Bonds’ was a ‘one stop’ shop for all model-engineering needs, and from the earliest days of hydroplane racing they supplied castings and parts to customers own requirements and for published designs. By the mid 20s it seemed appropriate that they should market a suitable engine of their own and so in 1926, Bonds’ designer Mr S.W. Phillips produced the drawings for a marine engine called the "BONZONE". With a bore of 1 1/8^th and stroke of 1 3/8^th the capacity was approximately 25cc. The name was a word play to indicate that this was entirely a Bonds’ engine rather than to someone else’s design. As can be seen from the illustration, the engine was a basic OHV four stroke with a vertically split aluminium crankcase and a cast iron barrel, available either with a copper water jacket or shrunk-on aluminium cooling fins. The finned head was of gunmetal with valves inclined at 75 degrees. The camshaft was across the axis of the engine, connected to the crankshaft with 2:1 skew gears. Lubrication was intended to be via an oil pump on the timing case driving off the end of the crankshaft. Until such time as an oil pump could be produced the cam and tappets ran in an oil bath, with the main and big end bearings relying on ‘splash’ lubrication. The camshaft was extended through both sides of the timing case and a standard contact breaker assembly could be fitted to one of these extensions. It was not until late 1928 that Bonds’ made castings available for the engine, priced at £3 for the set, but without the oil pump and carb, which were not yet ready. By March 1929 it was possible to buy all the parts to build the engine at a lower price of £2.15.0 (£2.75) or a finished engine that could be yours for £12, unfortunately still without a carb or any ignition system. The carb castings became available in June for slightly less than £1 and included a genuine ‘AMAL’ float. The finished carb would allow the engine to be "throttled down to a tick over or immediately accelerated". 1/8^th of a horsepower at 2000 rpm was claimed for the "BONZONE" with maximum revs up to 6000 which, given the size and weight of the flywheel, would be impressive to say the least.

Strangely, in the same month that the last items for the "BONZONE" became available, Bonds announced a new engine, billed as ‘the latest petrol engine’ which they were able to place on the market at a very cheap price’. For £6.10.0 you could have a ready to run 25cc OHV four-stroke motor, almost half the price of a "BONZONE". There was no family resemblance and the engines shared nothing in common, so the origins of the motor must be questioned. Further doubts are raised when E. Gray and Son of Clerkenwell Road advertised the identical engine in 1931 as the ‘GRAYSON’, with the attribution "designed on existing models produced by Mr F.N. Sharpe". Not only was the price identical, but with the exception of the carburettor and the cylinder fins, so were the engines, even to the quoted bore and stroke at 1-¼ inches. Mr Sharpe had won a Bronze Medal in the 1930 ME Speedboat competition with one of these engines in his boat ‘Mona’ (not to be confused with the Bonds' boat illustrated), which had attained 27mph and therein could lay the background to this motor with the ‘dual’ identity. The engine in his boat was based on a set of castings from Economic Electric who were also producing engines commercially in the late 20s and early 30s, although just to confuse things further, there are distinct similarities between this motor and Westbury’s early KIWI. How Mr Sharpe persuaded both Bonds’ and Gray’s to manufacture and market the engine is open to conjecture, but Bonds’ quickly dropped it from their lists, no doubt realising that they were infringing Economic Electric’s rights. This though, may well have spurred them to produce a ‘Cheaper’ engine of their own.

By 1931 the "BONZONE" had vanished from the Bond’s catalogue to be replaced by the ‘New’ Simplex. The crankcase and cam drive were the same as used on the earlier engine, but what had changed was the crankshaft, which now gave a stroke of 1 ¼". More noticeably, the cylinder barrel, available with 1 ¼ bore for 25cc or 1 5/16^th to give a nominal 30cc, now had a shrunk on alloy water jacket or shrunk on aluminium cooling fins of much smaller diameter. The most radical change, and probably not for the better was to the cylinder head. Although now in cast iron rather than bronze, the angled valves were replaced with vertical ones, which necessitated the domed piston being discarded and replaced with a flat topped one, almost certainly for cheapness. The quoted power was now 3/8^th bhp at 4000rpm with 6000rpm as maximum so it offered no real advantage over the "BONZONE". Flywheel size was reduced from the 5" of the previous engine to 4" for the Simplex, although smaller diameters were available to order. The basic Simplex cost £6-10-0 in 1931 with the carb 10/6 (52p) extra, almost half the price of the "BONZONE". With iron head and barrel, the Simplex is definitely in the ‘door stop’ category and with this in mind a ‘racing version of the engine was later produced, using Elektron magnesium alloy for the crankcases and pistons, but still with the same head.