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Mercruiser Part *Cover Nut

GLM Aftermarket cover nut for stern drive lower gearcase

  • GLM P/N 21120 replaces Mercury 79448 or Sierra 18-9858
  • Removal and installation instructions shown below
  • Tech support Exploded view drawings
  • Compatible with all Mercruiser models from 1964 and up (except Bravo 3)

21120 Cover nut lower unit

21120 Cover Nut

P/N 21120 OEM 79448 $21.99

Help with Removing This Part

Begin by prying straight the tabs on the locking washer around the nut. If you damage the tabs you'll need to replace it. Use tool #90190 (or Mercury #91-61069T), which can be purchase below, to remove the nut. Using the tool, turn it counter-clockwise. In the event that the part is completely seized into the housing due to corrosion, you can use a drill to drill out the frozen piece. Remove it along with the key washer and the aligning key. When re-installing this item, make sure to clean around the internal threads in the lower unit before using the tool to install (turning clockwise) the new item.

Customers who ordered P/N 21120 also purchased:

90190 Mercruiser tool bearing carrier retainer wrench

90190 Mercruiser tool bearing carrier retainer wrench

P/N 90190 Retainer wrench tool removes and installs the cover nut in front of the bearing carrier. Replaces OEM 91-61069T, Sierra P.N 18-9858. $112.99

11380 Tab Washer

11380 Tab Washer

Tab washer P/N 11380. This part will need to be replaced if you damaged the tabs on the old one when removing the nut. Replaces OEM 14-79447, Sierra P/N 18-2299.

87510 Seal Kit 26-33144A2
87510 Seal Kit 26-33144A2

P/N 87510 Lower gear case seal kit is required when re-assembling the parts in lower unit. Replaces OEM 26-33144A2, Sierra P/N 18-2652.