Thoughts on Rotax engines?

[Fearless Tower]

Looking for any thoughts and advice on care and feeding of Rotax engines, the 503 in particular.

Would like to hear from anyone with actual experience operating them....not looking for heresay and rumors.



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[N801BH]

Looking for any thoughts and advice on care and feeding of Rotax engines, the 503 in particular.

Would like to hear from anyone with actual experience operating them....not looking for heresay and rumors.



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The motors I build for my race sleds use the 503 /583 /670 series model... They are pretty stout for a 2 stroke, but............

 

[Fearless Tower]

The motors I build for my race sleds use the 503 /583 /670 series model... They are pretty stout for a 2 stroke, but............

And.......What's the but?


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[poadeleted20]

I hate the "clunk" with which the Rotax 912 in my trainee's CTsw stops -- sounds like it seized or something. In addition, my mechanic had a horrible time trying to tune the two carburetors together (anyone who has owned a dual carb MG knows the problem). Other than that, and getting used to the much higher RPM readings (this was an issue for the GO-300 in the Cessna Skylark years ago), it's just another engine as long as you operate it by its book.

Can't speak to any other model.

 

[Geico266]

I hate the "clunk" with which the Rotax 912 in my trainee's CTsw stops -- sounds like it seized or something. In addition, my mechanic had a horrible time trying to tune the two carburetors together (anyone who has owned a dual carb MG knows the problem). Other than that, and getting used to the much higher RPM readings (this was an issue for the GO-300 in the Cessna Skylark years ago), it's just another engine as long as you operate it by its book.

Can't speak to any other model.

The clunk is caused by improper shut down. Try shutting down with the idle set to 2,000 rpm, then pull the throttle all the way back to idle, then click off one mag, then the next. This should all take about 2 -3 seconds. What you are trying to do is lower the rpm from idle to shut down constantly. What is happening is the mass of the prop, gear box, and engine are fighting each other.


Balancing the carbs is not difficult at all. I use a mercury balancer I bought 20 years ago.

 

[Geico266]

503 is a good motor, but not for aircraft. Old school technology, cheap to fly, but it is not a question of if, but when the motor quits.

 

[Fearless Tower]

Try shutting down with the idle set to 2,000 rpm, then pull the throttle all the way back to idle, then click off one mag, then the next.

Are they mags in the same sense as normal aircraft mags?

One airplane I was looking at had a VW engine with auto type distributor.

The Rotax powered one I saw today had switches on the panel labelled right and left mag.



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[poadeleted20]

The clunk is caused by improper shut down.

No, the clunk is caused by the magnets on the gearbox.

 

[bbchien]

The clunk is from the crankshart coming apart. I had the pleasure of that many moons ago in an U/L.

No two stroke Rotaxes for me any more. It was a 503.

 

[wabower]

Whatever causes it makes me cringe when it happens. Sounds like my cheap direct-drive table saw.

 

[Geico266]

No, the clunk is caused by the magnets on the gearbox.

There are no magnets on a CT Rotax 912 gearbox, and they don't cause the clunking you describe. It is caused from prop mass inertia.

 

[Old Geek]

Are they mags in the same sense as normal aircraft mags?

The 912 has a system that Rotax calls magnetos, but they are quite a bit different than normal aircraft mags. There's a rotor and stator similar to a motorcycle alternator, along with inductive pickups. The big windings on the stator generate a voltage used to charge a capacitor. The inductive pickups trigger discharging the capacitor into a coil pack that handles two cylinders. Add more windings, pickups and coil packs until you have 2 independent ignition systems. There is also a clever arrangement of pickups that passively advances the timing at speeds much above idle.

I like the 912 engine alot. A good mechanic can balance the carbs and set the idle in about 20 minutes and I've never needed it done more often than at annual.

As to the 503, it's a 2-stroke and that's enough for me not to like it.

 

[GCA319]

I hate the "clunk" with which the Rotax 912 in my trainee's CTsw stops -- sounds like it seized or something. In addition, my mechanic had a horrible time trying to tune the two carburetors together (anyone who has owned a dual carb MG knows the problem). Other than that, and getting used to the much higher RPM readings (this was an issue for the GO-300 in the Cessna Skylark years ago), it's just another engine as long as you operate it by its book.

Can't speak to any other model.

