Mercury Outboard Connecting Rods, Pistons, Driveshafts, Camshafts, & Crankshafts

Mercury Marine Engine Connecting Rods, Pistons, Driveshafts, Camshafts, & Crankshafts Resources and Information 

Connecting rods, pistons, driveshafts, camshafts, and crankshafts are essential to any functioning marine outboard motor. PartsVu is happy to offer a wide variety of these certified Mercury outboard parts to fit your Mercury outboard motor. We regularly publish helpful resources over on our blog, like this guide on how to change your Mercury outboard spark plugs.

We also offer helpful resources to help you maintain your Mercury outboard motor, such as:

• Mercury Outboard Specs & Capacities Chart
• Mercury Outboard Engine Schematics
• Mercury Outboard 100-hour Service Guides

Mercury Outboard Connecting Rods, Pistons, Driveshafts, Camshafts, & Crankshafts FAQs

What is an outboard motor connecting rod? / What are Mercury outboard connecting rods?

A connecting rod connects the pistons to the crankshaft inside your Mercury outboard engine. As the pistons move up and down, the connecting rod turns the crankshaft in turn. This turns the linear motion of the pistons into rotational motion– essential for the engine’s operation.

What is an outboard motor crankshaft? /What is a crankshaft in a Mercury outboard motor?

The crankshaft inside your Mercury outboard motor is an essential engine component that converts the linear motion of the pistons into rotational motion, thereby creating propulsion. 

What are outboard motor pistons? 

Mercury outboard engine pistons turn the energy produced during combustion into mechanical motion. Each time combustion occurs in the piston chamber, the pistons move up and down moving the connecting rod and turning the crankshaft, ultimately creating propulsion. 

What is an outboard motor camshaft? / What is a camshaft in a Mercury outboard motor?

The camshaft is a rotating component that controls the timing and duration of the engine's valve openings. The Mercury outboard camshaft turns in synchronicity with the motion of the pistons, and activates the intake and exhaust valves for the cylinders. 

What is a piston in a Mercury outboard motor?

The piston is a vital component of the engine that moves up and down inside the cylinder. It is responsible for compressing the air and fuel mixture before ignition and converting the energy of the expanding gases into mechanical motion.

What is a driveshaft in a Mercury outboard motor?

The driveshaft is the component that transmits the power generated by the engine to the propeller. It connects the transmission to the lower unit of the outboard motor and is responsible for turning the propeller.

How do I change my Mercury 4-stroke outboard spark plugs?

For most applications, the spark plugs come pre-gapped, but it is advisable to re-check gap to make sure that plugs were not damaged during manufacturing or shipment.

While removing the old spark plugs, keep track of which plugs come from which cylinders.

• Note if the plug appears to be wet from water, oil, or gasoline.
•  Note if the plug exhibits evidence of heavy carbon deposits or other fowling as well as any rust – all indicative of problems.

If you were to take your engine to a dealer for your 100-hour service, they would perform a compression test by connecting a compression gauge to the individual cylinders and using the starter motor to turn over the engine. By measuring the engine’s ability to pressurize the cylinder, you can glean information about the condition of the engine internals. To perform this test at home, you will either need a remote starter button, or a friend who can turn the ignition key with the kill lanyard removed.

This cranking with the ignition disabled will also prime the fresh oil around the block, reducing friction at startup after the service. Repeat testing for all cylinders and compare results. Readings will vary from gauge to gauge, so the test is more about measuring the difference in readings with ideal results being less than 10 percent variance.

After the compression test is completed – or skipped – you can now begin installing your new spark plugs. For ease of future removal and to reduce the risk of thread damage to the cylinder head, apply a tiny amount of anti-seize compound to the threads of the plug. Use care to avoid contacting the electrode or porcelain center of the plug. Thread the plugs into the cylinder head by hand using caution not to cross thread.

Most modern spark plugs use a crush washer that will press down and provide a tight seal as you tighten. Full torque is between 18-21 ft. lbs. Reinstall the plug wires or coils in the same order they came off. Mercury’s service manual recommends using Loctite 271 (Red High Strength) on the bolts that hold the pencil coils over the spark plug, but we find Loctite 242 (Blue Removable Strength) might be a better choice.

How do I change my Mercury 2-stroke outboard spark plugs?

