# Rotax 582 Alternative Possibility

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#### Armilite

##### Well-Known Member
Although I understand your displacement/7cc argument, the 582 is rated for 64 HP. A 600R E-TEC is rated for 125 HP. Part of that is increased RPM, which goes to greater longevity if you're only running them at 6500 RPM, but part of that is much, much better combustion efficiency.

The principal big game changers for two-stroke engines have been direct injection, HVOF ceramic coatings and electronic ignition and injection control, which benefit from big improvements in computer power in the 30 years since the 582 was introduced.

The 600R and 850 E-TEC are purported by snowmobilers to have much better longevity than their predecessors and competitors. If you go out to buy a new Skidoo, they're upgrade options from the stock 4-strokes. (You can buy one off eBay used.)

Other improvements in the overall design over previous generations include the mono-block cylinders, an electronically-controlled three-position exhaust valve, more accurate balancing, integrated electric start, and much higher combustion efficiency. The 600R and 850 E-TEC actually run clean enough to pass California's emissions standards.

So yeah, if you plugged up the injectors and stuck new heads and a carburetor on a 600R, you could downgrade it to only a little better than what a 582 produces, but it would still be more reliable. I hope nobody would try to do that.
===========================

First you have to understand a 582UL is the same Core Engine as a Skidoo 580/582/583 which in a Sled is rated 97hp@7750rpm with a Tuned Pipe. Your 600 eTec is 116.7hp@8100rpm! You can see at 6500rpm it is 68.2hp@6500rpm!

Longevity on any Engine depends on WHO is Maintaining it, Flying or Riding behind it, and the Oil & Octane Gas they are using!

Avg Skidoo would fail around 3000 miles, Avg Trail Speed is 35mph, 3000/35 = 85.7 hrs. Rotax 582UL's have a 300hr TBO. E-Tec's Fail around 4000 miles. 4000/35 = 114.2 hrs! I got 6 Sleds, I bought all used. All have around 3200-3600 miles today.

(1) 1995 Yamaha Vmax 600 Never been touched.
(2) 1994 Yamaha Vmax 600 Had a New Base Gasket replaced recently. Replaced Pistons when I got it account guy had change the Jetting for the Mountains and never changed it back an burned a Hole in one Piston.
(3) 1998 Skidoo 670 never been touched!
(4) 1993 Arctic Cat 550 EXT, New Exhaust Gaskets.
(5) 1972 Skidoo 292 TNT my Vintage Racer.
(6) 1976 Arctic Cat Jag 2000 I got given to me for free, the guy had a Seizure.

I got probably 19 Skidoo Engines, some Singles and some Twins, and (1) JLO Single, most are complete Engines that all Run. A few need Carbs. Rotax Engines from the 70's, 80's and 90's. The JLO is the oldest at 2020-1970 = 50 years!

(3) 670's 1993+
(1) 617 Early 1990's Pro4
(2) 470's 1993+
(3) 503's 1993+
(3) 277's 1980's
(4) 335's 1971-1972
(1) 340 TNT 1971
(1) 247 1972
(1) 299 1970
(1) L-372 JLO 1970

I also probably got enough parts to assemble 3-5 more engines.

Do E-Tec's have better Emissions, Yes! I would really like to compare an e-Tec against a 582UL using either Hirth Blue Max or Amsoil Saber at 100:1. I, and most people don't really care about emissions! Hp and Reliability is what we care about. The 582UL is using a Muffler, not a Tuned Pipe like your e-Tec is. A 582UL with an R&D Aero Tuned Pipe. 80.7hp@6500rpm.

Do similar CC e-Tec's make more HP, Yes, account they use 594cc vs 580cc and a Higher 8000 vs 7750rpm and much Bigger Carbs/EFI than the Older Engines. That 582UL is using Bing 54 36mm Carbs, that 600 e-Tec is using a 54mm Throttle Bodies.

Unless Skidoo just started using Ceramics on their new Engines, they haven't in the Past. I have been preaching using Ceramics for many Years!

E-Tec's with EFI should get better fuel use, it doesn't really make you more hp. The Engine will Start better and run Smoother! You can add EFI to any older Engine, Ecotrons, Mega Squirt, has EFI Kit's. I have also promoted SFS EFI for Old Singles and Twins. Weber makes a nice DCOE EFI that can be adapted.

