What to expect for the Rotax 447

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flyboy67109

Well-Known Member
I have a question about the Rotax 447. First, what should I expect for fuel consumption. I was seeing on several sites that they say it's 5.5 gal/hr. That seemed really high as the Cessna 150 burns 6 gal/hr with an engine almost twice as big. I would thing it should be <3 gal/hr. Those of you that have it, what do you usually burn?

Second, what is a fair price for the Rotax 447. I've seen prices range from $1300 rebuilt to almost$3k new. Are there other options I should consider such as motor cycle engines that would be more cost effecient?

Finally, how similar to small engines are these? I've rebuilt Briggs and Stratton engines without any trouble from the little 1.5 hp lawn mower to the 10hp tiller. But we're talking going fro a 1 cylinder to a 2 cylinder engine with an extra spark on each. I've also rebuilt a 78 Toyota Corolla some time ago. Is the Rotax something I can work on or will I need to have it sent in to a specialist to work on each time a coughs?

Lyle

wally

Well-Known Member
Hi, I don't know much about the rotax but I have heard that replacing the rod bearings at the crank end is a must-do item at the factory recommended time. If not, it will "spontaniously dissemble itself" sometime shortly beyond that time.

Lyle

Dana

Super Moderator
Staff member
I have no direct experience with the 447 but I get 3.3 gph at cruise with the 35hp Cuyuna so it doesn't seem out of line... 2-stroke engines are a lot less efficient than 4-strokes.

As for working on it, these are pretty simple engines; you shouldn't have much trouble. The two piece crankshaft is one thing, another critical thing that doesn't apply to a 4-stroke B&S is the crankcase sealing (case gaskets and shaft seals must not leak or you fry your engine).

-Dana

Thoughts on the bailout: Back in 1990, the Government seized the Mustang Ranch (a legal Nevada brothel) for tax evasion and, as required by law, tried to run it. They failed and it closed. Now, we are trusting the economy of our Country and 850+ Billion Dollars to a pack of nitwits who couldn't make money running a *****house and selling booze.

George Sychrovsky

Banned
Two strokes burn 0.1 gal per hour per hp, for 447 (40 hp) using 75% cruise power as a bench mark that’s 3 gal per hour.

Well-Known Member
OK, my comments are based on 500 hours or so experience with 447s.

First, the 447 is a very reliable engine. I've never even heard of a crankshaft failure on a 447. I think any concern about big end bearings is misplaced. The 447 crank is essentially the same as the 503 crank but is less stressed. Steve Beaty reports that he has run a 447 over 1200 hours without ever touching the inside of the engine. The Rotax factory does not approve rebuilding crankshafts...they only sell new cranks.

Second, all the 447s I owned would burn between 2.5 and 3 gal/hr at 5300-5500 rpms.

They are easy to work on, but require a couple of special tools to pull the flywheel and front gear if needed.

Charlie

flyboy67109

Well-Known Member
Thanks, Charlie. That's good news. I don't even have the plans yet so getting the engine is still a ways off.

Double Eagle

Well-Known Member
How can you tell if the crankshaft need replacing in the 447? Can you take measurements?

greywuuf

Active Member
first let me qualify this by saying I have never worked on a Rotax 447 ( at least an Aircraft rated one) but if it is anything like every other Rotax ( and the air cooled 447 that they used in the snowmobile line in the early 80's) and most two stroke engines in the world if is not a two piece crank. they may sell two seperate assemblies as replacement parts but it has more than two pieces. It is a roller bearing crank as compared to a single piece plain bearing crank that most people are familiar with. The only way to replace the main ( or lower rod bearings) it to press the pieces apart using a hydraulic press and "special tooling" an assesment can be made of the radial and axil play in the bearing without dis assembly but you can not measure it in the traditional sense. I will be back here as soon as I can with a link to a very good picture from another forum shortly.

Dan

greywuuf

Active Member
here is a link to a good picture of the main parts of the 447 over on rotarywingforums
Gil's Hornet build. - Page 5 - Rotary Wing Forum
notice the crank apears to be several round chunks of iron with hardened steel pins in between (because it is ) the pins are pressed into the "cheeks" or flywheels ( the iron parts ) with somtimes as much as 20 tons showing on your press gauge.

Dan

Double Eagle

Well-Known Member
Dan thanks for the information. I wonder if any one knows what to look for, when you have the engine down for seals and gaskets? I was given an engine with unknown hours, but it looks nice and clean from the outside.

Gil

greywuuf

Active Member
I know what I look at on any two stroke I tear down, but since I am not aviation two stroke experienced ( and I am constantly told its differant) and the fact that I dont know how to illistrate what I mean by "general condition" and such I should refrain from giving any advice on that. I wil lhowever say that two strokes are not very similar to 4 stroke and will recomend that you have someone more experienced with them give it a look see. It has been mentioned before that the crankcase integrety plays a vital role in the engine operation, IE: gaskets and seals to include the sealant between the case halves and between each cylinder have to be good, otherwise you WILL burn down the engine (runs lean) it also can make them very hard to start and hard to jet etc.

Dang where is my spell check, the more I look at several of these words the more sure I am that I have corrected them enough to be certain they are spelled incorrectly.

Dan

one thing you can do to ease your mind about not getting a "bad" engine is to look over the internals and make sure it shows no sign of earlier explosions, no gouging of the internal surface of the case, rod ends are not horribly discolored ( blued from heat ) and that all of the bearings turn freely and are not "crunchy" or noisy ( roller bearing that are clean and realatively dry will be noisy and even bad ones can be quieted for hand inspection with heavy oil, thus the experience thing ....so we are looking for normal noise) also check that the main bearings have not spun in the case ( dont know how common that is in the rotax line but is a big problem with high HP sleds ) you have to split the case to do this. I dont know how far you want to tear into this thing. The first couple of things I mentioned can be done by just pulling the jugs. I would get a manual or an experienced freind to help you look it over though before you just randomly took it all apart to see..... unless you plan on completely stripping it down anyway then it cant hurt to just tear it down and clean it all up good and inspect it and see if anything looks amiss. if you happen across some other two stroke engine at a garage sale or ?? it might be helpful to take that apart and look at how it differs from the 4 strokes you are used to.There is nothing magic inside them just differant.

if it does not exhibit any of these big problems then it can be used (maybe not as is but you know that it can work )

Double Eagle

Well-Known Member
Will the 447 spin a 72" diamenter prop OK?

Dana

Super Moderator
Staff member
Will the 447 spin a 72" diamenter prop OK?
It all depends on the redrive ratio...

Dana

Silence is golden, but duct tape is silver...

Double Eagle

Well-Known Member
I have a 2.58 gear box. I want to build a Lee Miranda if I can find some more information on one. Will it really fly?