January 1987 R/C Modeler
Vol. 24 - No. 1 - Pg. 218
Site Sponsor: R/C Modeler
Type: Single cylinder, 4-stroke cycle, air cooled, glow ignition
Bore: 27.0mm (1.063")
Stroke: 22.8mm (.898")
Displacement: 13.06cc (.799 cu. In.)
Compression ratio: 15.5:1
Weight: 19.5 oz. (with muffler)
Rpm range: 2,000 - 11,500
Manufacturer: Saito Seisakusho, Ltd., Chiba Prefecture, Japan
U.S. Importer: United Model Distributors, Wheeling, Illinois
In the June 1986 issue we reviewed the Saito FA-65 and were quite surprised at the engine's high power output as it surpassed all previously tested .60-.65 displacement size 4-stroke engines by a considerable margin. Our review engine for this month, the Saito FA-80, is basically a bored and stroked version of the FA-65 using the FA-65 crankcase, and like the FA-65, proved to be a real powerhouse. The FA-80 was capable of turning the same propeller sizes 400-600 rpm stronger than the already strong FA-65, and with no significant increase in weight. Although Saito lists the weight of the FA-80 as being almost an ounce and a half lighter than the FA-65, actual weight measurements of the two engines without the mufflers was 18.6 oz. for the FA-65 and 18.5 oz. for the FA-80. The slight weight difference is due to the FA-80 having slightly thinner cylinder wall thickness. The FA-80, being a larger displacement engine, uses a slightly larger muffler weighing .9 oz. whereas the smaller FA-65 muffler weighs .7 oz. - hardly enough to matter. With both engines sharing the same crankcase, those desiring more power than that provided by the FA-65 have only to remove the engine and install the larger displacement FA-80 with no change in aircraft balance, etc. This is at the expense of slightly higher fuel consumption naturally. The FA-65 uses approximately 1.4 ounces of fuel per minute at full throttle and the FA-80 1.8.
Although this article will be somewhat repetitious of the previous FA-65 review, several design changes have been made to the FA-80. So let's take a look at the newly released Saito FA-80 and see how Saito went about increasing the .65 displacement size engine to .80 cubic inches.
The FA-65 has a bore of .976" (24.8mm) and stroke of .866" (22.0mm) and the FA-80 has a bore of 1.063" (27.0mm) and stroke of .898" (22.8mm). This results in a bore increase of .087" and stroke increase of .032", increasing the FA-65's already "overbore" bore/stroke ratio even more. Saito has always taken the overbore design route with their 4-stroke engines rather than long stroke designs in order to utilize larger valve sizes, evidently feeling that there is more power to be gained through large valves and better gas flow than by stroking the engine which is usually an aid to low rpm torque in the rpm range that the 4-stroke engines favor. The proof is in the performance and you cannot argue that the FA-80 is not a strong running engine. Of course, in the case of the FA-80, Saito was forced to put the majority of the displacement increase into the bore increase in order to use the same cylinder casting. Increasing the stroke any more would have meant a new taller cylinder casting. Connecting rod angularity must also be taken into consideration. If the stroke were increased any more a longer connecting rod would have been required to keep the rod angularity from being excessive, resulting in the necessity of a taller cylinder casting. As it is, Saito, with only a small stroke increase, was able to still use the FA-65 connecting rod and cylinder casting.
New 2-needle type carburetor with slide plate choke assembly.
The FA-80 uses a two piece pressure die-cast aluminum crankcase/cylinder assembly with removable backcover, and the cylinder and head cast as an integral unit. The FA-80 shares the same lower crankcase section with the FA-65 but the upper cylinder/head unit, although appearing to be the same as that used on the FA-65, has had the cylinder outside diameter increased from 1.300" to 1.345" with the fin diameters remaining the same. Even though the cylinder o.d. has been increased to accommodate the bore increase, it was also necessary to decrease the cylinder wall thickness .020" - from approximately .095" to .075". Saito chose to put the bore increase into the cylinder casting rather than resort to a thinner walled sleeve or liner. The brass liner has actually had the wall thickness increased .010" from the FA-65's .065" to .075" (approximately). Actual precise measurements are a little difficult to make due to the pressed or cast in design of the non-removable cylinder/liner assembly.
The FA-80, like the FA-65, uses a chrome plated brass cylinder liner, high silicon content aluminum piston, and a single unpinned expansion type ring. Whereas true ABC type piston/sleeve assemblies rely on the fit of the piston for the compression seal, Saito fits the piston looser and relies on the cast iron ring for sealing. This is actually the more desirable way to go in a non-racing type engine.
Camshaft and spur drive gear. Flat cam lobe toe holds valve at maximum lift for longer duration.
