Rotax NGK BR8ES problems
Spark Plugs: The proper spark plug for use in most of the Rotax engines is the NGK B8ES, or other brand name equivalent, (Champion spark plugs are not recommended, nor are they factory authorized for ultralight use.)
If using a spark plug with an BR/B in its heading, (usually used for ignition noise suppression) such as NGK BR8ES, a resistor cap should not be used. This is because of the double resistance supplied when using both a resistor plug and resistor cap. It is advisable with engines running in the inverted position to use a spark plug with an extended electrode. This aids in stopping spark plug fowling. Look for a BP in its heading (NGK BP 8ES).
When removing or installing the spark plug cap make sure that the cap is turned, in the rotation necessary to tighten the screw on cap on top of the spark plug, otherwise the improper removal of the cap results in the backing off of the screw on cap and the possible loss of spark to the engine, when the spark plug cap falls off.
This is the style of NGK BR8ES spark plug that should be used, with a steel cap and a small spark plug gap.
The recommended gap on the spark plugs is .015 of an inch. These plugs are capable of running for over 20 hours trouble free on a points and condenser engine and up to 50 hours trouble free on a dual CDI ignition engine (if proper fuel and oil are used and the engine is in proper tune). They should be checked on a regular basis however, and replaced at the first sign of a miss or after severe flooding of the engine.
If using a cylinder head temp gauge, removal of the ring on the bottom of the spark plug is recommended, since the gauge sending unit replaces it. (Cylinder head temperatures should range in the 300 to 400 degree F range.)
In practice, a properly tuned engine should show a nice chocolate, or brown color on the spark plug, white indicates an engine running hot, while black indicates one running to rich. Any sign of aluminium on the spark plug indicates a problem of a very serious nature, and requires your immediate attention!
This is the style of NGK BR8ES spark plug that should NOT be used, it has an aluminum screw on cap and a larger spark plug gap!
Rotax aircraft engine ignition problems
Ignition: The most widely reported problem with the Rotax ignition system is in the failure of the ignition coils, and pickups on the Dual CDI engines. Coil failure and the wearing of the point arms, causing improper timing on the points equipped engines. The only solution for the coil failures is to replace the coil, it is also a good idea to have an extra one on hand.
If ordering an EXTRA coil for the CDI engines order the PTO side coil, it will fit on both sides. The problem with the wear on the point arms generally occurs in the first 10 to 15 hours of operation and if the owners manualrecommendation for all engines is followed, the owner will have had his timing checked during this period of time.
On the subject of the owners manual, this is a very complete and concise document, and if read and followed, will eliminate most of the problems associated with some of the most widely reported engine problems.
A video put out by Ultralight Flyer web video magazine which is approximately two hours in length, would be an investment I would recommend. It is available either on the web, in video format, or on DVD. This video takes you through the complete tear down and reassembly of your Rotax engine, showing proper torquing procedures, how to time your engine, etc. etc. etc., and is very professionally done.