125018 O-Ring | Genuine Volvo Penta Part

🔧 Product Description

This is a genuine Volvo Penta O-ring seal in the 29.7 x 3.53 mm size, supplied as the late-design version of the seal for this location. It provides a static sealing joint between mating components on a broad group of classic Volvo Penta petrol and diesel marine engines and their drive assemblies. Because O-rings of the same generic name differ only by section and diameter, confirm the 29.7 x 3.53 mm dimension before ordering.

🚤 Compatibility

• Engine Family: AQ, MD, TMD, AD, AQAD, BB, TAMD, MS, B, AQD, MB
• Year Range: Approximately 1970s-1980s

Full model list at the end of this description.

⚙️ Key Features

• OEM Volvo Penta part number 125018
• Dimension: 29.7 x 3.53 mm
• Late-design (later production) version of the seal
• Fits classic Volvo Penta AQ, MD, TMD, TAMD, AD, BB, MB and MS series marine petrol and diesel engines
• Supplied as a single O-ring
• System type: Internal clutch, shaft or gear-housing oil seal
• 8 used per assembly

🔌 Function

The O-ring forms a compressed static seal between two mating surfaces or around a shaft or fitting, preventing oil, coolant, fuel or water from escaping the joint. Correct section thickness and inside diameter are essential for the seal to seat and hold pressure.

⚠️ Common Signs of Failure

• Weeping or dripping fluid at the joint the O-ring seals
• Hardened, cracked or flattened rubber that has lost its round cross-section
• Swollen or softened material from fluid or heat degradation
• Loss of system pressure or air being drawn into the joint
• Visible nicks, cuts or extrusion of the ring from its groove during disassembly

🛠️ Service Notes

• Always fit a new O-ring — never refit one that has been removed, as it has already taken a set in its groove
• Clean the groove and both sealing faces and check them for nicks, scoring and corrosion pitting; a damaged groove will leak however good the new seal is
• Smear the ring with a little clean lubricant compatible with the fluid it seals, then roll it into place by hand so it sits untwisted and fully in its groove
• Never lever an O-ring over a sharp edge or thread with a screwdriver; use a blunt plastic tool and protect any edge the ring has to pass
• Assemble the joint squarely and tighten to the figure and sequence given in the workshop manual for your engine — over-tightening extrudes the ring and causes the very leak you were curing

🔄 Supersession & Cross Reference

OEM / Related Numbers

• 875628 earlier MS3 gasket kit
• 876400 later MS3 gasket kit
• 850413 MS3 reverse gear, ratio 1.91:1
• 850417 related slip clutch
• 852072 related slip clutch
• 925256 companion O-rings
• 925069 companion O-rings
• 942353 companion O-rings
• 958879 related sealing ring

📦 Condition

• Genuine Volvo Penta part
• Brand new
• Supplied in original or equivalent packaging

🔎 Full Model Compatibility

Typically suits:

• Volvo Penta AQ130C, AQ130D, AQ130A, AQ130B
• Volvo Penta AQ170B, AQ170C, AQ170A
• Volvo Penta BB115A, BB115B, BB115C
• Volvo Penta BB170B, BB170C, BB170A
• Volvo Penta BB260AV, BB260B, BB260C
• Volvo Penta MB20A, MB20B, MB20C
• Volvo Penta TMD40A, TMD40B, TMD40C
• Volvo Penta AQ115A, AQ115B
• Volvo Penta AQ260A, AQ260B
• Volvo Penta AQAD40B, AQAD40A
• Volvo Penta AQD21A, AQD21B
• Volvo Penta MD21B, MD21A
• Volvo Penta MS3B, MS3C
• Volvo Penta 100S, 110S
• Volvo Penta TAMD40A, TAMD40B
• Volvo Penta AD40B
• Volvo Penta AQ120B
• Volvo Penta AQ125A
• Volvo Penta AQ140A
• Volvo Penta AQ165A
• Volvo Penta AQD40A
• Volvo Penta B20
• Volvo Penta BB140A
• Volvo Penta BB145A
• Volvo Penta BB165A
• Volvo Penta MD30A
• Volvo Penta MD40A
• Volvo Penta TAMD30A
• Volvo Penta TMD30A