E-Tech Engines have been out for Years know, and Nobody that I know of has put one on a Plane. When that happens, it will be a Game Changer to see their Weakness!

Skidoo/Rotax has had a Crank Bearing issue for Years. They have tried going Bigger didn't really Help, they have went with a Sealed Bearing in the eTec, didn't work. There are some Hybrid Crank Bearings that use Steel Races with Ceramic Balls that I think will do the trick. But they Cost more than Standard Bearings. Need less Oil, Run Cooler, last 3x of Standard bearings they say.

600 eTec 68.2hp@6500rpm. I believe the 600HO is 125hp.

#### Armilite

##### Well-Known Member
You have to be EXTREMELY careful with adapting non aviation versions of Rotax and other engines for aviation use.
When using cog belts, they tend to fail without warning, usually by a bunch of the cogs being ripped off, then it turns into extreme airframe damaging vibration as the engine RPMs jump each time the stripped area passes by, and jerks the whole system as the remaining cogs catch in the few seconds before the belt or the drive is completely destroyed. This is not so bad on small engines, but when you have engines >35 HP, things are likely to dynamically disassemble before you can get the engine switched off.
Avoid using cog belts, use serpentine belts instead, they have a much safer failure mode, but they require more tension which causes other issues, see below.
Most of the bigger Rotax engines (especially jet ski and snow mobile engines) I see people adapting to belt drives have an extremely short life span, usually less than 200 hours and they are often damaged to the point that rebuilding does not make sense.

