diesel engine for all but a few specialized applications. The American 1/2-A revolution had a parallel in Britain during 1951-52 when no fewer than four British manufacturers (Allbon, Frog, ED, and Elfin) all released half-cc diesels. However, the craze for really small diesels passed relatively quickly and things soon got back to normal.

Glow-plug ignition was accepted in Britain as being superior only in the larger displacements and for specialized purposes such as all-out speed competition. This had allowed the British-made ETA racing glowplug engines which had first appeared in 1949 to become established as worthy contenders in the racing field, but most of the other early British glow-plug models had fallen by the wayside rather quickly.

The most durable non-racing survivor of the early British glow-plug era was the trusty old standby Frog 500 of 4.92 cc displacement. This engine first appeared in 1949 and was deservedly a firm favourite among control-line sport and stunt fliers for many years thereafter. ED also offered a glow-plug conversion for their 2.46 cc Mk III Racer, although this didn't attract much attention since the Racer tended to perform better as a diesel! The same was true of the AMCO 3.5 PB model, which was also offered for a time in glow-plug form. Apart from the short-lived JB glow-plug models and a glow-plug version of the Frog 149 Vibramatic, that was about it for general-purpose British glow motors as the end of the 'fifties approached—for the most part, diesels still predominated.

By 1959 the British model engine industry was stagnating to a certain extent and British modellers were ready for something different. In addition, interest in radio control was on the rise. This set the stage for 1959 to become the turn-around year for glow-plug motors in Britain.

1959—the year of the glow-plug in Britain

The early 1959 introduction of the excellent Merco .29 and .35 glow-plug stunt engines was widely publicised and showed British modellers that domestic manufacturers were fully capable of producing world-class engines of that type. The innovative and technically very successful Davies-Charlton Tornado Twin of 5 cc displacement was another outstanding British glow-plug achievement in the same year.

Moreover, the importation of the excellent glow-plug motors being produced in Japan was on the rise, spurred on by some very positive published test reports and high-profile contest successes. In addition, the popularity of R/C flying was increasing and British modellers were becoming ever more aware of the superior throttling capabilities of glow-plug motors as opposed to diesels. These factors resulted in the British marketplace becoming increasingly receptive to the broader use of glow-plug ignition in place of the previously almost universal diesel.

In the smaller displacement categories, the importation to Britain of the Cox range of 1/2-A glow-plug motors had begun in the late 1950's through the AA Hales organization, and people had certainly taken note of the excellent quality and performance of these little units. The major objection in Britain to the use of the mainstream Cox 1/2-A models was their adherence to radial mounting—British modellers had by then come down firmly in favour of beam mounting as a rule. In addition, the fact that one was more or less forced to use the relatively bulky built-in tank was widely seen as a disadvantage—British modellers generally preferred to choose their own tank arrangements depending on the application. I can clearly recall the Cox .049 models being criticised on the flying field in very much these terms.

In early 1959 a number of British manufacturers evaluated the situation and decided pretty much simultaneously to enter the 1/2-A glow motor market themselves. This led immediately to a virtual replay of the 1951-52 half-cc diesel revolution, albeit this time with 1/2-A glow-plug motors as the contestants.

Now there were three potential pathways to entry into this market—innovate, convert or copy. The first option involved the development of an all-new design from scratch—an expensive proposition, albeit one with perhaps the greatest potential. The second option was to take the very simple route of producing a glow-plug conversion of an established diesel design. This would side-step the bulk of the development and tooling-up costs very nicely but would probably fall short of producing the optimum results—the simple switch from diesel to glow-plug ignition rarely results in the best-possible performer.

Allen-Mercury did not have an established diesel design in the appropriate displacement category, so the conversion option was not open to them. However they clearly wanted to minimize both the time and the costs associated with the development of their own .049 glow-plug model. They therefore elected to take the third option, which was to side-step the entire development process at one fell swoop by simply purchasing the rights to an established design which had already been fully proven by others. The design with which they became associated was that of the Wen-Mac .049, then in its seventh year of production.

The manufacturers of the A-M range, DJ Allen Engineering, had been established in 1954 by Dennis Allen, who had been a prominent control-line stunt flier during the pioneering era in Britain following WW2 and had acquired extensive experience with model engines going back to his days as the head of Henry J Nicholls' engine repair service in the late 1940's. He had subsequently worked for Allbon and the later makers of the AMCO range before setting up in business on his own account. A particularly valuable asset for Allen's new company was the involvement of Len "Stoo" Steward, a long-time club-mate of Allen's and the former manufacturer of the "K" range of engines.

