The Kemp and K 1 cc models

by Adrian Duncan

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    First Variant—the Kemp 1 cc Model
    Second Variant—the Kemp Mk I Eagle Sideport Model
    Third Variant—the K Mk II Eagle FRV Model
    Additional Resources

In other articles on this website, we have traced the history of the directly-related Kemp and K engines from Gravesend in Kent, England. We have presented a detailed review of the Hawk 0.2 cc models which were successively manufactured both by the original 1946 Kemp Engines company and by its successor, the K Model Engineering Co, which took over from Kemp Engines in mid 1948. We've also examined the later 2 cc and 5 cc models made by the successor company. To complete our coverage of the Kemp and K series, it's appropriate that we take some time to look at the series of 1 cc models which formed part of the combined range.

The Kemp and K 1 cc models were produced in three quite distinct versions. The initial model was designed by company founder Harold Kemp in 1947, joining his earlier 4.4 cc K4 model in the Kemp Engines range as his second-ever diesel design. We'll begin with that first 1 cc model.

First Variant—the Kemp 1 cc Model

Introduced in mid 1947, the initial Kemp 1 cc design featured downdraft crankshaft front rotary valve (FRV) induction, being in fact the only one of the three variants to exhibit this feature. The carburettor assembly included a spring-loaded cut-off which was controlled by a hairpin-style spring release.

The engine is encountered today in two distinct sub-variants. The primary variant had a tank, prop nut and cooling jacket of magnesium alloy. However, some surviving examples feature an aluminium alloy cooling jacket and tank along with a conventional prop nut. It's possible that there was actually only one variant and that the aluminium alloy components were later factory replacements for corroded magnesium items. We'll probably never know for sure ...

Mike Clanford's published collection included engine number 030 of this series, seemingly confirming that the engines were numbered starting from number 001. Mike also owned engine number 0719, while the late OFW Fisher reported owning engine number 0762. The fact that my good mate Paul Rossiter owns previously-illustrated engine number 829 (no "0") of the primary variant with magnesium fittings suggests that the two seeming variants were not produced successively by the factory, since this is the highest reported number for one of these units. This tends to support the notion that all of the original factory products featured magnesium components and that the aluminium items were indeed factory replacements which could be purchased as aftermarket replacements.

The number on Paul's engine also seems to confirm that perhaps 900 examples of this first Kemp 1 cc model were produced, probably over a period of 9 months or so—this was at a time when Kemp Engines was a tiny 3-1/2 man operation, which explains the low monthly production figure. However, relatively few of these appear to survive, making this an extremely rare model today. The well-known propensity for magnesium to revert to its naturally-occurring state through corrosion probably has a lot to do with this ...

This model was still appearing in trade advertisements in early 1948, as attested by a Henry J Nicholls advertisement from the February 1948 issue of Aeromodeller. It sold for the considerable sum of 5, a high price indeed for a 1 cc diesel at the time in question. For comparison, the contemporary 1 cc FROG 100 model was priced at only 3, while for 4 17s 6d (4.87 today) one could purchase the far more powerful 2 cc ED Comp Special.

These prices actually reflect an often-overlooked facet of modelling life in the early post-war period—model engines weren't cheap! At the time of which we are speaking, a man earning 8 per week would have been considered well-off by prevailing British economic standards—many earned considerably less. Placing this in perspective, the cost of even a very basic model engine at this time was over half of an average man's weekly before-tax income. When we consider this matter from the perspective of purchasing power, we can see that the prices that we pay today for these same engines on eBay aren't really all that different from those of yesteryear ... in fact, in many cases they're quite a bit less!

Second Variant—the Kemp Mk I Eagle Sideport Model

The Mk I Kemp Hawk 0.2 cc sideport model was released in January 1948 to an extremely positive market reception. The immediate success of this model seems to have got Harold Kemp thinking about a less expensive replacement for the original 1 cc model, designed along parallel lines to the Hawk. The outcome was the March 1948 release of a completely redesigned sideport 1 cc model bearing a strong family resemblance to its smaller sibling. It sold for a somewhat more competitive price of 3 18s 6d, which was still considerably more than both the competing ED Mk I Bee (introduced in August 1948) and FROG 100 models.

The company's "bird of prey" nomenclature which appears to have begun with the Hawk was continued for the new model, which was named the Eagle. The company's newly-adopted "K in a circle" trademark was also featured on the crankcase casting.

