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Thread: Rotax 912 and viking

  1. #1

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    Default Rotax 912 and viking

    Hey all , I saw a Viking 130 that seems like a reasonable option, wondering if you all have heard much about it or have experience running one long term. Obviously cost difference between it and the Rotax 912 is a considerable factor, but worth spending the extra money if the 130 just isn't up to the reliability.


    Thanks

  2. #2
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    Default Re: Rotax 912 and viking

    I would not consider anything but a Rotax for the Kitfox. Far lighter, more dependable from what I've seen and heard, and if a guy wants to go with a used Rotax there are more of them out there all the time. And often for $10,000 or less. Other parts like motor mounts and such are easier to get as well. I have a 80 HP in my flying KItfox 4, and a 100 HP 912 in my nearly completed Kitfox 4. Can you tell that I'm a fan of Rotaxes??? JImChuk

  3. #3
    Senior Member Dave S's Avatar
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    Default Re: Rotax 912 and viking

    Just a sidebar on sourcing used engines. One of my pals from the local EAA chapter recently purchased a 912ULS with 6 hours on it from Wentworth of Crystal MN for $10,000. Wentworth is a long time aircraft salvage yard. Such a purchase does require some additional checking, like probably a gearbox inspection and some parts like the regulator and starter solenoid will probably have to be purchased separately but this can be a real money saver for the right person. Don't know if CA has salvage yards like this or not.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  4. #4
    Senior Member Eric Page's Avatar
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    Default Re: Rotax 912 and viking

    Compare all-up installed weights carefully. Also, you'll be entirely on your own for an engine mount and cowling, unless Viking provide them for the Kitfox. The Kitfox factory does not support Viking installations. A Viking powered Kitfox might be a fleet of one; if others exist, I don't think they've appeared on this forum.

    I was very excited about a higher horsepower automotive conversion when I started this journey. After doing a lot of research, reading this forum extensively and watching another builder with an auto engine (not Viking) get so frustrated that he removed it and sold the airplane, I changed my mind. I now have a 912iS in the garage, waiting for me to get off my butt and finish the airplane build.

    There's one aspect of the computer-controlled Rotaxes that angers me. Rotax charges $2,300 for a locked down $70 off-the-shelf USB dongle (which is almost always out of stock everywhere) to download diagnostic data, and the detailed information needed to decode that data is unavailable outside authorized service centers. To me, that's the primary argument (beyond lower cost) in favor of the carbureted Rotaxes. Tuning and syncing carbs can be a pain, but you don't need eye-wateringly expensive tools and a factory authorized charge-by-the-hour iRMT to work on them.

    If I had to make the decision again, I would likely do as Dave suggested: buy a used 912ULS, go through it with a fine-toothed comb, get the carbs and gearbox serviced, and maybe visit Hal Stockman for a big-bore kit. Cheaper, lighter and simpler.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

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    Senior Member bbs428's Avatar
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    Default Re: Rotax 912 and viking

    I agree with Eric whole heartedly!
    I found my 1993 912ul under a tarp in a barn (where I also found my KF5) - came out of a ground-looped kitfox IV. Got it for a song. A trip to Hal Stockman for a Zipper big bore kit and a fresh go through of the gearbox (added the slipper clutch) and complying with all the AD's plus an NR prop. It makes 110hp and its real performer! The $$ savings really added up.
    Now that I know the engine better, I find this older, carbureted Rotax 912 very easy to work on, not much different than one of my old, wet clutch Japanese motorcycle engines.

    You cannot underestimate the performance nor the resale value of the Kitfox with the Rotax engine. It's the standard engine package for this aircraft for a reason.
    Last edited by bbs428; 06-09-2024 at 01:16 PM.
    "Somebody said that carrier pilots were the best in the world, and they must be or there wouldn't be any of them left alive." Ernie Pyle

    Brett Butler
    Flying: N46KF, 1998 Model 5 Outback, 912ul 110hp, G3x with 2 axis a/p, Beringer wheels & brakes, SS7 firewall forward, NR prop, Custom paint

  6. #6
    Senior Member Dave S's Avatar
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    Default Re: Rotax 912 and viking

