The ignition modules have the same part numbers for the respective engines;
meaning that 'A' and 'B' modules are the same.
So, if one module has slightly more running-advance than the other (i.e. 22
deg. for one and 26deg for the other) and as stated this is controlled by
"....difference in the ignition timing will be achieved by different length
of the trigger cam......",
it follows that the starting-advance would also be less for module B.
If starting on one "mag" works for you, then it should be best to use the
'B' circuit.
Duncan McF.
----- Original Message -----
From: "rlborger" <rlborger@mac.com>
Subject: Re: Europa-List: Starter kickback
>
> Nigel,
>
> I remember the kickback thread and also remember being taught (many
> many years ago) that the dual ignition on aircraft engines were at
> different timing and that some engines disabled the more advanced
> ignition to improve starting. So, I dug up my ROTAX 914 Manuals (PDF
> format on CD provided with the engine) to see if ignition timing was
> documented. The ROTAX 914 Maintenance Manual, Sec. 9.4.1), Page 50
> describes ignition timing. I will try to quote the page verbatim
> (don't blame wording, punctuation, etc. on me), use of a fixed width
> font is recommended:
>
> Quote -----
>
> Ignition
> See Pic. 24.
>
> As already stated the engine is equipped with dual ignition of a
> breakerless
> capacitor discharge design (DCDI). That means that the ignition unit
> com-
> prises two independently working ignition circuits (separate trigger
> coil,
> electronic module, charging coil etc.).
> *NOTE: The ignition unit is completely free of maintenance and
> without any adjustment.
> Each ignition circuit consists of two ignition branches. Ignition
> occurs on
> cylinder 1 and 2 simultaneously every 360d as well as on cylinder 3 and
> 4 but
> 180d offset.
> *NOTE: Due to engine design ignition occurs also at overlap
> T.D.C.,
> but this is for engine operation insignificant.
> The engine is furnished with an automatic ignition adjustment
> controlled by
> the edge of trigger cams on the flywheel and the electronic modules.
> *NOTE: For easy engine start the ignition timing at start is 4d
> B.T.D.C.
> As soon as the engine runs the ignition timing will change over
> automatically
> to operation timing of
> 26d BTDC on ignition circuit A and
> 22d BTEC on ignition circuit B
> The transition from start ignition timing to the timing for operation
> takes place
> between 650 to 1000 rpm.
> *NOTE The different ignition timing for the top spark plugs and
> the
> bottom spark plugs take into account the differing ignition
> lag resulting in better knock behaviour.
> The difference in the ignition timing will be achieved by
> different length of the trigger cam.
> Trigger cam for ignition circuit A (raised position) is
> approx.
> 4 mm (.16") longer.
>
> Unquote ---
>
> From this information, I don't see that shutting off one ignition
> circuit would help. Unless a bit less energetic start of the
> combustion is all that may be needed.
>
> Now this if for the 914, the 912 and 912S may be different. You might
> check the appropriate maintenance manuals and see what they say about
> timing. From there, perhaps, a suitable solution might be determined.
>
> Just my tuppence...
>
> Good building to those still building
> Good flying to those fortunate souls,
> Bob Borger
> Europa Kit #A221 N914XL, XS Mono, 914, Airmaster C/S
> (65%) tail kit done, wings closed, cockpit module installed, pitch
> system in, landing gear frame in, rudder system in, outrigger mod in,
> Fuselage Top on, lift/drag/flap pins in. Working in - 24 Instrument
> Panel, 25 Electrical, 29 Main Gear, 30 Fuel System, 32 Tail & 34 Door
> Latches.
> 3705 Lynchburg Dr.
> Corinth, TX 76208
> Home: 940-497-2123
> Cel: 817-992-1117
>
> > There was a thread recently about kickback during start with the
> 912S. This
> > can be quite vicious and I had it happen quite often especially on
> cold
> > starts. Apparently it can also lead to damage to the starter sprag
> clutch.
> > The problem is worse with the 912S than the 912 or the 914 due to its
> higher
> > compression ratio. It was pointed out that it happens because, with
> the
> > Rotax ignition system there is no provision for retarding the
> ignition during
> > start. With this in mind it occurred to me that the speed of ignition
> may
> > be slightly slower if the engine was started with just one ignition
> system
> > working. I have since found that I get less kickbacks when I start
> using
> > just one ignition system. It is obviously important to remember to
> reselect
> > both magnetos after engine start. This technique is only possible if
> you
> > have separate magneto and starter switches although it would be
> possible
> > to add extra wiring to short out one ignition system during start
> with a
> > key starter.
>
>
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