fbpx

 

I have an older (2005 w/350 hours) style 912 case and do not enjoy the comfort of the "Soft Start".  I worry about the history of damage that can occur over time.  I try to be gentle but I do worry!  Any helpful hints that may give me some comfort that I am not in "self Destruct" mode...?

 

  • Re: NO SOFT START

    by » 3 years ago


    There are thousands of engines like yours without any issues. Biggest thing is just do the prescribed maint. when you're supposed to and don't sit and idle at too low an rpm. Good maint. is key to longevity. 


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


    Thank you said by: RotaxOwner Admin

  • Re: NO SOFT START

    by » 3 years ago


    You are not in self-destruct mode, but if it makes you feel you are at least doing  Something, Anything .....

    The "B" module fires 4 degrees after the "A" module.
    So you can think of it a being the Lesser Advanced (Softer) evil.

    Try this if it makes you feel better.
    If you have the Option** ...
    Crank the starter with BOTH ignitions OFF.
    After about 2 propeller revolutions or you hear half a dozen or so cylinder compressions go by and the engine is cranking as fast as it is ever going to go...
    Turn ON the "B" Ignition.
    It should start instantly with a motor that already has a lot of forward momentum built up.
    Once running, energize the "A" Side.

    If you really overdo it, you might get a BANG out of the exhaust from the unburnt fuel in the muffler.
    It might scare the neighbors but will do no real harm.

    ** If you have an OFF-A-B-BOTH-START Key Switch, then you are S.O.L.  (Shucks, Out of Luck!)


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.


  • Re: NO SOFT START

    by » 3 years ago


    There is some confusion on the timing of the 912 / 914 series start timing it seems.  The ignition modules have a few different options.  The "normal" version is fitted with a timing circuit and the advance is done by sensors that look at a trigger bar on the flywheel.  Normal start timing for decades was 4 degrees BTDC, before top dead centre.  At about 650 to 1000 RPM the pulses talk to the timing device in the module and it will shift from reading the trailing edge of the trigger bar on the flywheel to the leading edge.  This would then take it from 4 BTDC to running timing of 26 BTDC.  The exception to this is the type 914 engine, it has both at 4 BTDC for start and A advances to 26 BTDC but the trigger bar on the B side is shorter and only takes the B to 22 BTDC run timing.  This is done to better operate with the turbo and the spark plugs are all A on top and all B on bottom.  (912 are cross wired to A is top 1&2 bottom 3&4 with B bottom 1&2 top 3&4) 

    Bill is correct that starting on one ignition is the best option to get the engine to fire as this in effect has a slight delay of the kernel inside the combustion chamber taking a slight bit longer to fill the head with pressure.  This is also what accounts for the slight RPM drop when we do an ignition check even when it is at 4000 RPM, the spark takes a bit longer to burn all the fuel in the head so it is a little bit less power.  

    in 2010 Rotax introduced the soft start to help with high compression 912 100 HP engines.  The modules were changed and inside an additional circuit was added that has a very basic timer to delay the shift from the trailing edge reading to the leading edge of the flywheel bar.  The 3 to 5 second delay is the soft start.  in addition at that time they also changed the timing itself from a 4 BTDC to a 3 ATDC, this can be seen visibly by the pronounced longer trigger bars on the flywheel.  So in essence the 2010 soft start really was a combination of shift delay and change in the actual timing from 4 BTDC to 3 ATDC.  

    If you have a 914 or a 912 (80HP) that use the small black starter normally it is not an issue.  Those engines have a 9 to 1 compression and are not really an issue.  The 100 HP engines have 11 to 1 compression, normally fitted with the larger high torque starter, and can really use the soft start system to reduce wear on the gearbox and also the sprag clutch systems.  Again if you can start on one ignition, it will help you.  

     

    Cheers


You do not have permissions to reply to this topic.