Cylinder Heads and Blocks for Yamaha Outboards

Yamaha Outboard Replacement OEM Cylinder Heads and Blocks Resources and Information

PartsVu.com is happy to offer a broad selection of replacement OEM cylinder heads and blocks for Yamaha outboard motors. If you have questions about performing maintenance on your Yamaha outboard, chances are you’ll find the answers in our blog. 

We also regularly release new helpful resources like: 

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

Looking for more components and products to service your Yamaha outboard engine? Feel free to shop our complete selection of Yamaha outboard parts.

Yamaha Cylinder Heads and Blocks FAQs

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

Performing Yamaha spark plugs and compression maintenance on your outboard is one of the keys to its overall longevity and reliability.

Begin this step of your Yamaha 100-hour service by removing the plastic shrouding over your spark plugs or ignition coils. Yamaha engines come from the factory with NGK brand spark plugs, and PartsVu carries a wide assortment of these OEM plugs. In most applications, the spark plugs come pre-gapped, but it is advisable to re-check the gap to make sure that no plugs were damaged during manufacturing or shipment. Again, the information in your owner’s manual is helpful – or you can consult our Yamaha Engine Specifications and Capacities Chart. 

As you remove 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, other fouling, or rust – all indicative of other problems. If you were to take your engine to a dealer for 100-hour service, this is the point at which they would perform a compression test by connecting a compression gauge to the cylinders individually and using the starter motor to turn the engine over and check its ability to pressurize the cylinder. If you are going 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 is complete. 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 a 10 percent variance.

With the compression test completed – or skipped – you can now begin installing your new spark plugs. For ease of removal and to reduce the risk of thread damage to the cylinder head, apply a drop of oil with the tip of your finger to the threads of the plug using care to avoid wetting the electrode or porcelain center of the plug. Thread the plugs into the cylinder head by hand using caution not to cross thread. NGK uses 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 and use a small amount of Yamaha grease for the threads of the bolts, coils, and covers.

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

If you are confronted with water in your Yamaha outboard engine, the first place to look before disassembling the engine and checking for a porous Yamaha outboard engine block, cracked Yamaha cylinder head, eroded exhaust-water passage, frozen oil cooler, or other labor-intensive issues, is the Yamaha thermostat. Remember that some engines have two thermostats, like Yamaha’s V-engines.

To locate the Yamaha thermostat(s), be sure to refer to the service manual as the location varies by the engine. The service manual procedure states that you should put the thermostat in a pot of hot water and check if it opens and closes at the correct temperature. If you do not have access to this method, then an infrared temperature gun can be used at the thermostat housing to get an indication of engine temperature. Again, refer to the service manual for the correct temperature operating range.

If you’ve determined that the engine is running cold, it’s a good indicator that the thermostat is stuck open. Remove the thermostat housing and inspect it. If it is stuck open, replace the thermostat with a new one, and be sure to do several oil and filter changes to ensure water is removed from the engine’s oil.

You might be wondering how water gets into the oil due to a thermostat being stuck open. If the engine is running cold, the hot oil meeting a cold engine can produce condensation. The condensation eventually condenses into water and falls into the oil. With an engine running cold, water isn’t the only pollutant getting into the oil. The piston rings (running cold) won’t fully expand to thoroughly seal against the Yamaha outboard cylinder wall and may allow a small percentage of raw fuel to constantly seep past them and collect in the sump. Prolonged running with this condition can cause the oil to develop a milky residue. Debris can also get stuck in thermostats and prevent them from retracting back to the closed position.

If you suspect water in the engine oil, there are a couple of quick ways to check. One way is to remove and look at the underside of the oil cap to see if there’s moisture in it. Another way is to pull out the dipstick to check for moisture in the oil. Either method is effective. Yamaha thermostat issues can be prevented by flushing the engine regularly per the owner’s manual.

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

For most boaters, pull Yamaha four-stroke outboard spark plugs every two hundred hours or every other season and check for proper color and wear. They should be a light brownish color and have relatively sharp edges. When necessary, replace with the exact manufacturer and part number that your outboard’s manufacturer stipulates. The brand type and style of spark plugs used in your outboard are designed as they contain specific performance attributes that are engineered for your outboard’s operation.

What is a leakdown test?

A Yamaha outboard engine leakdown test indicates the condition of each of the engine’s cylinders and the overall condition of the motor. Similar to a compression test, it involves spraying compressed air into each cylinder and using a pressure gauge to measure a percentage of pressure that’s lost after a short period.

Also, part of doing a leakdown test on a motor is to listen for any signs of leakage. By listening closely to each cylinder and the areas around them, you’ll better understand where leaks may be present.

The goal of a pressure test is to confirm whether the motor has any air leaks. The presence or absence of air in engines often leads to leaking of fuel-air mixtures and leakage of fuel during operation. 

Additionally, these leaks may become infiltration points for water and moisture from the aquatic environment, resulting in internal corrosion, sub-optimal performance (i.e., at idle, low RPMs, and high RPMs), and other issues.

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

• Step #1: Begin by carefully removing the top Yamaha cowling, Then, remove the ignition coil cover at the rear of the motor.
• Step #2: Remove the spark plugs. Be sure to lay the spark plugs in numbered order to reinsert or replace them after the test.
• Step #3: Remove the flywheel cover from the top of the motor.
• Step #4: Mark the flywheel with a marker at 0°, 120°, and 240°. These positions will indicate where you’ll rotate each pair of cylinders to the top-dead-center positions (see Steps #11 and #12 below).
• Step #5: Rotate the crankshaft with your ratchet and socket to the top dead center for Yamaha Yamaha cylinder #1.
• Step #6: Adjust the regulator on the leak down tester to 0% to calibrate it for an accurate reading. 
• Step #7: Connect the leak-down tester by screwing it into the spark plug port at cylinder #1. Next, connect the tester to the compressor and take a measurement. Be sure to firmly hold the crankshaft to prevent it from rotating.
• Step #8: Rotate the crankshaft 360° (one full rotation) to put Yamaha cylinder #4 at the top dead center.
• Step #9: Connect the leak-down tester to cylinder #4. Then, take a measurement while holding the crankshaft to prevent it from rotating.
• Step #10: Set Yamaha cylinder #3 to the top dead center at the 120° mark. Next, repeat step #7 through Step #10 for Yamaha cylinders #3 and #6.
• Step #11: Set cylinder #2 to the top dead center at the 240° mark. Then, repeat step #7 through Step #10 for Yamaha cylinders #2 and #5.

Step #12: Replacement is the same as disassembly. Be sure to replace spark plugs in numbered order and apply an anti-seizing compound on the threads for easy removal/replacement in the future. Also, firmly reattach the ignition wires for a solid connection.