Metallic tapping sound from 1985 Merc 140 MR engine coupling
(Pulaski, VA )
7/10/16 - Status: Boat maintained well, with est. 400 running hours since 1985. Just completed maintenance on entirety of 1985 Alpha (MR) stern drive (has 1985 Merc 140MR hp (181 cid - 4 cyl. engine), lower and upper stern drive as follows: Removed prop & bearing carrier & installed new oil seals; new water pump & oil seals and seals on upper shaft; new shift shaft & seals; new oil rings on upper gear assembly; checked U-joints & yoke - good condition; lubed U-joints; new oil rings on yoke shaft; all upper and lower gears in excellent condition with very minor wear & no pitting; splines on yoke shaft in excellent condition; replaced water hose & bellows on upper gear, exhaust & shift; new shift cable; new gimbal bearing & oil seal. Note: Installed all seals throughout & gimbal bearing with recommended driver tools and used the recommended lubricants, gear oil, U-joint & spline lube. Used recommended alignment bar that inserts into engine coupling with 3 to 4 fingers - firm fit & bar can be removed with 3 to 4 fingers. Engine oil & oil filter replaced as normal, with engine ignition and carburetor calibrated.
PROBLEM: Conducted in water test to ensure proper engine and stern drive operation at dockside. At idle speed 650-700 rpm, observed entirety of engine stern drive functions over course of 1 mile.. Conducted series of left & right turns, & straight runs at 1500 RPM, no problems or unusual sounds emanating from engine/stern drive. Above 1500 RPM (did not exceed 2000 RPM), a fast, metallic tapping sound was emanating from around the engine coupler, with no smell of rubber or vibration, no knocking sounds. Propeller and in all other engine/stern drive functions were fine. The fast, metallic tapping sound occurred regardless of the position of the stern drive, with the tapping sound would cease at 1500 RPMs or lower. At no time is there a loss of power or propulsion.
Your insight would be greatly appreciated as to what is causing this. Many thanks in advance. RBell, Virginia