**********************************************************************************************************************************And here is my little story……..FOR 912 LOVERS…POOR STARTING HABBITS/BACK FIRING/VIOLENT KICKBACKS/HYDRAULICKING..the engine appears to hydraulic lock..ie it fires once or twice and then stops violently..
It’s great when you receive and own your first 912 engine and it works well in the beginning,well this is normally how the story goes and to our utter disgust,these wonderfull machines could also end up sulking like your ex-wife if you don’t know enough about the going’s on inside this beauty……well,a good guideline for you and to print this and hang it onto your hanger wall,will save you many tears….
REASONS FOR BAD STARTING;
All info is subject to Rotax recommendations which does change from time to time and it is important to consult your local agent/latest installation manual/operators manual/maintenance manual as well.
1)Faulty starters..not often a problem and you do get up to a 900w unit and minimum cranking current at 75Amps…a starter is normally good for 1500hrs….then new brushes are needed..
2)Sprag clutches do break and go south as a result of the violent kickback and they start to slip when they are cold resulting in low crank rpm..this is a 1 way unit and freewheels in the other direction….
3)Low volts or faulty start switches or bad earth wires or thin starter wires become evil ….good batteries are very important…
4)Batteries with min 17a/h and 200A cranking current should be selected..
5)A starter engaged light should ideally be used on all installations..
6)Don’t start with a low battery..ensure you have a good charge rate and check your voltage prior to engaging the starter…
7)Faulty solenoids..
Faulty sprag clutch and or housing or both…..remember the gear which engages onto the sprag must also be checked for pitting….this replacement becomes a major engine splitting problem to remove this gear if damaged…so do not continue starting if this engine behaves badly during start –up…9)Excessive long wires to starter motor is a problem..to high a resistance…or they are to thin…
10)Long wires from the battery is a problem….the amps drops badly over distance…
11)Below 5 degrees Celsius…things start to change badly and perhaps pre-heating of your engine is recommended…ie blast the engine with a heater on a stand for at least an hour in extremely cold conditions….pre-heaters are available for sub zero conditions…
12)Plug gaps could be gapped smaller to 0.5 mm…try this as well..
13)Gearbox friction torque is also a major role player in the starting sequence and resultant kickback…have your gearbox checked for this problem as it is not recognised by operators…
14)Use the correct recommended oil grading and DON’T use additives at all…
15)A new flywheel with retarded timing is available(Only for older engines)
16)The new engines now have all these latest equipment and also the yellow labelled start modules…yours is likely to have the standard green labelled units and they can certainly now be replaced with the advanced soft start modules from Rotax or Bullyhawks piggy back unit which retards the sequence for 2 seconds prior to starting and then hands over to the standard modules electronically which once running ,advances the timing on both packs…
17)To soft engine mounts and lose carburettors could result in frothing of the fuel and spilling into vent lines…this goes hand in hand with shaking carbs which is as bad and also ensure that the carbs are perfectly balanced and that both chokes and throttle bodies are perfectly timed…
18)Trigger gaps or lose triggers (5 of them )is also seriously important and should be double checked before engines are installed by manufacturer as the engines have to be removed for this repair….
19)Loose or damaged flywheels or be careful of hornets laying down mud …..this could bend triggers……use anti bug repellants…sounds crazy,and even for any pito areas….
20)Blocked jets….serious whilst starting ….
21)Blocked vent lines off carb bowl...
22)Insufficient choke enrichment….
23)Mal aligned crankshaft…
24)Bent propeller shaft or damaged propeller shaft….the splines are hammered because of the kick –back…..
25)Damaged gears….same reason as above…
26)Incorrect spark plugs or most commonly the plug wires have been put back onto the wrong cylinder after servicing…..
GOOD STARTING HABBITS AND TECHNIQUES….1st start cold/normal and you have turned the prop through four cycles if regularly used…
1)After a good pre-flight check and you are ready to start ensure full and free throttle operation and then close it fully,as this is essential for the choke to work properly..
2)With your mags off,crank the motor for oil pressure…max cranking at 10 seconds and then rest the starter for 30 seconds…..full chokes ,mag’s on and then crank till she fires and then catch on throttle whilst slowly reducing choke input….continue checking for oil and fuel pressure during this critical time….and don’t rev a cold engine at all and never over 2000rpm….for at least 3 min….
WARM START..
1)By experience…a quarter throttle is needed and the reason is that fuel might have evaporated down the inlet manifold and gives an over rich mixture…some throttle will clear it…
SUB SERO TEMPS AND FIRST START……see full details and on pre-heaters and techniques is seriously important as you can imagine how this engine can break if incorrectly handled as the oil is thick and hydraulic lifters etc..can seriously be affected by jamming or slowing for the want of a better word….sprags are also affected by this as the oil is sticky and the rollers can not kick out and lock to engage ….
The above is a great guide to identifying a problem and should be used as such only…..Rotax must be consulted for any variations and or changes….
Safe flying….Andy Kaspersen