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Thread: 912 engine preheater

  1. #1

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    Default 912 engine preheater

    My 1999 vintage Rotax 912 100hp (without soft start) is difficult to get started whenever the temps drop below 60 degrees F which is most of the time where I live.
    I have installed the latest generation 912 flywheel which supposedly retards the ignition even more at start up and a new battery and starter.
    My next step is to convert to the latest generation Rotax ignition modules with the built in soft start feature.
    My definition of hard to start is when after going thru the starting routine, it does not immediately start and idle like the car I drive to the airport.
    I feel sorry for the starter when it repeatedly acts like it is pushing against a wall and wonder when the engine will need to be removed to replace the Sprague clutch from the abuse.

    Everyone but me has already figured this out, but I recently found that preheating is amazing.

    I have known about the Reiff 912 phone activated preheat systems for years but hesitated because the system requires several hours to get up to temperature and I never know when I plan to fly.
    I thought that it was hard on the engine to leave the heat on full time but I learned that the condensation that forms from cycling the heat on and off is what damages the internals.
    Then I rationalized that if I lived in southern California where for several months of the year the night time temps do not drop below 80, how can it hurt the engine to leave the pre heat on full time?
    Hal Stockman from Rotax 912 Big Bore Kits, suggested I go to Napa auto parts and pick up some 2" x 5" self adhesive 50 watt engine block heater strips.
    I found these strips on Amazon for $18 each and installed 2 on the bottom of the 912 engine case and one on the oil tank and found a thick moving blanket to drape over the cowl to help retain the heat.
    I came back the next day and was shocked how warm the cowl felt.
    The oil temp gauge indicated 112 degrees and it started on a near freezing day like my car does.
    I disconnected one of the case heaters and the next day the oil temp guage indicated 96 degrees before start up with the same immediate easy on the starter and Sprague start up.
    This still leaves a starting issue when away from home in the cold mornings of the Idaho Backcountry but that is only a few days a year.

    I would be interested if there are any comments regarding leaving the preheat on full time other than constant power usage?

    Has anyone converted to the Rotax modules with the built in soft start and noticed an improvement when starting the high compression 912's with or without a big bore kit?

    Thanks
    Herman

  2. #2
    Senior Member HighWing's Avatar
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    Default Re: 912 engine preheater

    Herman,
    Not an answer to your direct question, but possibly helpful, a local guy with an early 912ULS with nearly 1500 hours on it developed a starting routine that works for him. I use it on my 80 hp and it results on easy quick starts with no bouncing around.

    He will start with throttle full closed, Ignition off, Crank for about ten seconds with full choke. Rotate throttle to an approximate fast idle. Ignitions on and crank again with full choke. Presto. I don't think he has yet to install the aftermarket - for him - Sprague Clutch.
    Lowell Fitt
    Goodyear, AZ


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  3. #3
    Super Moderator Av8r3400's Avatar
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    Default Re: 912 engine preheater

    Herman, do you have an auxiliary fuel pump? I put one in the Mangy. When it's cold, I will run the pump for a few seconds with the choke pulled, to bring fuel up into the carbs, through the enrichers and then shut it off. Only then do I go into the start procedure.

    I think this may be doing the same thing as what Lowell is suggesting by cranking with ignition off first.
    Av8r3400
    Kitfox Model IV
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  4. #4
    Senior Member jiott's Avatar
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    Default Re: 912 engine preheater

    It seems to me that 10 seconds of cold cranking is awful hard on the battery. Wouldn't it be better to do this cranking with the ignition ON; you may get a start long before the 10 seconds are used. Just wondering.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  5. #5
    Senior Member HighWing's Avatar
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    Default Re: 912 engine preheater

    I guess it would depend on the battery. I have used the technique for many years. I don't fly as much as I used to and the ten seconds pales compared to what the engine needs to recover from its 3 month deep sleep to full awake. Than add in the shakes and rattles before it begins to roll suggests a much stressful start considering the moving components. Then again, back in the day, the early ULSs shook mercilessly when starting frequently throwing the carburetors out of the sockets. This is why the "soft start" and "slipper clutch" bandaids were eventually developed. The stress of the rattling prop blades against the gearbox backed up against the crank and pistons was in my view something I didn't ever want to deal with, yet I did witnesses it first hand during our week long group flights together. With my 80 hp Rotax, ten seconds of smooth cranking followed by an instant start to idle after another couple of seconds with little if any stress on the engine seems like much less stress on the $$$ part with possibly a bit more stress on the cheaper much easier to replace part. My friend has been flying his IV with ULS for over 15 years.
    Lowell Fitt
    Goodyear, AZ


