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Arksey(at)aol.com
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 Posted: Mon Sep 01, 2008 8:20 am Post subject: info from course on rotax 2 stroke engine |
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Hi gang,
while doing a google for info on compression on a rotax 503 I ran into this info taught at a 2 stroke engine class. I found it interesting and am passing it on to the group. Have been doing lots of flying and the Kolb firestar is a fun thing for a old man. Hope to see you all at the Kolb homecomming...
Jswan firestar ll michigan
βThe weakness of the two-stroke engine is air temperature and air densityβ
Rotax has identified 16 reasons for engine failures on two-stroke engines. Every one has been the subject of a Service Bulletin from Rotax to correct these or to educate the operators. These are:
1. 1. The Inertia Moment of the Propeller exceeding the capability of the engine. Addressed by a Service Instruction on how to select a propeller SI 11 UL 91. Ensure your prop does not exceed 3000 kg-cm2 or 1025 lb-in2.
2. 2. Contaminated Fuel β Usually due to water, bugs or dust. All of these normally get into the fuel system via air transmission.
3. 3. Storage And Aging Of Fuel β No fuel should be used if it is more than three weeks old. Mixing with newer fuel, however, can extend the life of older fuel. A maximum content of 5% alcohol is acceptable. Alcohol causes the oil to separate and not do its job as effectively. Alcohol also absorbs water, which can cause corrosion.
4. 4. Fuel Pressure And Carb Venting β The fuel supply line must be <11 feet in length. The fuel pump pulse line must be <11 inches in length and as short as possible to increase effectiveness. The pulse line must be very rigid and not capable of being compressed to collapse by the fingers. The fuel pump diaphragms should be checked annually for deformation. The deformation must be less than 200% of the diaphragm thickness. The diaphragms are made of Mylar and are subject to deformation from both use and aging. The carb vent lines should be a 1800 line with four drilled holes. The holes must total twice the diameter of the vent tube.
5. 5. Calibration of the Carburetors and the Jets β To adjust the air idle screw properly screw it in to the bottom of travel (be careful not to turn it beyond the point of just touching the bottom to ensure it doesnβt become damaged by over-tightening). Back it out Β½ turn for rough adjustment. This should give 850 β 9500F idle EGT. Backing the screw out makes the idle leaner. Permissible adjustment of the Rotax 503 is + ΒΌ turn. Movement of 1/8 of a turn should give a change of 500F.
6. 6. The Type of Air Filter and the Maintenance Done to It β Ensure the right type of K&N filter is installed. If the filter has <50% light visible then it is still serviceable. The filter must be serviced with the K&N filter service kit. The oil applied not only makes the filter work correctly but also helps prevent carb icing, by keeping moisture out.
7. 7. The Brand of Oil Used β The oil is critical to preventing wear in the engine. Use no-ash oil. Do not use fully synthetic oil, use a mineral-based oil instead. Recommended is the Sinto Racing Performa Two-Stroke engine oil. Gearbox oil recommended is the ANSoil 75W140 Synthetic Gear Lube.
8. 8. Engine Mount and Cowling Blocking Air β The installation must allow free flow of air through the engine.
9. 9. Any Inappropriate Cooling System Installed β There have been many problems with adapting automotive or other radiators for the Rotax liquid cooled engines. These are not designed for the same purpose.
10.10. Insufficient Time For Engine Warm-Up β To avoid cold seizures on take-off, air-cooled engines require 8 minutes of warm up and a CHT of not less than 2500F
11.11. Engine Mount Design β Ensure that the engine mount does effectively reduce vibration.
12.12. Improper Monitoring of Engine Systems β Using the wrong engine instruments or not using engine instruments at all to monitor the health of the engine.
13.13. Exhaust System β Modification or leaking system. The exhaust system is a tuned system and it must be installed right and work right to enable to engine to produce any power at all.
14.14. Corrosion prevention β Follow the Rotax recommendations regarding engine corrosion prevention and preservation. Use the choke to stop the engine on the last flight of each day to ensure a good coating of oil is deposited in the crankcase. Block the intake and exhaust anytime the aircraft is not flying.
15.15. Maintenance Schedule β You need a comprehensive maintenance schedule to ensure that all the correct items are taken care of when they need to be done. This cannot be done by memory.
16.16. Preflight Inspection β Before every flight do a preflight inspection to look for problems. The inspection at the beginning of the day should be more extensive.
Other Maintenance Notes
Compression Test β if conducting a compression test there should be a maximum of 10% difference between cylinders. Cylinders normally average 120 lbs. 90 lbs is the minimum.
Setting the Idle With Dual Carbs β The large screw on the carb is the idle speed adjustment. Verify the height of the slider with a drill bit β must be the same height. Idle should be set to 2000-2200 rpm. Both sliders must reach the top of the opening at the same time. Use the cable screw adjustment to achieve this. The cable should have 1/16β slack at idle. To ensure both sliders are closed.
