Remos oil hoses diameter - Rotax requires 11 mm
Posted: Thu Jan 18, 2018 2:28 pm
NTSB posted a factual report about the fatal crash of N28GX. The airplane was maintained with no expense spared, which was unusual for a rental to tell you the truth. However, the investigation found a sheared drive pin. Apparently, Rotax claims that hoses were too small and that causes pulsating oil flow, fatugue, and failure of the pin.
Note that you can fly with a broken pin for hundreds of hours and not know that anything was wrong unless a piece of pin breaks off and jams something or starts grinding the housing.
I know Michael Sz. would never install random hoses from AutoZone. They probably came from Remos' warehouse in Arkansas. I never heard about the hose size restriction.The engine crankcase, camshaft, oil pump shaft, and oil pump drive pin were submitted to the National Transportation Safety Board (NTSB) Materials Laboratory for additional examination. The examination indicated that the camshaft had a yoke machined into the end opposite the drive gear that drove the oil pump shaft. As designed, a drive pin passed through the body of the oil pump shaft, which engaged the camshaft yoke. The camshaft yoke did not exhibit any abnormal wear or deformation. The bearing bore in the crankcase that corresponded with the oil pump drive yoke exhibited scoring on the inner surface about mid-depth. The depth of the scoring was about 0.024 inch. The scoring was consistent with the profile of the oil pump shaft drive pin. The drive pin fractured inboard of the outer diameter of the oil pump shaft on both sides, leaving a portion of the drive pin within each side of the shaft. Examination of the fracture surfaces revealed crack arrest marks consistent with a fatigue fracture. Hardness measurements made across the diameter of the drive pin were consistent with the manufacturer's design specification. Although the drive pin had fractured, it remained engaged to the camshaft yoke and continued to rotate the oil pump shaft. Additionally, the postaccident engine disassembly revealed ample lubrication throughout the engine, and there was no evidence of oil starvation.
According to the engine manufacturer, a fractured oil shaft drive pin is indicative of an oil system with restrictive hoses and fittings that can result in a pulsating oil supply to the oil pump. The pulsating loading of the drive pin can result in a fractured drive pin. The Rotax 912 installation manual stipulates that oil hoses have an inside diameter of 11 millimeters. The oil hoses recovered with the wreckage had inside diameters that measured 9 millimeters. Additionally, the Rotax 912 installation manual stipulates full-flow angled fittings for oil hose connections. Examination of the oil cooler revealed a right-angle fitting that did not meet the engine manufacturer's full-flow fitting specification.
Note that you can fly with a broken pin for hundreds of hours and not know that anything was wrong unless a piece of pin breaks off and jams something or starts grinding the housing.