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Did I forget to apply silicone to my springs?

Roger Lee

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Hi All,


Here is a reply to a question I put forth to Rotax Tech Support because some seem to see it too many different ways. This is right from the horse's mouth so to speak.

The question is, "Do I need to apply silicone to my exhaust springs"? If I do, "Do I fill the entire center of the spring with the silicone or do I just apply a nice 3/8" wide by 1/4" tall bead down the side"? Well here is what Rotax Tech Support had to say.

Directly from Kodiak Support which is the importer to the whole US.




Hello again Roger


Springs for the exhaust, the question comes up from time to time, and as always speculation of the correct way is based on some misunderstanding of the function and purpose of the practice of silicone application. Silicone, high temp in this application, is used to dampen the vibrations that can lead to the premature breakage of the spring when it is in normal use.


Reasons for breaking are varied but overstretching, (attachment of the spring tang to the pipe and muffler too wide) and using a tool that leaves a mark on the spring are the most common. Always pull the spring on with a spring tool, do not use pliers, cutters, or any tool that is able to leave a mark in the spring. Lets remember that the material is heat treated after it is twisted. Any mark creates a weak spot in the wire.


The idea of safety wire on the spring also has to be considered, it too can create a problem. When you wire the spring you have some options, I prefer to wire from eyelet to eyelet and pass inside the spring, you must leave a small amount of slack in the wire, unlike any other time you do safety wire. The reason is simple, we have to allow for some moment of the joint, otherwise the wire can break.


Now, the silicone as discussed has to dampen vibration, so it only needs to cover the spring in a small area. The correct method is to draw a bead over the top of the spring, NO MORE THAN 1/4 to 3/8 INCH wide. I like to start from one spring tang, draw the bead from there, starting at one contact end of the safety wire, go across the top of the spring and to the other spring tang. This will deaden the wire vibration, and it will capture the small spring loop at each end should the wire break.


HEAT, it something that we have to consider, if you do not allow the spring to breathe, to cool, it may overheat and fail prematurely. So the idea is to leave the spring to move and to cool with the air, we do not want to stop the spring movement or from keeping cool.


I hope that this long winded explanation helps, your free to pass it on.



So the bottom line is YES you do need the silicone on the exhaust springs which is in the maint. manual and used to be a Rotax SB. No don't fill the centers (old thinking) because it causes the springs to overheat and fail prematurely and you can not check the safety wire to see if it is broken which does happen fairly often if you have it on too tight.

This silicone is the high temp stuff. It can be black or red.

Do not put a tiny little wimpy bead down the side of the spring as it won't do any good. You need some substance width wise and height wise to make it a good dampener.

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The old manual says to fill the spring with silicone. This isn't a good idea and hasn't really been taught in the Rotax schools. The original SB out on this was do use a bead down the side just as it is taught in the Rotax school. I have never attended a Rotax school that had you fill the spring. I wish they would pull it out of the manual once and for all. The proper way is listed in the previous post and has been the standard for many years. The post come right from Eric Tucker that is the instructor for Rotax around the world and the main accident investigator when a Rotax is involved. The problem with the Rotax manual updates is that they want to add or delete one thing and end up leaving out the other items on a page.

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