===> Most People have stopped using Belt Drives since Rotax Gear Drives are more reliable 700 hrs! A B Gear Drive is $825 vs Belt Drives are$950-1200. A Serpentine Belt Drive is the Best to use today if you have too. Skidoo/Rotax Engines is the same Core Engine as there Rotax counter part. <==== Problems pop up: 1) The bearings on the PTO end just do not take the load of a belt drive, they are too small. If you look at the aviation versions of similar Rotax engines, they either double up the PTO bearings, use a much larger bearing, or both. (However, some of the newer ski engines use the larger bearings, so you have to pick your engine carefully.) ===> The reason they Fail is people over tighten the Belts! Oil Injection can also Fail. <=== 2) Rotax uses plastic ball retainers and loose tolerance main bearings on the aircraft engines, and they often use tighter bearings with metal ball retainers on non-aviation engines. In aviation use, it is common for the metal retainers to get damaged and cause the bearing to fail in a really bad way loading the inside of the engine with metal fragments as it destroys the cases before the crank breaks from the rod bearing failing due to contamination from the failed main bearing. (If you are lucky, the rod bearing just melts and locks up, and you can salvage the cases, but it almost always makes both cylinders, head(s) and pistons into scrap metal, as 2 stroke engines that use a Y exhaust tend to inhale into the other cylinder exhaled parts from the other.) 3) The cases crack. The reason that Rotax does not want the ski or sled engines adapted for aircraft use is the alloy of the cases is different for the aircraft engines. If you put them side by side, they are the same shape, but the metal is different. They use a more expensive alloy (and or heat treating) on the aviation engines, that is more resistant to cracking under the conditions of driving a propeller. =====> False, they use the same Bearings, some Sled Engines used the Black Plastic Retainers that melt if the PTO gets too Hot, the Aviation Engines use the Steel Retainers, that are better, but eventually can Rust and then Fail. You should use the Nylon Bearing Retainers. <===== 4) The crankshafts break. Most of the aviation crankshafts have a larger diameter shaft between the cylinders, and tend to use larger diameter bearings from end to end. Rotax and third parties produce a damper that can be installed at the MAG end of the engine. This only seems to increase the chances of the non-aviation cranks breaking due to the added mass at the opposite end of the PTO. ===> Very few Cranks break. Only the 582UL & 618UL went from a 24mm Crank Pin to a 26mm Crank Pin, to try and solve the Crank Bearing Failures, which it did not. Skidoo/Rotax use a Rod with only (1) Slot on the bottom, No Hole on Top which is for Oiling the Bearings. Most aftermarket Rods have Dual Slots on Bottom and Dual Holes on Top. What Rods Rotax Rick uses, that's why he offers a 450hr TBO if you use his 40:1 Oil on his 670's (92hp) which uses a 24mm Crank Pin. They went to a 27mm Crank Pin on the 2000+ Sleds and still didn't fix the problem. <===== 5) The aviation versions of the Rotax engines use cageless wrist pin bearings, most of the non-aviation engines use caged bearings. The caged bearings will almost never make the 200 hour mark alive. This one is easy to solve though by swapping to a cageless bearing. Some older Rotax aviation engines were shipped with caged bearings. Rotax issued a service letter years ago to replace them with cageless bearings with good reason. As it turns out, I have seen many Polaris, Yamaha, and Kohler engines that have been converted for aviation use fail at the caged bearings as well, so this problem is not Rotax specific. ====================== The Sleds went to cageless Bearings also, but too many people complained about them Skidoo switched back. The Cage is what Fails, either from Rust or Heat. You can Coat them to make them last longer, but the Cageless are better account you have almost double the Rollers to handle the Forces! Cageless are Double the Cost. The Rod Shims can Fail also. I think a Ceramic Coating would make them last longer, or use a pure Ceramic Shim. Now I have never had a Caged Bearing Fail and I'm 63 years old! I have never had a 2 Stroke I'm using Sieze either, except my first 50cc Bike Motor when I was about 10 years old! I have had 2 Strokes on Bikes, Sleds, Lawn Mower, Weed Wackers, Go Carts! The Oil you use, and Ratio you use makes a difference! #### Armilite ##### Well-Known Member I should add that you could go out and get the same ceramic coatings for an older engine if you wanted, and it might be worth doing. ======================== #### koyama ##### Active Member Although I understand your displacement/7cc argument, the 582 is rated for 64 HP. A 600R E-TEC is rated for 125 HP. Part of that is increased RPM, which goes to greater longevity if you're only running them at 6500 RPM, but part of that is much, much better combustion efficiency. The principal big game changers for two-stroke engines have been direct injection, HVOF ceramic coatings and electronic ignition and injection control, which benefit from big improvements in computer power in the 30 years since the 582 was introduced. The 600R and 850 E-TEC are purported by snowmobilers to have much better longevity than their predecessors and competitors. If you go out to buy a new Skidoo, they're upgrade options from the stock 4-strokes. (You can buy one off eBay used.) Other improvements in the overall design over previous generations include the mono-block cylinders, an electronically-controlled three-position exhaust valve, more accurate balancing, integrated electric start, and much higher combustion efficiency. The 600R and 850 E-TEC actually run clean enough to pass California's emissions standards. So yeah, if you plugged up the injectors and stuck new heads and a carburetor on a 600R, you could downgrade it to only a little better than what a 582 produces, but it would still be more reliable. I hope nobody would try to do that. You have to be careful with making the assumption that turning a 2 stroke slower reduces internal stress and wear, more often than not it is incorrect. It is the bore