The Mercury 2-stroke spark plugs and compression 100-hour service step begins by removing any plastic covers covering your spark plugs or ignition coils. Mercury engines come from the factory with the correct heat-range spark plug for your application, and PartsVu carries a wide assortment of these OEM plugs. For most applications, the spark plugs come pre-gapped, but it is advisable to re-check gap to make sure that plugs were not damaged during manufacturing or shipment.

While removing the old spark plugs, keep track of which plugs come from which cylinders.

•  Note if the plug appears to be wet from water, oil, or gasoline.
•  Note if the plug exhibits evidence of heavy carbon deposits or other fowling as well as any rust – all indicative of problems.

If you were to take your engine to a dealer for your 100-hour service, they would likely perform a compression test by connecting a compression gauge to the individual cylinders and using the starter motor to turn over the engine. By measuring the engine’s ability to pressurize the cylinder, you can glean information about the condition of the engine internals. 

This cranking with the ignition disabled will also prime the fresh oil around the block, reducing friction at startup after the service. Repeat testing for all cylinders and compare results. Readings will vary from gauge to gauge, so the test is more about measuring the difference in readings with ideal results being less than 10 percent variance.

After the compression test is completed – or skipped – you can now proceed with your Mercury 2-stroke spark plugs and compression service by installing your new spark plugs. For ease of future removal and to reduce the risk of thread damage to the cylinder head, apply a tiny amount of anti-seize compound to the threads of the plug. Use care to avoid contacting the electrode or porcelain center of the plug. Thread the plugs into the cylinder head by hand using caution not to cross thread.

Why should I use Mercury fuel additives?

Quickare treats and stabilizes fuel at every fill-up which is necessary because just about all gasoline today contains up to 10% ethanol. Left untreated, ethanol-blended fuel can break down leading to gum and varnish build-up which causes internal engine corrosion. Fuel additives such as a bottle of Quickare keep fuel fresh between fill-ups for up to three months.

The second step within Mercury’s fuel care system cleans your engine and fuel system. All combustion motors develop carbon deposits and the best way to clean those deposits is to add Mercury Quickleen to your fuel tank. Simply add a bottle of Quickleen to your outboard fuel tank once per year to remove carbon deposits, prevent engine knocking, piston seize up, and extend spark plug life. Aggressive fuel system cleaner within Quickleen works to quickly and thoroughly remove carbon deposits from carburetors and fuel injectors, intake valves, spark plugs, piston crowns, and cylinder heads.

Likely, there are periods when your boat is stored or is used infrequently, which can lead to issues with your engine running. If your boat will be sitting for an extended period of time, you need to add a fuel stabilizer like Mercury Marine Quikstor to prevent both regular and ethanol-blended fuels from breaking down, oxidizing, and causing fuel system corrosion, and eventually affecting the engine’s performance. Before storage add a bottle of Quickstor to your fuel tank, then run the engine so that the treated fuel circulates throughout the engine and fuel lines. This extended fuel stabilizer prevents gum and varnish from forming in the engine, fuel lines, and tank and stabilizes fuel for up to one year, thereby successfully averting any fuel-related problems. One ounce of Quickstor treats five gallons of fuel, so a 12-ounce bottle treats 60 gallons.

How do I select the right parts for my Mercury outboard motor?

PartsVu’s Mercury Outboard Maintenance Parts Library is the perfect reference when you need to replace common parts. That’s because these parts charts make it simple to find the right parts for your particular engine to perform regularly-scheduled maintenance. 

For Mercury outboard motors, perform maintenance after 100 hours of service or one year of operation (whichever comes first). More extensive service is recommended after 300 hours of service or three years.

After this period, maintenance is often more regular as the engine ages and parts wear out. For example, 1,000 hours generally requires an in-depth assessment by a qualified mechanic. Also, if you’re usually running your Mercury outboard in a more demanding manner, the manufacturer recommends more frequent servicing.

When selecting the correct Mercury Outboard Parts, there are some essential things every boater must keep in mind before purchasing and installing parts:

• Choosing Mercury OEM parts (original equipment manufacturer) over after-market parts often yields better long-term results for your engine as these components and products are specifically designed to meet the precise tolerances of Mercury engines.

• Check (and recheck) to ensure that you have the exact part number that matches your Mercury outboard engine. It’s important to do this because Mercury has many engine models that look very similar but contain slight differences in performance. Therefore, unmatched parts may not fit uniformly, leading to malfunctions, underperformance, and severe engine damage.

