Challenger Muffler Maintenance

The muffler on most Challenger Ultralights is a simple 3 piece design that is held together with springs. This is true for the Rotax 447, 503, and 582 engine installations. The springs allow the muffler to flex and absorb the engine vibrations. Without this flexible set up the stresses would cause cracks to form in the metal and the muffler would eventually fail in service.

This is more than just a noise issue. Two stroke engines require a tuned exhaust to function. A broken muffler will cause engine failure.

There are other after-market methods to assemble and install the Challenger muffler but the spring method is the factory approved way and is the most common.

The muffler springs can break over time. They can rust because they are exposed to the elements and heat. Therefore, examining them should be part of every pre-flight inspection.

The springs should be completely retained with safety wire so that in event of a breakage in flight, the parts will be held and not pass through the propeller. Additionally the safety wire and spring should be impregnated with a high temperature silicone sealant that will also act to retain any broken parts.

The muffler should be assembled using a copper anti-seize lubricant on the muffler joints. This anti-seize lubricant with further facilitate the flexing of the muffler. Over time this lubricant will dissipate and need to be replaced. The Rotax Maintenance Manual Schedule on page 10.2 actually recommends re-lubricating the muffler joints every 25 hours of engine operation. Most operators consider this to be too frequent. At least once per year though is recommended, perhaps as part of the annual inspection process. The muffler joints should never be allowed to rust and bond rigidly together.

The muffler springs should be inspected to make sure they are not broken and not becoming rusted. Old muffler springs should be replaced. An after-market stainless steel muffler spring is available through some Rotax engine maintenance companies such as Light Engine Services in British Columbia. Other wise, the black steel springs can be purchased for about $7.50 a pair at Canadian Tire in the snow mobile section. The Rotax Maintenance Manual Schedule on page 10.2 actually recommends replacing the muffler springs every 75 hours of engine operation.

At some point the muffler body itself may start to show rust. The rusty muffler can be sanded and then repainted with a high temperature enamel spray paint such as is found in many hardware stores. This paint is often advertised for use on gas barbeques. Again, Canadian Tire is one source for this.

To facilitate muffler maintenance you will require the following items in your Challenger Ultralight tool kit:

• Spare Muffler Springs
• Aviation Lockwire .025 or .032 size
• Copper Anti-Seize Lubricant
• High Temperature Silicone Sealant
• Needle Nose Pliers
• Safety Wire Pliers
• A box wrench for loosening the muffler mounting bracket
• A cloth rag or paper towels for clean up.

Challenger Muffler Maintenance Procedure

1. Cut the safety wire and remove it from all the muffler springs.
2. Using the needle nose pliers, pull the springs off of the muffler. Be careful that a section of muffler does not fall and damage the aircraft fuselage.
3. Remove the old high temperature silicone sealant from the springs and inspect their condition. Replace as necessary.
4. Lubricate the muffler ball joints with copper anti-seize lubricant.
5. Re-install the muffler and springs. Note that the middle of the springs should not touch the muffler ball joint. If they do touch, bend the welded mounting loops up so the springs are clear of the joint.
6. Safety wire the springs by passing the safety wire through the length of the spring and also through the mounting loops. Bend the end of the wire over so it will not cut you during later inspections.
7. Add lots of high temperature silicone sealant in a bead along the whole length of the spring. It should penetrate the coils of the spring. It should also envelope the safety wire.
8. Clean up any mess. This is a good time to check that the EGT sensors are still tight

Keep in mind that the spring mounting pattern for the Rotax 503 and the 582 are not the same. The 503 uses a 7 spring pattern and the 582 uses a 6 spring pattern.

A final tip for healthy muffler maintenance is to stuff an oily rag into the exhaust port of the muffler when the aircraft is not in use. The oily rag will form a moisture barrier and prevent moisture from corroding the muffler on the inside. Remember to remove the rag before engine start up.