Starting McDonald semi-diesel tractors
Starting these machines is always a public spectacle on the rally field, and comparisons are often made between the starting techniques for Lanz Bulldog, McDonald and Field Marshal tractors.
McDonald tractors differ from the others in having the engine the opposite way round - the head is to the rear not far from the driver's feet. Starting involves heating the hot bowl under the head either with the original Primus style blow lamp that is warmed up with methylated spirits until hot enough to burn the normal fuel, kerosene. These blow lamps provided a good, hot flame, and the hot bowl would soon become 'cherry red'. Today. most use LPG torches, but these do not give as much heat and hence heating time is longer. During the heating phase, the main bearings should be given their daily shot of oil with the oil syringe supplied in the toolkit, and the lubricator turned 20-30 times to prime oil supply to the piston and big end bearing. When considered hot enough, one pump of fuel with the throttle lever should produce a strong puff of white smoke from the open decompressor cock. If it looks good, the decompressor is closed, the throttle set 3/4 way up the rack, the flywheel starting handle pulled out, and the flywheel vigorously bounced back and forth against compression. If all is well, it should fire on the second bounce and commence running. With luck, it might start in the right direction, but if not, this must be corrected by allowing it to come to a near stop, then giving the throttle a sharp movement at the critical point and the engine will fire again. With practice and timing, reversing its direction can be achieved, though not always at the first attempt. The audience will usually cheer if it has taken a number of tries.
All McDonald semi-diesel engines use 'total loss' lubrication, that is, the oil pumped from the lubricator to the piston goes up in smoke, or rains down as black spots on its surroundings, and the oil supply to the big end accumulates in the crankcase and must be drained frequently, usually into the fuel tank to be used up as fuel. In the case of tractors, a small waste oil accumulation tank is fitted, which has to be drained daily.
These engines have quite low compression, of the order of 5:1 only. This is the reason heat is required for vaporizing the fuel when starting, and is why they are termed 'semi-diesel', but it also makes these engine tolerant of a wide variety of fuels, from conventional diesel, to straight unrefined crude oil, even sump oil as long as it does not contain solids. The renowned torque developed by these engines is due to the slow burning characteristics of heavier fuels.
Several years ago the McDonald T6C tractor was part of an exhibit at the Sydney Royal Easter Show. As this is a 14-day event, it was not possible for me to attend every day, so there was a roster for Club members to attend. I was asked to prepare starting instructions for the tractor should it have to be moved, or just started to entertain the public. The following starting instruction were the result. Needless to say, it did not get started other than when I attended for just three half-day rosters. I wonder why? When it was started, being located in a relatively closed-in place, the sound of the exhaust reverberated far and wide, attracting many onlookers, but maybe causing concern to livestock handlers. It is after all, quite a big engine, about 14 litres in a single cylinder, and a 6" (150mm) diameter exhaust pipe.
Starting instructions for McDonald T6C tractor
1. Ensure handbrake is on.
2. Check that gears are in neutral (either or both levers in the centre position in the gate) and that clutch is disengaged (clutch lever pulled to rear of tractor – may require significant pressure).
3. Open decompression lever located at rear of head. Turn 1 or 2 turns anti-clockwise. It may require a bump to start it moving.
4. Ensure throttle is set to minimum. The lever is on left-hand mudguard and should moved to the rear-most position. Hold away from mudguard to move over rack.
5. Set LPG cylinder at rear of tractor. Place burner on gearbox cover with nozzle facing hot bowl underneath the head. Turn on cock at burner, then turn on at cylinder so that low gas pressure results, and light burner. Adjust flame at gas cylinder only until a good flame is directed at the hot bowl. It will take about 10-15 minutes to become hot enough. Continue to monitor flame intensity and direction. The flame may go out if too much pressure is used, or in windy conditions.
6. Proceed to flywheel, and using the spring loaded pull out handle, rotate the flywheel until the arrow is uppermost.
7. Proceed to the other (exhaust) side of the tractor, and rotate the handle of the lubricator 25-30 times. This will be found behind the exhaust up under the bonnet. Try to avoid contact with the exhaust manifold which can be rather greasy.
8. (optional) If it has not been started for several days, the main bearings should be oiled. This is done by drawing a charge if oil into the brass syringe (in tool kit), removing the brass caps adjacent to the clutch and behind the flywheel, and filling the tube with oil. One fill is sufficient. Ensure the caps are replaced.
9. If it is thought the hot bowl may be hot enough, operate the throttle lever forward and back once only. Ensure it is returned to the rear-most position. White smoke should escape from the base of the decompression lever.