Glad I'm not the only one who hates that . I've noticed that the plugs have a tendency to foul ALOT around here in the summer (with DA approaching 9-10,000 and no way to manually control the mixture).

 

[Geico266]

No, the clunk is caused by the magnets on the gearbox.

Glad I'm not the only one who hates that . I've noticed that the plugs have a tendency to foul ALOT around here in the summer (with DA approaching 9-10,000 and no way to manually control the mixture).

Are you guys burning car gas or 100ll?

 

[zaitcev]

I think we can all agree that 503 and 912 have little in common. If anything.

Dr. Bruce's testimony is worrisome for me in particular because everyone who's aiming for a legal ultralight in my ultralight club flies those 503s. Most are trike pilots though. Everyone else is registered as E-AB.

On second thought, I met a guy who apparently crashed more ultralights than I have types in my logbook. And he says he's not had even a bone break once. So maybe 503 is ok after all

 

[zaitcev]

I've noticed that the plugs have a tendency to foul ALOT around here in the summer (with DA approaching 9-10,000 and no way to manually control the mixture).

Well, N28GX seems to be doing fine, flying out of SAF. So I dunno, maybe ask who's Michael's mechanic?
-- Pete

 

[GCA319]

Well, N28GX seems to be doing fine, flying out of SAF. So I dunno, maybe ask who's Michael's mechanic?
-- Pete

Michael explained why it does it so often, but I forget his explanation...I see the guy who does all the MX for 8GX from time to time , so maybe I'll ask him. I'm pretty new to the Rotax world, so understanding the inner workings of the 912 has been a bit of a learning curve.

 

[GCA319]

Are you guys burning car gas or 100ll?

Car gas.

 

[CT4ME]

'Pretty sure the 503 is no longer produced... the 582, water cooled, is the only current 2-stroke. Parts for the 503 will be produced for quite a while.
The 912 stops "abruptly" because of the high compression... no spark, no explosion, no turning. Quickly. 'Don't think it is even possible to hand prop a 912.
Someone told me the CPS catalog has a section on Care & Feeding of Rotax 2-strokes.

 

[GCA319]

'Pretty sure the 503 is no longer produced... the 582, water cooled, is the only current 2-stroke. Parts for the 503 will be produced for quite a while.
The 912 stops "abruptly" because of the high compression... no spark, no explosion, no turning. Quickly. 'Don't think it is even possible to hand prop a 912.
Someone told me the CPS catalog has a section on Care & Feeding of Rotax 2-strokes.

It is not. Makes sense now that you explain the reasoning behind the abrupt shut down.

 

[Henning]

Looking for any thoughts and advice on care and feeding of Rotax engines, the 503 in particular.

Would like to hear from anyone with actual experience operating them....not looking for heresay and rumors.



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I only have a bit of experience with the 503 but in general I like it. Reasonably reliable, easy and cheap to work on, parts readily available and makes good power. It's not a 4 stroke so you can't treat it like one, you baby it and you'll regret it, 2 strokes are meant to run. It seems a lot like the old Ski Doo engines which were good. I always use some model airplane fuel into my 2 stroke fuel as it helps keep me from fouling plugs and adds that nitro pop to the exhaust smell that I enjoy, typically I use Bel Ray oil. I used to get a product called DragOn Snowmobile Oil which had the nitro already in it, but I haven't seen it in decades.

 

[Geico266]

Looking for any thoughts and advice on care and feeding of Rotax engines, the 503 in particular.

The 503 uses a single set of points to fire a single ignition. Yep, one spark plug per cylinder. There is an after market kit to go to dual ignition, but you might as well upgrade to the blue head 582.

Here is a link to the CPS (California Power Supply). Rotax 2 Stroke care and feeding articles.

http://www.800-airwolf.com/articles.htm

 

[Geico266]

'Pretty sure the 503 is no longer produced... the 582, water cooled, is the only current 2-stroke. Parts for the 503 will be produced for quite a while.
The 912 stops "abruptly" because of the high compression... no spark, no explosion, no turning. Quickly. 'Don't think it is even possible to hand prop a 912. .

The shut down "clunk" has many contributing factors. The high compression is only a factor of several. Prop inertia, gear box drag, slipper clutch drag / movement, engine compression drag all fighting each other on shut down. Lowering the rpm by dropping one mag, then the other for a smoother shutdown will help. Make sure the carbs are balanced and engine idle is able to be reduced to 1400 RPM. Don't idle there, this is just for shut down. ,

You are correct, the 912 cannot be hand propped. The Duccati ignitions do not fire under 200 rpm.