• Proper maintenance is essential when it comes to extending the life of your Mercury outboard motor and should always be mandatory to retain the value of your outboard motor. While Mercury outboards are built to last, hazards like salt water, humidity, excessive heat, electrolysis, and demanding usage eventually take their toll on your motor.

• Proper storage for your Mercury outboard is required to preserve your motor for the long term. Failure to properly winterize your Mercury outboard can cause components to degrade while the engine sits and is exposed to the elements. Therefore, properly store your outboard when it is not in use.

Why is my Mercury outboard leaking water from the crankshaft seal?

If your Mercury outboard motor is leaking water from the crankshaft seal, there are a few potential causes:

1. Damaged or worn crankshaft seal: The crankshaft seal is designed to prevent water from entering the engine through the crankshaft. If the seal becomes damaged or worn, it can allow water to leak into the engine.
2. Corroded or pitted crankshaft: If the crankshaft is corroded or pitted, it can cause the crankshaft seal to wear more quickly and allow water to leak into the engine.
3. Improperly installed crankshaft seal: If the crankshaft seal was not installed correctly during the last service or repair, it may not be sealing properly and could be allowing water to leak into the engine.
4. Excessive pressure or vibration: If the engine is running at high RPMs or experiencing excessive vibration, this can put additional stress on the crankshaft seal and cause it to leak.

It's important to address a leaking crankshaft seal promptly, as water in the engine can cause serious damage to internal components. We recommend taking your outboard to a qualified technician who can diagnose the problem and recommend the appropriate repair. In most cases, the faulty seal will need to be replaced, and the crankshaft inspected for any damage or wear that could cause the new seal to fail prematurely.

How to remove driveshaft from Mercury outboard?

The process for removing the driveshaft from a Mercury outboard can vary depending on the specific model and year of the motor, but here is a general process that should work for most models:

1. First, make sure the outboard is in neutral and the ignition is off. Disconnect the battery cables to prevent accidental starting.
2. Remove the propeller and the propeller nut. Depending on the model, you may need a special tool to remove the nut.
3. Remove the lower unit from the outboard by removing the bolts that hold it in place. The location and number of bolts can vary, so consult your owner's manual for specific instructions.
4. Once the lower unit is removed, you should be able to see the driveshaft. Use a pair of pliers or a wrench to remove the bolt or nut that secures the driveshaft to the engine. Be careful not to damage the threads or the shaft itself.
5. With the bolt or nut removed, you should be able to pull the driveshaft straight out of the engine. Be careful not to drop it or damage it in any way.
6. Inspect the driveshaft and the seal that it passes through for any signs of wear or damage. If necessary, replace the seal or any worn components before reassembling the outboard.
7. To reinstall the driveshaft, simply reverse the steps above. Make sure the shaft is properly aligned with the engine and that the bolt or nut is tightened to the correct torque specification. Finally, reinstall the lower unit and propeller.

What are the best brand of after market crankshaft (Mercury outboard motors)?

There are several reputable aftermarket brands that manufacture crankshafts for Mercury outboard motors. Some of the most well-known brands include:

1. Wiseco: Wiseco is a popular brand that offers a range of high-performance crankshafts for Mercury outboard motors. Their crankshafts are made from high-quality materials and are designed to provide improved performance and reliability.
2. ProX: ProX is another well-respected aftermarket brand that produces high-quality crankshafts for Mercury outboard motors. Their crankshafts are engineered to meet or exceed OEM specifications and are backed by a solid warranty.
3. Hot Rods: Hot Rods is a brand that specializes in high-performance crankshafts and connecting rods for a wide range of motorsports applications, including outboard motors. Their crankshafts are made from high-strength steel alloys and are designed to withstand the stresses of high-performance use.
4. OEM: If you prefer to stick with the original equipment manufacturer, Mercury Marine also offers a range of genuine OEM crankshafts for their outboard motors. While these may be more expensive than aftermarket options, they are designed to meet the highest quality standards and are backed by Mercury's warranty.

Ultimately, the best brand of aftermarket crankshaft for your Mercury outboard will depend on your specific needs and budget. It's important to do your research and choose a reputable brand that offers the right combination of performance, reliability, and value for your application.

Where can I learn more about Mercury Outboard Parts?

PartsVu understands that boaters want to learn how to perform their own Mercury outboard maintenance. From maintaining your Mercury outboard, Mercury sterndrive, and MerCruiser engines, there’s always something new to learn and save money. That’s why PartsVu offers our comprehensive blog, The PartsVu Xchange. 