The idle adjustment needs doing often due to wear and cable stretch. Start by adjusting the idle β move the screw in until first slider movement, then increase one full turn. Then check the full throttle adjustment.
Next adjust while running, using EGT as a guide.
At full power the EGT should indicate 1050 β 11000F, but not lower than 10000F and not over 12000F.
The engine runs with an EGT hotspot between 4100-4600 rpm by design. The ideal value (temperature) for this range is 11000F - 12000F, but not above 12000F, of course! Adjust using the jet needle. Each notch on the needle is 500F warmer (moving up the needle) or cooler (moving down).
On the Rotax 503 the difference between cylinders should be <500F. Check this with a vacuum gauge or by EGT once the idle is set. Then adjust to eliminate the EGT differential at cruise with adjustment to the cable screw.
Silencing Options
The Rotax intake silencer will reduce horsepower by about 2-3%, while the after muffler will not cost any power. The total noise reduction possible is about 20% from both of these. The intake silencer makes a bigger difference in total noise while the after muffler clips the peaks on the exhaust pulses in the noise output. The intake silencer and the after muffler can be installed independently.
EGT Probes
The EGT probe fittings in the Rotax exhaust manifold are actually at the hottest place in the exhaust system. This is due to the fact that the hot exhaust keeps burning after it leaves the cylinder.
EGT probes should be set to the same height to ensure that they give the same readings.
Carb Installation
The carbs are designed to angle slightly down when viewed from the side. If they donβt do this then the intake manifold needs removing and reversing. The down-angle is to prevent flooding of the carbs. The rubber carb mounting sockets are actually vibration isolation for the carbs to help prevent foaming in the float chambers.
Spark Plugs
The correct spark plugs for the upright Rotax 503 are the BR8ES plugs. Use the ones with the solid core, not the spring core, as these ones do not retain the spark plug lead caps!
Do not clean spark plus β replace them.
The spark advance is set to 40 advance at idle and 260 at full power. If the spark timing is out by more than 0.004β then the crankshaft is bent and requires replacing.
Spark plugs should be installed with Permatex 22064 Dielectric Tune-Up Grease to prevent seizing.
Do not turn over the engine without all sparkplugs grounded, to prevent damage to the diodes in the dual electronic ignition units.
Regulator/Rectifier
The small regulator/rectifier requires a minimum 1A load to operate. This can be achieved by the use of a light.
Rotax 503 Fan Belt
The fan belt needs checking regularly as per the maintenance schedule. The central retaining nut should be safetied with Locktite 221/222 (Purple).
The fan can only be safely removed with the special tool available from Rotax. The fan shims are stored behind the pulley, on the fan shaft.
Exhaust System
Exhaust system springs should not touch the exhaust pipes, as that will prevent them from doing their job. The spring brackets can be bent to raise them to ensure that the springs clear the pipes.
The springs should be lockwired to prevent loss of the springs and ensuing prop damage in pusher installations. The lockwire should be loose enough to allow the springs to move. Use a screwdriver under the lockwire when installing it to ensure that the wire is loose. Use a bead of hi-temp silicone on the springs to absorb vibrations and also to help retain any parts should the springs break.
There are two spring lengths available from Rotax. Springs can be stretched if required to fit. A proper spring fit means that the springs should only be stretched with a pull of 1/8 β ΒΌβ on installation.
The exhaust manifolds should be mounted with just two screws even though there are four holes. This is to allow flexing in the system due to thermo-expansion.
Apply anti-seize compound to the exhaust ball joints every ten hours on a new installation for the first 40 hours to ensure a good application.
CHT Probes
The CHT probes should be routed under the cowling and then in between the fins to provide the most secure routing.
βBβ Gearbox
The βBβ Gearbox requires a check of the spring washers every 100 hours. This check requires a hydraulic press to accomplish and so is best done by an engine maintenance shop.
It's only a deal if it's where you want to go. Find your travel deal here.
[quote][b]
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Mon Sep 01, 2008 8:34 am Post subject: info from course on rotax 2 stroke engine |
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Jim S:
Very good info for the two strokers, or is it double strokers???
Hope I see you and a lot mor Kolbers at the homecoming in about 17 days. James Tripp and I are flying up Thursday morning.
john h
mkIII
| Quote: | Hope to see you all at the Kolb homecomming...
Jswan firestar ll michigan
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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olendorf
Joined: 06 Jul 2006
Posts: 140
Location: Schenectady, NY USA
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| Posted: Tue Sep 02, 2008 5:04 am Post subject: Re: info from course on rotax 2 stroke engine |
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Lots of good info there!
I have one comment.
"Spark plugs should be installed with Permatex 22064 Dielectric Tune-Up Grease to prevent seizing."
I would not use Dielectric grease for this. You want a good electrical contact. I believe the proper method is to use engine oil on the threads and make sure you change the plugs according to the schedule.
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Scott Olendorf
Original Firestar, Rotax 447, Powerfin prop
Schenectady, NY
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