My 503 does that as well if you just drop the throttle back to idle too fast, internals have been inspected and all is good. Also, I have found that you need to be smooth on the decrease in throttle. also, some 503s don't like to idle at 2000 and 2150 seems to be perfect. Very informative video for folks that don't know what this is.
It's a learning experience for me. The idle is set at about 2150 - 2200 on my engine, and it too goes into that rattle only after dropping throttle fast from a higher RPM. So, going forward, I will have to be smooth and a bit slower when pulling back to full idle on the engine. Glad you liked this short video. Cheers.
I have lost 4 good friends the result of a rotax 2 stroke failure! I hate them with a passion! It's not "If it fails" It's when? Little or no warning, Bang, Stoped!
Yes, there are also 4 strokes placarded against operating at certain rpm ranges, probably due to other issues but you do have to watch out for these things.
I remember hearing of 4 stroking with regards to a 2 stroke engine. But I've never seen it happen....till now. The idle on the engine is set to 2200 RPM, so that's good. So I just have to make sure I don't slam the throttle back to idle, and do it smoothly and slow.
What you're hearing is the piston rocking or piston slap. Even on a piston that is within the correct tolerance you will hear this. Maybe slightly less but it will still be there. An engine accelerates for a very small time then decelerates the rest of the way around. As it accelerates it flexes the belt or will call it loads the belt or the B box knuckle joint or the C or E gearbox hardy disc. As it is un-flexing it it causes the pistons to rock causing the rocking noise. As the rpm's increase there is less TIME between the accretion & decelerations , so the piston does not rock as much. Just take a 503 prop & rock it back & forth . You will hear that slap. I recommend setting your idle at whatever rpm thats needed to keep from burning up your brakes while taxing. As soon as your stop increase the idle to 2300 + rpm's. Rotax Rick
I think the four-stroking explanation makes more sense. My 582 does the same thing, and it reliably transitions out of this regime, suddenly, at 2,000-RPM. Exhaust gas timing issues that happen at a certain frequency seem to be a more likely cause, if it was mechanical slapping it should transition more gradually. At least that's my $.02. I would also think piston slap that is that loud would bust up the skirts and score the wall in pretty short order. Either way, it is a hassle for a plane on floats since you can't really set the power low enough to power sail.
So what kind of damage does the 'death rattle' cause? All my motorcycle 2 strokes had that stumble at idle but it was never a problem. I idle my 582 over 2k just because I don’t like the torque reversals on the redrive.
It is hard on the engine, and can cause damage to the crank, connecting rods and even the engine case. It occurs because of a phenomenon called “four stroking”. At low speeds the engine does not have enough inertia to overcome the compression of next pistons compression stroke PLUS there is a late returning pressure wave in the exhaust. The intake timing and exhaust timing are all messed up. Therefore the engine slows down and the cylinder fires before there is adequate fuel transferred to that cylinder. It does not occur in four strokes because there are valves that control fuel/alr and exhaust. The only thing that fixes the death rattle is rpm. That’s why Rotax does not want you to idle the engine below 2000 rpm.
LOL! That's a special order prop from Aircraft Spruce, used primarily for time travel and dimensional shifting. A real bargain, and allows superluminal velocities when configured properly. I'll post a link to it, but will have to date it 2048 as they are out of stock till then.
So what was it??.... A Big End or Small End Bearing. I Imagine a 4 Stroke Rotax Engine with a Big End Bearing Fail, you would also experience Low Oil Pressure.
What is the problem? If Rotax recommends idle rpm above 2,000, why run at less? Read your installation manual. Never go to idle unless the runway is made. You could also adjust the throttle idle stop.
The idle is set at 2200 RPM, which is what the Rotax service center recommends. However, when throttling back to idle, the engine can at times enter this state if the throttle is reduced too fast. The correct solution, is to reduce smoothly to near idle, let it stabilize for a few seconds, then slowly drop to full idle.
Also make sure the throttle cable is as straight as possible if needed, big curves, no sharp bends. Idle adjustment is on the carbs with a spring loaded tapered screw, it should not drop to below recommended rpm, check the choke is closing completely, and air filters are clean and oiled. If it were me I would bring the idle up so it never gets too low. Check both carbs are set exactly alike too.
LOL The "death rattle" is a term coined by people who own these engines. Sounds dramatic, and if you let the engine idle below 2000 RPM for an extended time, it can cause damage to the engine. So....just don't let it idle that low and it's all good. The manufacturers specs clearly state that the engine RPM at idle must be above 2000. I did not know this, so I called Rotax, and they brought me up to speed on this engines personality.
Lots of good news info …Thank you!
You're welcome.
My 503 does that as well if you just drop the throttle back to idle too fast, internals have been inspected and all is good. Also, I have found that you need to be smooth on the decrease in throttle. also, some 503s don't like to idle at 2000 and 2150 seems to be perfect. Very informative video for folks that don't know what this is.
It's a learning experience for me. The idle is set at about 2150 - 2200 on my engine, and it too goes into that rattle only after dropping throttle fast from a higher RPM. So, going forward, I will have to be smooth and a bit slower when pulling back to full idle on the engine. Glad you liked this short video. Cheers.
