Item #1 Says to retorque the heads and manifolds at two hours. In practice, most folks retorque those items at some time after two hours and up to 10 hours. To retorque those, I loosen one item at a time and retorque it in the original criss cross pattern as described in the initial torque sequence.
Items 5, 6, 19 and 20. Referring to inspection and replacement of spark plugs and fuel filters. Once you are familiar with your particular engine and how it starts best, you will have very little problem starting it. However, when it begins to get hard to start, it normally is time for a spark plug change. Some pilots fly the plugs until the engine begins to miss but that is extending plug life out into a dangerous area.
Each time that I change the plugs, I also change the fuel filter. Using this method, I have never had a fuel filter problem in 20+ years of flying Rotax engines.
Items 8, 9, 10 and 11. Referring to contact breakers (points). Again, I take lots of time to set the gaps and timing to the absolute end of the allowable range and run it that way until it begins to get hard to start.
Item 12. Anyone still running a V belt drive on a Challenger should immediately ground that plane!!!!! Change the drive out to a cog belt after carefully checking the crankshaft for damage.
Item 15. Oil control cables. Most cables these days do not require oiling. If a cable is dragging, replace it. If you oil it, it will only attract dust and dirt and usually winds up with worse problems from the contamination. Operating areas and conditions will be a consideration here.
Item 16. Propeller tracking is easy to do and this schedule would be fine. However, propeller balancing requires removing the propeller and this is unnecessary unless there is some reason to suspect the propeller is out of balance. This will apply more to wood props than carbon fiber props.
Item 18. This is not a bad schedule but operating areas and conditions vary greatly. I usually just run it until I feel it is time to clean it. Intuitive more than arbitrary.
Item 19 and 20. See 5, 6, 19 and 20 above.
Item 23. Again, there is no need to replace the needle and jet unless you suspect some damage or excessive wear.
Items 30 through 36. A good bit of this is arbitrary and unnecessary. One should not be flying these engines in conditions requiring this schedule. Doing the precise measurements of piston and cylinder diameters, ring grooves and end gaps is certainly desired on disassembly of the engine when that disassembly is required but there is no good reason to disassemble the engine just to take these measurements.
Item 40. This states that you should do a ‘general overhaul’ of the engine at 300 hours. Nothing wrong here except that to Rotax, a ‘general overhaul’ includes replacing a $1000 crankshaft unnecessarily. Normally, a ‘top end overhaul’ is needed at ‘about’ 300 hours. This will vary quite a bit depending on operating conditions, maintenance, oil and how the engine has been flown.
A ‘top end’ is normally needed at ‘about’ 300, 600, 900 and sometimes even 1200 hours. The need for a ‘top end’ will be determined by the amount of carbon buildup in the ring grooves and whether or not the rings are stuck or are almost ready to stick. This consists of removing he engine from the aircraft, removing the heads, cylinders, pistons, rings, wrist pins and wrist pin bearings. All carbon buildup will then need to be physically removed. All the parts then can be carefully examined and measured. Once all the parts are cleaned and determined to be within factory specifications, the engine can be reassembled and reinstalled.
In addition to the normal ‘top end’, usually the crankshaft seals are inspected externally and if shown to be leaking or seeping, they will be replaced. The need for this replacement of seals normally will be about 600 hours and sometimes 300 hours. The crankshaft end bearings will be examined carefully and replaced if needed on disassembly for crankshaft seals. A crankshaft replacement is needed only if the crankshaft falls beyond factory minimums and cannot be brought back within specifications.
The following are a few general observations and practices of long time Rotax service personnel, some authorized and some not, and a few long time Rotax pilots.
The general consensus is that the #1 cause of engine in flight stoppage is fuel starvation. The primary causes of this is usually poor maintenance, component failure or poor design and installation. It is often a combination of several of these things.
On Experimental class aircraft, fuel systems are normally designed and installed by the original builder and range from super simple to super complex. Both methods have advantages and disadvantages.
On a super simple system, there is normally a pickup of some sort, the fuel filter, the Mikuni Pump and the carbs along with the fuel lines. This system relies on proper maintenance but offers few items for failure. This is the method that I personally prefer. The Mikuni Pump is probably the most reliable item supplied with the Challenger Kit. With a rebuild every 3 or 4 years, it will last for many years. Replace all the fuel lines when any of them begin to get hard and non pliable. Replace the fuel filter at every spark plug change. Using this method and keeping your fuel clean, you will enjoy many years of trouble free flying.
There are many who desire a bit more redundant system. They often employ back up electric fuel pumps and other items into the system. This system also requires proper maintenance but offers a back up if the Mikuni Pump should fail or if the filter gets a bit too restricted. This method also offers more possible points of failure and more potential fuel or air leak connections.
There are many more fuel systems that get extremely complex trying to cover any possible fuel system problem. Many of these systems cause as many problems as they try to guard against.
Although Rotax recommends changing the crankshaft at 300 hours, this is normally unnecessary. Most crankshafts will easily run 500 hours or more with reasonable maintenance and operation. Many will run far more than that. Some even run beyond 1000 hours but these should be monitored closely and maintained and operated correctly.
George Hurt
Adventure Aviation
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