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  6. #6
    Senior Member jiott's Avatar
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    Default Re: 912 engine preheater

    Herman, leaving the heater on continually would concern me about an electrical malfunction and fire. In your mild climate just plug in the strip heaters when you get to the hangar and I'll bet that in 1/2 hour (about the time it takes to do your pre-flight and prepare to fly) it will be warm enough to start easily. I use a cheap "milk-house" heater whenever it is 40F or below and one hour of heating is plenty for me (my engine 912uls has the soft-start).
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  7. #7

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    Default Re: 912 engine preheater

    Thanks for the responses.

    The start procedure I use includes turning on the electric pump to make sure it is making pressure and to fill the float bowls if needed.
    I then pull the enrichener with the throttle fully closed and turn over the engine with the ignition off for 5 seconds.
    Then I wait 15 seconds, advance the throttle to a fast idle, engage the starter and then flip both mag switches to give the starter a head start on the mags.
    In warmer weather this works almost flawlessly.
    Go camping at altitude in the Idaho Backcountry where it often gets near freezing at night in June and you sometimes wonder if the starter or sprague will destroy themselves before it starts.
    Once started that day it fires off perfectly.

    Larry, the enrichener seems to getting plenty fuel into the venturi without enrichening with the electric fuel pump on.
    I have learned that too much enrichener and it will act flooded when it finally starts.
    I wish I had your updatedignition system even though your engine starts fine with out the soft start feature.

    Lowell, ever since you gave me the starting routine, it starts great in warm weather but not cold.

    Jim, I also am concerned about the power constantly on for fear of fire.
    in the past it was common procedure to leave a 100 watt bulb going inside the aircraft to keep the avionics warm.
    I am sure the 100 watt bulb is safer than heat strips.
    Maybe using a low amperage circuit breaker than the traditional 20 amp would add some safety in case of a short develops.
    I will experiment, but doubt a 1/2 hour will do much.
    Reiff, the company that makes the pre heaters suggests 3 hours to get 20 degrees temp increase with their 150 watt system and I am only using 100 watts at the time.
    They say these lithium batteries actually crank better if you place a load on them for a few seconds and then wait several seconds.
    Seldom does it freeze here but it sure has the last few weeks.

    I may fly several times a week but for only 30-45 minutes.
    So having an engine that starts simply and does not feel like it is destroying itself makes it a more enjoyable process.
    Maybe I have a problematic starting older 100 hp but it sure runs well once started.
    I am hoping pilots with similar high compression engines would have the answers.
    My goal is to install the Big bore Hi compression kit which will only make the starting more difficult.

    Herman
    Last edited by herman pahls; 12-28-2016 at 01:39 AM.

  8. #8
    Senior Member Norm's Avatar
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    Default Re: 912 engine preheater

    This has morphed into a starting sequence procedure so I have a newbie question.

    Does anyone use a primer on the 912. I am fairly new to 912 operation and I know when I put a primer on my 582 the starting was much easier. Would this work on the bings on the 912 as well as it does on the 582?
    Norm
    Airdrie Ab, Can
    North of Calgary
    Flying SuperFox Model IV

  9. #9
    Senior Member SkySteve's Avatar
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    Default Re: 912 engine preheater

    Norm,
    I have an 80hp 912. I did install a primer and use it for all "first starts" of the day regardless of temps. I prime 5 or 6 pumps, do not use the enricher, pull the throttle out about 1/4", switch mags on and turn the key. It starts every time. Our temps range between 100 F and -20F but I don't fly below about 25F. I do not have an engine heater. My plane is always hangared.
    Steve Wilson
    Huntsville, UT
    Kitfox 85DD
    912A / 3 Blade Taper Tip Warp Drive
    Convertible Nosewheel & Tailwheel
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  10. #10
    Senior Member Norm's Avatar
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    Thumbs up Re: 912 engine preheater

    Thanks Steve Think I will do the same.
    Norm
    Airdrie Ab, Can
    North of Calgary
    Flying SuperFox Model IV

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