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Friarpuk

Rotax ULS 912 Magneto Issue

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Hi I have about 500 hrs on my Rotax 912 and recently on startup it one of the magnetos is dead for about one minute and then comes good. Has anyone heard of this or had this issue? Any pointers would be appreciated!

 

Thanks

 

Friarpuk

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Hi Friarpuk, suggest you direct your question to Mark Kyle of Kyle Communications here.

He knows a great deal about 912 ignition.

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Sounds like it is on the way out and coming to life when warming up a bit.

Try pre heating it with a hairdryer a bit and see if it works straight away.

This is a common testing method.

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Rotax had issues in that the cdi would fail in start mode but ok when it’s running. Gets to the stage when both fail you will fly it one day the next it won’t start because now both have failed in start mode. Expensive parts.

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We did a 100hr recently were the owner was have increasing difficulty starting. When complete we could not get a start, changed the ignition modules (square boxes) from another engine, instant start, swapped back to original, perfect start each morning over a few days. Suspect a poor connection in the plugs.

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And the cdi boxes have a long history of vibration cracking the wires as they enter the box ... not able to repair so it’s replace as they fail.

 

Expensive but hey you can run an ic engine without that ignition element.

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I read a while ago (here, I think) that an Australian Rotax guru put a lot of poor starting (and the resultant clutch damage) down to poor earthing, specifically using the aircraft shell as earth rather than running a separate battery negative wire for the starter. Given that starting the Rotax depends (amongst other things) on turning it over at an adequate rate, that made every sense to me.

 

It is also important that the trigger coils at the rear of the engine are gapped correctly. I have seen correct adjustment there make a huge difference to starting and a noticeable difference during mag checks. These are easiest checked using brass feeler gauges: the steel ones will stick to the rotor magnet and give the impression that the gap is snug when it is not.

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I read a while ago (here, I think) that an Australian Rotax guru put a lot of poor starting (and the resultant clutch damage) down to poor earthing, specifically using the aircraft shell as earth rather than running a separate battery negative wire for the starter. Given that starting the Rotax depends (amongst other things) on turning it over at an adequate rate, that made every sense to me.

A minimum of 200 rpm is required to "fire" the engine. This is part of the safety mechanism to allow you to "burp" the engine without it firing.

Alot of engines seem to be wired with smaller than minimum spec starter cable size too. It should be 16mm2 cable minimum (mulitstrand/flex) and the further the battery is away from the starter, the larger the cable size.

I've seen people try to start a rotax with a half flat battery and (as you alluded to) there is the risk of damaging the sprag clutch which is a 3 to $4000 repair. Best to always start with a fully charged battery.

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A risk with inadequately earthed engine is the current will go there along other paths like cables etc. it's common to run 2 earth wires to be certain to the engine as it's in rubber mounts. and insulated.. If you are concerned, crank your engine for say 10 seconds and then check all connections and leads for heating up. If a wire is getting hot put in a bigger one. Moving the battery is used as a correction for Cof G at times as it's a large weight with a significant effect on Balance point. If you are tempted to use the aircrafts frame ensure it's adequate to carry the current at all places it's likely to pass through. You should be able to get aluminium stranded wire which is much lighter than copper if you have long distances.. Nev.

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Posted (edited)

FriarPuk

Thats a common fault with older ones. Funnily enough I just tested a couple of the latest style modules for another savannah driver down south and one of his latest version modules does the same thing. This is the first I have heard of world wide of this fault in a later generation module. On my test rig it took about 1 min of running before it fired but only went for a couple of seconds then stopped for about 15 sec then started again twice like this then it started running no problem at all. I cold tested it by putting it in the fridge for a couple of days and it started straight up but when it got to around 28degC ambient the module started playing up again

 

What type are they?... the original 4wire type or 6x4?... if the engine is older than about 2007 it will most likely be 4 wire then from 2007 to around 2011 they went to 6x4 for a while and then the older 6x6 without softstart then after 2011 they are the later ones which are 6x6 and also have softstart

 

If they are 4wire check the brass bullet connector on the red wires coming from the generator. I have found a few guys have got modules from me only to find out it was a dodgy connection into that brass female bullet connector. The red wire supplys the voltage for the module to fire on the older units. usually not any trouble with the latest plugs except for craked and corroded wiring as Rotax modules use auto style wire out of the modules. Mine use all silicone wire. 200 degC and 600v

Edited by Kyle Communications

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Downunder I can assure you the later modules will fire a bit lower than 150rpm. Rotax used to quote I think 220 or 240rpm firing but it was usually around the 200 for the older modules. The latest modules will fire at 150 regularly so still be very carefull when burping the engine

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Posted (edited)

Hi I have about 500 hrs on my Rotax 912 and recently on startup it one of the magnetos is dead for about one minute and then comes good. Has anyone heard of this or had this issue? Any pointers would be appreciated!

