Mercury MerCruiser 42799 Water Pump Pulley — 2-Groove, GM V8 Sterndrive & Inboard

Mercury MerCruiser 42799 — 2-Groove Water Pump Pulley, GM V8 Sterndrive & Inboard

Overview

The Mercury MerCruiser 42799 is a 2-groove water pump pulley for select older MerCruiser GM-based V8 sterndrive and inboard engines. It mounts to the engine’s circulating water pump and drives the accessory belt arrangement on the matching front-cover and intake-manifold assembly. This part is discontinued and no longer available from Mercury — once existing stock is gone, no further supply is expected. If you need this pulley, order before stock clears.

Fitment note: Pulley fitment depends on the exact engine model, serial number range, water pump style, crankshaft pulley arrangement, and whether the engine uses a 2-groove or 3-groove pulley setup. Always confirm using the MerCruiser engine serial number before ordering — older GM V8 engines used multiple front-drive pulley arrangements that are not interchangeable.

Compatible Applications

• MerCruiser 230 MIE — 2-groove front accessory drive (confirm serial range)
• MerCruiser 260 MIE — 2-groove front accessory drive (confirm serial range)
• MerCruiser 5.0L / 305 CID — selected configurations (confirm serial range)
• MerCruiser 5.0L MIE — selected configurations (confirm serial range)
• MerCruiser 5.7L / 350 CID — selected configurations (confirm serial range)
• MerCruiser 5.7L MIE — selected configurations (confirm serial range)
• MerCruiser 5.7L Ski — selected configurations (confirm serial range)
• MerCruiser 5.7L Competition Ski — selected configurations (confirm serial range)
• MerCruiser 330 GM 454 — selected configurations (confirm serial range)
• MerCruiser 340 MIE — selected configurations (confirm serial range)
• MerCruiser 7.4L / 454 CID MIE — selected configurations (confirm serial range)
• MerCruiser 454 Mag Alpha — selected configurations (confirm serial range)
• Always confirm by engine model and serial number — multiple front-drive pulley layouts were used across these engine families and serial ranges

When to Replace

• Pulley is bent, cracked, or has visible physical damage
• Pulley is wobbling or misaligned at the water pump shaft
• Groove wear is accelerating belt wear or causing belt tracking issues
• Squealing, vibration, or repeated belt failure is traced to pulley condition
• Heavy rust or corrosion is compromising structural integrity or belt contact surfaces

Installation Notes

• Confirm the replacement pulley matches the groove count (2-groove) and pulley diameter of the original — do not substitute a 3-groove pulley where a 2-groove is required
• Inspect the circulating water pump, pulley mounting surface, and belt alignment before installation
• Related hardware: pulley-to-water-pump screw 47277 and lock washer 39107 — replace if worn or corroded
• After installation, verify belt tracking and alignment across all driven pulleys before running the engine
• Inspect the serpentine or V-belt for wear while the pulley is off — replace if cracking, glazing, or fraying is found

Technical FAQ

• Why does the groove count matter? The 2-groove pulley is matched to a specific belt and crankshaft pulley arrangement. Installing a 3-groove pulley where a 2-groove is required (or vice versa) results in belt misalignment, belt failure, or accessory drive damage. Always match by groove count and serial-confirmed application.
• This part is discontinued — what are my options if it’s unavailable? If OEM stock is exhausted, options include sourcing a compatible aftermarket equivalent or having a machined replacement fabricated. Confirm dimensions and groove profile before substituting any non-OEM part. A marine engine specialist familiar with older MerCruiser GM V8 setups is the best resource for alternative sourcing.
• Can I reuse the pulley screws and lock washers? Inspect them closely. If they show corrosion, thread damage, or have been previously overtightened, replace with Mercury OEM hardware (screw 47277, lock washer 39107) or equivalent-spec fasteners. Fastener failure on a water pump pulley can cause immediate belt and cooling system damage.
• My belt keeps slipping after installing a new pulley — what should I check? Verify pulley alignment with all other driven pulleys using a straightedge. Misalignment from a worn water pump bearing is a common cause of belt slip or tracking issues on older GM V8 MerCruiser engines.

Parts Desk Insights

Best Use Case: This pulley is the right part when an older MerCruiser GM V8 engine is losing belts, showing vibration from a damaged or worn water pump pulley, or being rebuilt and the original pulley is beyond reuse. Because it’s discontinued, it’s worth ordering as a spare at the same time if the engine is a long-term keeper — once stock is gone, sourcing this pulley becomes difficult.

Common Issues: The most frequent mistake is not confirming the groove count before ordering. A 3-groove pulley from a similar engine looks nearly identical but will cause immediate belt misalignment. The second common issue is assuming the pulley is the problem when the water pump bearing has actually failed — a failed bearing causes wobble that damages the pulley and belt, so always inspect the pump before ordering a replacement pulley.

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