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Cat C12 Engine

Cat C12 Engines For Sale

Caterpillar C12 Engine

The C12 Caterpillar is an inline-six diesel engine intended for marine propulsion. Its wide range of horsepower ratings, 345 mhp to 497 mhp, makes it suitable for various sea-growing vessels. The C12 CAT enjoys a solid reputation thanks to its above-average performance and even better fuel economy. Its high fuel efficiency makes the C12 the definition of environmentally friendly, and it’s all thanks due to the electronically controlled fuel system that allows it to meet EPA Tier 2 commercial, IMO II, and EU IW or RCD emission standards, with the exception of the 497 mhp (490 bhp) rating at 2,300 rpm (which meets IMO I and EU RCD standards).

The C12 caterpillar is the same size, footprint, and even utilizes the same connection points as the 3196 engine. Further, the C12 can even use the same optional attachments. This makes it an attractive replacement engine choice.

Engine Applications and Uses

  • Marine

Common CAT C12 Engine Problems & Failures

Cataloged below, you'll find some of the most commonly experienced engine problems from customers inquiring about replacing their C12 CAT engines. Unfortunately, some of the failures listed typically mean complete engine replacement is the only option. However, if some of these issues are caught soon enough, most of the engine can be salvaged.

  • AERA Association MemberSpun Crankshaft Bearings
  • Cracked Cylinder Head
  • Dropped Valves
  • Camshaft Failure
  • Crankshaft Failure
  • Lifter/Roller Failure
  • Connecting Rod Failure
  • Scored Pistons and Liners
  • Overfueling
  • Lack Of Oil or Oil Pressure
  • Extreme Blow By

Caterpillar C12 Engine Replacement Options

When it comes to the health of your used engine, there could be a group of issues contributing to its poor performance. Worst case scenario, you could be left with your only choice being to completely replace the engine. Less severe issues may only require you to replace some parts or components. Of course, many engines can continue to run “OK” for a number of years. These tired C12’s are typically the best refresh candidates. In the end, cost, time, and availability will ultimately determine your decision, which is exactly why we spell out the pros and cons of buying a new CAT C12 from the dealer below.

Remanufacturing Process

A remanufactured C12 long block from Big Bear Engine Company is a great replacement option for the customer who has experienced a catastrophic internal engine failure. And this is an especially beneficial option if that customer still has functional, reusable external components that can be salvaged from their old engine. Perhaps most importantly, long blocks are a great alternative to buying new when you’re trying to reduce some of the costs associated with replacing an engine.

Our dedicated team of machinists and engine builders execute the full core tear down, cleaning, inspection, and machining of the engine before it leaves our facility, to ensure excellence each time.

We’ll also note that all of our remanufactured CAT C12 long blocks are built with a combination of both reman and new parts. We do not recondition or refurbish old engine parts. Instead, we completely rebuild your old C12 back to OEM specs.

Thorough Cleaning

Upon receiving your C12 CAT, it is stripped. The block, head, rods, crankshaft, and camshaft are all carefully cleaned in a chemical jet wash or hot tank to remove stubborn impurities that could eventually facilitate both early component and/or engine failure.


Each crankshaft is precision machined to exact tolerances, polished and magnafluxed. It is then inspected by our highly attentive quality control department.

Cylinder Head

The cylinder head is resurfaced to guarantee the proper sealing surface is present with the block, and that it has a finish compatible with the current crop of head gasket materials on the market. Valve height is mic’d and the head is also vacuum tested to ensure correct valve seating.


C12 blocks are inspected for both cracks and imperfections using magnetic particle to ensure precise identification. Its cylinders are then bored, honed, and inspected to precise tolerances. After that, we execute a process that’s geared toward eliminating the age-old culprit known as blow-by. This is achieved by torque plate honing particular engines to eliminate the chances of cylinder distortion after the head is installed and torqued to the block.


Every camshaft undergoes careful inspection and then is precisely machined to provide correct lift. Lobes are measured with a micrometer to ensure OEM tolerances are met.

Connecting Rods

Connecting rods are first cleaned, and then machined to OEM specifications before being honed to the standard diameter of original equipment (for even distribution of stress across the bearings). New bushings are fitted and machined in all bushed rods. Each rod is also carefully inspected for bend and/or twist.

New Parts

All of our C12 Caterpillar long blocks receive a standard set of new parts such as pistons and rings, bearings, gaskets and seals, and liners. These new parts assure optimal performance and reliability throughout the life of your engine. New parts are a combination of OEM and aftermarket, when available.

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Remanufactured Engine Standards

We believe that to remanufacture is to make as close to new as possible. This means that all wearable parts are automatically replaced. All C12 core material is thoroughly inspected and examined against the original equipment specifications for correct dimensional tolerances. Replacement parts are either new or requalified. If new, parts are made in an identical production process as the original equipment. Testing is also performed to manufacturer specifications and original production standards.

CAT C12 EngineCAT C12 Long Block Parts List:

  • Block
  • Complete Loaded Cylinder Head
  • Crankshaft
  • Connecting Rods
  • Timed Front Gear Group
  • Pistons
  • Rings
  • New Upper and Lower Gasket Set
  • Liners
  • Intermediate Cover
  • Followers/Lifters
  • Camshaft
  • **1 Year Warranty

*Note: We can provide a new oil pump, oil cooler, water pump, turbo, injector and fuel pump for additional cost(s) with the long block, but these components will not come assembled to the engine.

**1-Year Warranty: First 6 Months Parts & Labor, Second 6 Months Parts Replacement Only. Ask your sales representative for a full copy of our remanufactured long block warranty

CAT C12 Specs

Engine Data

ConfigurationInline-Six (I-6), 4-Stroke Diesel
Stroke5.90-inches (149mm)
Bore5.10-inches (129 mm)
Displacement12.0L (732 ci)
Rotation (from flywheel end)Counter-Clockwise

Give us a call today at 844-340-4114 for immediate sales and support for the Cummins 4BT, Cummins 6BT, 6CT, ISC, 855, QSB 4.5 L or CAT 3306. If you have any questions, check out our FAQ Page. We are always ready to help or just listen to your crazy off-roading adventures!

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