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Thread: Mounting 618 and 670 to KF-IV

  1. #1
    rdooley79's Avatar
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    Default Mounting 618 and 670 to KF-IV

    I've been working on mounting the 618 to the Kitfox.

    If you have a 582 you might consider swapping out to one of the larger Rotax 2 cycle engines. Here are the things that I've found doing the swap on my plane.

    First the mag end bell housing is slightly longer than the 582. Also the total height is a little taller. This introduces the problem of needing to shim the engine up to clear the bell housing but not hitting the spark plugs on the cowling.

    Step 1, shim the engine mount further from the firewall.
    -I used four AN washers between the mount and the firewall this was perfect and allowed the engine to slip in snug but not tight!


    Step 2, shim the engine up with found 1/4 inch thick pieces of aluminum or steel. If using aluminum you'll need to use a washer so as to not have the aluminum only bearing the engine weight against the steel engine mount. Over time the aluminum being soft will deform without a washer to provide a harder metal contact point. I used a large washer to spread the load over the aluminum shim evenly. I also added a second washer just to make the bell housing fit with a little more room. You'll need to get longer bolts to make this all work as a result. You can use the short bolts to get everything lined up and then swap them out so you don't mess up the threads in the process.


    Step 3, mount the exhaust, (I'm on this step now and will provide pics with the exhaust hung.


    Step 4, hook up to gauges, throttle, choke, electrical and radiator. Everything is the same as your 582. Mount the prop on the gearbox.

    Step 5, Run her up and set the prop pitch for max static RPM of 6200. This should be a good climb and cruise as well as give you buffer if full power and not be right at red line. Red line on the 618 is 6800. I don't like to go over 6500.
    Kitfox IV - 1200 (1994) #1830
    Rotax 912
    Grove Gear, Wheels, Brakes
    22" Desser Tundra Tires

  2. #2
    JimS's Avatar
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    Default Re: Mounting 618 to KFIV

    I wish you great amounts of good fortune with your 618. Your IV should perform really well with it. That being said.... we have in our flying group one of Bombardiers top R&D guys. He had a 503 in his Chinook that he replaced with a 618 as it was on floats. He couldn't keep the RAVE valves from breaking. Fought with it about 3 years and finally went back to a 582 for reliability. Not trying to scare you off ...just keep a close eye on them.

    JimS

  3. #3

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    Default Re: Mounting 618 to KFIV

    My 618 is a monster compared to my friends 582. I love it.

    Be sure your rave valves are the new steel option rather than the problem ridden aluminum ones.

  4. #4
    rdooley79's Avatar
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    Default Re: Mounting 618 to KFIV

    yep rave valves are the new steel ones.

    Rotax Rick built this 618. His running guidelines are very critical to getting the temps up quickly to heat the engine evenly.

    In the 8 hours I've ran this engine on my trike, it's AMAZING!

    The issues with power valves seem to be related to carbon, temps and therefore what mixture and oil is being run. Rotax Rick only wants Amsoil Interceptor specifically made for "power valve" in these engines. There is no carb build up at all in my recent inspection. pre-mix 40:1, no injection systems. Also the needle, main jet are set a little differently than "stock". So far it's running perfect temps.

    From the feedback on the 670 if it's fed this way, you don't have RAVE valve issues.

    I'll let you all know how it goes. Incidently there is a 670 getting built in the next couple weeks that will quickly go in to the KF. The 618 is going back on the trike. I hate having BOTH planes down. been over a month since I flew!

    Thanks for the best wishes guys! I'll keep this info coming.
    Kitfox IV - 1200 (1994) #1830
    Rotax 912
    Grove Gear, Wheels, Brakes
    22" Desser Tundra Tires

  5. #5
    rdooley79's Avatar
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    Default Re: Mounting 618 to KFIV

    Quote Originally Posted by JimS View Post
    I wish you great amounts of good fortune with your 618. Your IV should perform really well with it.
    What would happen when the RAVE valves broke?
    Kitfox IV - 1200 (1994) #1830
    Rotax 912
    Grove Gear, Wheels, Brakes
    22" Desser Tundra Tires

  6. #6

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    Default Re: Mounting 618 to KFIV

    Perfect. RR built mine as well.

  7. #7
    JimS's Avatar
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    Default Re: Mounting 618 to KFIV

    Quote Originally Posted by rdooley79 View Post
    What would happen when the RAVE valves broke?
    From what I understand, significant power loss, not complete but a lot.
    Jims

  8. #8

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    Default Re: Mounting 618 to KFIV

    I had one of the old aluminum ones break and fall into the cylinder. My piston was quite beaten up, but i never noticed any change in performance. It wasnt until I pulled off the head at Rotax Rick's shop that we noticed the problem.

    I know my experience may not be the norm, but it sure gave me confidence in these little motors.

  9. #9
    rdooley79's Avatar
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    Default Re: Mounting 618 to KFIV

    Now that is good info. I know Rick has made a point to use the steel ones since I got the 618.

    On a side note. I shipped off the old 582 to Rotax Rick this morning. He's going to use all the parts from it to build a 670 and keep the remaining parts as partial payment towards the 670.
    He offers a head machined from the stock 670 head. It has the recirculator port on the top and dual plugs just like the Blue Head. But for half the price.
    This baby will put out about 90hp with only about 10lbs extra weight over the 582.

    I'd like a 912 motor but would constitute an entire FWF swap along with all the accessories. That's a ton of money and time for a heavier motor and more cost. But 4 cycle is very nice.

    TBO on a 670 is 450hours and is supposed to burn about 3.5-4gph.

    I'll definately keep the info coming for anyone who might be interested in going to a larger Rotax 2 cycle motor.
    Kitfox IV - 1200 (1994) #1830
    Rotax 912
    Grove Gear, Wheels, Brakes
    22" Desser Tundra Tires

  10. #10
    JimS's Avatar
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    Default Re: Mounting 618 to KFIV

    How's your 618/670 running?

    JimS

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