In a number of respects, the side-port Eagle was well out of the design rut for a 1948 engine of that configuration. Firstly, it featured over-square internal geometry, having bore and stroke measurements of 0.437" (11.10 mm) and 0.400" (10.16 mm) respectively for a displacement of 0.98 cc. The idea here was presumably to keep the overall height down—the long-stroke sideport designs of the day tended to be taller than ideal for mounting purposes, particularly when cowling was involved.

Another unusual feature for a sideport model was the engine's use of four radially-disposed exhaust ports in combination with six transfer flutes cut internally into the lower cylinder wall and terminating just below the exhausts. These transfer flutes were arranged in an arc to either side of the rear-facing induction port—a scheme very similar to that later used in the home-constructed Ransom and Weaver 1 cc diesel, plans for which appeared in Model Maker during 1952. These arrangements gave the engine unusually large bypass and exhaust areas for a piston-ported engine.

The Eagle also broke with British design tradition by using a hardened steel piston in conjunction with a ball and socket arrangement for the little end of the hardened steel conrod. The use of this material for a piston operating in a hardened steel cylinder placed a premium upon manufacturing fits, since a steel-in-steel combination has a far greater tendency to tighten up when hot than the more common iron-and-steel setup. Moreover, an engine built to this material specification would take forever to free up if assembled too tightly. My own engine number 76 suffers to a degree from this issue, being perhaps a little more closely fitted than ideal. Although it starts and runs just fine, it does tend to run "tight" and sag if pushed hard. My other example number 522 is perfectly fitted.

The use of a ball-and-socket small end bearing was by no means new—it had previously appeared in several American designs such as the Mite diesel and was later widely used in small glow engines by the likes of Cox, WenMac and Holland in the USA. However, in the context of British model engine design, the Kemp's use of this feature was an innovation which was to be applied to other engines in the K range but not generally adopted by other British manufacturers. Following the demise of the K engines in 1950, this arrangement did not reappear in British model engine design circles until the 1960 advent of the KeilKraft Cobra 049 glow, which exhibited a strong Cox influence.

Internally, the little Eagle contained a couple of surprises of the "..why on earth did he do that!" variety. The steel piston with ball and socket conrod little end has already been mentioned. Next was the truly heroic crankpin diameter and associated conrod big-end. The use of a hardened steel con-rod resulted in the creation of a high surface area "hard on hard" bearing. This is never a great idea, although it is perhaps acceptable on a low revving, well lubricated small diesel—ED used the same approach quite successfully on several of their smaller models up to 2 cc.

The next major oddity is the method of assembling the upper cylinder components. The upper cylinder liner was externally threaded to accept a screw-on cooling jacket which seated on a location flange just above the exhaust ports. On the early examples this was followed by a steel ring which was somehow secured to the cylinder liner, perhaps by being internally threaded like the cooling jacket. There's no question that this steel ring was well secured to the liner in some way, because it is the threaded holes in this component alone which hold the cylinder head in place—the threads for the head retaining screws do not extend into the cooling jacket itself on these early examples. It seems likely that this ring screwed onto the same threads as the jacket and acted in effect as a lock-nut to keep the jacket from unscrewing. I've never cared to disturb my near-mint example number 76 to find out.

Once this assembly was complete and tightened down really hard, the three holes for the cylinder head attachment were evidently drilled and tapped in their correct locations to keep the finned cylinder head in a fore-and-aft orientation. The fact that this was done with the ring in place is seemingly proved by the fact that the holes for the tapped threads extend into the material of the cooling jacket, although the screws themselves do not do so. The lock-nut effect would keep the jacket from becoming loose and upsetting the head alignment. A nice touch was the inclusion in the head of a threaded insert for the single-armed steel compression screw.

As mentioned above, the early examples relied solely upon the threads formed in the steel ring to retain the head, very short screws being employed. The six cooling grooves below the steel ring were accordingly machined out to full depth since the jacket did not have to accommodate any assembly threads for the head screws. Illustrated engine number 76 features this arrangement. On the later versions as exemplified by illustrated engine number 552, the uppermost groove was machined out to a far lesser depth in order to create sufficient thickness for a reasonable thread length within the jacket itself, together with the use of longer assembly screws. The steel ring now served as a spacer rather than as the sole means of retaining the head. Its retention was only necessary in order to preserve the engine's overall geometry. The drilling and tapping of the holes in the jacket for the head retention screws was presumably carried out as before after tightening.

