Marine Crankshaft Seals – Functions, Failure, & Replacement

The functioning of the crankshaft involves the continued flow of lube oil across the main bearing journal and the engine oil at the front and rear extensions of the crankcase. There are drill holes on the crank web to allow smooth passage of lubricant along different parts. The crankshaft regulates the flow of oil through the bearing and the journal as the crankpin moves upward and the connecting rods move downward under the influence of combustion forces. However, the oils may still flow out of the system through the extension at both ends. Herein, marine crankshaft seals (also called oil seals) take center stage. This post highlights the functions and importance of marine crankshaft seals. Read the entire guide to explore why vessel owners always need a pack of new crankshaft seals handy.

What are Marine Crankshaft Seals/ Oil Seals

The crankshaft has a robust housing or crankcase to integrate the crankshaft within the engine block. There are open extensions beyond the crankcase at both ends. During high vibration in the engine, the oils can leak from both the front and the rear extensions. A marine crankshaft seal is a type of metal shell. It sits at both extensions with the help of a soft rubber lip loaded with a spring at the inner circumference. These seals create a protective closure to prevent oil spilling, contamination, and wastage. Marine crankshaft seals perform an extra role in securing the engine oil system. These heavy-duty components prevent seawater from entering the crankshaft and engine parts, as well as oil contamination. There are two types of marine crankshaft oil seals to protect the engine oil system:

Front-end Crankshaft Oil Seal

It is mandatory to secure the extension behind the timing chain and the pulley with the front crankshaft seal. The function is similar to that of the rear-end oil seals but may vary in size and structure. Since the extension lies at the front of the engine, the failure and leakage in these seals do not affect the engine's parts or performance. However, oil leaking from the front-end seal results in heavy grease deposits on the timing gear, causing potential damage.

Rear-end Crankshaft Oil Seal

The rear crankshaft seal is located on the backside of the engine, at the point of transmission between the oil pan and the engine block. It is very close to the flywheel and the main journal. Hence, the impact of vibration is higher on these seals compared to those present at the front end. Rear-end oil seal failure, or leakage causes a loss of engine oil in significant quantities. These seals are constantly under pressure and always deal with heavy fluid presence during the engine operation. The rear crankshaft seals feature a molded lip for secure fixation to the crank using a snap spring.

Crankshaft Seal Failure and Replacement

The soft and pliable marine crankshaft seals also exhibit signs of wear and tear after a specific number of maintenance hours. There are several reasons for worn-out crankshaft oil seals and oil leaking from the extension, even after replacing the faulty one with a new piece. Here is a quick roundup of crankshaft seal failure in marine engines:

Cheap Aftermarket Parts

In most cases, oil leaking from a new rear-end crankshaft seal is often evident in equipment with one or more aftermarket parts. A cheap oil seal on the market is a lucrative choice for boat owners to save a few dollars on replacement crankshaft seals. However, the poor material quality and inaccurate fittings are vulnerable to damage within a few days of operation. At Alfa Marine Spare Parts, the sales representatives always match the required components with the exact part number of an OEM product. Equipment manufacturers produce these items specifically for the corresponding crankshaft models. It ensures safety and accurate dimensions for secure fittings. Explore the crankshaft oil seals in our product gallery below. We have also provided additional details to support an informed purchase decision.

Missing the Engine Oil Changing Schedules

Once the marine engineers flush out the old engine oil and replace it with fresh fluid, the engine and crank continue to function effortlessly with the new oil. However, the dose is based on specific engine miles and replacement after reaching the designated hours. The engine oil accumulates enormous heat and pressure while running for extended periods. The impact of the heat and chemicals in the oil gradually harden the seals around the edges. The hard seals are prone to wearing quickly and fail to protect the extension from leaking. Another cause of oil leaking from new marine crankshaft seals is the rapid formation of grooves in the seal. The groove can loosen the seal structure considerably. Seals with grooves lack the required tension at the sealing surface, preventing oil from escaping through the extension. The engineers often recommend using additional parts (a repair sleeve) to resolve these issues in the crankshafts. Covering the balancer sealing surface with a thin and tight sleeve is a safe option. The technicians may apply a special adhesive to the sleeve to strengthen the bond around the sealing surface.

Faulty or Misaligned Crankshaft  

The marine crankshaft seals can leak due to problems in other parts of the crank. Here are a few issues in the crankshaft that may cause engine oil leakage from the seals at both ends:

• Worn or chipped crankshaft bearings
• Bending in the main shaft
• Up and down movement of the pulley bottom
• One or more engine parts are worn out
• Faulty seal installation

Gap Between the Metal Shell and the Recession

Marine technicians use sealers to press the seals into the recessed area. The sealant provides a friction fit on the shell and keeps the seal in its intact position. Only high-quality sealants can fill the gap between the shell and the recess, preventing oil spillage. Otherwise, the fluid can easily flow out through the void area between the recessed area and the metal shell.

