Maintenance Tip: Engine Split Rings Revisited

Maintenance Tip: Engine Split Rings Revisited

I’ve looked at a lot of King Airs in my day, and one of the things I always check is the split ring placement. Many times, I find them correctly installed on the engine exhaust port flange. But I still see some installed on the exhaust stack flange, and this is a big “no-no.”

Back in 2012, I addressed the subject of split ring reinforcers and their placement in the Mar/Apr and Nov/Dec issues of this magazine. At that time, the King Air 200 manual had it wrong – it depicted the split rings outboard of the stack flange rather than inboard of the engine flange. Confusion abounded.

There are plenty of shops and mechanics that are getting it right, but I still find some with no idea what the split rings are even for, much less where to put them. I even ran into a shop that knew what the correct placement should be but installed them incorrectly in accordance with the 200 manual. They said in order to sign it off they had to be in compliance with the manual. The poor owner of that King Air had to take it to another shop to get his split rings removed and reinstalled correctly.

The original, very short-lived, exhaust stack for the 200 (top), and the stovepipe stack (bottom).

The Purpose of Split Rings

The split ring is a two-part backup ring installed on the backside of the engine exhaust port flange. The various King Air manuals call them “stiffeners” or “reinforcements.” When installed correctly, split rings support to the engine flange once the exhaust stack is bolted on.

The very first model 200s did not come with split rings. The original stacks Beech Aircraft had designed left big swaths of soot on the nacelles. Owners complained vigorously. So, the company designed a longer, smoother, stack to carry the exhaust further away from the nacelles. It was perfectly round and looked like a stovepipe. Back in the day, that’s what we called them. The nacelles were cleaner, and everyone was happy except for the engine manufacturer Pratt & Whitney.

The stovepipe stack was heavier and the flanges on the engine exhaust ports weren’t designed for that much weight and could crack. If that happened, the engine had to be split, and the power section removed to make the repair.

I remember this was a big deal at the time. Although split rings were already in use on the 100s and A100s, the exhaust stack issues on the 200s prompted a lot of discussion about the integrity of the engine exhaust port flange, and the use of split rings for reinforcement.

A split ring (one-half of a pair shown) is a backup ring divided into two halves which are installed on the backside of the engine exhaust flange.

Proper Positioning

Unfortunately, as time went on, the purpose for the split rings was forgotten. People were putting them on the exhaust stack flange, where they do no good at all. Further complicating the issue was the mistake in the 200 manual.

Remember, if not directly reinforced by split rings, the engine flange cannot bear the weight of the exhaust stack. Over time, stress fractures develop, and the engine flange can crack. Even the exhaust duct on the engine can crack.

I’ve seen it all. I’ve had to split engines, send power sections to engine shops for repair, and submit expensive invoices to King Air owners – all due to split rings installed in the wrong place or missing completely.

Let’s review: The exhaust stacks bolt onto the engine exhaust duct ports. The flanges of each fit flush to one another. The bolts go through the stack flange, then the engine duct flange, followed by the split rings. The flat surface of each split ring goes against the engine port flange, with the rounded surface facing away from it. If the aircraft has UV shields, they go on after the split ring.

A UV shield (deflector) found on King Airs with the “cat’s eye” fire detection system. It prevents sunlight from hitting the forward optical fire detector.

UV Shields

Any King Air with the “cat’s eye” engine fire detection system (i.e., no fire loop) has UV shields installed at the engine exhaust duct flange. These crescent-shaped pieces of metal prevent sunlight from hitting the forward optical fire detector (fire detector shield or UV deflector are other names). They, too, are frequently installed in the wrong position, between the top split ring and the engine flange. This prevents the top split ring from distributing the weight load of the stack. The split rings must have direct contact with the engine exhaust port flange all the way around.

Model 200 Manual Mistake Corrected!

At last, the King Air 200 maintenance manual has a diagram showing correct placement of the split ring reinforcements. See Figure 401 (Revised) below right. You can see the exhaust stack (#4) with its flange. Left of that is another flange. Although not labeled, this is the engine exhaust port flange. The reinforcements (#2) go in between the engine flange and the fire detector shield (#1). The bolts (#3) go in from the stack side. Stack flange, engine flange, split ring, UV shield. Hallelujah!

A Few Exceptions

Outside of the 300 series, I can’t think of a King Air that doesn’t have split rings. The earliest King Airs (A90s, B90s and a few early C90s) came from the factory with a short, lightweight exhaust stack and no split rings. But later, Beech Aircraft designed a replacement stack that was longer and heavier, and split rings were required.

Exhaust stack on left; engine exhaust port on right. Stack is loosely bolted to align holes. Top split ring is already installed; bottom split ring is held to indicate the position where it will be installed, flush against the engine port flange.

Very recently, Pratt & Whitney has beefed up the exhaust port flanges in a few cases, so some of the newest King Airs are exempt from split rings. The maintenance manual identifies by aircraft serial number which King Airs need them and which do not; most do.

There may be an after-market stack that does not need split rings, but I doubt it. The STC paperwork should make this clear. If ever there was a question whether or not to install them, I’d put them on.

I don’t see a downside to split rings and I’d rather be safe than sorry when it comes to protecting the exhaust ducts and flanges on your engines. I’ve seen what happens when split ring stiffeners are installed incorrectly or are missing entirely. It’s a road you do not want to go down.

The King Air 200 maintenance manual has a corrected diagram, Figure 401 (Revised), showing the right placement of the split ring reinforcements.

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