Through his previously-established connection with Nicholls, Allen was able to secure a marketing agreement through Nicholl's Mercury Models division, and the engines were accordingly marketed under the Allen-Mercury label. The venture was a success from the outset, and by 1959 the Allen-Mercury partnership had best-selling diesel models in 1 cc, 1.5 cc, 2.5 cc and 3.5 cc displacements. The A-M .049 thus represented the fifth displacement category into which Allen-Mercury had thrown their hats. As such, it had no predecessor in diesel form.

Now, there has never been any controversy surrounding the statement that the A-M .049 was a clone of the then-current Wen-Mac .049—indeed, the promoters openly stated that it was marketed by them in Britain under license from the Wen-Mac Corporation. The question which has been asked from time to time, and which we're asking here yet again, is whether or not it was actually manufactured by DJ Allen Engineering or whether it was simply an example of "badge engineering" in the form of a Wen-Mac product made expressly to be marketed in Britain by Allen-Mercury and identified as an A-M product simply to give it a "made in England" cachet. It seems best to begin our examination of this question by taking a comparative look at the two models.

Description

We may as well start right out by saying that the A-M and Wen-Mac .049 models were very similar indeed. Except where specifically noted, the following description applies equally to both models.

A side-by-side comparison of the A-M .049 with its Wen-Mac counterparts quickly reveals that the A-M version is basically a clone of what Tim Dannels calls the 8th model of the Wen-Mac Mk II engine (Peter Chinn incorrectly described it as a copy of the Wen-Mac Mk III, which was not introduced by that name until 1961!).

In design terms, the Wen-Mac and A-M .049 engines were typical American-style small "sports" glow-plug motors of their day, with pressure die-cast cases featuring provisions for both radial and beam mounting, screw-in cylinders, radial cylinder porting using milled slots for both transfer and exhaust, crankshaft front rotary valve (FRV) induction and a ball-and-socket small end on the con-rod. The Atwood connection was clearly in evidence, since the cylinder in particular bore an unmistakeable resemblance to that used on earlier Atwood designs such as the 1954 Cadet.

Quoted bore and stroke of the Wen-Mac were 0.420 in (10.67 mm) and 0.360 in (9.14 mm) respectively for a displacement of 0.817 cc (O.0499 cuin). This was just within the American 1/2-A class displacement limit of 0.05 cuin. Ron Warring published measured figures for the A-M of 0.421 in.(10.69 mm) and 0.364 in. (9.24 mm) respectively for a slightly larger displacement of 0.829 cc (0.506 cuin) which is just over the US 1/2-A limit. However, the discrepancies are small enough that they may be merely incidental or may relate to the measuring techniques used. In practical terms, my own direct experiments have proved that major working components from the two engines are both indistinguishable and directly interchangeable.

The unhardened leaded steel cylinder screwed into the crankcase in the conventional manner. An unthreaded portion of both the cylinder and the case created an annular passage around the entire cylinder circumference at transfer port level, just below the exhaust port flange. This annular passage fed the three transfer slots and was in turn supplied with mixture from the lower crankcase by two quite large vertical channels in the sides of the case which interrupted the female threads into which the cylinder screwed. This arrangement was similar to that used in the OK Cub engines and was also employed in the competing Davies-Charlton Bantam .046 cuin model.

The screw-on aluminium alloy cooling jacket also doubled as the cylinder head. It was threaded for a short-reach plug and sealed to the cylinder with a gasket. The backplate too was a screw-in item of aluminium alloy. The A-M engines were not provided with tanks, although some examples were fitted with centrally-tapped backplates suitable for tank mounting. Several variants of the Wen-Mac engine were in fact provided with tanks, which likely explains the existence of such backplates.

The piston and con-rod were both of hardened steel. The con-rod engaged with the piston through a ball-and-socket bearing at the upper end, the ball section of the rod being retained in place by a small circlip placed internally around the open end of the socket.

Both engines used a one-piece hardened steel crankshaft with a distinctive conical side profile to the front of the unbalanced full-disc crankweb. Journal diameter was 0.218 in, with a central gas passage of 0.125 in diameter. Induction was through a round port drilled into the shaft and having a diameter of 0.137 in. This port drew mixture from a tubular venturi of substantial length.

