Page 44 - REPOWER REFERENCE GUIDE (2020)

Engine and Drive Installation Requirements
Sterndrive and Inboard Engine Installation Requirements

IMPORTANT: It is the responsibility of the boat manufacturer or installing dealer to properly locate the engine and install the
exhaust system. Exhaust systems that are installed improperly will allow water to enter the exhaust manifolds and combustion
chambers, severely damaging the engine. Water ingestion damage to the engine will not be covered by Mercury MerCruiser
Warranty unless the damage results from defective Mercury Marine parts.
Through‑the‑Transom Exhaust Systems
These systems are the design of the OEM or installing dealer. Factors that affect how well the system operates include:
• Exhaust hose lengths
• Muffler designs
• Slope of exhaust hose
• Shutters
• Waterline‑to‑exhaust‑elbow height
Testing should be performed to ensure that water is not being reverted to the engine. Refer to Section 7 ‑ Exhaust System for
assistance with proper installation and to Section 10 ‑ Testing the Installation to verify water reversion is not occurring.
Through‑the‑Propeller Exhaust Systems—Sterndrive
This system is a Mercury MerCruiser design. Important considerations for this type of exhaust system are:
• Sufficient exhaust elbow height (see note)
• Shutters are in place
• Exhaust bellows or tube are installed
NOTE: Elbow height with the boat properly loaded (top of elbow to water level) should be verified before delivery to the
customer. Refer to Section 10 ‑ Testing the Installation for further details.
Transom Specifications
When repowering boats previously rigged with other than a MerCruiser engine, a transom adapter kit (827691A1) is available
for some models.
The transom must comply with the following specifications for proper power package operation. Failure to comply could result
in the following:
• Insufficient transom thickness and/or material with inadequate strength could allow the transom to deflect under operation
from propeller thrust. This could cause an engine coupler or U‑joint shaft failure.
• Correct transom thickness and parallelism is critical for proper mating of the transom assembly and engine components. A
transom that is out of specifications could cause improper exhaust pipe alignment, exhaust pipe mounting flange leakage,
insufficient transom assembly fastener (and pilot) engagement, and U‑joint knocking.
• Compliance with the outer transom surface flatness specifications is required to prevent water leakage into the boat.
• Proper trim operation requires that the transom angle be within the range indicated.
Transom Specifications

Material Marine grade plywood covered with fiberglass, aluminum, or a
comparable material.
Between 51 and 57 mm (2 and 2‑1/4 in.) for 20.3 cm (8 in.) to
Thickness either side of the vertical centerline.
Parallelism (in transom assembly mounting area, for Inner and outer surfaces must be parallel within 3 mm (1/8 in.).
20.3 mm [8 in.] to either side of the vertical centerline).
Flatness (in transom assembly mounting area, for Inner surface: Flat within 3 mm (1/8 in.).
20.3 mm [8 in.] to either side of the vertical centerline). Outer surface: Flat within 2 mm (1/16 in.).

Page 4A-2 © 2019 Mercury Marine 90-8M0149179 eng NOVEMBER 2018