Continental: IO550 D12; Broken Through-Bolt; ATA 8520

Continental: IO550 D12; Broken Through-Bolt; ATA 8520

(A Cessna A188B follows behind this engine.)

“This broken through-bolt,” says the submitter, “is located under the top of the oil cooler adapter plate, (passing) through to the number six cylinder—top front. It broke off flush at the cylinder base while in flight. The bolt’s end—which broke off with the cylinder base nut—flew out of the front of the cowl, put a gouge in the face of the prop blade, and then hit the top of the cowl, leaving a large dent. When it broke, the opposite end of the bolt was forced back against the oil cooler adapter plate with such force (the deformation penetrated) the plate (to its opposite,) gasket side. This through-bolt is the replacement (bolt) installed last August 2005 due to the original through-bolt also breaking at the same location (it managed 650 hours).

“A new cylinder base nut (P/N 652541) had been used (in this last installation), and (it was) torqued with a calibrated torque wrench to 800 inch pounds in accordance with Teledyne Continental Motors Service Bulletin 96-7C. It is ironic both bolts broke at the same location with identical break lines, the first with 650 hours since remanufacture and the replacement with 200 hours. I contacted a TCM technical representative—he said he has seen through-bolts break like this just sitting in the TCM assembly shop overnight.” (The provided part numberfor the bolt given as 6416311052. It doesn’t generate the expected data base response. However, the SDRS data base reflects at least 14 additional reports answering to part number 6419311075 as found in the next report.

More information on this subject will be forth coming. Read also the next report.)

Part Total Time: 200.0 hours.

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