The brass spraybar was internally threaded to accommodate the externally-threaded blued steel needle. The Wen-Mac spraybar was pressed into the venturi and was angled to the rear on the right-hand side, keeping the fingers reasonably well clear of the prop disc. On the A-M, the spraybar was secured with a nut and was set at right angles to the engine's axis, allowing assembly from either side of the engine at the cost of placing the fingers uncomfortably near the prop disc while adjusting the mixture.

The A-M needle was tensioned by a piece of plastic fuel tubing which was fitted over the end of the spraybar and gripped an expansion on the needle body. A rather Mickey-mouse solution, it must be said—a small coil spring as used on the Wen-Mac version would seem better, although the plastic tube does help prevent air leakage past a loose thread.

The patented Wen-Mac Rotomatic starter which was fitted to both models was an ingenious device, if rather impractical in some ways and also completely unnecessary given the almost casual ease with which these engines could be hand-started. It consisted of two housings in the form of shallow steel "dishes" arranged face to face, the rearmost of which was riveted to the crankcase by a pair of screwed drive-plugs while the other was pressed onto a splined section of the shaft forward of the main journal. This front housing incorporated the prop driver and turned with the prop. These two components contained a coil "clock" spring and a mechanism to allow for the one-way engagement of that spring.

The coil spring was contained in the rearmost (fixed) steel housing. Its outer end was hooked onto the lip of the housing, while the inner end was attached to a tubular steel sleeve which was mounted on a suitably machined portion of the front of the main bearing housing and was free to rotate. This steel sleeve in turn engaged with a "clutch" device contained in the front (rotating) housing. This clutch device was sealed within the front housing, hence we are unable to show any images of the internal mechanism. However, it worked in the same manner as in the earlier pull-cord starter developed by Wen-Mac, which was fully described in the "Latest Engine News" feature in the February 1959 issue of Model Aircraft.

In any case, the principle is simple enough. The clutch device included a centrally-perforated flat steel plate which engaged with two flats machined into the front end of the central steel sleeve to which the coil spring was attached. The steel plate had a pair of wedge-shaped cutaways on its outer edge. There were two small steel-plate "rollers" arranged so that when the prop was wound backwards the rollers became wedged between the steel plate and the outer lip of the rotating housing so that the steel plate and the sleeve with its attached spring moved with the housing, thus winding the spring as the prop was turned. When the prop was released, the spring naturally spun the prop in the direction of engine rotation and the rollers were released as the spring tension was relieved, leaving the front housing and prop free to turn on their own with the steel plate and rollers remaining stationary inside.

The advantage of this set-up was that there was no fiddling about hooking the end of the starter spring to the prop or to an external cam plate—one just rotated the prop backwards for a turn or so and then released it. The disadvantages were that it added a considerable degree of complexity and hence cost as well as a great deal of excess bulk at the front of the engine. It was also disproportionately heavy, contributing 0.6 ounces (17 gm) to the 1.76 ounce (50 gm) weight of the engine—some 34% of the total. It had the added disadvantage of restricting the length of beam mounts if these were to be used. Finally, the fact that the steel plate and rollers remained stationary within the front housing while the engine was running almost certainly added some frictional power losses to the system.

Quite apart from all of this, the other bad thing about this unit was the fact that it invariably failed in service after a relatively short period of use! This was a widely-acknowledged problem even at the time—an article about spring starters in the 1960 issue of Aeromodeller Annual highlighted this issue. The failure always occurred in the spring itself at the point where it was attached to the central steel sleeve. The only fix was the fitting of a new spring/sleeve combination, which would have been a challenge for many owners given the fact that one had to remove the pressed-on rotating portion of the starter to gain access to the spring. Most people probably didn't bother because the engines were so easy to hand-start anyway! However, this explains why almost all "experienced" starter-equipped Wen-Mac and A-M .049's encountered today have broken springs.

The A-M .049 On Test

The A-M .049 was announced in a full-page advertisement which appeared in the July 1959 issue of Aeromodeller. The ad stated that the engine would be available "soon". As events proved, examples actually began to appear in the model shops in late September 1959, by which time the engine was appearing in Allen-Mercury's regular advertising. It sold for a most competitive price of �1 19s 6d, although this was soon to be undercut by the D-C Bantam at only �1 14s 6d.

The AM .049 was one of the subjects of an unusual triple engine test by Ron Warring which appeared in the January 1960 issue of "Aeromodeller". This test featured three of the four contenders in the British 1/2-A glow-plug sweepstakes. The only one missing was the Cobra .049, the appearance of which was delayed until later in 1960. Warring's test report on the Cobra was finally published in the October 1960 issue of Aeromodeller.

