JBM Industries makes a very high quality, custom wound, exhaust spring to help solve the problem of broken springs. Often you will return to your hangared plane, and find a broken spring. Springs can break when the aircraft is not in operation.
Hydrogen embrittlement caused by rust, and poor installations will cause springs to break, sometimes in a very short time. JBM has tackled this problem by manufacturing custom wound exhaust springs made of stainless steel. Stainless springs are usually used where high heat is involved, like furnaces or ovens, but we use it to make sure rusting is impossible.
JBM Stainless Exhaust Springs have a measurement at rest of 62mm between the hooks. These springs have extra turns of wire, so can expand a lot to give more latitude on installations up to about 4 inches. Fits most all Rotax exhaust but be sure to MEASURE!
Because loops are welded on by exhaust providers, be sure to measure the distance you need. JBM only manufactures one size.
Loops can be bent to allow for proper installation, as loops on exhaust systems are welded on by kit manufactures for their specific exhaust installations. Your aircraft might require 3, 4, 6, or even the 7 springs used on Challenger aircraft. Rotax 912 installations may require 8 springs. Please measure. Some loops must be heated with a torch to be bent back.
Example of poor installation is shown below. It is best to use a hook to install springs to prevent nicks from pliers on the hooks.
Heat can be used to bend the loops to adjust for proper spring length and tension in most cases. Springs should never touch the exhaust pipe, as wear and breakage of spring will increase.
Use of silicone sealant to fill the spring, or damp out vibrations is a bit of a messy solution and will not prevent broken hooks.. Use safety wire through the center of the spring to prevent broken pieces of spring causing propeller damage.
