NTSB Identification: CEN13LA103
14 CFR Part 91: General Aviation
Accident occurred Tuesday, December 11, 2012 in Dekalb, IL
Probable Cause Approval Date: 09/30/2014
Aircraft: AUMAN JL T-51, registration: N512JA
Injuries: 1 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The experimental amateur-built airplane experienced a total loss of engine power during a phase one test flight. The pilot performed a forced landing on a field where airplane nosed-over due to the rough condition of the field that precluded a normal landing rollout.
Before the phase 1 test flight, the pilot had returned the engine to the kit manufacturer for repair due to leaking engine coolant. Postaccident examination of the engine revealed catastrophic damage; the engine head bolt had been tighten above the engine manufacturer’s torque values, which indicated that the kit manufacturer used excessive torque on the head bolts in an attempt to repair coolant leakage through the engine head.
The postaccident examination showed that the engine was assembled with cast and not forged pistons, which should be used in high performance applications. The bending and thread damage on the intact connecting rod bolt for the forward right cylinder and the mating thread damage in the connecting rod were consistent with the bolt backing out until it sheared the remaining threads. Another bolt that backed out of position was also present on the connecting rod in the middle right position. Measurements of cylinder wall carbon lines showed a variance in size, which may have been due to hydraulic lock related bending of the connecting rods.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The improper engine overhaul by the airplane kit manufacturer, which resulted in a catastrophic engine failure.

Full narrative available

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