Why was this complicated assembly adopted? All that I can think of is that the original intent was to eliminate the need to rely upon tapped holes in the alloy cooling jacket for the head screws. The steel ring clearly offered a far better medium for the creation of those tapped holes. Why then did they switch to holes tapped within the cooling jacket for the later models? Beats me...

Another oddity is the seemingly excessive size of the mounting holes in the beam mount lugs. I once thought that my own two examples had both been drilled out, but other surviving examples consistently exhibit the same feature. They surely can't all have been drilled out, so I now assume that the holes were drilled to this size during manufacture. Presumably the idea was to leave some latitude for the owner to vary the side-thrust during the model trimming procedure. Either that, or Harold Kemp anticipated the use of extremely sturdy mounting bolts for these engines!

Looking now at the fuel supply arrangements, the tank and needle valve assemblies were completely conventional for the period in question apart from the size of the tank, which appeared quite excessive for an engine of this displacement. The brass inlet boss at the rear of the cylinder accommodated the delivery end of the venturi, which plugged into it. The boss was split, allowing the venturi to be secured in any desired orientation using a split collar.

At first glance, it appears that the inlet boss has been soft-soldered to the cylinder. This again is acceptable practice on a low revving, cool running diesel, although failures were not unknown on the ED Mk II Penny-slot and Competition Special cylinders which were similarly assembled with soft solder. But again, Harold Kemp's willingness to go the extra yard is evident—the need to replace a broken boss on engine number 552 revealed that the cylinder end of the boss is actually threaded 2BA, screwing into a tapped hole in the cylinder wall. The thread length is of course very short indeed, but the presence of the thread provides adequate mechanical rigidity while the soft solder locks the whole thing up and assures a gas-tight seal. It's worth noting that this assembly required that the bore be finished after the intake was secured to the cylinder.

The venturi, cut-off housing, needle mounting and tank top were cast as a single component. The needle valve was of the surface jet type, a very common arrangement at the time. The cut-off incorporated into the system was relatively complex but quite effective, being of the spring loaded plunger type which completely cut off the venturi tube at its delivery end. A necessary feature, since the little engine seems able to run forever on the contents of its massive tank! Once again, one wonders why the tank was so large—it looks ill-proportioned, positively dominating the rest of the engine!

All this must have added to the cost of manufacture, the time required for final assembly and hence the unit profit. But perhaps that is the modern-day, bean-counter driven, economic rationalist, bottom-line oriented view. Maybe Harold Kemp was an old-fashioned quality-driven manufacturer who took pride in his work and just wanted to do the best he could for his customers.

My engine number 76 seems to prove that the numbering sequence was re-started at engine number 1 when the sideport Eagle replaced the original FRV Kemp 1 cc model. Production of the Mk I Eagle evidently continued for a time after the K Model Engineering Co Ltd. took over the business in mid 1948, since the engine continued to be featured in the early advertisements placed by the new company. The highest presently-reported serial number for the sideport Eagle is Paul Rossiter's engine number 852, indicating that perhaps 900 or so examples may have been produced in total over a period of some 7 or 8 months.

Tests on surviving examples show that the engine starts easily and runs well, although neither its performance nor its price were competitive with those of the 1948 rear rotary disc valve ED Bee, perhaps a factor influencing the change to front rotary induction for the late 1948 Mk II version of the Eagle to be examined next. The following table shows typical prop/rpm figures extracted during present-day testing:

Prop (all GF)Speed (rpm)Approx. BHP
APC 9x65,000 0.030
Taipan 8x65,7000.034
Taipan 9x45,8000.038
APC 9x46,3000.046
APC 8x66,6000.047
APC 8x47,1000.039
Taipan 8x47,2000.038

Although there are a few inconsistencies likely due to missed settings, a plot of the above data generates a reasonably coherent power curve which implies a peak output of approximately 0.048 BHP at around 6,700 rpm with a sharp drop-off thereafter, which is typical of sideport designs. These numbers are actually not too shabby for a sideport engine of this vintage and displacement, although they're well down on the figures of 0.0575 BHP @ 8,100 rpm and 0.062 BHP @ 10,600 rpm reported by Lawrence Sparey in his Aeromodeller tests of the significantly cheaper FRV FROG 100 Mk I and ED Mk I Bee. Up to around 7,000 rpm the Kemp was actually ahead of the other two models, but its inability to maintain its torque at higher speeds prevented it from reaching comparable peak output levels.

