Broken Exhaust Springs?

Bill, I never heard of a spring puller until you just mentioned it, nor was I aware of the Rotax propensity to break springs and I’ve never heard of spring damage before. Anyway, I’ve got a new set of stainless Rotax springs to fit and thankfully they are cheap. I’m glad I asked the question on this website because I never would have guessed and would have kept damaging springs.

I’ve got some hard drawn high tensile fencing wire, so I’ll make a tool out of that and put some heat shrink over the hook for extra protection. I have a fresh tube of red rtv732 as well.

I use a loop or two of 100 lb braided nylon fishing line and pull with a screwdriver as a handle.  When it invariably gets trapped between the spring end and exhaust or muffler ear it’s easy to simply cut it and pull it out with no potential scratching of the spring.

I originally installed the exhaust springs according to previous suggestions of a safety wire to capture the parts when the spring fails and a bead of high temp RTV to keep the vibration down.

I found that the springs quickly eroded the lugs welded on the exhaust, probably due to the vibration.

When attending AERO in Germany several years ago I visited the Rotax factory display and saw a 912 iS engine with the exhaust springs wired in the middle pulling the centers of the springs tight against the exhaust pipe.

In order to build up the welded lugs and try to replace the metal lost to erosion from the springs, I wrapped each lug with a few wraps of small diameter safety wire.  At the same time I changed all of my springs and safety wired them as recommended by Rotax (as per the photo).

Since then I have had only one spring fail.  I can't say the time interval between spring failures is much different between the two methods, but the welded lug erosion is dramatically reduced if not eliminated.  The safety wire that I wrapped around the lug in the eroded area (the interface between the welded lug and the loop of the exhaust spring) was still in place and viable.

Attached is a photo of the factory engine installation of the exhaust springs.

Thank you all fo your advice and help, I would never have found this out on my own.

As a footnote to this discussion, I took the cowls off yesterday and removed the exhaust system springs. A total of three were broken despite my attempts at safety wiring to stop vibration. My observation is that these springs all failed at the same place - the ninety degree bend at the beginning of the tang. My eyesight and magnifying glass isn't good enough but as far as I can tell these were fatigue crack failures at a stress concentration. 

My conclusion is that installation scratches had nothing to do with this because the failure zone is not touched during installation, at least by me.

The new springs are stainless steel of some sort and a turn longer, so I assume the stresses are lower. I will also use the safety wire method shown in James photo.

If these keep failing then the spring needs a redesign or perhaps shot peering.