If you have kickback at start up of any kind you need to fix it. Start with balancing the carbs and resetting the idle speed, then add the "soft start" ignition module. Allowing the engine to kick back will damage the $2000 ( no labor for near engine tear down) sprag clutch. Don't ask me how I know.

I have over 2,100 hours flying in front of or behind Rotax engines for the last 15 years. Owned and sold a dozen aircraft with these engines and rebuilt or replaced several of them to keep them flying.

 

[Capt. Geoffrey Thorpe]

. 'Don't think it is even possible to hand prop a 912.

You are correct, the 912 cannot be hand propped. The Duccati ignitions do not fire under 200 rpm.

Where do you guys get your information?

Hand propping a 912 is easy.

Even in the cold. Fires right up.

Usually on the first flip.

I've done it many times.

Tie it down. Close the throttle. Tighten the friction lock to make sure it stays closed (mine, like most, is spring loaded to open). Turn on the mags. Make sure the throttle is closed. Pull the choke. Check to see that the throttle is closed and the friction lock is tight. Walk around front. Grab the prop about in the middle. Flip. Walk back around to close the choke. Make sure the friction lock on the throttle is tight. Untie and get in. Taxi away.

Piece of cake.

That's 200 engine rpm, not prop rpm. The gear reduction spins the engine pretty fast when you flip the prop. You don't have to be a gorilla. Just grab the prop in the middle and flip.

 

[zaitcev]

Michael explained why it does it so often, but I forget his explanation...

My point was that although Rotax requires oil changes at 1/2 interval with using 100LL, Michael never reported any unusual fouling on his 912. Note that Rotax self-adjusts for altitude, but it has an initial seating that may be too rich (while proportionally adjusted for altitude).

In any case, this is far from the issue of 503, which uses a gas-oil mix for fuel.

BTW, in case you didn't know, in addition to SAF, Holstein also sells alcohol-free gas near 0E0. I found out that a bunch of people at that field use it. Unfortunately, we still don't have an FBO selling mogas right on the field, and again the difference between mogas and autogas... is a looming mystery.

 

[Geico266]

Where do you guys get your information?

Hand propping a 912 is easy.

Even in the cold. Fires right up.

Usually on the first flip.

I've done it many times.

Tie it down. Close the throttle. Tighten the friction lock to make sure it stays closed (mine, like most, is spring loaded to open). Turn on the mags. Make sure the throttle is closed. Pull the choke. Check to see that the throttle is closed and the friction lock is tight. Walk around front. Grab the prop about in the middle. Flip. Walk back around to close the choke. Make sure the friction lock on the throttle is tight. Untie and get in. Taxi away.

Piece of cake.

That's 200 engine rpm, not prop rpm. The gear reduction spins the engine pretty fast when you flip the prop. You don't have to be a gorilla. Just grab the prop in the middle and flip.

I stand corrected. Since I always had 912s with 3 bladed props I never tried it, and none of my buddies did either. While you might be able to hand prop a 912 ( 80 hp) the 912S (100 hp) certainly is "no piece of cake". In either case Rotax recommends NOT hand propping any 912.

How many fingers you have left?

 

[KSCessnaDriver]

One of the aircraft I regularly fly is powered by 2 912-F3's, with a reversible prop. I love the power it gives, but the downside is, the gearbox does add some noise to the equation.

 

[CT4ME]

I stand corrected...too, maybe. Apparently you CAN hand prop the 912, although everything written says NO. Of the 18,800 Google hits under "hand prop rotax 912" 99% say it can't or shouldn't be done. Some of those hits are about accidents from people trying to hand prop the 912. I think they get help tying their shoes now.
Apparently, there may be a notable difference between the 80HP version and the 100HP version. With the high compression, and 3 blades, you won't find me trying.

BTW... rotax-owner.com has lots of info on Rotax

 

[brcase]

I stand corrected...too, maybe. Apparently you CAN hand prop the 912, although everything written says NO. Of the 18,800 Google hits under "hand prop rotax 912" 99% say it can't or shouldn't be done. Some of those hits are about accidents from people trying to hand prop the 912. I think they get help tying their shoes now.
Apparently, there may be a notable difference between the 80HP version and the 100HP version. With the high compression, and 3 blades, you won't find me trying.

