Yamaha Cylinder Heads & Blocks

YamahaOnlineParts.com provides replacements for the OEM cylinder heads and blocks for Yamaha outboard motors. Yamaha applies die-casting with high quality to craft their OEM cylinder blocks and cylinder heads for their Yamaha outboard motors. If you are wondering how to maintain your Yamaha outboard motor, it is likely that you can find the answers you need in our blog.

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Yamaha Cylinder Heads and Blocks FAQs

What is an outboard cylinder head?

The Yamaha outboard powerhead contains a critical component known as the cylinder head, which is located atop the cylinders and holds the camshafts, cams, sparkplugs, and shafts.

What is an outboard block?

The Yamaha outboard powerhead contains a critical component known as the cylinder head, which is located atop the cylinders and holds the camshafts, cams, sparkplugs, and shafts.

How do I perform spark plug and compression maintenance on my Yamaha outboard motor?

To ensure the longevity and dependability of your outboard, it is important to perform Yamaha spark plugs and compression servicing. Start this step of the Yamaha 100-hour service by taking off the plastic cover over the spark plugs or coils. Yamaha engines are normally equipped with NGK branded spark plugs, and YamahaOnlineParts.com offers a variety of these original plugs. Generally, these spark plugs come with the gap pre-set, however, it is recommended to double-check the gap to guarantee that none of the plugs has been harmed during the production or delivery process.

When taking out the used spark plugs, make sure to jot down which plug is from which chamber. If the spark plug is soaked in water, oil, or fuel, remember to make a note of it. Additionally, if the spark plug is coated in heavy carbon deposits, some other type of dirt, or rust, take note of that too since they may be indicative of more serious issues. If you were to have your motor serviced at a dealership for every 100 hours, they would employ a compression gauge to assess each cylinder and use the starter motor to spin the engine and check the pressure of each chamber.

To conduct this examination in your own home, you must either have a remote start button or someone to turn the ignition key with the kill lanyard taken away. Doing this with the ignition turned off will also propel the new oil around the block, diminishing the friction when the service is done. Test the cylinders again and review the results. Because of the difference in gauges, the assessment is more about noticing a discrepancy in readings with the best outcome being a difference of no more than 10 percent.

Once you have finished the compression test, or chose to skip it, you can start to install your new spark plugs. To make them easier to remove later and stop the threads of the cylinder head from becoming damaged, dip a finger in some oil and then apply a small drop to the plug threads. Be careful not to get any on the electrode or porcelain of the plug. Screw the plugs into the cylinder head by hand and take care not to cross-thread them. NGK has a crush washer that will press down and form a tight seal as the plugs are tightened to the recommended torque of 18-21 ft. lbs. Remember to put the plug wires or coils back in the same order as before and use a bit of Yamaha grease on the threads of the bolts, coils and covers.

How do I know if I have water in my Yamaha outboard engine block?

When you notice water in your Yamaha outboard engine, the first thing to check is the Yamaha thermostat. This is the most straightforward way to diagnose the issue before having to disassemble the engine and investigate a possible porous engine block, cracked cylinder head, eroded exhaust-water passage, frozen oil cooler, or any other laborious problems. It's important to remember that certain Yamaha engines, such as V-engines, have two thermostats.

To find the Yamaha thermostat(s), it is essential to consult the service manual as the location depends on the engine. The service manual indicates that you need to submerge the thermostat in hot water and ensure it opens and closes at the right temperature. If you don't have access to this technique, an infrared temperature gun can be utilized at the thermostat housing to measure the engine temperature. Once again, check the service manual for the correct temperature range.

If you recognize that the engine is not sufficiently heated, it is likely that the thermostat is not closing. You should take out the thermostat housing and examine it. If it is not closing properly, switch it out with a fresh one and make sure to do multiple oil and filter changes to make sure that the motor's oil is devoid of water.