Read up on the latest developments in boating, as well as search for everything you need to know about Mercury engine maintenance.

To get you off to a good start, these are some of the most important articles on Mercury Mariner outboard news, Mercury outboard crankshaft repair, and more:

• How To Protect Your Mercury Outboard
• Mercury Outboard Season Breakout
• Mercury Fuel Additives for Performance and Engine Life
• Guide to Mercury Marine Precision Oils & Lubricants

Where can I buy genuine Mercury outboard connecting rods, pistons, driveshafts, camshafts, and crankshafts?

Genuine Mercury parts can be purchased from authorized dealers or online retailers that specialize in Mercury outboard parts and accessories. It is important to use only genuine Mercury parts to ensure proper fit and reliable operation of your outboard motor.

What is stronger H-beam or I-beam connecting rods?

Both H-beam and I-beam connecting rods can be strong and reliable when properly designed and manufactured. However, H-beam connecting rods are generally considered to be stronger and stiffer than I-beam connecting rods, due to their thicker and wider cross-section.

What is the best metal for connecting rods?

The best metal for connecting rods depends on several factors, including the intended use of the engine, the desired level of performance, and the budget. Common materials for connecting rods include steel, titanium, aluminum, and various alloys. Each material has its own advantages and disadvantages in terms of strength, weight, and cost.

What is the difference between H and I-beam connecting rods?

The main difference between H-beam and I-beam connecting rods is their shape. H-beam rods have a thicker, wider cross-section that resembles the letter "H", while I-beam rods have a thinner, narrower cross-section that resembles the letter "I". H-beam rods are generally considered to be stronger and stiffer, while I-beam rods are lighter and more economical.

Do connecting rods add horsepower?

Connecting rods themselves do not add horsepower, but they can help support increased horsepower by providing a stronger and more reliable connection between the piston and crankshaft. Upgrading to stronger, more durable connecting rods can allow an engine to handle more power without experiencing failures or damage.

What does the driveshaft do?

The driveshaft is a component of the drivetrain that connects the transmission or transfer case to the rear differential in rear-wheel drive vehicles, or the front differential in four-wheel drive vehicles. Its primary function is to transfer power from the engine to the wheels, allowing the vehicle to move.

How do I know if my driveshaft is bad?

Symptoms of a bad driveshaft can include vibrations, clunking or rattling noises, difficulty shifting gears, and a shaking or wobbling sensation while driving. If you suspect that your driveshaft may be failing, it's important to have it inspected by a qualified technician as soon as possible to prevent further damage or failure.

What does a driveshaft cost?

The cost of a driveshaft can vary widely depending on the make and model of the vehicle, as well as the specific type of driveshaft needed. In general, replacement driveshafts can cost anywhere from a few hundred to several thousand dollars.

Can I drive with a bad driveshaft?

Driving with a bad driveshaft is not recommended, as it can cause serious damage to other components of the vehicle and potentially lead to an accident. If you suspect that your driveshaft is failing, it's important to have it inspected and repaired by a qualified technician as soon as possible.

What are Mercury outboard piston kits?

Mercury outboard piston kits are packages that include all the components needed to replace a piston in your Mercury outboard motor. These kits typically include a piston, piston rings, wrist pin, and circlips.

When should I replace the pistons in my Mercury outboard?

You may need to replace the pistons in your Mercury outboard if you notice symptoms such as low compression, engine misfires, or excessive oil consumption. It's also a good idea to inspect your pistons during routine maintenance to ensure they are in good condition and not showing signs of wear or damage.

How do I know which size pistons to order for my Mercury outboard?

The size of the pistons you need will depend on the make, model, and year of your Mercury outboard. You can find this information in your owner's manual or by contacting a qualified Mercury dealer or technician.

What is a Mercury outboard piston ring compressor, and do I need one for my Mercury outboard piston replacement?

A piston ring compressor is a tool used to compress the piston rings and make it easier to install the piston into the engine block. While it's not strictly necessary to use a piston ring compressor for Mercury outboard piston replacement, it can make the process faster and easier.

What should I look for in Mercury outboard piston rings?

When selecting piston rings for your Mercury outboard, look for rings that are made from high-quality materials such as stainless steel or chrome. You should also ensure that the rings are the correct size for your pistons, and that they are designed to withstand the high temperatures and pressures present in your engine.