MATE Building Instructions - Page 10

 

TIMING THE CRANKSHAFT INLET PORT

  1. Wash the crankshaft and crankcase, oil the shaft and insert it into the bearing. Slip the big end of the conrod onto the crankpin, chamfered hole forward. Place the cylinder carefully over the piston and push the cylinder into the crankcase until it seats.
  2. Holding the cylinder firmly on its seat, turn the shaft anti-clockwise viewed from the front, until the top of the piston is seen to close the transfer ports. View this through an exhaust port. Practice a few times until you are sure you have this piston position exactly right.
  3. Hold everything steady and scribe a faint mark on the shaft, through the venturi, right at the intersection of the shaft and the venturi and to the right of centre viewed from the front of the engine.
  4. Remove the piston and rod cylinder assembly and turn the shaft until the scribed mark is precisely at the intersection of the venturi and shaft on the left hand side. Now scribe a full circle around the intersection. Hold the shaft forward in the case at all times and don't spin it whilst the surface is marked.
  5. Remove the shaft from the case and clamp or glue it into the vee block, centreing the scribed venturi hole under the milling machine spindle so that the spindle axis passes through the crankshaft axis. Centre-drill and drill a Ø5.5mm hole through to the crankshaft bore, no deeper than the centre. Remove the shaft from the vee block. Stone away any burrs, slightly radiussing the edges of the inlet port.

FINAL ASSEMBLY

These instructions have lead you to finish each part before proceeding to the next. So, with the possible exception of the piston/cylinder assembly there should be no further fitting required. Before proceeding with assembly, wash all parts again thoroughly in warm, soapy water, using a toothbrush or other means to clean all bores and recesses. Tap the crankcase in the palm of your hand to dislodge any swarf remaining in the screw threads. Rinse several times in clean water and dry quickly with tissues. If not proceeding to assembly straight away, oil steel parts against rust.

  1. Insert spraybar across venturi from LHS front, with the hole pointing down towards crankshaft. Lock in position with the nut, its shoulder against the flat on the venturi. Screw the collet right up to the nut, then back back off one turn. Push the needle into the collet until it seats in the jet. Test the seal by sucking through the spraybar from the other side. Solder the needle into the collet in this position. Unscrew the needle whilst sucking on the inlet side of the spraybar and you should feel the valve open and admit increasing volumes of air. Crush the collet slightly across the slitted end, if it turns too freely.
  2. Oil the crankshaft on its taper, and insert into the bushing. Place the prop driver with an 8x4 hard nylon propellor (Taipan, Graupner, Master or similar) and then the prop washer and nut. Make a suitable bush for the prop if it is a loose fit on the 5mm shaft. Tighten nut quite firmly with a spanner, not pliers. Does the shaft still float .25 - .5mm? If not, rectify.
  3. Oil the inside of the piston assembly and place the con rod with the chamfered side of the hole forwards, on the crankpin. Screw the backplate in and tighten with a steel blade in the slot. Oil the cylinder sparingly, slip it over the piston and insert it into the crankcase bore. Hold the assembly together with the fingers and rock the prop back and forth, moving the piston around BDC and up as far as the ports. Does it move easily?

    If not, rotate the cylinder 90 and test again. The cylinder can locate in any of four positions, the transfer ports being in line with the screws. Indexing the cylinder should not make any difference at all, but it just might. Once you've found the best position, take the cylinder off and file a small mark on the periphery of the lower flange, in line with the 4mm mark near the rear screw.

  4. Scribe a small mark under the lowest cooling fin, adjacent to a screw hole. Slip the fins over the cylinder with this mark aligned to the previously marked corner. Run the four screws down and tighten evenly in a cross pattern. Use a screwdriver that fits the screws properly, grinding the blade, if necessary. Oil the compression screw and screw it into the cooling fins until it contacts the contra piston.
  5. Hold the crankcase firmly and turn the engine over TDC with the propellor. Ideally it will feel smooth except as the piston goes above the exhaust port, when it will start to tighten up and you will also feel the resistance of compression. No compressed air should leak past the piston seal.
  6. The engine runs anti-clockwise when viewed from the front. Turn it in this direction and as the piston uncovers the transfer ports on the way down, you should clearly hear the release of crankcase compression through the ports. If not, you have a leak, either between the cylinder lower flange where it seats on the top of the crankcase, or around the backplate. Determine the location by immersing the whole engine in a jar of kerosene and watching for bubbles as you carry out the crankcase compression test again. Rectify the leak by inserting a thin paper gasket between the parts. In the case of a cylinder seat leak, scallop the gasket slightly so that it doesn't block the transfer passages.
  7. In the event the piston fit is too tight, disassemble and mount the piston again on the mandrel and lap a little more. A quick cure for a piston that was just a shade too tight, would be to put a small amount of white lead (no skin contact, please) on the piston and re-assemble the engine, turning it over several times before washing it very thoroughly. Don't try this with Brasso, as it is too coarse.