You may be curious how water can get into the oil if the thermostat is stuck open. If the engine is running cold, the contrast between hot oil and a chill engine can create condensation. This condensation will eventually transform into water and drip into the oil. When the engine is cool, water is not the only pollutant that can find its way into the oil. The piston rings, which are not in full form as the engine is cold, cannot form an effective seal against the cylinder wall of the Yamaha outboard. This may allow a minor portion of raw fuel to continuously leak into the sump. If this condition persists for a long time, the oil may develop a milky residue. Additionally, junk can get caught in the thermostat, preventing it from returning to the closed position.

If you think the engine oil might have been contaminated with water, there are two quick tests you can do. The first is to take off the oil cap and look at the bottom to see if there is any water present. The second is to take out the dipstick and examine it for moisture. Both of these methods are reliable. To keep Yamaha thermostat problems at bay, make sure to clean the engine periodically according to the instructions provided by the manufacturer.

When should I change my Yamaha 4-stroke outboard engine’s spark plugs?

Boaters should regularly remove and inspect the spark plugs from their Yamaha four-stroke outboard motor; it's recommended to do so every 200 hours or once each season. The spark plugs should have a light brown hue and the edges should still be relatively sharp. When it's time to replace them, ensure you are using the same manufacturer and exact part number as recommended by your outboard's manufacturer. This is important because the brand, type, and style of spark plug are designed to provide optimal performance for your outboard.

What is a leakdown test?

To assess the state of each cylinder and the whole motor of a Yamaha outboard motor, a leakdown test is done. This procedure is much like a compression test, where air is forced into each cylinder and the pressure that is dropped after a certain amount of time is estimated through a pressure gauge.

A leakdown test of an engine requires one to pay attention to the sounds of the cylinders and their respective surroundings in order to detect any potential leaks.

The purpose of a pressure test is to determine if there are any air leaks in the motor. When air is either present or absent in engines, it can result in the leaking of fuel-air mixtures and the spilling of fuel while the motor is running.

When fluids from the surrounding environment seep into these openings, it can create a number of problems, including inner corrosion, lack of responsiveness (either when the engine is stationary or running at low or high speeds), and other difficulties.

How do I perform a leakdown test on my Yamaha outboard engine?

Start by taking off the top Yamaha shielding cover and afterward, take out the spark plug casing situated at the back of the engine.
Take out the spark plugs and make sure to arrange them in numerical sequence for when you need to put them back in or exchange for new ones.
Take the flywheel cover off from the engine's upper part.
Utilizing a marker, label the flywheel at the 0°, 120°, and 240° points. These markings will represent the locations to which each set of cylinders need to be turned to reach their top-dead-center spots (see Steps #11 and #12).
Utilizing a ratchet and socket, turn the crankshaft of the Yamaha Yamaha cylinder #1 to the highest point of its stationary position.
To ensure an accurate reading, adjust the regulator on the leak down tester to zero percent.
Attach the leak-down tester to the spark plug port of the first cylinder by screwing it in place. Then, link the tester up to the compressor and take the reading. Be certain to grasp the crankshaft tightly so that it won't spin.
Turn the crankshaft in a complete circle so that the Yamaha cylinder number 4 is situated at the highest point of its stroke.
Attach the leak-down tester to the fourth cylinder before stopping the crankshaft from turning and recording the measurement.
Move the third cylinder of the Yamaha engine up to the highest point where it stops and make sure it is at the 120° mark. Afterward, repeat the seventh to tenth steps for the third and sixth cylinders of the Yamaha motor.
Position cylinder #2 to the highest point of inactivity at 240°. Afterward, repeat steps 7 to 10 for Yamaha cylinders #2 and #5.
Taking out and putting in components is the same process. It is important to make sure to change the spark plugs in a sequence and use an anti-seize substance on the threads to ensure it can be taken out and put back in quickly. Additionally, ensure that the ignition cables are firmly secured to make sure the connection is good.