Very informative video. Thanks for taking the time to make it.
Glad it was helpful!
I have lost 4 good friends the result of a rotax 2 stroke failure! I hate them with a passion! It's not "If it fails" It's when? Little or no warning, Bang, Stoped!
Yes, there are also 4 strokes placarded against operating at certain rpm ranges, probably due to other issues but you do have to watch out for these things.
I remember hearing of 4 stroking with regards to a 2 stroke engine. But I've never seen it happen....till now. The idle on the engine is set to 2200 RPM, so that's good. So I just have to make sure I don't slam the throttle back to idle, and do it smoothly and slow.
What you're hearing is the piston rocking or piston slap. Even on a piston that is within the correct tolerance you will hear this. Maybe slightly less but it will still be there. An engine accelerates for a very small time then decelerates the rest of the way around. As it accelerates it flexes the belt or will call it loads the belt or the B box knuckle joint or the C or E gearbox hardy disc. As it is un-flexing it it causes the pistons to rock causing the rocking noise. As the rpm's increase there is less TIME between the accretion & decelerations , so the piston does not rock as much. Just take a 503 prop & rock it back & forth . You will hear that slap. I recommend setting your idle at whatever rpm thats needed to keep from burning up your brakes while taxing. As soon as your stop increase the idle to 2300 + rpm's. Rotax Rick
I think the four-stroking explanation makes more sense. My 582 does the same thing, and it reliably transitions out of this regime, suddenly, at 2,000-RPM. Exhaust gas timing issues that happen at a certain frequency seem to be a more likely cause, if it was mechanical slapping it should transition more gradually. At least that's my $.02. I would also think piston slap that is that loud would bust up the skirts and score the wall in pretty short order.
Either way, it is a hassle for a plane on floats since you can't really set the power low enough to power sail.
I always thought it was gearbox chatter caused by worn compression washers.
Sounds lean, put a bigger pilot jet in. Ajust slow speed air screw.
So what kind of damage does the 'death rattle' cause? All my motorcycle 2 strokes had that stumble at idle but it was never a problem. I idle my 582 over 2k just because I don’t like the torque reversals on the redrive.
It is hard on the engine, and can cause damage to the crank, connecting rods and even the engine case. It occurs because of a phenomenon called “four stroking”. At low speeds the engine does not have enough inertia to overcome the compression of next pistons compression stroke PLUS there is a late returning pressure wave in the exhaust. The intake timing and exhaust timing are all messed up.
Therefore the engine slows down and the cylinder fires before there is adequate fuel transferred to that cylinder. It does not occur in four strokes because there are valves that control fuel/alr and exhaust.
The only thing that fixes the death rattle is rpm. That’s why Rotax does not want you to idle the engine below 2000 rpm.
its not a problem unique to Rotax, my Hirth 3203 will make the same noise if you unload the engine too quickly.
Good to know. I can't remember it ever happening on my snowmobiles, but then again, they have a much larger flywheel to keep the inertia up.
It’s because you have a shape-shifting prop, that reverses direction of rotation 😂🤣.
LOL! That's a special order prop from Aircraft Spruce, used primarily for time travel and dimensional shifting. A real bargain, and allows superluminal velocities when configured properly. I'll post a link to it, but will have to date it 2048 as they are out of stock till then.
So what was it??.... A Big End or Small End Bearing.
I Imagine a 4 Stroke Rotax Engine with a Big End Bearing Fail, you would also experience Low Oil Pressure.
Could not having the air cleaners installed be a factor?
No. I asked that question when I spoke to the Rotax rep. Good question though.
What is the problem? If Rotax recommends idle rpm above 2,000, why run at less? Read your installation manual. Never go to idle unless the runway is made. You could also adjust the throttle idle stop.
The idle is set at 2200 RPM, which is what the Rotax service center recommends. However, when throttling back to idle, the engine can at times enter this state if the throttle is reduced too fast. The correct solution, is to reduce smoothly to near idle, let it stabilize for a few seconds, then slowly drop to full idle.
Also make sure the throttle cable is as straight as possible if needed, big curves, no sharp bends. Idle adjustment is on the carbs with a spring loaded tapered screw, it should not drop to below recommended rpm, check the choke is closing completely, and air filters are clean and oiled. If it were me I would bring the idle up so it never gets too low. Check both carbs are set exactly alike too.
Good by Rotex
Wha use a two stroke engine in the first place ?
Power to weight ratio is much higher than a 4 stroke.
Who sent you the email?
What does Rotax say?
Bob from Small Engine Services in B.C. He is the Rotax service dealer for Canada. A very trusted and knowledgeable person.
And your going to get 10,000 feet off the ground, lol maybe it you that will have death rattle
LOL The "death rattle" is a term coined by people who own these engines. Sounds dramatic, and if you let the engine idle below 2000 RPM for an extended time, it can cause damage to the engine. So....just don't let it idle that low and it's all good. The manufacturers specs clearly state that the engine RPM at idle must be above 2000. I did not know this, so I called Rotax, and they brought me up to speed on this engines personality.
Or just fly wit 4 stokes.🤓