10. To positively check if it is hot enough, rotate the flywheel backwards and forwards 90 degrees or so. A cloud of white smoke should be expelled via the decompression lever. Leave the flywheel with the arrow towards the front of the tractor.
11. If confident it is hot enough, close the decompression lever by rotating it clockwise till firm. Set the throttle lever ¾ of the way up the rack.
12. For the next step it may be an advantage to stand on a wooden block for extra height. Pull out the starting handle on the flywheel and rotate it firmly in the direction of the arrow, then with as much effort as possible, pull it against compression in the opposite direction. Swing back again if it is not going to fire strongly enough to overcome compression by itself. It cannot backfire or do any injury, but don’t hang on if it is obviously going to run. Take great care not to go close to the fan belt and fan pulley.
13. Allow it to get up to speed, then adjust the throttle setting to the desired speed. If it is planned to run it for any length of time, a reasonable speed is necessary to keep the engine hot. It can be idled back, but will cool down if left to idle for any length of time.
14. If the engine fails to start, the most probable reason is too much fuel. To rectify, close the throttle lever, open the decompression lever, then rotate the flywheel several full rotations until no further white smoke is emitted. Then close the decompression lever again, set the throttle ¾ way up the rack, and rock the flywheel again.
15. The engine may start in either direction, and will not run properly backwards. To reverse direction, there are two methods. 1 – repeat the starting procedure, giving more effort when rocking the flywheel to induce it to fire in the right direction. 2 – With the engine running backwards, cut the throttle until the engine just fails to turn over compression, then rapidly operate the throttle lever, and with luck it will fire in the opposite direction. This may have to be repeated several times if necessary.
16. Once the engine is running in the correct direction, the gas can be turned off at the cylinder, then at the burner, and the cylinder etc moved away. The clutch lever should also be pushed forward to engage it (gears must be in neutral!). This will result in the belt pulley rotating, which saves wear on the clutch bushings.
17. Check that the radiator blind is fully extended up and secured in the top-most holes. If the engine starts backwards, the fan usually blows off the blind. The coolant is unlikely to get very hot with short runs under no load.
18. To stop the tractor, move the throttle lever to the rear-most (off) position.
Note: The tractor is prone to emitting oil from the exhaust when running, and this will rain down on the surroundings, permanently stain clothing, cars etc. So try and minimize running time with public in close proximity.
McDonald tractors differ from the others in having the engine the opposite way round - the head is to the rear not far from the driver's feet. Starting involves heating the hot bowl under the head either with the original Primus style blow lamp that is warmed up with methylated spirits until hot enough to burn the normal fuel, kerosene. These blow lamps provided a good, hot flame, and the hot bowl would soon become 'cherry red'. Today. most use LPG torches, but these do not give as much heat and hence heating time is longer. During the heating phase, the main bearings should be given their daily shot of oil with the oil syringe supplied in the toolkit, and the lubricator turned 20-30 times to prime oil supply to the piston and big end bearing. When considered hot enough, one pump of fuel with the throttle lever should produce a strong puff of white smoke from the open decompressor cock. If it looks good, the decompressor is closed, the throttle set 3/4 way up the rack, the flywheel starting handle pulled out, and the flywheel vigorously bounced back and forth against compression. If all is well, it should fire on the second bounce and commence running. With luck, it might start in the right direction, but if not, this must be corrected by allowing it to come to a near stop, then giving the throttle a sharp movement at the critical point and the engine will fire again. With practice and timing, reversing its direction can be achieved, though not always at the first attempt. The audience will usually cheer if it has taken a number of tries.
All McDonald semi-diesel engines use 'total loss' lubrication, that is, the oil pumped from the lubricator to the piston goes up in smoke, or rains down as black spots on its surroundings, and the oil supply to the big end accumulates in the crankcase and must be drained frequently, usually into the fuel tank to be used up as fuel. In the case of tractors, a small waste oil accumulation tank is fitted, which has to be drained daily.
These engines have quite low compression, of the order of 5:1 only. This is the reason heat is required for vaporizing the fuel when starting, and is why they are termed 'semi-diesel', but it also makes these engine tolerant of a wide variety of fuels, from conventional diesel, to straight unrefined crude oil, even sump oil as long as it does not contain solids. The renowned torque developed by these engines is due to the slow burning characteristics of heavier fuels.