Buy OEM Marine Crankshaft Seals Online

Do you want to purchase crankshaft oil seals at the best market prices? Visit our official site for the unending array of genuine marine spare parts from Caterpillar, Cummins, Perkins, Yanmar, and more. Shopping at Alfa Marine Spare Parts is safe, easy, affordable, and convenient for fleet owners, shipbuilders, offshore units, and ship repair service providers. Whether you're looking to purchase bulk items or a single piece, our best-in-class services offer peace of mind and value with comprehensive warranties, fast shipping, and more. Here is a list of top-rated marine crankshaft seals of all types. Click on the part number to navigate to the main product page for more details.

Genuine Cat Crankshaft Seals

The NPI-style and Lip-type Cat crankshaft seals secure the front and rear extension of the crank. These small components protect the engine oil and the crankshaft lube oil from leaks and spills. Moreover, such marine crankshaft seals create a secure barrier to prevent engine oil contamination. The primary material composition in Cat crankshaft seals comprises ACM (polyacrylate), Carbon Steel, Teflon Plastic, and Polytetrafluoroethylene (PTFE). Here is a quick roundup of crankshaft seals for Caterpillar marine engines in our inventory: 7E-7589 4W-5360 - Crankshaft Rear Seal Used In Cylinder Block 434-9887 - Crankshaft O-ring 285-4073 - Crankshaft Seal Assembly 227-0838 - Crankshaft Seal Assembly 169-4166 - Crankshaft Seal (CW Rotation) 3S-7569 - 0.195" Thick Rear Oil Seal Adapter used in Crankshaft 4W-2569 - Standard Rotation Rear Crankshaft Conversion Seal with Adapter and Gasket 7C-7473 - SEAL GP-CRAN-7C-7473 450-6178 - SEAL GP-CSHA-450-6178 276-4756 - SEAL GP-BASI-276-4756 239-8429 - Crankshaft Seal Assembly (Front) 187-8971 - SEAL GP-CSHF-187-8971 172-1768 - SEAL AS-172-1768 147-5088 - SEAL A.-WTR-147-5088 7C-3571 - SEAL GP-7C-3571 244-1645 - SEAL GP-BASI-244-1645 128-0317 - SEAL GP-128-0317 376-2593 – crankshaft seal kit 4R-9999 - Reman Crankshaft Seal Excluder prevents oil leakage and ensures proper sealing around the crankshaft in the engine, maintaining optimal performance

OEM Yanmar Crankshaft Seals

YM-129795-01800 - FRONT CRANKSHAFT SEAL - 4TNV88-GNP / 4TNV88-XMS YM-129648-01780 - REAR CRANKSHAFT SEAL - 4TNV88-BPHB YM-129120-01780 - REAR CRANKSHAFT SEAL - 4TNV88-BDHQ / 4TNV88-BDHQ(T) / 4TNV88-BDSA CH11379 - CRANKSHAFT OIL SEAL - 2306 / 2806 / 2506TAG3 / 2506C / 2506TAG4 (FRONT) CH11304 - CRANKSHAFT OIL SEAL - 2306 / 2506 / 2806 / 2506TAG3 / 2506C / 2506TAG4 (REAR)

Genuine Perkins Crankshaft Seals

T410666 - CRANKSHAFT OIL SEAL - 1204F-E44TTA / 1204E-E44TA / 1206E-E70TTA (FRONT) T406781 - CRANKSHAFT OIL SEAL - 1206E-E70TTA / 1206F-E70TTA (FRONT) 2418F705 - REAR CRANKSHAFT OIL SEAL - 1206E-E70TTA / 1206F-E70TTA 2418F704 - CRANKSHAFT OIL SEAL - 1204F-E44TTA / 1204E-E44TA / 1204F-E44TA 2418F437 - OIL SEAL (FRONT) 2418F701 - OIL SEAL - 4.236 / 1004 / 1006 (REAR) 2418F437 - REAR OIL SEAL 2415344 - FRONT OIL SEAL - 3.152 / 4.203 / 900 T412661 - SEAL - 854E / 854F (REAR END) T400452 - OIL SEAL - 854E / 854F (FRONT END) 50209107 - OIL SEAL - 100 / 400 (REAR) 50209083 - OIL SEAL - 100 / 400 (REAR) 198636090 - OIL SEAL - 100 / 400 (FRONT) 2418F475 - OIL SEAL - 4.236 / 6.354 (REAR) 36883119 - REAR OIL SEAL - 3.152 / 4.203 36883116 - OIL SEAL - 4.236 / 6.354 (REAR) If you cannot find the required crankshaft spare part or engine component in our gallery, please don't hesitate to contact our sales support team. We can help with the purchase of rare marine engine parts. Expect the shipping in 5-7 business days (subject to availability of the item in our stocks).