The Cuyuna 430 and Cuyuna 340 are a family of two-stroke, twin-cylinder piston

snowmobile A snowmobile, also known as a snowmachine (chiefly Alaskan), motor sled (chiefly Canadian), motor sledge, skimobile, snow scooter, or simply a sled is a motorized vehicle designed for winter travel and recreation on snow. Their engines normally ...

engines that were redesigned to serve as

ultralight aircraft Ultralight aviation (called microlight aviation in some countries) is the flying of lightweight, 1- or 2-seat fixed-wing aircraft. Some countries differentiate between weight-shift control and Aircraft flight control system, conventional three-a ...

powerplants.Cuyuna Development Company: ''Cuyuna Engines'', Cuyuna Development Company, undated

Development

While developing the Pterodactyl Pfledge flying wing ultralight in the late 1970s, designer Jack McCornack experimented with a number of possible engines. Early flights used a German-made Sachs engine, but the high exchange rate and long lead times for this engine convinced him to try other options. McCornack settled on a

engine produced by the Cuyuna Development Company as having the best potential. In 1979 he modified the engine with a

crankcase A crankcase is the housing in a reciprocating engine, piston engine that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, res ...

extension, an additional main bearing, lowered the

compression ratio The compression ratio is the ratio between the maximum and minimum volume during the compression stage of the power cycle in a piston or Wankel engine. A fundamental specification for such engines, it can be measured in two different ways. Th ...

using an additional head gasket and substituted a smaller Mikuni

carburetor A carburetor (also spelled carburettor or carburetter) is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Ventu ...

, amongst other modifications. The original snowmobile engine produced . Lowering the compression ratio not only de-rated the engine, but also made pull-starting easier and allowed it to run on lower-

octane Octane is a hydrocarbon and also an alkane with the chemical formula C8H18, and the condensed structural formula CH3(CH2)6CH3. Octane has many structural isomers that differ by the location of branching in the carbon chain. One of these isomers ...

regular auto fuel. The resulting engine worked well, was de-rated to produce at 5,500 rpm and proved reliable in service. Citing liability concerns over producing a two-stroke engine for human-carrying aircraft applications, Cuyuna declined to produce the modified engine. Instead, Cuyuna decided that the resulting engine was different enough from the base snowmobile engine that they would supply assembled and test-run shortblocks as parts to McCornack's company, ''Pterodactyl Limited'', who would then complete the engines and be the manufacturer, allowing Cuyuna to continue producing snowmobile engines. After two years of poor sales of snowmobiles, due to a dearth of snow and no lawsuits against Pterodactyl Limited regarding the engine, Cuyuna agreed to build the engines themselves. The 430 was also produced in a reduced bore version called the 340. The modification reduced its displacement to 339 cc and output to at 5500 rpm. The standard 430 has a bore of .

Variants

;340D :Direct drive version, at 5500 rpm,

recoil starter Rope start (also called ripcord , ''pull start'', or ''rewind start'') is a method of starting an internal combustion engine, usually on small machines, such as lawn mowers, chainsaws, grass trimmers, ultralight aircraft, small outboard mot ...

. ;340R :Reduction drive version using a belt drive system, at 5500 rpm, recoil starter ;430D :Direct drive version, at 5500 rpm, recoil starter. ;430F :Reduction drive version using a 3:1 gearbox system, dual carburetors, producing .Cliche, Andre: ''Ultralight Aircraft Shopper's Guide'' 8th Edition, page D-17. Cybair Limited Publishing, 2001. ;430R :Reduction drive version using a belt drive system, at 5500 rpm, recoil starter ;UL II : version

Applications

Specifications (430D)

References

{{2si Air-cooled aircraft piston engines Two-stroke aircraft piston engines