Augmenter Exhaust Springs

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    The springs that support the exhaust stacks at the rear of the engine nacelles where they enter the over-wing tubes on my 1956 C-310 break frequently. It has gotten better with time and shop adjustments on clamping tension. My mechanics also have a few other ideas they want to try if this persists. But I was wondering if anybody has found a more permanent solution, other than ordering these springs by the gross?!!




    I’ve owned 310s and maintained/flown several others. Your spring problem is a new one on me. Here’s how I set up the springs during overhauls and routine engine maintenance.
    1) Make sure the stacks are as close to the center of the augmenter hole as possible.
    2) The end loops on the springs need to be able to “move” and rotate on the bushings where they attach. They should not be pinned down tight. In other words, the loops should not “bend” at any time.
    3) The springs should have some tension on them. Move the attachment ring slightly forward on the exhaust stack to supply some tension.
    4) This is a major factor: These engines can be subject to large oscillating movements at low RPM. These movements are amplified at the aft end of the tailpipes. Remove the top cowl and run the engine. You will be surprised when you see the amount of tail pipe movement at idle. Increase RPM and find a smooth area – probably about 1000 RPM or so.
    5) Properly adjust the idle RPM and mixture. Check out the ignition system and fuel delivery nozzles. Do all you can to smooth out the engine at low RPM.
    6) Don’t idle the engine unless absolutely required. Use the RPM you found in #4 above (about 1000-1100 RPM) when not in motion.
    I overhauled both IO-470s on one of my 310s and set them up properly. Following the above steps, I did not have a single spring failure in the 300 hours after the overhauls. I sold the aircraft and the new owner has about 100 hours with no spring problems.

    I hope this helps – Larry Denning



    Thanks for that very detailed response. My shop and I have done most of what you suggested, except for the uncowled idle checks while watching the pipes. However, I do know what you mean about smooth idle points and watch that carefully. We’ve done a good bit of engine tuning following carb overhaul, and you are on point with idle speed and smoothness. My engines seem to like 980 left, 1020 right. (Don’t you just love digital tachs?!)

    I will share everything you suggested with my shop.

    Thanks again,


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