    A point worth evaluating when considering an auto conversion engine (or one of a kind) as opposed to a rotax (or continental/lycoming) in a kitfox is to check with your insurance company and ask them the ins and outs of insuring a plane with a modified auto engine compared to other options.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  7. #7
    Super Moderator Av8r3400's Avatar
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    Default Re: Rotax 912 and viking

    Quote Originally Posted by bbs428 View Post
    I agree with Eric whole heartedly!
    I found my 1993 912ul under a tarp in a barn (where I also found my KF5) - came out of a ground-looped kitfox IV. Got it for a song. A trip to Hal Stockman for a Zipper big bore kit and a fresh go through of the gearbox (added the slipper clutch) and complying with all the AD's plus an NR prop. It makes 110hp and its real performer! The $$ savings really added up.
    Now that I know the engine better, I find this older, carbureted Rotax 912 very easy to work on, not much different than one of my old, wet clutch Japanese motorcycle engines.

    You cannot underestimate the performance nor the resale value of the Kitfox with the Rotax engine. It's the standard engine package for this aircraft for a reason.

    One thing with the carbureted engines: Correctly doing a large (1") balance tube negates the need to do anything but a mechanical sync ever again. This is something that Rotax should do right out of the box.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
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  8. #8
    Senior Member jiott's Avatar
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    Default Re: Rotax 912 and viking

    There's just one thing I don't quite understand about the big balance tube, and you guys that say you never/seldom do a pneumatic carb balance. I get it that the big balance tube will easily feed extra air/fuel to the side that is demanding more and the engine will continue to run smoothly. You may feel the engine is smooth and happy, but the truth is that it is still out of balance. If any air/fuel in any amount is moving thru that balance tube, no matter what size it is, the engine is out of balance-one side is pulling harder than the other. The bigger balance tube just allows you to keep flying with worse out-of-balance engine than the standard balance tube without knowing it. I am not saying this will damage the engine in any way, but it certainly is not using the engine in the most efficient way. Even if I had the big balance tube, I personally would want to do a pneumatic carb sync once a year or so to keep my engine efficiently balanced. I have a hunch that is why Rotax factory has never bothered to enlarge the balance tube. A properly tuned, balanced and maintained engine carb system should only need a very small balance tube to make up for the fact that is is impossible to build a dual carb system where each carb draws exactly the same amount of air/fuel thru the whole rpm range. To each his own and I certainly don't think there is any harm in a large balance tube, but to me it is useless based on how I personally want my engine to run.

    Don't take this wrong, I really don't mean to put anyone down; I just wanted to express my personal philosophy on this subject, and would be very interested in your response to my 2 cents worth.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  9. #9
    Senior Member jiott's Avatar
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    Default Re: Rotax 912 and viking

    I think I see a flaw in my reasoning, because the balance tube is downstream of the carbs. Even if the carbs are out of balance a large balance tube will make sure the engine itself is not out of balance. It will get exactly what it wants, but will be drawing from one carb more than the other-probably no big deal. I personally will feel better if both carbs are being used equally, but it probably has no effect on engine efficiency unless the carbs are WAY out of balance. Sorry to mislead anyone, but I like to reason these things out for my own satisfaction. Still interested in anyone's comments.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  10. #10
    Senior Member bbs428's Avatar
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    Default Re: Rotax 912 and viking

    In my case - Hal Stockman installed the bigger balance tube on my engine. A little difference per side is nbd now.
    That being said, I still checked the sync at the carb when I first got it running. It was close, and I did get it closer. I plan on checking it as needed or at every annual. I use my old motorcycle sync tool. It is four vacuum gages (I used two) you can adjust it to eliminate the pulsing to get a real smooth reading.

    Not sure how accurate the measurement is, especially with the bigger tube downstream.
    I guess if one was bound and determined to get the sync perfect, one could isolate each side with a gate valve on the big crossover tube.
    Not sure if it's worth the extra time and effort. Tbh - how much closer could you get it?
    "Somebody said that carrier pilots were the best in the world, and they must be or there wouldn't be any of them left alive." Ernie Pyle

    Brett Butler
    Flying: N46KF, 1998 Model 5 Outback, 912ul 110hp, G3x with 2 axis a/p, Beringer wheels & brakes, SS7 firewall forward, NR prop, Custom paint

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