Metallic tapping sound from 1985 Merc 140 MR engine coupling

by Roger
(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

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Jul 20, 2016
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Update: Loud Metallic clicking-REPLACED Starter
by: RBELL

Folks, sorry for the delay in posting. I appreciate your respective thoughts on this matter.
... Note that I removed the stern drive late last week and conducted run engine tests to ascertain location of the loud (metal on metal) metallic clicking that increased in loudness and rapidity as RPM increased. The loud metallic clicking continued.
... Late last week, I removed the boat's original 1985 Delco - Remy starter and conducted a a series of extended bench tests of engage/disengaging the nose gear, which the starter did quite satisfactory. There was no handing or looseness in or at the starter's nose gear.
... Ordered new replacement starter from DB Electrical of Kingsport, Tennessee of who I have found be very reliable and forthcoming on their products. Installed new starter this evening and conducted a series of starts, operating timeframes to ensure that engine was at normal operating temperature, and ran RPMs up to 2500. Engine cranked immediately, maintained 700 RPM to allow engine to warm up to operating temperature. Increased RPMs to 1500, 2000, and 2500.
... Results: The loud metal on metal clicking did not occur at any time throughout these run engine tests. HALLELUJAH. I can only speculate as to why the original 1985 Delco-Remy starter was possibly engaging enough to slightly burr the edge of the flywheel ring gear. The vibration may have caused the nose gear to release and float to the edge of the ring gear without engaging.
... I will remount the sterndrive. Hopefully the weather will permit me to conduct a test on the lake sometime late this week.
... I will keep you informed and post the results of these tests on the lake.

Many thanks to you for your guidance on this matter.

Best, Roger Bell
Pulaski, VA
Purchased new in 1985 Cheetah 166 Bowrider
140MR hp Merc.& Alpha Stern Drive