In his report on the A-M .049, Warring stated that the new engine was "basically the American "Wenmac" motor, with certain material modifications consistent with British practise". One of our tasks here will be to test this statement. The report also identified DJ Allen Engineering as the "manufacturers" of the A-M .049—another point which we shall subject to scrutiny.

Warring was very complimentary about the engine's handling and performance, finding a peak power output figure of 0.052 BHP @ 14,000 rpm, a very good figure for a sports glow-plug .049 and one which matched or exceeded the performance of several contemporary small diesels of similar displacement and weight. When one considers that the engine weighs only 1.16 ounces (33 gm) without the starter, the reported power-to-weight ratio is actually pretty impressive. Warring commented in particular upon the engine's better-than-average torque production and its consequent ability to turn larger-than-normal props for a glow motor of its displacement. Present-day experience bears out his comments completely—the A-M is indeed a quite sturdy performer for a 1/2-A glow-plug engine of its rather utilitarian design.

Warring noted quite correctly that starting was perfectly straightforward without the starter, reinforcing our earlier comment that the starter was unnecessary. He did however criticize the engine on several points. Firstly, he noted correctly that the use of beam mounting was compromised by the fact that the protruding radial-mounting web on the rear of the main casting required that the bearers be notched for clearance. Because of this inconvenience as well as that imposed by the presence of the starter, he considered that the engine as supplied was set up primarily for radial mounting, not the preferred system in Britain at the time. Secondly, he criticised the location of the needle valve control, which he rightly stated to be far too near the airscrew for comfort and safety. He also expressed some justifiable reservations about the use of plastic tubing for tensioning the needle.

Despite these criticisms, Warring's report was generally most favourable. He summed up the engine as "a well-engineered and well-produced glow motor selling at a remarkably low retail price". In performance terms, he characterised the A-M .049 as being "an easy enough engine to start and handle, with plenty of "pep". And if you do happen to like slow-running engines, this is one of those glow motors which will swing quite large propellers happily"

A further test of the A-M .049 by Peter Chinn appeared in the April 1960 issue of Model Aircraft. Chinn again stated quite clearly that the engine was "made in England by arrangement with the Wen-Mac Corporation of Los Angeles". He was quite impressed with the engine, although he too criticised the use of plastic tubing to tension the needle valve and also had trouble with the starter, the spring of which failed in the manner described above after only about 100 uses!

Despite this problem, Chinn characterized the A-M as "a likeable little engine" and as the most powerful of the three British 1/2-A glow engines tested by him up to that point (the others being the Frog .049 and the D-C Bantam). He obtained an output of 0.052 BHP @ 14,300 rpm, a very comparable result to that obtained by Warring in his earlier test. He described the running qualities as "even" and praised both the engine's ease of handling and its low price.

The A-M .049 thus came through its baptism of fire at the hands of the professional testers with (mostly) flying colors and with its British manufacturing origin being staunchly upheld. Let's now turn our attention to the latter issue.

The A-M and Wen-Mac .049's Compared

We noted earlier that the A-M .049 is basically a clone of what Tim Dannels designates as the 8th model of the Wen-Mac Mk II engine. This variant featured a long intake venturi and was supplied both with and without the patented Wen-Mac Rotomatic starter. It appeared in 1959, which is consistent with the introductory date for the AM .049.

A later version of the same model appeared in 1960 as the 11th variant of the Mk II Wen-Mac .049. This had a large "V" cast onto the right side of the case but was otherwise unchanged. It is one of these latter models which is featured in the attached illustrations.

These images should reinforce the similarities between the Wen-Mac and A-M models. But what about the differences? Warring hinted at modifications to the material specification to conform to British practise. Where are these changes to be seen?

As it happens, direct comparison of multiple examples of both engines in my possession reveals no evidence whatsoever of any departures in material specification between the two models, apart from the use of an aluminium spinner nut on the A-M in place of the steel hex nut seen on the Wen-Mac. The material specification set out in the description provided earlier applies equally to both units. One is forced to wonder whether Warring had access to an example of the Wen-Mac for comparison purposes or if he was simply taking someone else's word for it. Either way, his claim is un-substantiated by direct examination. It's worth noting that the normally meticulous Chinn made no reference to any such differences.