 

Thanks

 

Friarpuk

 

Hi Friarpuk. I had on-going ignition problems with my 912 after about 20hrs from new. When carrying out the pre take-off ignition checks, I would regularly experience RPM drops of 400 to 1000RPM, even to the point that the engine would basically quit but then spring back to life again. I tested and suspected lots of things. Checked earth connections. Changed all of the spark plugs etc etc. Eventually, in order to isolate a CDI unit failure/problem, I swapped the CDI unit (6 pin) plugs around. (The ones that come out of each CDI) This immediately fixed the problem, but I didn’t know why. (proved it wasn’t a CDI fault anyhow)

 

Alas, after probably another 20hrs the problem reoccurred. Long story short, after pulling most of my hair out, and thinking life without an aeroplane would be much simpler, I stumbled on THE fault. One of the two brown wires (that go to the ignition switches) had been fretting itself on the bracket that holds the CDI units. When I swapped the 6 pin plugs over, it had temporarily re-routed the wire so it sat off that bracket, and the engine ran perfectly for a while.

 

I could see an area of slight discolouration on the suspect wire, and double checked my suspicion with a multi meter. Sure enough, there was bare wire earthing itself onto the bracket. Effectively, each time the wire touched the bracket due to vibration, it had the same effect as switching off one of the ignitions.

 

Anyway Friarpuk, it may not be your engine’s problem, but it’s worth a look. Here’s a pic. If you follow the brown wire down and enlarge the pic, you can see the fretted area.

 

Cheers. Perry

 

18D1EBF1-5A4B-4504-B2B4-CC6F8C2F734C.thumb.jpeg.d510ec049be2384c7f37d388f63cb6f4.jpeg

Edited by Guest

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Thanks for taking the time to tell me of you experience. I will look into it.

I suspected that it might be something like that.

Wiring those plugs to the magneto switches in the cockpit, I recall, was a bit of a pain in the posterior.

 

Regards

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A minimum of 200 rpm is required to "fire" the engine. This is part of the safety mechanism to allow you to "burp" the engine without it firing.

Alot of engines seem to be wired with smaller than minimum spec starter cable size too. It should be 16mm2 cable minimum (mulitstrand/flex) and the further the battery is away from the starter, the larger the cable size.

I've seen people try to start a rotax with a half flat battery and (as you alluded to) there is the risk of damaging the sprag clutch which is a 3 to $4000 repair. Best to always start with a fully charged battery.

No problem re battery not being charged. I run a solar panel to trickle charge the battery, keeping it topped up all the time.

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Posted (edited)

FriarPuk

Thats a common fault with older ones. Funnily enough I just tested a couple of the latest style modules for another savannah driver down south and one of his latest version modules does the same thing. This is the first I have heard of world wide of this fault in a later generation module. On my test rig it took about 1 min of running before it fired but only went for a couple of seconds then stopped for about 15 sec then started again twice like this then it started running no problem at all. I cold tested it by putting it in the fridge for a couple of days and it started straight up but when it got to around 28degC ambient the module started playing up again

 

What type are they?... the original 4wire type or 6x4?... if the engine is older than about 2007 it will most likely be 4 wire then from 2007 to around 2011 they went to 6x4 for a while and then the older 6x6 without softstart then after 2011 they are the later ones which are 6x6 and also have softstart

 

If they are 4wire check the brass bullet connector on the red wires coming from the generator. I have found a few guys have got modules from me only to find out it was a dodgy connection into that brass female bullet connector. The red wire supplys the voltage for the module to fire on the older units. usually not any trouble with the latest plugs except for craked and corroded wiring as Rotax modules use auto style wire out of the modules. Mine use all silicone wire. 200 degC and 600v

I built my Skyranger in 2009 after purchasing the engine from Flood Imports in 2008. I believe it is a 6 wire plug.

