Min RPM to generate spark (582 Rotax)

[LSaupe 123]

Had an odd one yesterday.  Snow finally melted down enough to get the bird out (on wheels).  Havent flown it in about a month.  About 15F outside.  Freeflight went well and battery showed its usual 12+ voltage (static).

Engine spun over fine, though a little slower than normal.  No light off and eventually flooded the engine.  Put the battery on a charger and off to breakfast.  Came back around noon, temps now up around 25F.  Engine spun over a bit faster but still no joy.  No spark indication as well on the Tiny Tach.  Put a spare set up plugs in (originals were wet.)

Make a long story short, with plugs in the engine and a spare set of good plugs hooked to the plug wires (resting on the heads), I was getting no spark.  Pull one plug from each cylinder to relieve compression (leaving all 4 leads still with plugs installed) results in good spark owing to the faster RPM.  I actually saw this as at spun up at a certain RPM they both came to life.  I had also previously pull off both ignition shut off leads just to be sure of no intermittent groundings.

Put the plugs back in, charged the battery and still nothin.  Added jumper cables from the car and it fired right up and ran great.

My understanding is that the ignition system is independent of the aircraft power system, so low voltage during starting should not have an effect is this correct (as would happen during a recoil start)?

Is there a minimum RPM to generate enough voltage to set the CDI system in motion?  Or.. is what I am seeing some sort of precurser to failure?  

Are the stators independent on these systems or do both CDI's share the same stator windings?

 

 

 

[Av8r_Sed 82]

I don't know of any published minimum RPM numbers.  Stator windings are independent.  I'd recheck the plug gaps.  I think a lot of us use .018" as a gap.  Also might inspect your plug leads carefully and possibly renew them.  I never got any warm fuzzies on how they terminate on the coils especially.

[1avidflyer 1983]

I believe you need 300 RPM to generate a spark with the Rotax 2 stroke ignition.   If you put synthetic oil in your gearbox, that will help to get the RPMs you need for the colder weather.  JImChuk

[Av8r3400 1178]

Check your ignition switches. Do you have a left-right-both-start switch?  If so get ready of it. 

[LSaupe 123]

Thanks Larry.

yep, I have independent toggle switches, vice using the key.  I did disconnect them early on in troubleshooting  however, to take those out of play just in case.  I have seen these hand propped  before so still surprised at the speed I need here.  Follow on starts now will a warm engine and charged battery went fine.  

We will see what the next cold start brings.  Maybe (hopefully) just a weak battery and thick gearbox oil.

[1avidflyer 1983]

You can hand prop a Rotax with CDI, but just barely.  You really have to flip it over fast.  I never was able to do it on a cold (winter time) engine.  JImChuk

[tcj 150]

Spark plug gap from the book is .16"-.18".  In cold weather a .16" plug gap will start easier.  The gap on new plugs right out of the box is usually (maybe always) way to wide.

[akflyer 1427]

I have seen it published that you need a minimum of 250 RPM to get a spark.  I also run my plugs at .016" as I start getting a miss when they are in the .018" range.  I also change my plugs more often than most do.  Plugs are cheap and I have the cowling off every few flights anyway just to look things over.

As Jim noted, the oil in the gear box REALLY slows the engine down when its cold.  That was one thing I really loved about the clutch was the cold weather starts.  Bu the time the engine was up to temp it was transferring heat to the gear box and getting it warm before I take off.  When its really cold I use the preheater to warm both the engine and gear box as I took the clutch out and with really cold oil its not easy to get a good start.

 

[C5Engineer 1170]

300 rpm is the magic number. 299 and no fire. Try the more expensive platinum NGKs and switch your gearbox oil over to Royal Purple 85W-140. I have an E box and being able to pull start mine has saved me many times in Idaho when it's cold. 

[LSaupe 123]

0.016" it is then.  Gonna drop in a new set of plugs before I fly again and see how she goes.   Thanks for all the feedback. 

[TJay 1041]

300 rpm is the magic number. 299 and no fire. Try the more expensive platinum NGKs and switch your gearbox oil over to Royal Purple 85W-140. I have an E box and being able to pull start mine has saved me many times in Idaho when it's cold. 

really you had good luck with Royal Purple? I used that is a B box once and within 5 minutes it started to foam up and drip out of the breather on top. Switched to mobil and never happened again. Maybe the E box has more room for the Oil to expand in?

[1avidflyer 1983]

Some B boxes have an oil slinger piece.    On the back end of the large gear if I remember right.  I think it was tried for a while and deemed not necessary.   Maybe that is why  the oil foamed in one gear box, and not the other.  Just a guess though.  JImChuk