So are there any differences? Well, as it happens, there are a few. Firstly, the A-M's crankcase casting clearly comes from a modified set of Wen-Mac Mk II version 8 dies—the basic shape is identical, but the engine's A-M .049 name is cast in relief onto the crankcase on both sides in place of the Wen-Mac identification. A further difference is that the A-M crankcase is left in its as-cast state with crisp, sharp edges, while the Wen-Mac cases appear to have been tumbled to soften the edges and then chemically brightened. The A-M's finish is far more characteristic of typical British productions than that seen on the Wen-Mac cases.

In terms of the casting itself, the stubs cast onto the sides of the intake venturi for the spraybar are differently oriented—as mentioned earlier, the Wen-Mac spraybar is angled back to the right (looking forward in the direction of flight), while the A-M spraybar is set at right angles to the engine's axis. This orientation on the A-M is actually a retrograde step in one respect because it is this feature which brings the needle valve control so close to the propeller disc.

This is not the only difference in the spraybar arrangements. The spraybar on the Wen-Mac is simply pressed into a hole which is drilled through the aforementioned stubs on the sides of the intake, while the A-M spraybar is of conventional British pattern in that it is retained by a nut in the usual manner. The thread is 6 BA, seemingly confirming a British origin for these components at least.

Another difference in the form of the castings is to be seen in the above overhead view of the two engines. The beam mounts on the A-M have outer edges which are parallel to the engine's axis until the front of the crankcase is reached, at which point they taper sharply inwards to form the mounting lugs for the starter. The beams on the Wen-Mac begin to taper immediately in front of the radial mount flange, thus creating far less substantial beam mounts. The clear implication is that A-M expected that at least some of their customers would actually want to try beam-mounting the engine, and hence provided somewhat more substantial bearers.

The only other difference that I can find is that the prop mounting thread on the A-M is 5/32 Whitworth while that on the Wen-Mac is 8-32 NC. These two threads are however virtually identical—they are only a few thousandths different in diameter (the Whitworth being very slightly smaller) and have the same pitch of 32 TPI, albeit with slightly different thread angles. You need a micrometer to measure the difference. The idea was presumably to ease the pain for any British owner needing to replace the prop nut—a 5/32 Whitworth nut is pretty much a force-fit on an 8-32 thread.

But apart from this, the two engines are identical. All components are completely interchangeable, to the extent that an A-M piston is a good fit in a Wen-Mac cylinder, and vice versa. Even the needles share the same American 1-72 NF thread. Apart from the minor differences in the crankcase castings, the prop mounting thread and the needle valve arrangements, we're talking in effect about one and the same engine. So who did make the A-M? Let's turn our attention to that intriguing issue.

Who Made the A-M .049?

We have to begin this discussion by recalling the rationale behind Allen-Mercury's approach of purchasing the rights to an existing design rather than developing their own model from scratch. This must surely have been to sidestep the thorny issues of development and tooling-up costs. Unlike International Model Aircraft and Davies-Charlton, A-M did not have an existing 1/2-A diesel model to convert to glow-plug operation, so the only alternative open to them if they did not wish to make the considerable investment necessary to produce their own design from scratch was to purchase someone else's.

There was also the issue of manufacturing cost. In order for the A-M .049 to be competitive, Allen-Mercury must have known that they would have to keep its selling price below �2—no easy challenge, and one which would require them to adopt any and all available means to reduce the unit manufacturing cost of each component.

The design that they chose incorporated structural features that departed significantly from contemporary British practise and certainly bore no relationship whatsoever to any of A-M's previous products. It also incorporated a relatively complex spring starter unlike anything that A-M or any other British manufacturer had ever produced. In order to manufacture this engine in their own factory they would have to create or purchase a completely different set of tooling and employ significantly different manufacturing techniques and material specifications. Their new model also required a revised crankcase die for its manufacture.

If we were to believe that DJ Allen Engineering actually manufactured this engine, then we have to believe that having bought the rights to the existing design they then incurred the additional expense of setting up an entirely different production line in terms of tooling, materials and manufacturing techniques. This would surely go a long way towards defeating the original purpose of the exercise, which was to circumvent development and production challenges along with their associated costs to the extent possible.

I have always personally found it far easier to believe that they took full advantage of the fact that Wen-Mac was already making what was in effect the same engine in the tens of thousands in America and simply contracted with them for the manufacture and supply of some modified dies as well as a small batch (by Wen-Mac standards) of components made to Allen-Mercury's specifications. Since Wen-Mac already had the dies for the Mk II version 8 model of the Wen-Mac, it would be very easy for them to make a revised set of dies with the changed identification and the revised beam mount profile and spraybar mounting.