Someone forgot to tell me it couldn't be done. So when the pilot I was flying with inadvertently ran the battery down I hand propped it.

I wouldn't recommend it as a normal procedure but it does work when done properly.

Brian

PS as for hand propping accidents did they have an accident because the were hand propping or was it because the were not following the Hand Propping rules? Most things aviation are dangerous when the rules are not followed.

 

[Capt. Geoffrey Thorpe]

I stand corrected...too, maybe. Apparently you CAN hand prop the 912, although everything written says NO. Of the 18,800 Google hits under "hand prop rotax 912" 99% say it can't or shouldn't be done. Some of those hits are about accidents from people trying to hand prop the 912. I think they get help tying their shoes now.
Apparently, there may be a notable difference between the 80HP version and the 100HP version. With the high compression, and 3 blades, you won't find me trying.

BTW... rotax-owner.com has lots of info on Rotax

First "hit" on the search.
"If you can actually turn the prop fast enough to excite the ignition, you will surely loose a hand as the next blade comes around."

Clueless.

Second, third,fourth, fifth hit talking about checking the oil (people don't seem to realize that the 912 does not have an "impulse" on the magneto)

sixth "Would not try to hand prop a Rotax 912S. Much higher compression than the 912 or the 914"

Possibly.

8th is this thread

I'm up to page 5 on the list and not a single accident, much less someone having a hard time tying their shoes. Can you be more specific?

 

[CT4ME]

Capt. Geoff...
Your posting is just about the only thing I've found that said it can be done. Do you have a 100HP? Please set the record straight and post a video. Quite frankly, I WANT to see it can be done, as the thought of being stranded on a small dirt 'strip on the Baja has always haunted me.

 

[BurtM]

Balancing the carbs is not difficult at all. I use a mercury balancer I bought 20 years ago.

Well, that's encouraging!

Knowing that we need the same manometer that we used to balance the old Honda Scrambler 305 motors is really, I don't know, awesome, or something.

What's next? Spark advance on the left of the wheel and throttle on the right just like Grandpa's Farmall?

 

[Henning]

Well, that's encouraging!

Knowing that we need the same manometer that we used to balance the old Honda Scrambler 305 motors is really, I don't know, awesome, or something.

What's next? Spark advance on the left of the wheel and throttle on the right just like Grandpa's Farmall?

Yep, same one we used on MGs and and everything else, simple stuff. I wish I could tune my advance to meet my mixture in flight... FADEC is interesting, I wonder if Continental's system allows the ability for laptop monitoring and fine tuning....

 

[Capt. Geoffrey Thorpe]

Capt. Geoff...
Your posting is just about the only thing I've found that said it can be done. Do you have a 100HP? Please set the record straight and post a video. Quite frankly, I WANT to see it can be done, as the thought of being stranded on a small dirt 'strip on the Baja has always haunted me.

No, I don't have the 100 HP. And, I have never taken a video of my 80 HP. But, if you can be patient I will (it may be a couple weeks - I've got a pile of things going on right now).

But, why not try it yourself and report back here?

Exactly three things can happen.

1) It will start up. (You did tie it down first and make sure the friction lock was tight, right?)
2) It will kick back and your hand will slip off the prop (assuming you didn't do something foolish like wrap your fingers around the back of the blade - any engine can kick back)
3) It will not start and you will wear yourself out trying

What's the downside?

Questions:
Does it start with the starter?
How fast does the starter spin the prop? I assume it's not much faster than my 80hp.
Does the starter do something magic other than turn the prop no faster than you can flip it by hand? On my ride the starter seems to be a bit anemic - sometimes it comes to a halt on the first try when you come up on compression.

The things I've found different about the Rotax are that the throttle is spring loaded to open and with the gear reduction the prop does not always stop at a convenient to flip spot - I turn it slowly with the mags off if necessary (just like when you turn it to check the oil). Without an impulse mag it is a lot less likely to fire when turned slowly than most aircraft engines.

 

[lr60plt]

I operated a Rotax 503 out of an airport in the middle of west palm beach for a while. It seems it IS possible to have a semi-reliable one, its just up to you to do things correctly. Make sure the parts on it are 100%, maintenance by the book, inspect it a LOT and most importantly have a properly set up fuel delivery system. It seems most of the 503 failures ive read about are due to fuel starvation.

