SAITO FA-82a

Model Airplane News, Nov 2004 by Gierke, C David

BIG POWER IN A SMALL PACKAGE

More than 20 years after It introduced its first 4-stroke, the FA-30, Saito is considered one of the world's top producers of high-quality 4-stroke powerplants. This tradition continues with the latest addition to the line: the FA-82a.

The Salto .8Za, with its single-piece cylinder barrel and head, has outstanding power for its size and weight compared with other 4-strokes. By eliminating the conventional cylinder sleeve (liner), Saito's ringed, high-silicon aluminum-alloy piston rides directly within its chrome-plated, pressure-diecast aluminum cylinder barrel. This true AAC (aluminum barrel, aluminum piston, chrome-plated barrel) system closely matches the piston's expansion to that of the cylinder barrel for great performance and longevity.

Another plus of Saito's integral cylinder/head system is its superior heat-transfer qualities. With its sleeveless design, there are fewer interfaces between combustion gases and the outside air, providing better cooling performance than that found in engines with "drop-in" sleeves (in which heat must move from the piston to the inside of the sleeve, to the outside of the sleeve, to the inside of the cylinder barrel and, finally, to the exterior of the cooling fins).

DESIGN FEATURES

The exterior of the Saito .82a reveals exquisite, aluminum-alloy pressure die-castings and a composite plastic backplate. The one-piece cylinder barrel and head are mounted on the crankcase with four machine screws. The glow plug is positioned in the cylinder head so that it faces the rear-an important safety feature, considering the rapidly rotating propeller! The valve-train components (cam gear, tappets, cam-gear housing, pushrods and pushrod covers) are at the front of the engine in traditional Saito fashion. The fuel-metering, 2-needle-valve updraft carburetor has eliminated the choke valve. Saito states, "Due to the excellent fuel-draw characteristics of the Saito engines, the use of the choke was determined not to be necessary." The engine (minus muffler) weighs 462 grams (16.3 ounces), so it's very light for its displacement.

The FA-82a is also available in a "Golden Knight" version with a glossy black finish and gold valve covers.

* Internal components. Twin ball bearings are fitted to the crankshaft for support; the front bearing is a 23mm unit that is sealed front and rear. The rear, 27.6mm bearing is fitted with a rear shield. A breather nipple is below the cam gear (under the crank), ensuring adequate lubrication to the cam, tappets and pushrods. Some lubrication (provided in the fuel) blows past the piston ring from the combustion chamber and into the crankcase, where it is pumped by the reciprocating action of the piston throughout the crankcase, finally exiting through the breather.

* Sleeveless cylinder barrel. The integral cylinder barrel/head represents significant challenges in die-sinking and pressure diecasting, along with chrome-plating and blind-bore honing technologies! Bronze valve guides and seats are machined and press-fit into the cylinder head, providing an excellent seal and long operation. If I could speak with Saito engineers, I would offer one constructive criticism and a suggestion concerning their otherwise magnificent cylinder barrel/head: because the glow plug doesn't protrude completely through the head, several threads from the tapped hole form rough edges, making the combustion chamber prone to preignition owing to potential hot spots. By counterboring the bottom of the glow-plug hole prior to bottom-tapping the ¼-32 thread, the extended nose of the 4-stroke plug could be made to form a smooth transition with the hemispherical combustion chamber.

* One-piece crankshaft. The crankshaft is machined in one piece, including the crankpin and integral pinion gear for valve-train actuation. Shaft nose threads are M 7×1 (metric). The piston is produced from another diecasting; it contains a single, non-pinned Meehanite (fine-grain cast iron) compression ring. The wristpin (free-floating variety) contains Teflon end pads. The connecting rod is made of a forged aluminum alloy; there are no bronze bushings on the wristpin or crankpin ends of the rod.

The cam-gear housing contains the cam gear and cam-gear shaft. The cam-gear shaft is immobilized within the cam gear by a single setscrew from the front of the gear housing. The cam gear's intake and exhaust lobes are centered within the cam housing by two steel washers on the camgear shaft. The bronze tappet (lifter) guides are pressed into place on the top of the cam-gear housing. The housing is attached to the crankcase with four machine screws.

* Drive components. The Saito FA-82a is a pushrod-actuated, poppet-valve engine. Besides the half-speed camshaft that is driven from the crank, the system components consist of two hardened and ground tappets; two hardened and ground pushrods; two steel rocker arms with machine-screw rocker-arm pivot pins; and two alloy-steel poppet valves with return springs and steel retainer washers. The rocker-arm brackets that retain the rocker arms via the pivot pins are part of the cylinder barrel/head diecasting. The chrome-plated, diecast aluminum-alloy rocker-arm covers are held in place by two machine screws. The covers are sealed to the head by two paper gaskets. An adjustment screw and locknut allow the user to manipulate the valve lash (clearance between the end of the valve stem and the rocker arm). Saito provides a 0.004-inch (0.10mm) feeler gauge for this adjustment, along with the appropriate Alien wrenches. The pushrods operate within steel tubes (covers) that are sealed at both ends by synthetic rubber endcaps.