to stroke ratio on a 2 stroke that determines the RPM of least engine stress. Also, it is somewhat counter intuitive as longer stroke ratios (in relation to displacement) tend to do better with higher RPMs (to a point). Generally piston damage is the result of turning a 2 stroke engine too slow via lubrication failure due to excessive piston heat. The 600R that I experimented with started running exhaust temps over 1150 when the RPM was dropped into the 6000s at full throttle. That is well into the danger zone. At 7200 RPM, temps were acceptable, around 1000, but after less than 30 hours, a rod bearing failed. I have set this project aside for now, I will get a new crank and come back to it later after I finish reverse engineering the computer. It is clear that the stock software is not going to fly (literally). You suggested that the 600R is more accurately balanced? I don't see this, there are no trim marks on the crank, rods, or pistons. What information is this statement based on? I guess you could say that if there was any balancing at all it is better balanced than the 582, as the 582 is not balanced at all. A good point is that adding a computer and GDI to a 2 stroke is a complete game changer, and it would be fantastic to see this applied to a widely available aviation engine. I have experimented with GDI on a Rotax 447. I was seeing about 5-6 horsepower increase with about half of the fuel burn. Just the fuel efficiency alone is a great reason to go with GDI, not to mention that you have very clean emissions. #### koyama ##### Active Member ====================== The Sleds went to cageless Bearings also, but too many people complained about them Skidoo switched back. The Cage is what Fails, either from Rust or Heat. You can Coat them to make them last longer, but the Cageless are better account you have almost double the Rollers to handle the Forces! Cageless are Double the Cost. The Rod Shims can Fail also. I think a Ceramic Coating would make them last longer, or use a pure Ceramic Shim. Now I have never had a Caged Bearing Fail and I'm 63 years old! I have never had a 2 Stroke I'm using Sieze either, except my first 50cc Bike Motor when I was about 10 years old! I have had 2 Strokes on Bikes, Sleds, Lawn Mower, Weed Wackers, Go Carts! The Oil you use, and Ratio you use makes a difference! View attachment 94922View attachment 94923View attachment 94924 I have never seen a caged bearing fail except in aviation use, or from corrosion in jet skis. What is interesting is that I have seen caged bearing failures in Kawasaki, Polaris, Cuyuna, Kohler, as well as Rotax engines that are used in aviation. What I see is the wrist pin and rod starts to wear unevenly. This is caused because the pressure from combustion does not push on the bearing long enough for the paths of subsequent rollers to overlap. (There is a small area that never sees a roller under combustion pressure.) The minute the wrist pin or rod gets low spots on it, is the minute the cage eats itself, and things go south from there. With a cageless bearing, there is overlap in the travel of the individual rollers, so the wrist pin wears evenly, and they can get extremely loose and not fail. Typically when I fly, I will take off at 6300 RPM and then later throttle back to ~5500 RPM, and stay there for the majority of the flight. When I am flying with more weight, it might be closer to 6000 RPM. There is no other vehicle that runs the engine at >80% of available engine for hours at a time the way it does in a plane. This is the reason that it is not possible to compare things like motorcycles or even jet skis and such to what the airplane engine goes through. If you had a 60+ horsepower engine in a 300 pound motorcycle at 80% power you would likely be dead in the first 10 minutes. This is what we do all day long in a plane. Comparing an airplane application to a motorcycle or lawnmower just does not make sense and leads to the wrong conclusions. In my 11,000+ flying hours behind 2 stroke engines, and working as a 2 stroke aviation engine mechanic since 1987 I have found out a bit about what makes them work and what makes them fail. With the Rotax engines, it is mostly operator error, with nearly every other engine I have worked with, it is some flaw in the engine design that makes it not suited for aviation use. The bottom line is that engines like 447, the 503, and the 582 do not really have any failure points. (Other than the older 582s that eat water pump seals.) They typically only die from operator error. I can't say that changing anything in the engine would help. Adding ceramic parts would only tend so complicate things for no reason. #### koyama ##### Active Member =========================== The 582UL is using a Muffler, not a Tuned Pipe like your e-Tec is. This is not (exactly) correct. The Rotax stock exhaust is tuned, just not in the way that most people think of 2 stroke tuning. The big can that people call a muffler does provide some poor muffler functionality... (Rotax sells what they call an after muffler to make up for this.) However, if you look at it more closely, you will see that it is a horn with holes at the big end. More precisely, it has a taper, it is small at the engine end and big at the can end. Inside the can, the horn terminates with a number of holes where it vents into the outer portion of the can. The outer portion of the can acts as a pulse terminator or smoother to provide an even pressure environment for the holes to vent into. This is known as wide band tuning. Think of a cup with a hole in the bottom, if you pour water in slowly, it is mostly empty (large volume of air lower frequency resonance) as you pour quicker the cup fills up (smaller volume of air higher frequency resonance). This is basically what happens but with air in the pipe, the increased back pressure at higher flow provided by the holes increases the resonant frequency. This tuning approach broadens the torque range of the engine, and it is not very displacement sensitive, the same setup can be used across a wide range of engine sizes. When we talk about "tuned pipes" we generally are talking about a double horn. (Two horns connected at the big end with a specific taper and volume.) This causes a specific peak