The piston is machined from a high silicon aluminum permanent mold casting and has an unusually short height. When you increase the stroke of an engine .032" as in the case of the FA-80, the piston travels .016" higher and .016" lower. In order to keep the piston skirt from interfering with the crankshaft counterweight when the piston is at the bottom of the stroke, it was necessary to use a piston of extremely short height. The height of the piston is only .669" (7mm) as compared to the diameter of 1.060" (.003" smaller than the sleeve bore). A short skirted piston, in conjunction with a short connecting rod, can lead to piston rock and accelerated ring wear. Whether this might prove to be a problem with the FA-80, only time will tell. This is one of the problems one runs into when attempting to increase the displacement size of an existing engine design without increasing the overall dimensions.
Being of high silicon content, no bronze bushings are used in the piston wrist pin holes and a 6mm dia. hardened steel tubular wrist pin is used in conjunction with floating Teflon wrist pin pads, that is the Teflon end pads are simply .055" thick round discs without shanks that would normally be pressed into the ends of the wrist pin. The pad thickness has been increased considerably over the .020" thick pads used in the FA-65. Care should be taken when disassembling the engine not to lose or misplace the pads. One or both could easily fall out and go unnoticed. The FA-80 uses the same forged aluminum connecting rod that is also used in the FA-65 with bronze bushings at both the crankpin and wrist pin ends.
Piston, wristpin, and con-rod assembly. Note extremely short piston height and floating Teflon wristpin end pads.
The one piece hardened steel crankshaft is machined from a chrome-molybdenum forging and supported by two ball bearings - a 28mm o.d. x 15mm i.d. bearing at the rear and a .875" o.d. x .375" i.d. (non-metric) double shielded bearing at the front. The rear bearing is the same as that used in the FA-65 but the front bearing has both larger outside and inside diameters. The counterweight is of the constant thickness design cut away on either side of the crankpin and would balance out the full weight of the connecting rod, wrist pin, and approximately 3% of the piston weight. This resulted in a smooth running engine for the displacement size. One major design change has been made to the FA-80 crankshaft and that is splines have been cut directly into the crankshaft journal to drive the front mounted camshaft to spur gear. The FA-65 uses a separate drive gear that slips over the crankshaft and is pinned in position. Although a larger front bearing is used, the shaft then steps down to an 8mm (.315") dia. and uses the same collet type prop driver as used on the FA-65 with a 7mm dia., 1mm pitch, thread for the prop nut.
Valve, valve spring, and keeper. Note undercut head to cause less fuel flow restriction.
Other than the slight increase in outside diameter as mentioned previously, the FA-65 and FA-80 upper cylinder assemblies appear to be the same. Phosphur bronze bushings have been pressed into the head to serve as valve guides and seats. The 10mm dia. hardened steel valves, the same as used in the FA-65, are inclined at a 20 degrees angle with the rocker arm supports cast as part of the head/cylinder assembly. The rocker arms appear to be machined from steel bar stock rather than a casting or forging and then heat treat/hardened to form very hard wearing surfaces. The pivot points have been off-set to provide an approximate 3:4 ratio increasing the total valve lift. The same combustion chamber shape as used in the FA-65 has been retained which is basically a shallow hemi with a deeper heart shaped recess surrounding the valves with the glow plug at the tip off-set towards the exhaust valve. The deeper heart shaped recess also retaining the shallow hemi-shape. This unusual combustion chamber shape works exceptionally well allowing the use of considerably higher than normal compression ratios. When we first started the running tests of the engine, we became aware right away of the engine's high compression ratio. The engine did have a tendency to bite and kick at times, especially if slightly overchoked or loaded. Whereas most 4-stroke engines like to be good and wet for starting, you do have to be careful with the Saito FA-80. However, this did not present any real starting problem once the engine's starting characteristics were understood.
Expecting to find the compression ratio on the high side when checking the combustion chamber volume, we were surprised even more at the actual ratio. The combustion chamber volume was exactly .9cc to the bottom of the glow plug hole. This computes to a full stroke compression ratio of 15.5:1 - the highest of any 4-stroke engine we have ever examined. The cylinder was flushed dry of oil with solvent, air blown dry, and checked three times to verify the .9cc volume. 15.5:1 is exceptionally high, but yet, the engine showed no signs of detonation or tendency to throw the prop. Saito has obviously come across a combustion chamber shape that allows the use of extremely high compression ratios without detonation. Saito was more or less forced into higher compression ratio due to increasing the stroke and displacement of the engine while still retaining the same FA-65 combustion chamber. So whether by design or accident, I would guess that those at Saito responsible for the FA-80's design might have been somewhat surprised themselves at the lack of detonation with such a high compression ratio.
Crankcase, cylinder and backplate. Cylinder and head a one piece unit.