Several years ago the McDonald T6C tractor was part of an exhibit at the Sydney Royal Easter Show. As this is a 14-day event, it was not possible for me to attend every day, so there was a roster for Club members to attend. I was asked to prepare starting instructions for the tractor should it have to be moved, or just started to entertain the public. The following starting instruction were the result. Needless to say, it did not get started other than when I attended for just three half-day rosters. I wonder why? When it was started, being located in a relatively closed-in place, the sound of the exhaust reverberated far and wide, attracting many onlookers, but maybe causing concern to livestock handlers. It is after all, quite a big engine, about 14 litres in a single cylinder, and a 6" (150mm) diameter exhaust pipe.
Starting instructions for McDonald T6C tractor
1. Ensure handbrake is on.
2. Check that gears are in neutral (either or both levers in the centre position in the gate) and that clutch is disengaged (clutch lever pulled to rear of tractor – may require significant pressure).
3. Open decompression lever located at rear of head. Turn 1 or 2 turns anti-clockwise. It may require a bump to start it moving.
4. Ensure throttle is set to minimum. The lever is on left-hand mudguard and should moved to the rear-most position. Hold away from mudguard to move over rack.
5. Set LPG cylinder at rear of tractor. Place burner on gearbox cover with nozzle facing hot bowl underneath the head. Turn on cock at burner, then turn on at cylinder so that low gas pressure results, and light burner. Adjust flame at gas cylinder only until a good flame is directed at the hot bowl. It will take about 10-15 minutes to become hot enough. Continue to monitor flame intensity and direction. The flame may go out if too much pressure is used, or in windy conditions.
6. Proceed to flywheel, and using the spring loaded pull out handle, rotate the flywheel until the arrow is uppermost.
7. Proceed to the other (exhaust) side of the tractor, and rotate the handle of the lubricator 25-30 times. This will be found behind the exhaust up under the bonnet. Try to avoid contact with the exhaust manifold which can be rather greasy.
8. (optional) If it has not been started for several days, the main bearings should be oiled. This is done by drawing a charge if oil into the brass syringe (in tool kit), removing the brass caps adjacent to the clutch and behind the flywheel, and filling the tube with oil. One fill is sufficient. Ensure the caps are replaced.
9. If it is thought the hot bowl may be hot enough, operate the throttle lever forward and back once only. Ensure it is returned to the rear-most position. White smoke should escape from the base of the decompression lever.
10. To positively check if it is hot enough, rotate the flywheel backwards and forwards 90 degrees or so. A cloud of white smoke should be expelled via the decompression lever. Leave the flywheel with the arrow towards the front of the tractor.
11. If confident it is hot enough, close the decompression lever by rotating it clockwise till firm. Set the throttle lever ¾ of the way up the rack.
12. For the next step it may be an advantage to stand on a wooden block for extra height. Pull out the starting handle on the flywheel and rotate it firmly in the direction of the arrow, then with as much effort as possible, pull it against compression in the opposite direction. Swing back again if it is not going to fire strongly enough to overcome compression by itself. It cannot backfire or do any injury, but don’t hang on if it is obviously going to run. Take great care not to go close to the fan belt and fan pulley.
13. Allow it to get up to speed, then adjust the throttle setting to the desired speed. If it is planned to run it for any length of time, a reasonable speed is necessary to keep the engine hot. It can be idled back, but will cool down if left to idle for any length of time.
14. If the engine fails to start, the most probable reason is too much fuel. To rectify, close the throttle lever, open the decompression lever, then rotate the flywheel several full rotations until no further white smoke is emitted. Then close the decompression lever again, set the throttle ¾ way up the rack, and rock the flywheel again.
15. The engine may start in either direction, and will not run properly backwards. To reverse direction, there are two methods. 1 – repeat the starting procedure, giving more effort when rocking the flywheel to induce it to fire in the right direction. 2 – With the engine running backwards, cut the throttle until the engine just fails to turn over compression, then rapidly operate the throttle lever, and with luck it will fire in the opposite direction. This may have to be repeated several times if necessary.
16. Once the engine is running in the correct direction, the gas can be turned off at the cylinder, then at the burner, and the cylinder etc moved away. The clutch lever should also be pushed forward to engage it (gears must be in neutral!). This will result in the belt pulley rotating, which saves wear on the clutch bushings.
17. Check that the radiator blind is fully extended up and secured in the top-most holes. If the engine starts backwards, the fan usually blows off the blind. The coolant is unlikely to get very hot with short runs under no load.
18. To stop the tractor, move the throttle lever to the rear-most (off) position.
Note: The tractor is prone to emitting oil from the exhaust when running, and this will rain down on the surroundings, permanently stain clothing, cars etc. So try and minimize running time with public in close proximity.