This is Jorge from Spain (writing from Africa). I have an ongoing problem with my engine, a rotax 912 80hp. I hope any of you guys could bring me some light.
The engine has little hours, 190hrs, but it was standing on the ground for some years. I inspected the engine trough but after some flying one could feel a vibration wich became stronger with the hours.
After discarting other factors, it became obvious the problem was comming from the ignition. The accessible part of the system was checked by a mechanic (I have no clue about electricity), conexions, cables, etc and the ignition boxes cross connected showing a problem on the back part (stator, charging/trigger coils ...).
At the same time, being the carburators throughly rigged, synchronized and inspected, the spark plugs on cylinders 1 & 3 (that is right side cylinders feed by right carburetor) were showing a notorious difference on color.
#1 totally white #3 totally black ... Will try to post some pics.
Because of the work, I didn't had the time for further investigation but I want to get ready for the next round so I know where to aim when I arrive home!
So my question is, did any of you had problems with this part of the ignition system? Is it like a weak point on the engine or well known rotax problem there?
Do you think the spark plugs problem is related to the ignition or I do have two different troubles here?
Your help is highly appreciated!
Thanks in advance,
Jorge
There is a lot of great info on this board. I fought the same problem you are having last year- best advice I can give you is more than likely it is still in your carbs vs. your ignition. I would go back and verify that your intake manifolds are not leaking anywhere, check and make sure the needles and seats are good- pilot jets and venturis are clean, diaphragms don't have any rips or tears and move smoothly, etc. in my limited experience usually ignitions work or they don't. With such low hours on it that means it's been sitting a lot- and carbs are more than likely the problem.
From what I am seeing of your plugs that is a normal indication when you throw fresh plugs in and fire it up, mess with the carbs, shut it down, mess with carbs, fire it up, sync, shut it down- you get the idea. If it is only one cylinder and you are sure it's not the carbs you can switch coils around and see if the fouling moves to a different cylinders- than it would indicate a bad coil.
the intake route was inspected and the old rubbers and seals replaced with new ones. Needles, seats and jets ... All new.
Actually it also happens on the other side ( cylinders 2 & 4) but it's less accentuated.
The spark plugs in the pic were running for about 5 hrs indeed, but the previous set I was running had the same colors.
Now you mentioned ... The diaphragms were not new but in good shape (flexible, no rips) it might be worthy to double check. Then I will start to play with the coils and see if that helps!
I managed to send a friend who is mechanic to check for the fault.
He took the engine out to check for the back part (ignition coils), I had to change the motor mounts rubbers and check for the water pump anyways ... So, after all, this fault happened just in a right time!
I wasn't there, but seems like one of the cables from the coils to the CDI boxes? was in bad state, the coils itself had to much gap and there was some corrosion.
Apparently, a fter fixing all that, the vibration is gone... But I am not there to check it by myself.
The guy made some pics wich I will share once I am back.
Larry, the vibration was on the background on the full range of RPM's being easier to hear and feel at low settings of power or with one ignition off.
Tha fuel pump is new (changed it last year), not sure about the floats thought.
Well ... It's been close to a year since my problems started and I am still fighting with this engine. Not only I didn't fix it, but it became worst. Guys I need help!
My engine will have troubles to start if it's too cold and, when I manage to make it work, it will run "smooth" for the first 15-20 seconds, then the vibration begins. After the first start up it would start again easily but the vibration sticks there since the beginning now.
It's shakes more on low RPM's (1500-3000), smooths out just a bit on mid range (3000-4500) but in general shakes like a tractor! The vibration is such that one of the filters will come off and there is fuel on the carb air intake.
My CARBS were totally rebuild, all components new, but that didn't help. I even have tried with another 2 different pairs, with new components as well, and the vibration was exactly the same. Every time I swop the carburators I performed a mechanical and vacuum synced.
Following that line, the rubber adapters (carburator to intake) are new too. Since is a kitfox III, the cable route it's been check and adjust to the minimum play possible. Nothing! ......... So for me, carburation is not the cause.
PROP is a warp drive, wich is been balanced and checked on blade angles. Then I tried with a friend's prop and the shake kept the same.
Mechanically the engine its been troughly inspected. Valves, springs, cylinder compressions, crankshaft centered, tappets are new, no chip on oil and oil pressure correct, reduction gear ok ... Everything was within tolerances and there was nothing to suspect for the cause of this vibration.
Engine mount, bolts torque and its shock absorbers (new) are checked as well.
New style fuel pump too.
All the components in the ignition system were checked or/and replaced:
- Stator. It's affected by a rotax bulletin about the quality of cables and indeed the ones to the CDI boxes were in a bad state, so I replace them.
- Pick ups. Resistance is checked, they are old style and its gap is correct.
- CDI's. I tried with another set that I borrowed from a friend ... Nothing!!
- Dual ignition coils. Replaced
- spark plugs, connectors and ignition cables are all new (gap checked, cable properly screwed in, resistance is checked, etc).
- firing order checked and all connections cleaned and checked a million times !
So here comes the funny part about my gremlin: The IGNITION test will be just perfect and will show a drop of around 100 RPM's with no change on the vibration with one particular switch off, but visually checking the spark quality by removing the plug and cranking the engine shows an irregular not rythmical sequence, like it will miss every now and then without a pattern (?????).
So I reached that point were I feel like setting the whole @/#*thing on fire !!!
My next plan before that, after reading this thread, is trying again with the modules ... maybe those CDI boxes I borrow were also failing???
Anybody knows if the ignition components from a 912 100hp are exchangeable with the 80hp ?
Any other reason to suspect of the stator other than the bad quality of the cables? It was checked with a multimeter once it was fitted with new cables and all values were correct.
Jorge,I understand what you are going through,as I have had similar issues.
(I was so frustrated I seriously considered an engine swap to a 582)
The front plugs being darker is normal(fuel/airflow and manifold design,later manifolds were modified to try to minimise this effect.
The 100hp parts fit and work as these are what I am using
I have posted a brief description of my "remedy"which may help.
I had the early pickups(non replaceable wires)which I believe may have been a major contributor as my symptoms were similar to yours,
Replacing these made an instant improvement.
Don't let it get you down,the destination will make the journey worthwhile
What do you have the plugs gapped to? Rotax says .025-.028", I have found that .020-.023" works better. These are not powerful ignitions to jump a large gap. The spark is weak to see visually and a large gap can make it worse.
Ignition modules are not all the same. They have different plugs depending on the serial number of the engine. However, if you have the 4-pin plugs on your engine and swap 4-pin plugs off a 100 hp engine they will be the same function. I just converted mine to run the new style (cheaper) 6-pin plug modules.
What exactly was done to the gearbox to "ok" it? The output shaft stack should be disassembled and new spring washers and shims installed for a "routine" maintenance. These spring washers weaken over time and can cause vibration, especially with a heavy prop like a warp.
Silly question, but have you ever indicated the prop flange? Maybe a run-out issue or unknown damage happened? What about tracking the prop tips to see if the hub was bent?
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