Like all 4-stroke engines in the Saito line, the FA-80 uses a front mounted, spur gear driven, camshaft. The FA-80 uses more moderate cam timing than that used in the FA-65 with the intake opening 44 degrees before TDC and closing 47 degrees after BDC, and exhaust opening 62 degrees before BDC and closing 20 degrees after TDC. As will be noted, the intake and exhaust use entirely different timing periods which is common practice in full size automotive type engines. Saito has also incorporated two other design innovations usually found in high performance automotive engines and that is to broaden the tip or toe of the camshaft lobe to lengthen the full open period of the valve and relieve or undercut the under side of the valve head to reduce gas flow restriction caused by the valve stem. As in full size automotive high performance engine practice, these minor modifications all add up to the total power increase.
Unlike the Saito FA-65 and other 4-stroke engines in the Saito line that use Saito's fuel metering type carburetor, the FA-80 uses a two-needle, rotating barrel type, carburetor similar in design to those that many other model engine manufacturers are now using. This type of carburetor, although of fairly simple design, has proven to work very well. Basically the new Saito carburetor is composed of a die-cast aluminum body with a chrome plated aluminum barrel. This is also a departure from previous Saito practice of using an anodized aluminum barrel. Chrome naturally has a much harder surface and better wearing characteristics than the anodize treatment. A high speed mixture adjustment needle is mounted on the body side and an idle mixture adjustment needle on the rotating barrel. In and out movement of the barrel as it rotates varies the idle mixture needle depth in the spray bar, in turn, regulating the fuel mixture. One nice design feature of this type of carburetor is the omission of an air bleed adjustment used previously on other Saito carburetors. Air bleed type carburetors require full throttle for choking, then reduced throttle for starting, etc. Forgetting to close the throttle back down after choking can result in a full throttle start. This is no big deal with the smaller displacement engines but when you get into the larger displacements, it can result in a larger prop coming at you full bore if your helper does not have a firm grip on the aircraft. Saito's new carburetor design worked very well as will be noted in the performance section that follows. As with previous Saito carburetors, a slide-plate choking device is attached to the carburetor so that the engine can be choked from outside the fuselage/cowl.
Crankshaft and bearings. Note splines cut directly in crankshaft journal that drive camshaft spur gear.
Saito recommends that fuel in the 5%-15% nitro range and 20% oil - either castor or high quality synthetic be used in the engine. Preferring synthetic oil to castor, a fuel mix of 17% synthetic (Klotz KL-200), 3% castor, 10% nitromethane, and balance of methanol was used. Following a 30 minute break-in period, the following rpm figures were recorded.
Temperature 80 degrees F - relative humidity 48% - barometric pressure 29.93"Hg.
12 x 6 Zinger 11,500
12 x 8 Zinger 10,350
13 x 6 Zinger 10,900
13 x 8 Zinger 8,700
14 x 6 Zinger 9,400
14 x 8 Zinger 8,300
15 x 6 Zinger 8,600
15 x 8 Zinger 6,900
When testing the Saito FA-65 featured in the June 1986 issue, we found the engine to out-turn all previously tested .60 displacement size 4-stroke engines by 400-800 rpm. Using the same fuel and prop sizes we now find the Saito FA-80 to out-turn the FA-65 by an additional 400-600 rpm. As the old saying goes - "there is no substitute for cubic inches." Although you would think that the increase in bore/stroke ratio would let the FA-80 show the most gain with the smaller propeller sizes, this was not the case. The 600 rpm gain over the FA-65 came with the 14 x 6 prop - the largest we ran on the FA-65. The overall handling was very nice with one or two flip restarts hot or cold following prop changes, etc. As mentioned earlier in the article, due to the high compression ratio, there was somewhat of a tendency for the engine to kick when starting - especially if overchoked and slightly loaded. However, simply holding the prop firmly and rotating a few times until the kicks softened, and then a hard flip had the engine running every time with no problem. Pulling the prop through and checking for the initial kick is very important, however. If you choke the engine until it sounds wet as is normal starting procedure for a 4-stroke engine, connect the starting battery, and then flip to start, you can expect the engine to kick back hard. The backward flip start method can naturally be used but I personally prefer flipping in the conventional direction. I get far more consistent restarts with the forward flip method. As with all 4-strokes and larger displacement engines, I recommend a heavy leather glove to save wear and tear on the fingers. I do not recommend "chicken sticks" with the 4-strokes as a kick with a chicken stick can result in a broken prop, i.e., a mashed or cracked trailing edge.
The minimum idle speed with the larger prop sizes was 1,850 rpm with the engine able to hold a smooth steady 2,200 rpm idle with excellent acceleration and deceleration characteristics. High speed needle valve adjustment range was quite broad with no tendency to detonate when set intentionally too lean with the large prop sizes. Really quite amazing considering the extremely high compression ratio.
The Saito FA-80, like other Saito engines we have tested, is a well-designed, ruggedly built engine with amazing power, excellent idle, and overall handling. Any of you fellows with .60 size 4-stroke engines who would like considerably more power should consider the Saito FA-80. It will put the performance back in that .60 size aircraft.
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