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MODELING
Micromotor MARZ-2,5. Tips for a modeler
Directory / Radio control equipment Immediately after purchasing a new micromotor, contrary to the strict prohibitions of the instructions, it must be ... completely disassembled. The only connection that can be left untouched is the crankshaft with a pressed main ball bearing. On many instances, the bearing is so tight that trying to release it without a special remover means knowingly ruining the parts. After disassembly, each part is thoroughly washed with a stiff brush in hot water and laundry soap. It is convenient to work with clipped toothbrushes and pipe cleaners or liquid mascara. Then it is useful to rinse the motor with kerosene or pure gasoline, but in most cases a water "bath" is sufficient. Immediately after cleaning the parts, they are dried on an electric stove until the water on a wet finger or cotton wool sizzles slightly when touching the heated parts. Heating should be controlled continuously, especially if there are several parts in operation at the same time - the speed of their heating is very different and depends on many factors: the area of contact with the tile, the mass and heat capacity of the material of the part, its configuration and external surface. Now you can take on the very refinement of the microengine. Let's start with the back cover, which carries the spool and carburetor assemblies. First of all, let's carefully examine the details of the carburetor. In most motors, the futorka sits in its place with an "inconceivable" gap. It can be eliminated by inserting a steel ball O 8-10 mm from the old ball bearing into the outlet conical hole of the futorka and lightly hitting it with a light hammer. The main thing is not to overdo it. It is better to gradually increase the blow until, when trying on, the futhorka will not enter the wall with a slight interference. This will eliminate fuel leakage outside the spray holes, resulting in unstable operation and poor starting.
The jet is examined, if necessary, the needle is straightened and sharpened: the width of the seat, clearly visible on the cone of the needle, must be the same around the entire circumference of the needle, even the slightest leak is unacceptable in the wrapped position of the jet. A factor that largely affects the operation and start of the engine is the inaccuracy of the jet landing on the wall tide. As a rule, the landing ends of the tide are either not machined at all or are roughly machined. This causes air to enter the carburetor. Of course, it is much easier for air to pass into a narrow gap than to suck in rather viscous fuel - hence the inability to start the engine, bring it to the mode, and even more so achieve stable operation on the model under constantly changing external conditions. It is possible to seal the jet by sawing the wall and placing elastic plastic washers under the nut and flange of the jet housing. Now it's up to checking the crankshaft and its installation in the crankcase. To begin with, burrs are removed from all corners and scale is carefully cleaned off the crank cheek. Many people forget that this scale often does much more harm than metal chips accidentally left in the crankcase! During operation, the main ball bearing must be securely covered from the ingress of any particles with a dense cloth. Once again, washing the shaft with the bearing and checking the ease of its rotation, put the assembly in the crankcase for control. Most engines do not have a crankcase seal around the crankshaft. The easiest way to check this is to try to suck air through the toe of the crankcase with the shaft and both bearings mounted (in a completely dry state). If there is no tightness, you will have to reproduce the sealing system used on the MK-12V micromotor. Immediately behind the main bearing, a paronite, cardboard (preferably from pressboard or electric cardboard), nylon or fluoroplastic washer with a thickness of about 0,5 - 0,6 mm is placed. In extreme cases, you can use a set of three pucks cut out of thick paper. Their exact size and shape can be achieved by cutting out the parts from the sheet material using a “circle cutter” (a tight compass with a fragment of a hard razor blade clamped in the drawer), and first the outer circle is formed and only then, from the same center - the inner one. It is better to use the tenth, but correct puck, than the first, even slightly inaccurate. The crankshaft should slide into the washer with little effort. This will make the first run-in a little more difficult, but after running in and running in, reliable sealing will be ensured for a long time. The installation of the shaft ends with gluing the main bearing in the crankcase with epoxy resin. Unfortunately, this operation cannot be avoided - the very first shift of the outer race of the bearing in the crankcase leads to the development of the seating surface, the loss of accuracy in the relative position of the cylinder axis and the shaft, and depressurization of the crankcase toe. The result will be a clear deterioration in the characteristics of the "pair" due to aluminum particles embedded in steel and cast iron. Gluing is carried out on unplasticized epoxy resin, it is possible to add bronze powder to the glue from the "gold-like" paint kit. The resin is applied in the smallest quantities to surfaces degreased with acetone, after mounting the assembly, the excess (with a good gluing, they should not be) are removed with cotton soaked in acetone. It should be noted that the installation of the main bearing on the resin makes sense only before the first start. Postponed "for later" - and it will definitely not be possible to seal the knot. After the resin has completely cured (after two days), a cylinder liner with a piston and a connecting rod is installed in the crankcase, the cylinder head is mounted, the rubbing parts are lubricated with liquid machine oil. The counter piston and propeller are also needed for a responsible check - control of the stability of the position of the connecting rod on the crank. In this case, the wall with the spool is not mounted in order to monitor the details when turning the crankshaft. You need to rotate it either slowly or quickly, simulating a launch, depressing and pressing the counter piston. If you are lucky and the engine is successful, the connecting rod will in any case sit close to the crank cheek. When it shifts from the cheek, they try to turn the piston over (often the hole for the finger in it is drilled inaccurately and due to the rearrangement, you can get rid of the sliding of the connecting rod). If this does not help, then the hole in the piston is made quite accurately and the upper head of the connecting rod will last a long time. The required position of the connecting rod will be provided by sawing the landing end of the crankcase under the sleeve. After the complete removal of the protruding sections of the crankcase tides under the screws, it will take a little (by 0,1-0,2 mm) to cut off the back side of the landing belt, grind the end on the glass with fine abrasive powder (it can be obtained by rubbing the skin on the skin) and, reassembling motor, check the operation of the connecting rod. If necessary, the operation is repeated. What is it for? As tests have shown, the resource, power, and mode of operation of the motor almost primarily depend on the correct position of the connecting rod. By tilting the cylinder liner axis back, it was possible to save the most "hopeless" engines, which were not helped by any other modification methods. So, having achieved the required, you can start the engine? No, unfortunately not yet. But there is little left: check the clearance (backlash) of the axial stroke of the spool and shorten the crankcase along the rear end. The goal can be considered achieved if the play does not exceed 0,3 mm, and before measuring, it is necessary to clean off the scale from the spool and grind its end face with fine sandpaper. In extreme cases, a steel washer with an internal ØO 2,5 mm is put on the crank drive shank to protect the connecting rod from accidental sliding back and its subsequent running-in in an off-design position, as well as from stripping the connecting rod with the rough surface of the spool cheek. Author: V.Tikhomirov
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