Edited by Friarpuk

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should be 1 of 6 way male housing and 1 of 6 way female housing if it is the 6x6 .... the 6x4 has 1 of 4 way male and a 6 way female and 2 flywires with bullets on them

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I

should be 1 of 6 way male housing and 1 of 6 way female housing if it is the 6x6 .... the 6x4 has 1 of 4 way male and a 6 way female and 2 flywires with bullets on them

I have a chance to go and check it out a bit more tomorrow. Will let you know.

Thanks

Heath

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I had the same problem - only noticed when both stopped working when cold. The way to test is to get a heat gun or hair dryer and warm the faulty unit for a while (2 or 3 minutes?) and then try to start off only the faulty unit. If it starts then the problem is that the older Ducati unit develop heat related solder cracks, when the unit heats up it the joint expands and contacts and it works OK.

This was described to me by the repairers that I send mine to (In the Netherlands, I can't remember the name but google the part number and repair). It cost about $800 for the pair and took about 2 weeks - they haven't missed a beat since. Bear in mind that this is NOT a certified repair.

Beats $1600 each new.

 

Note that they do not dismantle the units, they drill at the right spot and the right depth to expose the offending joints, resolder then fill.

Cheers

Murray

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Posted (edited)

So I went out to the airport and had a look. The Skyranger has many endearing features but it aint that easy to get a good look at the back of the engine. I think it is a 6 way male plug and a 6 way female plug. Not all the plugs have wires running through them. I gave everything a wriggle and nothing obvious stood out. Started the engine ran rough for ten seconds while rpm was around 1500 - 2000 pushed her up to about 2500 and it came good. I could not fault it in the run up so I went for a fly and as per usual did not miss a beat for the 1.7 hrs I was up. I constantly checked magies while up there and just the usual expected drop on both.

 

One of these days I am going to have to pull the engine out to fix it and the wretched oil leak I have that drops enough oil down onto the spat when the engine is cooling but is not enough to reach the bottom of the spat. The seal on the back of the engine is the culprit so the LAME says, along with it being a real bugger of a job and it needs special tools. Which translates into the LAME telling me it's going to be expensive. The silly thing is at this point in time I am only putting about 500 mls of oil in the engine between each 100 hrly.

 

BTW I did enjoy the flight yesterday. I circumnavigated the Bunyas to look at the wind farm emerging out of the nth western end of the range near Porter's Gap and then to say g'day to dad and my brother with flyovers at their places, a circle around Bell before flying back over the Bunyas before landing back in Kingaroy just on sundown.

Puk

Edited by Friarpuk

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You may want to look at doing the water pump seal while getting the oil seal changed.

It would be unfortunate not to replace it, and have it fail in the near future. ....

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You may want to look at doing the water pump seal while getting the oil seal changed.

It would be unfortunate not to replace it, and have it fail in the near future. ....

Indeed! Already on the list for the bank manager.:groan:

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Posted (edited)

Note that they do not dismantle the units, they drill at the right spot and the right depth to expose the offending joints, resolder then fill.

Cheers

Murray

 

All they do is drill in with a milling cutter and replace a small SMD transistor that is part of the kill circuit then epoxy it back up. This is maybe about 20% of the failure modes the older CDI have. The most common fault is the capacitor used for the discharge to the coil this also is affected by cold temperatures it loses its capacitance dramatically. I have seen a few modules that are intermittent with hot temperatures as well but not as common as the cold. The next most common fault is the kill FET dies and you cant turn off the engine if it is open circuit or it will not start if it is short circuit. Having pulled totally apart many modules I have never seen too many bad or cracked solder joints. Not saying they are not there because temperature cycling and vibration is hostile environment for any electronics.

Edited by Guest

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Hi Mark,

You are probably right - The explanation above was the one given to me by Carmo and I am just repeating it (with little actual knowledge on the subject)

They did repair mine and they are working fine - but I am sure that there are different problems that require different solutions.

If Friarpuk wants to get new ones - then we get into the soft-start debate .......

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I can tell you that there is absolutely no difference in circuitry between the old 6x6 and the new softstart 6x6. There is a add on circuit for the softstart but it just engages the normal CDI circuit when told to and it times out and disconnects. The difference is the later softstart module has some of the parts upgraded to higher current. You can use a later module on the older 6x6 with no difference except the changeover from retard to advance is done at a lower RPM than the older 6x6. The originals used to change at 1050 RPM but now change at around 800 RPM. The reason for the earlier changeover is the new devices tune on at a lower voltage so basically start quicker. The main difference is the flywheel. The trigger plates on the flywheel are different. This is the only difference between the older and later systems

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