Credit to Mark:
Any Sierra owners have problems with a rebuilt muffler rubbing a hole through the lower cowling? Have others paid $1100+ to overhaul a muffler or am I the only fool? MC-565 owner.
Price quotes for a flange-out “overhaul” (meaning all new stainless-steel tubing and muffler from the flange down) of this exhaust system usually has an FBO mechanic’s cost of around $1,400 – $1,500, if done right. An owner-purchased price quote will likely be higher. The rebuilders and parts wholesalers have to help support the mechanics to help them stay in business, so they’ll be there when you need them. The price difference also helps cover the FBO cost of the FAA paperwork and records that they have to keep and maintain for their parts acquisitions and repair work.
Exhaust system contact is, unfortunately, a rather common problem in the Sierra. A major contributing factor in cowling contact is the vibration signature of the high-compression IO360 engine used in these planes. While pretty smooth during flight, it tends to jump around a great deal during start-up and shut-down. The spot with the least clearance, where the contact first tends to occur, is the left front edge of the muffler, on the pilot’s side of the system.
The problem is exacerbated by the Lord engine mount cushions that were developed specifically for this installation, for a smoother cruise “feel” and for less vibration impact on the airframe. Because they are unique, with a correspondingly low production volume, they are relatively expensive. The “biscuits” have an uncommon number of bonded layers (two different configurations in each cushion set), and must be installed in the proper configuration. Two of the mounts (lower left and upper right) have a rubber coated solid spacer, while the other two have a silicone gel-filled spacer. All these parts have to be in good shape, or the muffler can hit the cowling. In fact, the stock Beech paper air filter element can even hit the cowling, which in turn can cause cracks on the induction air box. The STC’d Brackett unit gives slightly more clearance, and often gives slightly more manifold pressure. Air filter and muffler contact evidence may be one of your first clues to sagging engine mount cushions.
The installation pattern for these cushions is also unique, and they are often installed incorrectly. Proper placement and proper indexing at each corner of the dynafocal mount is critical. These cushions have a pre-formed “set”, and must be installed with the index pins correctly aligned. The Lord mount biscuit sets in this application have been a disappointment to me. Specifically, the gel-filled spacer is intended to take the “hammering” out of start-up and shut-down. The complete cushion assemblies are “supposed” to last to TBO. They never do. The gel spacers in particular can often be seen to have leaking gel in as little as 30-40 hours. You cannot buy the individual cushion components; only the sets. I have complained to Lord about both the short life and high cost, with the usual pabulum answers. In one instance they were nice enough to send a free pair of gel spacers, and to send a name of a possibly lower-cost source:
Herber Aircraft at 800-544-0050; ask for Ryan (she’s helpful)
Unfortunately, Barry Controls did not offer these cushions, due to the low volume requirements. I recently saw evidence that this may have changed; I’ll investigate that option again.