This of course assumes that the crankcases for the A-M were produced in England using modified dies supplied by Wen-Mac—the finish on the castings undeniably has a far more "British" character than that of their Wen-Mac cousins. There was no impediment to this once the dies were obtained—A-M are known to have contracted out all of their casting production. However, the possibility undeniably remains open that the crankcases were produced by Wen-Mac to Allen Engineering's specifications. But either way, some direct involvement from Wen-Mac has always been clearly implied.

Quite apart from that, Wen-Mac were already making the rest of the engine's components by the truckload each and every day, and the addition of a few more destined for the A-M version would be easily accommodated at a minimal unit cost—the economies of scale again! All that was necessary was to make a batch of crankshafts using a 5/32 Whitworth thread in place of the usual 8-32 NC (perhaps using threading dies supplied by A-M) and use standard components everywhere else apart from the spraybar. It's even possible that standard crankshafts may have been supplied, with Allen Engineering simply chasing the standard 8-32 NC thread with a 5/32 Whitworth die.

One piece of direct evidence supporting this notion is the previously-mentioned fact that some examples of the A-M .049 have backplates which are centrally tapped to accommodate a back tank, even though such tanks were never fitted as supplied. This is easily explained if the backplates were simply taken from Wen-Mac stock, since Wen-Mac did produce a number of variants of the Wen-Mac .049 which were fitted with tanks. Conversely, there was no reason at all for Allen Engineering to manufacture such backplates since they never offered tanks for these engines at any time.

The fact that the spraybar mounting thread is a very British 6 BA suggests a strong possibility that Allen Engineering made the British-style spraybar with its nut mounting in place of the pressed-in design used by Wen-Mac—this would have been well within their established range of capabilities and would have the advantage of making the replacement of a bent spraybar far easier for British owners. Moreover, this would allow them to claim quite truthfully (if challenged on the point) that at least some of the manufacturing took place in England! The required American 1-72 taps could easily have been supplied by Wen-Mac as part of the deal.

In addition, it's entirely reasonable to suppose that Allen Engineering most likely undertook the final assembly of the engines from components mostly supplied by Wen-Mac. But to believe that they would start making precision components such as cylinders, cooling jackets, pistons, con-rods, crankshafts, backplates, fuel needles and the like which were already being made by others at unit costs which Allen could never dream of matching is surely straining credibility.

It is particularly difficult to accept the notion that they would have wished to tackle the manufacture of the Rotomatic starter. Even Warring in his test report characterized this unit as being "an expensive item to produce". Its production would require the acquisition of expensive stamping equipment which had no application to any other A-M model. Neither for that matter did the starter itself. When retail price was such a critical factor, why would Allen-Mercury take on the task of manufacturing this somewhat specialized and costly unit when it was already available to them ready-made at a far lower unit cost than they could ever hope to achieve?

Thankfully, the invaluable first-hand information supplied by former Allen Engineering employee Michael Clarke renders it unnecessary to speculate any further on this point. Michael was employed by the firm throughout the period of their involvement with the A-M .049. He tells us that he paid little attention to the A-M .049 since it didn't interest him and he was fully occupied making the four diesel models which were still very much in production. However, he never saw any manufacturing of parts for the A-M .049 at the Allen Engineering workshops and is certain that most if not all of the parts were manufactured elsewhere. He was able to confirm that the engines were assembled at Allen Engineering, but that was as far as it went to his knowledge. He also supplied the interesting information that the assembled engines were not tested before being sent to the distributor!

Michael also believes that the A-M .049 did not owe its existence to any initiative on the part of Dennis Allen, but was in fact the result of negotiations between Wen-Mac and Allen's partner, Henry J. Nicholls of Mercury fame. Allen's role was evidently confined to the assembly of the engines in accordance with the deal negotiated between Nicholls and Wen-Mac.

It's hard to feel much surprise at this revelation—the AM .049 was very much an anomaly in the broad scheme of Allen's production program and would likely have been seen by Allen as more of a source of annoyance than anything else! The four diesel models were in full production and selling well at the time, and Michael recalls that there were only about six or seven staff during the period in question. Accordingly, tooling and staffing up to actually manufacture the .049 from scratch on top of the existing diesel production program would have been both a major inconvenience and a serious financial burden. Allen would never have taken on such a challenge on his own initiative, and Michael can recall no indications that he did so.

