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Rotax 912 trigger coil dissected


10 posts in this topic

Posted

Hey 

I would like to share my findings regarding the expensive rotax 912 trigger coils. It all started with a 300 rpm mag drop.....

The manual states the values regarding the resistance across the winding of the trigger coil (inside the plastic housing) and when I measured mine it was within limits. Then I measured the resistance between the center pole piece and ground....I had a high resistance and each trigger had different values (there is NO info anywhere about that measurement). I thought it should be an open circuit there ....and as I am curious by nature, a few hours later I had the trigger appart to see how it is built inside. Looking at the simplicity I would like to see these triggers cost 8 $ each.......and not the 200 $ rotax is asking us.

Also I found some of the center pole pieces to be covered in rust as there is no seal between the plastic casing and the pole piece going through. The high resistance I measured is normal I think as the center pole piece is in contact with the magnet and the magnet is stuck to the metal bracket. I actually am measuring resistance through the magnet.

That's it for my latest head scratching activity

 

 

P1110659.JPG

P1110658.JPG

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Posted

Do you measure any resistance between the coil wires and the pole piece or ground? Seems that should be an open circuit. If you do measure resistance between the winding and pole piece or ground that could be the problem even if the coil resistance is within spec.

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Posted

Do you measure any resistance between the coil wires and the pole piece or ground? Seems that should be an open circuit. If you do measure resistance between the winding and pole piece or ground that could be the problem even if the coil resistance is within spec.

Hey Chris,

you'r absolutely right, between any of the two coil wires and ground (or the wire cover metal mesh) you must have open circuit.

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Posted

Flywise,

Were you able to clean up the rust and make an improvement or do you have to destroy the coil when you take it apart?

Thanks for sharing,

Randy

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Posted

Flywise,

Were you able to clean up the rust and make an improvement or do you have to destroy the coil when you take it apart?

Thanks for sharing,

Randy

Hey Randy, I cleaned it all up, re-installed all the bits and my engine /ignition works like a charm now. You have to be careful not to break the plastic clip when you remove it and also when you re assemble the trigger you have to make sure the center pole piece is fully pushed in ( no play in/out) .

I don't think a small amount of surface rust matters but if there has been water or condensation inside the trigger and the center pole piece is rusted between magnet-metal plate then I believe you will have a problem (less magnetism in the pole piece)

Cheeeers

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Posted

Flywise:

I can relate to what seems like excessive prices for Rotax parts. most of the friends I fly with are always bitching about the prices. 

Of course, some  of this can be accounted for:

Rotax engines are ther most popular experimantal engine

Parts are Euro based and have to be shipped from Europe so add shipping.

That said, the Rotax engine itself is robust. It's the gear box and sprauge clutch that seems to give my friends headaches.

I have be flying behind the Jabiru 2200 in my Avid Flyer MK4 for over 3,000 hours and when I compare my engine with that of my Rotax drivers, I am amazed at the simplicity of the Jabiru and inexpensiveness of replacement parts. Many of which can be purchased from NAPA auto parts.

The weak point of the Jabiru is in the heads. I have had to replace the valve guides and valves. In we have had an exhaust valve head come off and damage the chlinder on mine and my friend's Jabiru. 

Jabiru is up to a generation 4 engine. This added roller cam lifters and oil feed to the rocker box through the push rods instead of through feeds from the side galleries to the rocker box as mine is.

I do like the fact that I can pull a head in 10 minutes.

Different 4 strokes for different pilots...

John M

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Posted

Flywise:

I can relate to what seems like excessive prices for Rotax parts. most of the friends I fly with are always bitching about the prices. 

Of course, some  of this can be accounted for:

Rotax engines are ther most popular experimantal engine

Parts are Euro based and have to be shipped from Europe so add shipping.

That said, the Rotax engine itself is robust. It's the gear box and sprauge clutch that seems to give my friends headaches.

I have be flying behind the Jabiru 2200 in my Avid Flyer MK4 for over 3,000 hours and when I compare my engine with that of my Rotax drivers, I am amazed at the simplicity of the Jabiru and inexpensiveness of replacement parts. Many of which can be purchased from NAPA auto parts.

The weak point of the Jabiru is in the heads. I have had to replace the valve guides and valves. In we have had an exhaust valve head come off and damage the chlinder on mine and my friend's Jabiru. 

Jabiru is up to a generation 4 engine. This added roller cam lifters and oil feed to the rocker box through the push rods instead of through feeds from the side galleries to the rocker box as mine is.

I do like the fact that I can pull a head in 10 minutes.

Different 4 strokes for different pilots...

John M

Hey John,

I have looked at the Jab engine and what put me off was the fact it is a direct drive and revs pretty high.... your propeller speed is between 2800 and 3100 rpm in cruise !!! On the rotax 912 your propeller speed in cruise is  2100 rpm thanks to the reduction gearbox and that allows for much more efficiency (larger diameter propeller). Also the Jabiru engine being the same weight has 15Hp less.

What upsets me with rotax is that they overprice parts not built by them and can be found much cheaper by the original manufacturer (Bing parts/ ducati parts/ ignition cables, NGK ignition parts, spark plugs, intake filters, fuel pump etc...)

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Posted

Flywise,

Thanks for the help!

Randy

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Posted (edited)

Hi...with a misfire/rough run on a mag check - check the plugs first - check the spark plug wires - are they affixed properly at both ends? - are they in one piece? - on the correct plug? - p-lead and mag switch? half loose screw on the mag switch? any chafing of any ignition wires anywhere? Any loose connections?

turnkey pcb assembly

Edited by CariKahn

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Posted

One other thing to add to the mix if it hasn't been mentioned already.  Make sure you don't have any coil wire grounds or any others for that matter broken.  With the vibrations, they do break.  On the 912 I got last year, one ground wire had the plastic still holding, but the wire was cracked, and I didn't see it till I took the coil off, the plastic held for a bit, and then cracked off.  Problem with the ignition found!  JImChuk

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