Rotax Engine Set Up - Adjustments you can do to make your Rotax aircraft engine safer and more reliable.

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Rotax aircraft engine set up.

Adjustments you can do to make your engine safer and more reliable.

Working on ultralight aircraft on a daily basis gives you some insight into the problems associated with the sport. One of the major problems is "lack of knowledge" about "ultralights." This includes engines. Rotax supplies about 80% of the worlds ultralight aircraft engines.

They come from Rotax complete with carb(s), exhaust, and gear box,  ready to bolt into or onto an ultralight. Up until this point Rotax has complete control of the "quality of the product." Having been to the plant in Austria and the distribution centers in Canada and the U.S. I can verify that the facilities and people involved are # 1 in the industry.

The problems start once the engine is taken out of the box! They start with the new engine owner and his or her lack of experience with engines. So lets start here and see if we can help get this new engine, up flying and performing to the best of its abilities. We will take it from the point in time that the engine is installed "DRY"on the aircraft. We will deal basically with two different engines air cooled and liquid cooled.

Inverted installation problem with the Rotax liquid cooled engines.
Okay here we go. If your engine is liquid cooled and is in an inverted installation you in all likelihood have had to drain the oil from the Rotary valve tank and relocate the tank so that it still sits above the engine.

While this may not seem like a big problem - it can be a very expensive one if done incorrectly. Rotax liquid cooled engines are designed to work with the spark plugs facing UP. When you place the plugs facing down, the Rotary valve chamber inside the engine develops a problem.

It becomes "air locked." Why? Because the system was developed to work upright - a plate was added to prevent the oil in the chamber from sloshing around - which could have resulted in lack of lubrication.

To prevent this a baffle plate was added. When the engine is turned upside down this baffle plate traps air in the top of the chamber - which can result in damage to the rotary valve gear if the engine is started. This damage will result in the necessity to completely tear down the engine! 

So to prevent this damage you MUST fill your rotary valve tank while the engine is sitting with the spark plugs facing up, then turn the engine over and install it.

Coolant: In order to run a liquid cooled engine we have to install coolant. Rotax recommends on the two stroke engines that a 50/50 antifreeze and water mixture be used. The antifreeze MUST be one that is aluminum compatible and the water used must be distilled. In summer applications I recommend a 95 % water - 5% antifreeze solution - this is considerably more efficient especially in hotter climates.

You will notice that there is an air bleeder on the one end of the cylinder head this vent goes back into the rad system. Failure to connect it could result in air being trapped in the front cylinder resulting in piston seizure.

The radiator reservoir must have an area in it to allow for expansion of the coolant.
It is also recommended that a thermostat be installed at this time - when supplied from Rotax the engine DOES NOT come with a thermostat.

Checking fan tension on two stroke air-cooled Rotax engines:

It is very difficult and in some cases nearly impossible to check fan belt tension on some aircraft. A neat little trick I use is to remove one of the little mouse ears from the fan cover. I recommend the carb side so that your not burning yourself on the exhaust checking the fan belt tension. With the mouse ear removed and the engine turned off you can check the tension using your finger anytime - quickly and easily.

Gear Box: Whether you are running an A/B/C or E gear box it requires oil. The proper way to fill the box is with the engine sitting on the plane LEVEL. There are two screws on the side of the box the lower screw is your upper fluid level. Remove the filler cap install 90 weight gear oil until the oil runs our the screw hole, wait until it stops draining and then reinstall the screw.

Inverted installation problem with the Rotax dual carb 503 engines.
If you are using a dual carb 503 in an inverted installation you must turn the aluminum intake manifolds over - once again the engine was designed to run spark plugs up.

On the 503 dual carb the inlets - when the engine is upright have a slight upward incline. When you turn the engine over this incline is NOW down, which necessitates the removal of the intake, turning it 180 degrees and reinstalling it.

Final Adjustments - Carbs
Okay the next thing we have to adjust is the carbs (dual carb models only). For correct jetting refer to the Bing Jet chart. For correct air screw mixture setting refer to the Bing Jet chart.

Before doing this procedure on dual carb models make sure that the two carbs are level with each other, you can do this by running a straight edge over the top of both carbs, it should lay flat on both carbs at the same time!

The idle on all of the Rotax, two stroke engines is 2,000 rpm with the proper prop load installed. To achieve this back your idle adjustment screws out until they are no longer touching the carb slide. Now adjust each in an equal amount of turns - I suggest 3 turns in. This way both slides are at the same location in both carbs at idle.

Next have someone apply throttle SLOWLY while you watch the slides. The slides should BOTH start up at the same time. If not adjust using the two adjusters located at the top of the carb.

Once you have them starting up at the same time open them all the way up and make sure that the slide is completely clear at its upper most throttle position. You now know you have both carbs starting at the same time and that they are both opening up to full throttle.

Final Adjustments - Oil pump
To bleed your oil pump - fill your oil ta
nk - which should be 3/4 of an inch above the pump at the highest angle of attack that you can reach. The pump is GRAVITY fed from the tank - thus you must always have gravity working for your.

Remove your bleeder screw until air stops coming out of the hole and no air can be seen in the line. Re-install the bleeder screw and cranks the engine over with the ignition turned off until no air can be seen in the lines going to the cylinders.

To adjust the oil pump: With the throttle at the idle position the line on the arm of the oil pump should align with the line on the oil pump body. You adjust this using the cable adjuster.

Rotax oil pump settings, Rotax 582 oil pump, Rotax oil pump set up for the Rotax 582 and Rotax 618.
The line on the arm and the line on the housing should align at an idle. To adjust use your oil pump arm cable adjuster.

For break in when using an oil pump it is recommended that in addition to the pump you use a 100 to 1 gas to oil mixture.

Spark Plugs: Yes I know they are brand new but they still have to be adjusted. The recommended gap is .015 thou to .019 thou - set them at .015 and they will wear out to .019. If you are using a spark plug that has an aluminum screw on insert on the top of the spark plug make sure that it is tight.

These have a habit of vibrating off - resulting in loss of ignition. They also wear and can cause "arcing" between the cap and plug. The Rotax supplies plug has a steel cap that does not wear or come loose - it does cost more.

Starting the engine:
With the engine, fuel pump, carbs, gear box installed and the tach and ignition wiring connected, the next step is to put the proper prop load on the engine, so that we can break the engine in. Now the maximum rpm is determined by which engine you have and how it is equipped. You can get this info from your manual or from this site.

To break the engine in we need for it to be able to pull about 300 rpm LESS than what it would pull if it were flying straight and level under full power.

e.g. - A 582 should pull straight and level under full power 6500 rpm - thus for break-in - with the plane tied down we should be able to pull  6200 rpm.

If you have a ground adjustable prop installed, and the plane securely tied down - start the engine up let it warm up for a few minutes - then apply a quick full throttle burst of power. If the engine over revs IMMEDIATELY back the power down and reset the prop to more pitch.

If the engine fails to reach 6200 then shut the engine down and repitch the prop - with less pitch. Repeat this until you reach 6200 rpm - or the rpm that is 2 to 300 rpm lower than that suggested in your manual.

If you have a standard fixed pitch prop and the engine over revs - STOP IMMEDIATELY and get another propeller DO NOT proceed with an improper load or your engine WILL seize up!

If you have a standard fixed pitch prop and the engine under revs - STOP IMMEDIATELY and get another propeller DO NOT proceed with an improper load or your engine load up and quit in flight!

With the proper prop load achieved you can now start your break in procedure, as per the Rotax schedule.

Rotax break in schedule

Also check out Bing Carb tuning and troubleshooting!

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