Still, given its easy starting as well as its ability to swing a fairly substantial airscrew at or near its peak, there's no question that the little Eagle would have made a highly acceptable powerplant for general sport-flying. It's clear from the above numbers that for most effective performance the engine should be propped for airborne speeds in the upper half of the 6,000 rpm range. A slow 8x6 or fast 8x7 would appear appropriate for control line use, with a fast 9x4 being the optimum for free flight applications. I'd recommend the 9x4 as the ideal bench-testing prop.

Third Variant—the K Mk II Eagle FRV Model

In the latter part of 1948 the K Model Engineering Co redesigned the Eagle from the ground up, producing the FRV Mk II Eagle which was introduced in December 1948 in both ready-to-run and kit forms. This engine shared virtually no components with its predecessor, being essentially a new design to occupy the 1 cc slot in the K range, re-using the Eagle name solely for brand-name continuity. It featured updraft FRV induction, a turned aluminium cooling jacket and an aluminium alloy back tank.

In most respects, the new model followed the design pattern established by the Mk I version of the 5 cc K Vulture, which had appeared in October 1948. In fact, apart from the use of updraft induction and the inclusion of a back tank it looked for all the world like a scaled-down version of the Mk I Vulture, complete with knurled brass "dog collar" below the exhaust ports to retain the cylinder.

The revised model sold for the rather startlingly low price of only 1 17s 6d (1.87 today), thus undercutting all of the contemporary opposition by a considerable margin. The kit was even cheaper at only 1 7s 6d (1.37). This kit included all major components fully machined and ready to assemble, including a factory-fitted piston/cylinder/contra piston set. The only custom fitting required from the constructor was the lapping of the crankshaft journal to fit the main bearing.

The introduction of this model coincided with a change in marketing policy, with the K Model Engineering Co now offering a factory-direct sales service. This may be a reflection of emerging marketing difficulties arising from a rash of well-publicized structural problems encountered with the Mk I version of the 5 cc Vulture. Sadly, the company never really recovered from the negative perception of its products which arose from this issue.

The serial number sequence for the Mk II version of the Eagle appears to have been re-started at engine number 5001 with a K prefix added to distinguish it from other contemporary K models. Paul Rossiter has engine number K5449, implying that at least 500 or so examples may have been manufactured. Nonetheless, this variant is extremely rare today, since it was only in production for some 5 months at most, likely at a fairly modest level. Its final appearance in a K Model Engineering Co advertisement came in April of 1949, albeit by that time in kit form only. It's not known how many examples were sold in kit form, but those that were presumably didn't receive serial numbers.

There is a certain consistency in the above production figures—it seems that production of the Kemp and K 1 cc models remained fairly steady throughout the company's involvement with that displacement category at around 100 units per month. Other models were produced at substantially higher rates, especially after the K Model Engineering Co took over. This makes it appear probable that their involvement with the 1 cc category was perhaps the company's least successful business line in commercial terms.


None of the various Kemp and K 1 cc variants are particularly common today. As we have shown, it seems highly unlikely that production of any one variant ever reached the 1000 unit mark—in the case of the Mk II Eagle, the number produced appears to have been significantly less. Consequently, these engines are relatively rare today, selling for quite respectable prices when they do appear. This is particularly true for examples in complete original condition, since these seem to be few and far between.

The final model of the series, the Eagle Mk II, was most likely driven from the marketplace by a number of factors. One was undoubtedly the presence in the contemporary marketplace of competing 1 cc models offering equal or superior levels of performance at lower cost—the ED Mk I Bee and Frog 100 Mk II models were prime candidates here, both out-selling the Eagle by very considerable margins. But a more insidious yet doubtless very powerful factor was almost certainly a progressive erosion of consumer confidence in the K range and its manufacturers arising from the teething troubles with the 5 cc K Vulture which we have recounted in detail elsewhere.

Whatever the reason, the withdrawal of the K Eagle Mk II in May of 1949 marked the end of the K Model Engineering Company's efforts to establish a footing in the 1 cc market category. The company's troubles which had begun with the Mk I Vulture did not resolve themselves in time to allow the company to reclaim its position in the marketplace, the result being that production of all models had most likely ceased as of early 1950.

The company continued to advertise throughout 1950, although this almost certainly represented an attempt to recover capital by liquidating existing New Old Stock. The final advertisement of them all appeared in the November 1950 issue of Aeromodeller. A sad end to a venture which had started with so much optimism and promise back in 1946.

Additional Resources