Original Posted By: TWINBOOM [mailto:TWINBOOM(at)email.msn.com]
Doug,You really know how to ask simple questions! Sorry to be tardy in gettingback to you but here is the first installment of the lineup as I see it:The A-40 is not part of the A series as it is a different design altogetherand discussion of it will not be had here. See Chet Peek's new book "Flyingwith Forty Horses".All (the other) A series are 171 cu in displacement 4-cylinder with 3-7/8"bores and 3-5/8" stroke. The number after the dash is the rated horsepower:either 50, 65, 75, or 80. There is an obscure hybrid variant of the Aseries called the A-100 and that will be discussed at the end of the series.It is a favorite of mine.First, the A-50 series:The A-50 series dash numbers range from the -1 consecutively to the -9.Some A series have up exhaust, meaning the intake port is on the bottom ofthe cylinder and the exhaust port is on the top of the cylinder. Up exhaustengines include the A-50-1, -2, -3, -4, -5, and -6. The A-50-7, -8, and -9utilize a cylinder with a down exhaust. Some of the cylinders have only onespark plug hole, on top, with a cast boss where one could concievably addthe lower hole. These are used on the A-50-1, -4, and -7 and, obviously,these engines only have one centrally mounted magneto driven directly bysplines machined into the rear of the crankshaft. This makes thiscrankshaft very unique to the original A-50 series. This crankshaft equipsmy very orignal A-50-5 that utilizes dual mags, even though the splines arenot used to drive anything. The A-50-2, -3, -5, -6, -8, -9 series all havetwo spark plugs per cylinder and use dual magnetos. The dual magnetos aredriven off of a gear bolted to the back of the crankshaft so these mags turnthe other way from the single mag setup. So some up exhaust cylinders haveone plug and other up exhaust cylinders use two. Same for the down exhaustcylinders. Single ignition models were not allowed to be certified after11/7/41.The intake elbows used on up exhaust engines have a round cross sectiongoing to a round cross section. The intake elbows used on down exhaustengines have a square cross section going to a round cross section.Magnetos are generally the SF-4L or AM-4 (with left hand rotation) for thesingle mag and SF-4R or AM-4 (with right hand rotation) for the dual magmodels. However, the A-50-2 is certified only with Dual Bendix ScintillaWL-4 mags or an Autolite IGW battery ignition (like the point system onyour 1959 El Camino). In addition to the SF-4R and AM-4, the A-50-8 and -9can also use dual Case 4-CAMA mags. Magneto timing varies from model tomodel anywhere from 24 to 28 degress BTDC with some timing different betweenleft and right mags. Impulse equipped magnetos and what they fit will bediscussed later.The A-50 series engines utilize a 5.4:1 "low" compression ratio and utilizea different piston from the other horsepower engines because of this.Holding them in my hands, it appears to be the same casting as certain A-65pistons except that the flat top is machined a little lower. The lowcompression A-50 series makes its rated power at a low 1900 RPM but yetusually uses a really large prop. The prop for my Aeronca 50-C is a 76-51.Big diameter and high pitch. What? On a 50 hp engine? Compare this to a72-42 used on an A-65. Big diameter equals really big disc. Think how a 50hp helicopter can lift up vertically with a big prop turning reallyslowly... Don't laugh at a 50 hp continental...One famous modestly modifiedAeronca 50-C flown by Johnny Jones flew from Burbank to NYC overThanksgiving weekend in 1938 NONSTOP and landed with enough fuel to go 700more miles!! I would like to recreate this flight one day!!Some of the A-50 engines utilize a "dry" sump crankcase/accessory case comboutilizing a remote oil tank. These are the A-50-1, -2, -3. The accessorycases I have for these are both of magnesium and I do not know if any whereever available in aluminum. The A-50-4, -5, -6, -7, -8, and -9crankcase/accessory case combo all utilize a 4-1/2 qt. kidney "wet" sump.Obviously, a "dry" sump crankcase cannot be used with a "wet" sump accessorycase and vise versa.A-50 series cases made prior to serial number 115395 (around late 1939) usea "hard mount" meaning that, if I remember right, four 5/16" bolts hold theengine to the motor mount without any rubber vibration damping. It wasexpected that the airframe designers would make motor mounts that wouldincorporate rubber suspension. This was rarely the case, however, andsubsequent serial numbers incorporated the conical rubber mount bosses thatwe see most prevalent today.A-50 series engines generally are equipped with Bendix-Stromberg NA-S3,NA-S3A1 (the A1 meaning mixture control equipped), or Marvel-ScheblerMA-3-PA carburetors. 1-1/4" venturis on the former and 1-7/32" on thelatter. However, the A-50-4J, -5J, -6J, -7J, -8J, -9J models use a HighFuel Injector Model A in place of the carb, hence the J suffix. All otheraspects of these engines remain the same.The unique crankcase, accessory case, and gear train on theA-50-6, -6J, -9, -9J allow the use of either an Eclipse Type 625 or E-80electric starter or a Mechanical Hummer X starter. The accesory case hasthe magnetos mounted horizontally, one left and one right with the "tops" ofthe mags pointing at 3 and 9 o'clock. Non-starter dual mag equippedaccessory cases mount the mags almost vertical, one left and one right withthe "tops" of the mags pointing at 11:30 and 12:30 o'clock. Conversion isdifficult, if not impossible, because the 20 or so parts you need arescarce. If you want these features, you really have find an engine alreadywith them.Some of the crankcases are cast and machined to accept an AC diapghram fuelpump just like the one on your 1959 Chevy El Camino. It runs off aneccentric bolted to the front of the camshaft. I am unsure if a fuelinjected engine can be equipped with a fuel pump, though, because the fuelinjector pump runs off of a gear that mounts to the smae part of thecamshaft. The fuel pump equipped models were intended for use in low wingaircraft that had wing tanks, like the Ercoupe.All A-50 series crankshafts had an SAE No. 0 tapered output shaft andutilized a separate hub and key for attachment of the propeller. I have anoriginal early A-50-5 and it is very apparent that the innards are oflighter wieght than later versions of the A series. The crankshaft has welldrilled crankpins. The gears have lightening holes drilled in them. Theconnecting rods are a slimmer design. Nothing wrong with all this. Just anobservation. I would not be using these lighter components to build up a 65or higher HP engine, though. So you have to know what you have."Dry" wieghts range form 160 to 176 lbs.There are other comments to be made about the A-50 series but they will waituntil discussion of each of the A series engines is complete.The A-65 is for next week.chris bobka-----Original Message-----