RPM of maximum power, and the horns must be modified to change this peak or for engines of differing displacements or porting. The wide band tuning that the stock Rotax UL exhaust provides does not provide a "peak", but a broad flat (or slanted) response that is needed when you are driving a propeller. So, sure the rated power is lower, but that is the desirable or required outcome for driving a propeller with a 2 stroke. I have flown "tuned pipe" 110+ HP 583 powered planes. They are terrible for every day flying and almost everything else, but great for climbing contests and destroying engines. #### n3puppy ##### Well-Known Member This is not (exactly) correct. The Rotax stock exhaust is tuned, just not in the way that most people think of 2 stroke tuning. The big can that people call a muffler does provide some poor muffler functionality... (Rotax sells what they call an after muffler to make up for this.) However, if you look at it more closely, you will see that it is a horn with holes at the big end. More precisely, it has a taper, it is small at the engine end and big at the can end. Inside the can, the horn terminates with a number of holes where it vents into the outer portion of the can. The outer portion of the can acts as a pulse terminator or smoother to provide an even pressure environment for the holes to vent into. This is known as wide band tuning. Think of a cup with a hole in the bottom, if you pour water in slowly, it is mostly empty (large volume of air lower frequency resonance) as you pour quicker the cup fills up (smaller volume of air higher frequency resonance). This is basically what happens but with air in the pipe, the increased back pressure at higher flow provided by the holes increases the resonant frequency. This tuning approach broadens the torque range of the engine, and it is not very displacement sensitive, the same setup can be used across a wide range of engine sizes. When we talk about "tuned pipes" we generally are talking about a double horn. (Two horns connected at the big end with a specific taper and volume.) This causes a specific peak RPM of maximum power, and the horns must be modified to change this peak or for engines of differing displacements or porting. The wide band tuning that the stock Rotax UL exhaust provides does not provide a "peak", but a broad flat (or slanted) response that is needed when you are driving a propeller. So, sure the rated power is lower, but that is the desirable or required outcome for driving a propeller with a 2 stroke. I have flown "tuned pipe" 110+ HP 583 powered planes. They are terrible for every day flying and almost everything else, but great for climbing contests and destroying engines. Very good explanation of the Rotax tuned exhaust. There have been articles of how modifying the "Tuned Length" of the standard exhaust can affect available thrust. But they never really gave much detail other than the length was changed. #### koyama ##### Active Member ======================== View attachment 94925 This picture is likely not telling the correct story. (My guess is someone is attempting to sell something using usual snake oil like marketing.) The piston on the left appears to have failed at the exhaust port. (This is a common failure that is 100% operator error, and has several causes.) As you can see there is extensive erosion on the top of the piston leaning to the exhaust port area. This is due to incorrect fuel/air mixture and/or incorrect or old fuel. (In particular you see this where the fuel and oil have been mixed for more than about 7 days, which seems to be about the limit for 2 stroke aviation and modern fuel that is available in the U.S.) The side of the piston below the exhaust port shows that there was a lubrication failure. This is caused by exceeding the maximum temperature at which the oil provides protection. It is likely that the coating being mentioned had nothing to do with anything. This is because the normal exhaust temperatures can be in around 1100F. Aluminum pistons melt around 1200F. It is clear that the 1200F was exceeded here, and coating or not, the aluminum piston under the coating will melt. The top causes of this particular failure listed in the order of frequency I have seen them: 1) Mixed gas that is older than 7 days. 2) On single carburetor engines, the horizontal line of the carburetor is not parallel with the crank. This is a big one! Many people tend to twist the carburetor in the socket so that it is more level in flight attitude. All this does is move the main jet so that the fuel flow favors one cylinder. NEVER DO THIS!!! The carburetor MUST be aligned with the crank!!! 3) Too much oil in the gas. (The more oil in the fuel, the leaner the engine runs for a number of reasons.) 4) Improper carburetor adjustment/jetting. (too lean at some point in the throttle range, usually around the 4250 RPM range.) 5) Fuel pump or fuel delivery issues, the float bowls are not being kept full. 6) On single carburetor engines, I am starting to see an alarming number of people that are moving away from the Bing carburetors to other designs that have the idle jet on the side. This causes the fuel to favor one cylinder as in #2 above. 7) Very rare, incorrect ignition timing. 8) Even more rare, incorrect piston to cylinder spacing. (This slows the flow of heat from the piston to the cylinder, allowing the piston to get too hot and melt. In the picture it is not possible to see the pattern on the top of the piston, that can be used to rule in or out this one, but this one is not likely from what I can see.) I have never seen this failure from the incorrect oil, that causes very different looking failures. The bottom line is that the piston failed due to excessive heat from one or more of the reasons above, and coated or not, it would have failed as the piston would have melted out from under the coating. One clue here is that the rings are destroyed. The rings are iron based, so they have a higher melting temperature than the aluminum. They failed because the aluminum that was holding them in place melted. As soon as they become loose in the grooves, they go out the exhaust, and fragments get caught between the piston and cylinder and cause the marks that are seen below on the