Michael confirms that the components for the .049 arrived already machined from an external source and were merely assembled at Allen Engineering. He agrees with our original assessment that they almost certainly came from Wen-Mac in America. The question might be asked why they stopped there—surely it would have been even easier to simply contract with Wen-Mac for the production of an Anglicized version of the engine? The answer to this point is probably two-fold—first, there was a desire to legitimize the claim that the engines were "Made in England", and second, there may have been tax and import duty savings arising from the importation from America of "spare parts" rather than complete engines.

Although it cannot be proved at this time, all the evidence to date overwhelmingly suggests that Henry J. Nicholls decided on his own account that he wished to participate directly in the British 1/2A glow-plug revolution through his involvement with the Allen-Mercury marque. He decided for the reasons set out earlier to approach an American manufacturer to see if he could acquire the rights to an established design. He probably chose Wen-Mac at least in part because that range was little known in Britain at the time and the engine would therefore have an enhanced novelty value. Moreover, direct comparisons would be far less likely.

Nicholls approached Wen-Mac to ask if they would be amenable to having Allen-Mercury market what was in effect their existing Mk II Rotomatic design under the A-M label. At the time in question, the slogan "Made in England" still had considerable clout on the home market and Nicholls would clearly be anxious to preserve at least the illusion of this through having the engine identified as a British product. For the reasons noted earlier, Dennis Allen would not have been at all keen on the idea of manufacturing this engine from scratch, but he was evidently amenable to assisting his business partner by undertaking the assembly work. In fact, he may also have wished to have a hand in the manufacturing to give the "Made in England" concept some credibility. Perhaps the spraybars, the chasing of the crankshaft threads, the casting and finishing of the crankcases and the final assembly met this need, as suggested earlier.

Wen-Mac were receptive to this idea—after all, they had nothing to lose and perhaps much to gain if the engine was a success. In effect, they were being offered the chance to undertake a test-penetration of the British market under a different name at someone else's expense. If their design failed, Allen-Mercury would lose whatever "face" was to be lost and would also absorb any financial losses, rather than Wen-Mac. And if it succeeded, not only would Wen-Mac have made a little money but they would have paved the way towards acceptance of their own products in the British market. There was no way that they could lose!

Given the above arguments, it would have been completely logical for Wen-Mac to agree to make the necessary revisions to a set of their existing dies to identify the engine with Allen-Mercury instead of Wen-Mac and also to make certain other minor modifications in accordance with Allen-Mercury's specifications. These included the use of a British prop mounting thread, the extension of the mounting beams and the transverse alignment of the spraybar, which would be used in conjunction with a conventional nut fixture for the spraybar.

At this point someone may be asking—given that the transverse alignment of the spraybar created the difficulties associated with the nearness of the needle control to the propeller disc as noted by Warring, why did Allen-Mercury specify this change? The answer must surely be that they wanted to maximize the engine's control-line potential. The use of a spraybar that was pressed in and angled to the right in a rearward orientation meant that the needle couldn't be switched to the left side for conventional sidewinder mounting. The change to a transverse spraybar secured by a nut meant that the needle could be placed on either side of the engine at will. It would also facilitate the replacement of that rather vulnerable component if necessary.

Apart from this, the engines would be standard Wen-Mac Mk II units just like all the others. It has always appeared inconceivable to me that Allen-Mercury would have deliberately incurred the extra expense of tooling up to make the components for these engines when someone in the USA was already doing so at a unit production cost that no British manufacturer could hope to match. There was never any possibility of Allen Engineering manufacturing this engine from scratch at a profit when its selling price was only �1 19s 6d including that expensive starter. Thanks to Michael Clarke, we now know that their involvement was limited to the assembly of the engines, just as we had supposed.

It's actually possible that the above scenario was initiated by Wen-Mac, who may have approached Allen-Mercury with the same suggestion, the long-term idea being to establish their design on the British market under the cloak of a known and respected British manufacturer. But regardless of who approached whom, all of the evidence points to the A-M .049 being basically a Wen-Mac product, perhaps with a British-made needle valve assembly and crankcase! It was assembled in Britain using components predominantly supplied by Wen-Mac, but that's as far as it went.

The End of the Line

We've seen that the A-M .049 was for the most part just another Wen-Mac product that was assembled in Britain. Despite this, it's beyond debate that the engine was sold under the Allen-Mercury banner as a product of Allen Engineering. We've also noted that it appeared on the market in late September 1959 and was the subject of very positive tests by Ron Warring and Peter Chinn. What happened next?

Well, simply put, not very much, and none of it good. Despite Warring's and Chinn's positive comments, too many British modellers noted that awkward and very vulnerable needle valve, the inconvenient arrangements for beam mounting and above all, that very bulky, heavy and unnecessary starter. I was one of them and recall my own reaction in exactly those terms. I wasn't interested, and neither was anyone else.

