I am a happy owner of a Diamond HK36R motorglider with a brand one year old 80 HP 912A engine. With only 150 hours on it, I have replaced the right rear exhaust pipe spring five times, the back side one, and the front spring on the same pipe once. All other springs are lasting fine. The failure is at the beginning of the bend for the attaching loop. Recently at annual, we tried putting RTV on the coils in case it was a vibration problem, but the spring seemed to snap only a little sooner.

I had spring problems on my new engine until I wired the springs. Use binding wire around the two springs to pull the springs towards the pipe. Just enough pressure to put a strain on the springs to stop the pulsing. I have not broken one since. TRD

Spring problems seem to be related to individual installations involving harmonics and vibrations peculiar to each installation. I've known people who had constant problems with springs and people who have never had a problem. I solved mine by switching to the spring loaded bolt and collar type connection about five years ago and never had another problem. These are available from any supplier like Lockwood, CPS, Leaf, etc..

Bill.

Is the spring bolt system available fo the 912?

Tim,

The new clamp system is available for the 912, I have them on mine. Be sure you specify the 912 if you buy them because the clamps for the two cycle engines are for a larger diameter exhaust pipe. They are pricey. CPS sells them for about $45 per joint. You'll never have to replace them though; mine are six years old. You might check LEAF, Lockwood, and Bear Perkins. They might have them cheaper.

Bill.

Spring tension can play a big part. i.e. If it is too tight. Many do not add enough silicone. I usually make my bead 1/2" wide and a 1/4" tall to give it some body and strength not to mention working it in between the coils. Another method is to actually fill the spring with silicone. Either way spring tension may be the culprit.

I had a similar problem with one of my springs, it and broke four times in 100 hours.
I meassured the distance between the loops holding the springs and found that the distance where the spring kept braking was greater than the rest. I fitted a slightly longer spring and that solved the problem.
I still tie locking wire down the centre of the springs just in case one beaks.

Everyone should safety wire their exhaust springs. Use the heavier .040 safety wire and do not try to wire it tight. It needs to move so leave it just a tad loose.