Rotax 80hp, ignition problems

[JorgeEC-YUQ]

All done,

Tom, the engine it's been opened for inspection two weeks ago. My mechanic was suspecting of a valve issue so he dismantled the cyl heads & body to inspect everything down to the engine block (including a visual inspection of the camshaft). Everything was within tolerances as per manual, including the reduction gear on the press bench, the cranckshaft eccentricity and the cyl. compressions. There was no founds to explain such a vibration. So initially it's not a mechanical reason.

The ignition cable is check on both ends (plug adaptor/dual coil) by checking the length of cable wich fits in and the pull test is done. Ignition cables are new, plug adapters are new ... Every time cutting a small piece of cable to ensure it will screw in properly. Ignition components have been check for resistance with multimeter on several occasions and all values are correct as per rotax manual (stator, grounds, dual coils, ignition cables and plug connectors).
The plug wiring order is been check as well and it's correct.

Since all this was checked with the engine stopped ... It might be a failure that it can be only reproduced with the engine running?

Main ignition switches. I didn't replace those but I bypassed them by directly connecting a cable to ground the CDI's to the airframe. Is that what you meant?

Another stupid thought of mine ... I tried by isolating the engine from the airframe by doing separate fuel and grounding to the CDI's. The only thing left that comes to my mind, is the power to the starter motor. Maybe it gets stuck or activated while the engine is running making some kind of interference? Anyone had any issue with this? I guess in such case my starter would had given up long time ago but ...

Thanks for all your comments, highly appreciate them!
Jorge

[JorgeEC-YUQ]

I would like to share this pics. Maybe it will help somebody in the future:

This is my stator and those are the cables going to the CDI boxes.They are protected with two covers, first is a heat protector (made of fiber glass I believe) and then the other made of metallic screen?.

It took me a while to discover this one. I probably checked this cables and its connections a million time since I read in this forum about many members having issues in this regard. I did the "stretch test" on the cable as well ... but only on the accessible/visible/unprotected part of cable which is about 8 inches before the CDI boxes.

I am not a mechanic, and I just can't understand electricity, that's why I paid a guy with experience to check everything again for me, also with multi-meter, showing correct values of resistance (after discovering the state of the cables, I will never understand how is that possible... )

It was by pure chance one day I was desperate enough that I decided to uncover the full length, discovering that the isolator of the cable was corrupted all the way down to the stator. It was so soft it was like chewing gum and would stick on my fingers! This is when I thought I had found my snag.

I sent the stator to a guy who re-welded aviation grade cable on it, put new protective covers, checked all the values with multi-meter again and confirmed that both coils are actually isolated (no short circuits). Re-install the stator back on the engine, re-install engine back on to the plane, start up the engine and.................. same vibration!!

I think this stator is a quiet simple design but, do you think is there any hidden reason why it could still be failing, even with new proper cables, being the cause of my vibration ???

Jorge

[JorgeEC-YUQ]

and here the video I took of my spark plug ...

https://www.youtube.com/watch?v=0s61h6TgHYE

Jorge

[Av8r3400]

The insulation on the stator getting "gummy" is the reason for Rotax's stator SB calling for its replacement. I don't know if other changes were made internally or not. I would have suggested that if you had it apart that far, not to repair your stator but replace it with the updated unit.

These shorts in the wires may have already damaged your new (?) CDI boxes.

Have you already put it all back together?

The spark looks normal other than it may not be hitting every time.

Note: never try to operate these ignitions without spark plugs or with the plugs insufficiently grounded to "check" the spark. This can and will damage the CDI boxes.

[JorgeEC-YUQ]

I put it all back together already ...

Yeap, looking back would have been clever to replace the stator but I didn't had any.
My local distributor would sell the full assembly, not only the stator, (with the new style connectors, so installation apart) for +1200 euros.
That without knowing for sure it would be the cause. Providing that this SB was referring, as you say, to the cable quality and that the stator, being so simple, would be operational it was my main motivation to try to fix my one ... that and the thousand bucks.

But maybe it would have been worthy indeed ...

Do you think this is the right track ? Is the spark is missing due to the CDI's being broken?

But I still don't understand ... could that mean the engine was always running on 3 cylinders and this is why the ignition test was somehow OK ??

My next plan is to swoop the full ignition from the 100 hp ... If that doesn't fix it this engine has to go.

Thanks for the note, good to know one shouldn't play with the spark plugs ... live and learn as they say!

Thanks for your responses,
Jorge

[Wheels]

I fought an engine vibration for months until a friend showed me a small crack at the top joint by the rubber isolation dampner.
I thought it was just cracked paint, but when I removed the engine, the crack became very visible. there were actually two? Kit fox came out with a more robust engine mount several years ago. It may be worth your time to use a magnifying glass and inspect every part of that mount, with the engine mounted is fine.
My favorite engine mechanic missed it for 18 months. I replaced the broken mount and the vibration was gone.

[JorgeEC-YUQ]

woow ... scary one!

I checked the engine mount looking for cracks before I repaint it when I had the engine off the plane... but I will re-check again after seeing your pics.

I found something interesting yesterday in other forum. About an old rotax engine (like mine, 12 years) having lost some of its magnetic properties on the stator. Due to age and heat? They call it lazy stator ...

You can find it here: http://www.recreationalflying.com/th...roblems.10397/

Any thoughts?

Jorge



Thanks for sharing!






Jorge

[Av8r_Sed]

I wouldn't put much stock in the "lazy stator" theory. It's basically iron laminations with wire coils around it. If the coils are connected and there's no short in the insulation, you will achieve strong magnetic fields. In other words, it will work or not but shouldn't slowly die.

[Paul Z]

Checking the Resistance should have caught that problem.

[JorgeEC-YUQ]

I am about to loss my temper with this plane...

It wasn't an ignition issue: I replaced the full ignition system on my 912 80hp with the parts of another 912 100hp and keeps vibrating the exact same.

Then I put all back together and installed the 912 100hp on the plane to make definitely sure it was an engine issue. Now it doesn't vibrate as much but still shakes a bit ... And the carburetors are ****ing fuel (overflow).

I found this video on the Internet which looks the same situation as my plane, so you have an idea of what I am talking about. Mine is only leaking on the left carburetor:

https://m.youtube.com/watch?v=PHS05n89kas

Needle valves are closing, the float valve levers are checked, floats are checked, new components... Seems like they can old the fuel level constant when the engine is stopped but when running they are become unable to, making it impossible to regulate, magnifiying the shake ... I guess.

The engine mount rubbers are new, I make sure there is not metal contact in the attachment points and the engine mount is been inspected for cracks (only visually). What am I missing? Could be something in the airframe producing this?