piston skirt. The picture does not provide the correct conclusion. Period. #### PIK-21 ##### Member This what the inside of the "pot" looks like. #### koyama ##### Active Member This what the inside of the "pot" looks like. View attachment 94971 Thank you for the picture. That really helps. Just some explanation (more details in my previous post on this subject): The can is divided into three sections, the two dividers that you see go all the way around and are welded to the inside parts to provide a mostly airtight seal. The center section is actually the resonant chamber, the only opening is the open end of the big pipe. So effectively, the engine exhaust and the holes in the big pipe are common to this chamber. The diameter and number of holes in the big pipe are used to set the width of the torque peak. The lower tapered pipe or "collector horn" has holes that vent into the right chamber. These holes are used to set the height of the torque peak. This approach is a critical part of the Rotax 2 stroke engine that is absolutely brilliantly designed that is widely misunderstood and undervalued. The fact that this works so well with such a wide range of engine sizes misleads many people to jump to the conclusion that it is not tuned, a compromise, or just a muffler. There is no compromise or cheap-out here, this is the brass ring for 2 stroke flight that nobody sees in plain sight! It seems that part of the reason for this misconception is people with vehicles other than aircraft have the goal of tuning for maximum power. This makes sense, as it is all about how much power you can get! In a 2 stroke powered aircraft this is exactly the wrong thing to do. (But we need more power! Power to weight is king!) When you use motorcycle like horns or other maximum power tuning with a 2 stroke, all you do is give up the torque curve you need for a prop, and it makes the plane very difficult and uncomfortable to fly. The thing I see completely missing is discussion about flyability... All I see is the amount of power to weight they are getting or how long it will last! You only hear this from people that have not actually done conversions and suffered the pain of flying an unstable power system. Or ones that have never flown a good one to have something to compare it to. I will repeat in other words just to be clear: With a "tuned pipe" (or double horn) you end up with an unstable power system. Sure, it works great at full power, you can get > 100 HP out of a 582. But the minute you throttle back, the engine bogs down, and temps run wild and erratic. Just a small change in throttle creates a huge change in power. Then if you lower the nose a couple of degrees, an increase on airspeed of a couple MPH causes the engine to get in the power band and it kicks up 2000-3000 more RPM, then you move the throttle back the smallest amount you can, and the RPM drops by 2500 or so... It is terrible! This is made even worse if you are using carburetors. C.V. carbs tend to help a tiny bit here, but the problem is that raising the nose of the plane just 1 degree can be enough to get the engine to depart the power band at a given throttle setting and change more than 2000 RPM. This makes an extreme air flow difference and associated mixture change from the carburetor (with no movement of the throttle) that just makes things even worse. This is what causes the erratic temperatures, detonation and engine damage. With a proper exhaust, the same throttle position will always result in a very similar RPM, this makes carburetor tuning straightforward and reliable. This alone is a good take home for people adapting 2 stroke engines to aircraft. The minute I see people posting statements that refer to the rated horsepower/output of sled or ski engines and make the comparison to what the aircraft engines are producing, (or even worse yet, compare aircraft usage to a motorcycle) it just highlights the fact that they lack experience in dealing with the issues that are unique to flight and driving a propeller. This alone is a very important reason as to why you can not make power comparisons between published information on non aviation 2 stroke engines and published data for an engine that is intended for aviation. Even in the case of aviation, I have seen numbers that are way off as well, so you have to be extremely careful about the source. I have seen reputable 2 stroke engine manufacturers sell engines for aviation that use "tuned pipes" from the factory. They are all TERRIBLE!!! They are just uncomfortable to fly with because of their unstable output. The only reason you would want this is if you were flying competition or aerobatics. (Even then, the instability is just not fun.) Critical point: Since the vast majority of land use 2 stroke engines use "peaked" tuning, the first thing that this tells you is the output numbers do not apply to aviation. You can not compare to properly setup aviation engines based on that data. Period... #### rotax618 ##### Well-Known Member I built an ICP Savanna (CH701 clone) and powered it with a Rotax 618, I flew it for more than ten years, with one engine seizure (my own fault - long decent with 1/2 throttle), It had slightly better performance than similar 80HP 912 powered Savannahs. It did not suffer from the rev hunting climb/decent problem. I concur with koyama about this phenomenon, the 618 had sufficient cruise rev torque and reserve power that the revs were stable but early Australian Lightwings were powered by Rotax532s they were very uncomfortable to fly, the revs rose and fell alarmingly with any slight thermal or down draught, the later 583 Lightwings were better, but the throttle hunting was noticible. #### koyama ##### Active Member I built an ICP Savanna (CH701 clone) and powered it with a Rotax 618, I flew it for more than ten years, with one engine seizure (my own fault - long decent with 1/2 throttle), It had slightly better performance than similar 80HP 912 powered Savannahs. It did not suffer from the rev hunting climb/decent problem. I concur with koyama about this phenomenon, the 618 had sufficient cruise rev torque and reserve power that the revs were stable but early Australian Lightwings were powered by Rotax532s they were very uncomfortable to fly, the