If your engine just doesn't feel right at all, completely disassemble it, find out what is binding and see if you can correct the fault. If it is a case of misalignment - for example, the cylinder bore not exactly at 90 to the shaft axis, the wrist pin hole not square in the piston, or the conrod bearings out of alignment - there is not a great deal you can do easily about it. My suggestion would be to proceed to run the engine, which, unless you have produced a real clunker, it should still do. It will have a relatively short life, as the out-of-line parts will wear themselves and their adjacent parts out much faster than normal. You will, however, have built an engine which runs and, on seeing this, view your less than perfect machining ability somewhat philosophically!

So, let us proceed to run your "MATE" for the first time.

PREPARATIONS FOR RUNNING

  1. Standard diesel fuel, an 8x4 propellor, 3mm bore neoprene fuel tubing, a metal fuel tank about 15cc and a set of four mounting bolts (6BA x 25mm) should be available at your local hobby shop. If you wish to mix your own fuel, equal parts of unsweetened castor oil, kerosene and ether (any grade) will work well. Experienced modellers may wish to add 2% IPN or similar ignition improver. Do not mix more than 100ml of fuel at the time. Fit the prop in a horizontal position coming up on compression.
  2. Cut a U-shaped slot in the end of a 12mm thick piece of maple or similar wood, roughly 90mm wide x 200mm long. Sit your "MATE" in the slot and mark through the mounting holes. Drill to clear the mounting bolts and fix the "MATE" firmly to the wooden mount, using washers under the screwheads. Clamp the wooden mount to a bench or box at waist level. Connect the tank to the needle valve inlet with about 100mm of the fuel tubing, making sure the top of the tank is no higher than the needle valve, to avoid flooding.

RUNNING THE "MATE"

  1. Close the needle valve and fill the tank with fresh fuel. Open the needle 2 turns, choke the engine by placing your finger over the venturi and turning the prop anti-clockwise a couple of turns. The fuel will be drawn to the need1e valve. Choke again for two turns of the prop only. Close the exhaust ports with the piston and squirt a little fuel into the closed port, against the piston.
  2. Place your forefinger against the prop hub and flick the engine over smartly, with a sharp wrist movement. If the engine doesn't fire after several flicks, increase the compression slightly, a bit at a time, and keep flicking. If the engine feels dry now, squirt a little more fuel against the piston. Do not choke again. The engine should start firing and, if the needle valve and compression settings are anywhere near correct, it will start running.
  3. If it slowly dies, open the needle valve half a turn, choke it once, prime it against the piston and start it again. If it spews fuel out of the exhaust and runs rough and smokey, turn the needle valve in a quarter of a turn and it should settle down. Increase the compression slightly to smooth out the miss. Run the engine in for about half an hour, turning fairly fast, but under-compressed (missing) and slightly rich (smokey exhaust).
  4. When your "MATE" is happy running at full power and shows no sign of overheating or tightening up, it will be fully run-in.

If you have done a good, workmanlike job and your engine runs really well, why don't you put it in an old timer type of F/F or R/C model about 1400 - 1600mm wingspan, or use it to power a sport C/L model?

However, if this is your very first attempt to build a model engine and your engine runs at all, I know you will think all the time, effort and expense and was worth it.

Congratulations! I'm sure you will be encouraged to build a better "MATE", or to design your own engine based on the "MATE" extruded crankcase section, or to build another type of kit engine, or even to design and build your own engine completely from scratch.

This is the result I had envisaged in the first place! Good luck, mate.

David Owen, "MATE" Designer, Australia 1989 (Revised 2005).

 

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