Not only that, but the Rotomatic starter quickly proved itself to be the engine's Achilles' Heel. Michael Clarke actually recalls that the entire first batch of 50 engines sent out from the factory were returned under guarantee with broken starter springs. A return rate of 100% must surely have few if any precedents within the model engine manufacturing industry! In Michael's recollection, shipments of the engine in that form ground to a halt fairly quickly thereafter, and he doesn't think that very many more Rotomatic models were made. This certainly goes far towards explaining the engine's relative rarity today.

Allen-Mercury doubtless heard the criticisms and to their credit, tried to deal with the starter issue by producing a batch of engines that were not fitted with the Rotomatic starter. These were being offered by Henry J. Nicholls as of April 1960 at a reduced price of only �1 14s 3d, thus undercutting the benchmark price of the D-C Bantam by a princely three pence! The elimination of the starter doubtless allowed the price reduction. In America, the Wen-Mac versions of the starter-less engines were sold as Wen-Mac Hustlers, but the more or less identical A-M versions were simply offered as an alternative to the Rotomatic version under the same A-M .049 name. These models were being offered for sale by Henry J. Nicholls as early as April 1960, selling for a mere �1 14s 3d and thus undercutting the competing D-C Bantam by a princely 3d!! This actually makes this version of the A-M .049 the cheapest model engine every offered to the British public. They were far more useable engines than the Rotomatic models, being both lighter at only 1.16 ounces and more amenable to beam mounting due to the absence of the starter.

Despite this effort, the damage was done. The A-M .049 found little success in the British market, being completely overwhelmed by the very successful Davies-Charlton Bantam despite being a vastly superior performer in my own direct experience. It only lasted at most about two years on the market, being phased out at some point in 1961. Certainly, it no longer appeared in Allen-Mercury's advertising as of February 1962. I can't recall ever seeing a single example in use on the Yorkshire flying fields which I frequented at the time.

Despite this, the Wen-Mac design did subsequently make a considerable impression on the British market. In January 1961, KeilKraft introduced their own plastic RTF powered by their own Cobra .049. Later that year in December, KeilKraft began importing Wen-Mac RTF models which were fitted with American-made examples of the Wen-Mac .049, clearly identified as such. The KeilKraft Hurricane appeared again in 1964, now powered by what appeared to be an American-made Wen-Mac .049 (no nut on the angled spray-bar). It's a pity that the A-M .049 didn't last long enough to gain the new lease on life which its use in these models would have represented.

The marketing arrangement between KeilKraft and Wen-Mac was to continue throughout much of the 1960's. The Wen-Mac .049 and its Testors/McCoy successors were also used to power KeilKraft's own RTF Hurricane, which lasted into the 1970's. So if Wen-Mac had seen the A-M .049 as a vehicle for introducing their design to the British marketplace, it appears that time proved them right, even if Allen-Mercury themselves scarcely benefited!

As far as Allen-Mercury themselves were concerned, the failure of the A-M .049 did not discourage them from continuing in the glow-plug engine business. On the contrary, they soon expanded their involvement with this type of engine through their taking up the manufacture of the Merco glow-plug engines in mid 1961. At that time, Dennis Allen remained very much involved with the company, but this changed in 1963 when Allen sold his interest in the business. With the continuing involvement of Merco's Ron Checksfield, the company and its successors carried on making the Merco range as well as revised versions of a number of the established A-M diesels.

Although the Angel Factory Colony no longer exists, Michael Clarke reports that the premises in which the A-M and Merco engines were manufactured are still in existence, albeit used for other purposes today. Michael also passed on the interesting piece of trivia to the effect that A-M and Merco were not the only model engine ranges to be manufactured on these premises—apparently the production of components for the far later Kingcat range also took place there, at least for a time. But that's another story...

As a result of its rather lacklustre sales history, the A-M .049 is actually among the rarer small British model engines today. Although I wasn't interested during the engine's hey-day, I developed an ambition to own one when I entered my collector period many years later. Despite being quite well-connected, it took me some years to find my first example, and the other two that I've since acquired didn't come easily either.

Still, keep your eyes peeled and you may come up with an example of one of the less successful and now largely forgotten products of the British model engine industry. And perhaps one that is unique in not being a British product at all! Just be aware that if you do find one, it will probably have a broken spring inside that dratted Rotomatic starter!