When i bought my airplane with the 503 in it....it looked like it was only a matter of time before the fuel system failed. I did a lot of research and re-did the entire thing. People put all sorts of things in line such as hand pumps and whatnot....they all contribute to failures. The fuel system needs to be as simple as possible, with the very least items to fail and those items left need to be of high quality (line/pickups/couplers...etc) and inspected or replaced often (like replacing ALL of the fuel line once a year with the condition inspection). You should even consider draining and replacing the fuel in the tank every month or two.

As said 503's are simple...but still need to be looked after. The fuel delivery sys (in my opinion) is the #1 item that can make or break the chances of that prop continuing to swing. Mine never quit on me.

 

[Fearless Tower]

I operated a Rotax 503 out of an airport in the middle of west palm beach for a while. It seems it IS possible to have a semi-reliable one, its just up to you to do things correctly. Make sure the parts on it are 100%, maintenance by the book, inspect it a LOT and most importantly have a properly set up fuel delivery system. It seems most of the 503 failures ive read about are due to fuel starvation.

When i bought my airplane with the 503 in it....it looked like it was only a matter of time before the fuel system failed. I did a lot of research and re-did the entire thing. People put all sorts of things in line such as hand pumps and whatnot....they all contribute to failures. The fuel system needs to be as simple as possible, with the very least items to fail and those items left need to be of high quality (line/pickups/couplers...etc) and inspected or replaced often (like replacing ALL of the fuel line once a year with the condition inspection). You should even consider draining and replacing the fuel in the tank every month or two.

As said 503's are simple...but still need to be looked after. The fuel delivery sys (in my opinion) is the #1 item that can make or break the chances of that prop continuing to swing. Mine never quit on me.

Thanks, that seems to jive with a lot of the research I have dug up in the past few days. Another fuel related problem it seems comes from making a lot of throttle changes or rapid throttle changes that can create either too lean or too rich of a mixture and kill the engine.

What kind of fuel burn were you seeing in the 503. I found one spec sheet that said 6.8 gph which kind of surprised me.....particularly since the plane I am looking at only has an 8 gallon tank.


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[Henning]

Thanks, that seems to jive with a lot of the research I have dug up in the past few days. Another fuel related problem it seems comes from making a lot of throttle changes or rapid throttle changes that can create either too lean or too rich of a mixture and kill the engine.

What kind of fuel burn were you seeing in the 503. I found one spec sheet that said 6.8 gph which kind of surprised me.....particularly since the plane I am looking at only has an 8 gallon tank.

That has always been the big detraction to 2strokes, they are fuel hogs, but unless you run WOT all the time you should see some better.

 

[Stevel]

The 503 uses a single set of points to fire a single ignition. Yep, one spark plug per cylinder. There is an after market kit to go to dual ignition, but you might as well upgrade to the blue head 582.

Here is a link to the CPS (California Power Supply). Rotax 2 Stroke care and feeding articles.

http://www.800-airwolf.com/articles.htm

Geico, your information has gotten stale.

I'm too lazy to look uo the year, but I know that the 503 switched to Ducati dual ignition for several years before they stopped making them at all. I have two 503 powered Flightstar Spyders and they are both dual ignition.

 

[Fearless Tower]

Geico, your information has gotten stale.

I'm too lazy to look uo the year, but I know that the 503 switched to Ducati dual ignition for several years before they stopped making them at all. I have two 503 powered Flightstar Spyders and they are both dual ignition.

I would agree. The airplane I am looking at clearly has the dual ignition.


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[Dan Thomas]

My point was that although Rotax requires oil changes at 1/2 interval with using 100LL, Michael never reported any unusual fouling on his 912. Note that Rotax self-adjusts for altitude, but it has an initial seating that may be too rich (while proportionally adjusted for altitude).

In any case, this is far from the issue of 503, which uses a gas-oil mix for fuel.

Because the only commonality between the 503 and 912 is the name on the engine. The 912 is a four-stroke, the 503 a two-stroke.

The automatic mixture adjustment will be sensitive to altitude, but higher temperatures will decrease the density of the air without any pressure reduction. The mix will get rich when temps are above standard values.

dan