revs rose and fell alarmingly with any slight thermal or down draught, the later 583 Lightwings were better, but the throttle hunting was noticible. The Rotax 618 has a variable exhaust valve (RAVE) that helps flatten the torque curve that literally makes it suitable for driving a prop. If the valves get stuck, (common with incorrect oil) they hunt all over the place. Also, the 618 features a different looking stock exhaust, but it is setup in the same way to flatten the torque curve as on the smaller engines. I have seen people fit tuned pipes to them, and the exhaust valves manage to compensate for it to some degree, but they hunt really bad with 3.5:1 and greater gear reductions. This is another point; the faster you turn the engine, and/or the greater that the gear reduction is, the more unstable the system is, so it is more sensitive to proper design. #### rotax618 ##### Well-Known Member Most 618 installations didn’t bother to fit a control cable to the RAV valves, Rotax said it was necessary but only for operations above 5000 ft where the air pressure was not sufficient to operate the RAV Bellows. This is true but the cables should always be fitted, it is necessary to exercise the valves on warm up to ensure that they are free, they do make a great difference to the torque at cruise revs. #### koyama ##### Active Member Most 618 installations didn’t bother to fit a control cable to the RAV valves, Rotax said it was necessary but only for operations above 5000 ft where the air pressure was not sufficient to operate the RAV Bellows. This is true but the cables should always be fitted, it is necessary to exercise the valves on warm up to ensure that they are free, they do make a great difference to the torque at cruise revs. The cables do not actually actuate the valves. They only change the curve (pressure) at which the valves are actuated. With or without cables attached, the valves function throughout their full range. Most non-aviation (sled and ski) engines that have RAVE installed do not even have control cables involved, or even a place to connect them. The bellows are operated from the exhaust pulse pressure, so the altitude has little/no effect on them. The cables are used to compensate for the port timing to pressure ratio. This is altitude (ambient pressure) sensitive, so changing the curve of the exhaust timing will change the amount of pressure in the lower cases, thus compensate for altitude to torque curve ratio. Cables connected or not, if even one valve gets sticky, the engine gets extremely torque/RPM sensitive and is unpleasant to fly. Note: There was some variation in the design of the cable mechanism over time. (As well as some installation variations.) Some of the later ones used the cable to force the gate open instead of just changing the curve via a spring tension. In all cases, if there is no cable connected, the valve is in full normal operation. Last edited: #### Armilite ##### Well-Known Member #### koyama ##### Active Member As you can see, it's not a Tuned Pipe, but a Muffler, or Sound Moderator. That statement is not correct. Look at my previous messages where I explained its operation. #### rotax618 ##### Well-Known Member I can assure you, with over 15 years experience flying behind and in front of 618 rotaxs that if you don’t connect the cables and you don’t exercise the valves before and after every flight they will carbon up and stick either open or closed on one cylinder, the result that one piston will pick up and seize, naturally you will immediately see it on the EGTs but that only gives you seconds before the inevitable happens. The 618 is a great engine but like all two strokes you have to play by the rules or the result is misery. #### henryk ##### Well-Known Member -Bogdan from Sendziszow actually at finish=at first MZ202,then M-18 modyfied 350cc opposiete... +BKB1 like KASPERwing. #### Attachments • 75.9 KB Views: 10 • 70.8 KB Views: 8 #### GTX_Engines ##### Member Mohawk Aero Corps (MAC) started fabricating Yamaha Genesis 2-cylinder (YG2) Phazer aircraft engine conversion kits last year, and got the first YG2 customer flying in May, a Quicksilver Float plane in New Orleans owned & built by Gil Audibert. One other YG2 kit has been sold to John Rountree in San Diego. The students at SDU have installed it on a gyroplane. The virus lockdown has shut down the project until further notice. That's it, just two YG2 kits sold in a year. I suppose if we get more in the air then "eventually" the Rotax flyers might actually get interested, but for now everyone is sticking with Rotax 582 and other smokers. No one else does a Yamaha Phazer 2-cylinder, 80 HP, 4-stroke conversion kit, although rumors have been circulated that someone else is going to provide something ever since the day I announced our first flying kit was in the air. I can't imagine anyone else actually spending a lot of time and money on this, given the extremely low sales and interest in it. Yeah, there's been lots of talk, but that's all it ever came to. No one has been stepping up and buying anything in the way of YG2 kits, though my sales for everything else remains terrific. So if you are serious about a 4-stroke alternative to the 582 (not just some rumored "possibility" of stuff in the future) by all means contact me. For more information write Info@Mohawkaerocraft.com. To the very best of my knowledge, the installed weight of a YG2 is about 10 lbs more than a 582. COST: Look, I've been doing this longer than anyone in business today (Todd Reick stopped selling kits years ago). The newer your engine, the more it will cost, of course. But typically your budget will be7500 - $8500, with a good, low hrs/mi, used, engine costing$2000-$2500. This should take care of everything, including mounting frame, exhaust, electrical and cooling. What MAC can provide: YG2 Engine, either drop-shipped direct of FOB MAC. Engine plugged, bead blasted, and clear sealed; and new spark plugs and filters -$600
PSRU - AK7 $1800; Rotax E$2350; Simonini C $1900. If you already have a Rotax C, great. Let's use that. Machining required for PSRU - AK7$0; Rotax and Simonini $200 YG2 PSRU Adapter -$1495
Clutch - centrifugal RK400 $550; MAC GT4 roller$695
YG2 wire loom, with core - $395 Exhaust -$750

