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IC Engine Exhaust repeatedly loosens in flight.

No Cause Fix Comment
1. Vibration. Balance the propeller, using a precision prop. balancer.

The Dubro balancer should meet all needs. 

Note the level of vibration that an out of balance prop. can impart to a model aircraft is very considerable.

A detailed prop. balancing article will be added to RCAerobase and a link placed here.
2. Quality of exhaust fixing bolts. Use high tensile socket head bolts throughout. 

While stainless socket head bolts have slightly less tensile strength than high grade alloy bolts, they are more resistant to deformation at the high temperatures of IC exhaust gases.

Contributed by Brian Winch.
3. Exhaust gasket failure or poor quality. Use several layers of plumber's teflon tape to create instant easy leak proof gaskets. 

While other materials can be used very effectively, this method is so quick and easy it takes some beating.

Contributed by Brian Winch.
4. Exhaust manifold fixing bolts, and/or the longer through bolts which often hold the cylindrical components of exhausts together become loose. Expect to re tighten after initial engine runs while the engine is hot. Caution: avoid burning your hands.

Some expansion of fixing bolts can take place, which is not equalised by contraction on cooling, resulting in loosening of the fixing bolts. Re tightening fixes this. This is best done on the ground in order to avoid losing exhaust components while airborne.

Contributed by Brian Winch.
5. Fixing bolts unlocked.

i.) Always lock all exhaust fixing bolts either by using double wound spring washers, or locknuts.

ii.) Use 0.7mm. stainless steel tie wire for lifetime guaranteed locking.

 

i.) Even with carefully balanced props., there is always vibration. If exhaust fixing bolts are left unlocked, then sooner or later they will come loose.

ii.) This method involves drilling the heads of the socket head bolts to accept the tie wire. The process is not without difficulty and should not be attempted without proper workshop facilities. 

Contributed by Brian Winch.
 6. Multiple component exhausts rigidly supported at multiple points, e.g. exhaust manifold and firewall. Airframe vibration will cause stress to the separate parts of the exhaust system as they will be forced to move out of synch. This can lead to damage and/or loosening.

Use anti vibration mounts for exhaust components after the manifold and ensure that connections between components are shielded against vibration e.g. silicone tubing and clamps. 

For a wealth of additional detail on this problem see Brian Winch's Article, Loose Muffler Blues in RCM&E April and May issues 2016.

 
Details
Category: Power: Piston
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Comments  

# Bob Hynes 2016-04-18 16:27
Article Revision History.
April 18th. 2016.
Brian Winch credited for points 2., 3., 4 and 5 ii.)
Pointed to Loose Muffler Blues article in RCM&E April,May 2016. Point 6.
# RC Aerobase Admin 2016-05-25 20:15

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