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Marvel Schebler float to replace Bing floats

in 912 / 914 Technical Questions 6 years ago
Has anyone tried the new MS80-430 solid epoxy floats. MS apparently has a good track record with their epoxy floats and claim that the epoxy floats will not absorb fuel.

They weigh 3.6-3.8g and would sink about 4mm further into the fluid. Will that create a problem?

  • Re: Marvel Schebler float to replace Bing floats

    by » 6 years ago

    These MS floats already weigh over 7 grams new and shouldn’t be used. They will sink some and may cause flooding at low rpm. If 7 grams wasn’t a problem then Rotax wouldn’t have us change out the original ones that weigh 7+ grams.

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

      
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  • Re: Marvel Schebler float to replace Bing floats

    by » 6 years ago

    Thanks Roger. The 3.5g limit does cover the new 3.2g Bing floats. Who is going to find out the float weighs exactly 7g when they look? I suspect that Rotax set the 7g limit to leave some margin.

    I now have one of the new 3.2g floats sitting in fuel and has gone over 4g. Rotax still has a problem.

    The 3.2g float sinks 2mm further into the fluid than the 2.6g floats. The MS 3.8g float sinks 4mm further into the fluid.

    Just experimenting, I did bend one float arm to accommodate the 4mm. That clearly would not work as the stop on the arm misses the carburetor and the footprint of the tab to pick up the float needle is way to small. The one I bent to accommodate 2mm does pick up the stop and the footprint of the tab does pick up the float needle. Not convinced yet that I want to fly that configuration.

    Guess I will keep muddling through with the sinking floats. I have enough floats to dry them out and enough spare gaskets.

    John.
      
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  • Re: Marvel Schebler float to replace Bing floats

    by » 6 years ago

    Hi John,
    The float by far has more influence here and hopefully the new Rotax float 861-118 is all good to go. The new floats out of the box seem to weigh in at 6.1 to 6.2 grams.

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

      
    Report

  • Re: Marvel Schebler float to replace Bing floats

    by » 6 years ago

    Let me play the Devil's advocate here... :evil:

    Where are these 2mm, 4mm deeper numbers coming from?
    Theoretical calculations or empirical measurements?

    The weight of the floats does not determine if they float or not.
    It is the Density of the floats relative to the fuel that determines float displacement.

    The carbs will tolerate a significant variation in fuel density.
    Warm fuel is less dense than Cold fuel.
    Avgas is less dense than MoGas; So warm Avgas would be the worse combination.
    And we know they all work without carb adjustments despite a possible 4% variation.

    We can assume that MS designed the floats as a drop-in replacement for the Rotax floats.
    Any variation in the float weight could be easily accommodated by varying the float volume or the location of the mounting stud.

    Perhaps comparing the weights of MS floats to Rotax floats is comparing Apples to Oranges.
    Does anyone have direct experience in using the MS Floats?

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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  • Re: Marvel Schebler float to replace Bing floats

    by » 6 years ago

    Hi All

    I installed the MS floats on Oct, 3rd. Out of the box the pairs weighed over 7 gms. , 7.46 and 7.42 to be exact. I called MS and inquired about the weight and the fact that Rotax specifies no more than 7 gms. Was assured that they tested these and they worked at that weight. So I installed. Today Oct 27th, in route to Marana AZ. The engine started running rough, intermittently. The exhaust gas temp on the right carb side would drop by 200 to 300 degrees. After a brief period of time all ran smooth and the temps returned to about a 40 degree split. I turned around and headed back to Prescott, AZ. On the way back, I had repeated instances of intermittent engine roughness. Each time, the exhaust gas temp on the right side would drop at least 200 degrees and there was a rather strong smell of gas in the cock pit. Upon return, I dropped the bowls on both carbs for inspection. The right set of floats appeared to be sticking slightly. If I gently shook the bowl they would release and float normally. The exhaust was black and oily. I replaced the MS floats with a usable set of Rotax floats in both carbs. Upon run up, the engine ran smooth but above 4000 rpm's the oil pressure dropped dramatically. I shut down and dumped the oil. It was evident that there was gasoline in the oil. I also removed and drained the filter. Closer inspection of the MS floats compared to the Rotax floats revealed that the hole in the floats for the pin were smaller in the MS floats and did dot have a brass sleeve as the Rotax ones do. It is my opinion that the MS floats(s) on the right carb stuck and flooded the engine with raw fuel. When they became un stuck due to vibration they floated again for a period of Time.

    I replaced the oil in the engine with fresh Aero Shell Sport Plus 4 an rand it up again. This time, oil pressures were normal and remained so through 5000 rpm static on the ground.

    Based on my experience, I would strongly caution against using the MS Floats. My hope is that the cylinders were not washed enough by the fuel to have caused any damage to the walls. Compressions felt normal but I will get gauges on the tomorrow. And bore scope the cylinders 1, 3 . Wanted to get this info out asap.

    If you have questions, I can be reached at boblid@icloud.com. If you leave a phone number I will be happy to call you back.
    Thank you said by: Tony Armour, Andrew Dunning, john gunn
      
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