Total Cost, starting with an engine cleaned up and ready to go at $3000, is$7995.

When I get my YG2 gyrocopter running I will start work on an alternative aircraft intake box that will fit under the cowl. For now, all we know is that the intake is critical to top power performance, as is proper length of exhaust (which is much easier to fabricate and get it right). When people butcher up and concoct their own air boxes for the YG3 and YG4's there has been enough HP so that a loss of ~7% at the intake plenum is acceptable. With the YG2 I don't see such a loss of HP as acceptable. Gil is back to using the stock intake box, after trying one they fabbed up and discarded.

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Yamaha Aircraft Engine conversion milestones:

2007 - Todd Reick, first Yamaha flying, a Vector YG3 120 HP on an Air Command single place gyroplane.
2008 - Todd Reick, YG3 conversion kits introduced
2012 - Greg Mills, first YG4, RX1 140 HP, Air Command Tandem gyroplane.
2012 - Greg Mills, first use of sprag clutch on Yamaha aircraft
2013 - Greg Mills, commercially available RX1 YG4 conversion kits introduced
2014 - Teal Jenkins, RX1 conversion kits introduced exclusively for Rotax C and RK400 clutch
2015 - Greg Mills, first YG4 purpose-built PSRU, Hy-Vo chain.
2015 - Tango Gyro, first mass-produced, purpose-built aircraft designed specifically for Yamaha Genesis engines. About 60 units sold as of 6 months ago.
2017 - Greg Mills, first (YG4) Apex 150 HP conversion kits introduced.
2018 - Steve Henry, first Airventure Grand Champion award flying a Yamaha, using Greg's Apex kit
2019 - Teal Jenkins, Apex gearbox introduced
2019 - Edge Performance, 300 HP Apex turbo aircraft kit introduced.
2019 - Greg Mills, first YG2 80 HP conversion kits introduced
2020 - Greg Mills, first Apex EXUP (valved exhaust) 160 HP kit introduced.

#### Armilite

##### Well-Known Member
I can assure you, with over 15 years experience flying behind and in front of 618 rotaxs that if you don’t connect the cables and you don’t exercise the valves before and after every flight they will carbon up and stick either open or closed on one cylinder, the result that one piston will pick up and seize, naturally you will immediately see it on the EGTs but that only gives you seconds before the inevitable happens. The 618 is a great engine but like all two strokes you have to play by the rules or the result is misery.
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There is also a difference between the 617 Sled version (Aluminum) and 618UL version (Stainless) RAVE Valves!

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