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Rotax 912ULS shakes alot at start

in 912 / 914 Technical Questions 11 years ago
I am using rotax 912ULS since 2003.Its total running hours are 100. Now it has a serious staring issue. Engine vibrates and shakes a lot while starting. I checked its complete ignition system (even changed CDI's, charging circuit, adjusted trigger coils gap, used new spark plugs and adjusted their gap), performed A B Kill, checked its starting circuit, performed carbs sync and cleaning, new battery fully charged, installed new heavy duty starter but still the problem is their.

Now the only thing left behind is its gear box. This engine doesn't have slipper clutch. Since my engine only has 100hrs TSN, so I assume that gear box overhaul is not yet due.

Is this possible that the problem is because of gearbox. Do I need to open gearbox for overhaul.

  • Re: Rotax 912ULS shakes alot at start

    by » 11 years ago

    It could be your old engine mounts. If they are from 2003 they need to be changed. When does it shake? At idle or high rpm range or both? What is the mag drop on each? Are the carbs pneumatically synced at idle and around 3500?
    What kind and type of prop?

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: Rotax 912ULS shakes alot at start

    by » 11 years ago

    Roger,

    After I found this problem on my long EZ, I removed my engine and installed it on test bench using new shock mounts. So I think that shock mounts is not an issue.

    It shakes during starting for almost 3 to 4 seconds and when I increase throttle upto almost 50 percent throttle engine gets started at around 4000 rpm spilling a lot of fuel through over flow tube of carbs and after severe vibration. Once it starts the vibrations vanishes and the engine behaves normal from idle till full throttle.

    Mag drop is less than 200 rpm for each of A & B and the difference between A & B is lees than 70 rpm. EGT's of all the 4 cylinders are also almost close showing no fault in one or two cylinders.

    I synchronize engine mechanically before engine start and once I start the engine I synchronize throttle (from idle till 3500 rpm) using carbmate synchronization tool. But when I restart the engine, the problem persist.

    And the last thing that I missed is I am using Airmaster ground adjustable 3 blade propeller. And my propeller pitch is 19.

    Roger my problem is almost similar to one mentioned in the doc. attached herewith this email.
    Europa-List_Rotax912SStartingProblems.pdf (You do not have access to download this file.)
      
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  • Re: Rotax 912ULS shakes alot at start

    by » 11 years ago

    Not an expert at all but experienced that kind of problem. It could be the sprag clutch. Do some research on the web and you'll find out that Rotax has a real problem with their sprag clutch on 912S.

    Good luck,

    Pat
      
    Report

  • Re: Rotax 912ULS shakes alot at start

    by » 11 years ago

    Hi Patrick,

    I think you'll find the worst thing that happens to a sprag clutch is its owner. I do agree that some have gone bad, but a very small number compared to the owner damaged ones. Of course when one goes bad the owner usually blames the sprag and not previous maint. or lack of maint. These owner neglected items cause sprag damage and it happens way too often.
    Rotating the prop backwards, poor slipper clutch gearbox torque, poor battery condition, too small a battery, kick backs not being addressed, poor or no carb sync adding to kick back issues, electrical issues adding to kick back. There are a few others, but these are the most common.
    Many of things things come about due to lack of knowledge and or training on the engine.

    An engine that has had proper maint. during its life and no abuse can usually see TBO with a sprag.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: Rotax 912ULS shakes alot at start

    by » 11 years ago

    Roger,

    I think you are right. Reality is most of the mechanics think themselves expert of this series of engines just by reading its manuals although they are not well trained and they don't have enough experience with these engines. They solve their problems most of the times just with the help of some topics on different websites.

    But Roger now I am in serious trouble and I need that engine back on track. So what do you suggest. Do you think that the problem could be of slipper clutch or should I go for sprag clutch first. How could I check condition of sprag clutch without dismantling engine.
      
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