Yamaha Lower Unit | Yamaha Outboard Lower Unit

Yamaha Lower Unit helps in changing the power of engine belongs to Yamaha outboard to rotation of the propeller shaft that moves the propeller. Moving the propeller moves the boat. Lower unit an essential part of your outboard and ultimately helps your boat move. If you have yamaha outboard and lower unit is not working then make sure to buy yamaha outboard lower unit of high quality such as SEI yamaha lower unit that comes with 3 years warranty. Keep in your mind that the lower unit requires periodical maintenance and care to keep it functioning. There is huge pressure on the lower unit oil inside when your boat moves because of the way the lower unit works. So keep it maintained for smooth journey. Outboard consists of three major parts; Powerhead (Engine), Midsection (Exhaust Housing) and Lower Unit (Gearbox or Gearcase). Below are major Yamaha lower units that fit most of the outboards.
Replaces most Yamaha 90 Degree V6 2-Stroke and some inline 4 cylinder 4-Stroke engines


Replaces most Yamaha 76 Degree V6


Replaces all Yamaha V4 2-Stroke and some 4-Stroke


Replaces all Yamaha 4-Stroke 250 HP


Counter Rotation - Replaces some Yamaha V6 2 & 4 Stroke


Replaces most 200HP/225HP and some 250HP Yamaha 76 Degree V6 Counter Rotation Motors


Replaces all Yamaha 4-Stroke 250 HP Counter Rotation




Yamaha 2 Stroke Models

In Marine industry, Yamaha is actively manufacturing 2 stroke models from 8 - 150 horsepower (HP) and High Pressure Direct Injection (HPDI) models from 150 - 300 horsepower.

Yamaha 4 Stroke Models

Yamaha didn’t limit the business to two-stroke only, they are also manufacturing 4-stroke Yamaha as the emissions standards are becoming stricter. Yamaha 4-stroke outboards include 2.5 HP to 350 HP. Compare to two-stroke, Yamaha 4-stroke are very heavy. We have listed Yamaha 150 four stroke for sale on our website.

Yamaha Lower Unit Rebuild Kit


We suggest that instead of buying Yamaha Lower Unit Rebuild Kit that is around $800, you should go for Complete Lower Unit instead. By paying extra $100 you can get lower unit. However, please browse Yamaha Outboard Parts page if you are looking to buy rebuild kits.

Some of the most frequently used Yamaha gearbox are listed below. You can see individual product pages for more details on them.

Yamaha 150 Lower Unit or Yamaha F150 Lower Unit

  • It's model number 90-416.
  • This lower unit comes with 3-Year Fault Free Warranty.
  • This lower unit is for Yamaha 150 horsepower engine.
  • It is new Aftermarket Unit, not Re-manufactured.
  • For installation also Includes break-in instructions.
  • Lower unit shifts in forward, neutral and reverse.

Yamaha 115 Lower Unit or Yamaha F115 Lower Unit

  • This is a 115hp lower unit which will fit models from 2000 to 2015.
  • This lower unit comes with 3-Year Fault Free Warranty.
  • The lower unit is best for Yamaha 115 horsepower engine.
  • This is not remanufactured but it's new aftermarket unit.
  • Includes break-in instructions for installation.
  • Lower unit can be shifted forward, neutral and reverse.

Yamaha F250 Lower Unit

  • It's model number 90-422 also 90-421 depending on the year.
  • This lower unit comes with 3-Year Fault Free Warranty.
  • The 250 horsepower engine's lower unit for Yamaha.
  • It is new Aftermarket Unit, not just remanufactured.
  • Includes break-in instructions to help in installation.
  • Lower unit shifts easily in forward, neutral and reverse.

Yamaha 250 Lower Unit

  • If It is 2 stroke then model number 90-421
  • If 4 stroke engine then 90-421 and 90-422 depends on the year.
  • This lower unit is for Yamaha 250 horsepower engine.
  • It is a new aftermarket unit, not remanufactured.
  • This lower unit comes with 3-Year Fault Free Warranty.
  • Includes break-in instructions.
  • Lower unit can easily shifted in forward, neutral and reverse direction.

Yamaha 225 Lower Unit

  • If It's two stroke engine then 90-421
  • If It's 4 stroke then anyone from 421 or 422 depending on the year.
  • This lower unit is for Yamaha 225 horsepower engine.
  • Includes break-in instructions.
  • Lower unit shifts in forward, neutral and reverse.
  • It comes with 3-Year Fault Free Warranty.

    Why Buy SEI Yamaha Lower Unit?

    In the aftermarket sterndrive business, SEI is a leading company and also has it’s own outboards. Apart from Yamaha outboard replacement, Sterndrive Engineering (SEI) also produces Johnson Evinrude and Mercury. Replacement sterndrives this company include Alpha Gen I and Gen II. Parts can be interchanged with the Original Equipment Manufacturer (OEM). Outdrives manufactured by SEI are brand-new and that they don’t remanufacture. So you’re safe with such compatible and totally new outdrives.

    What about Warranty? This is another thing that makes SEI drives standout in the market with 3 year fault-free warranty.

    What Does Fault-Free Warranty Mean? The term fault-free indicates that the unit your purchased from the company is covered failures that may demand the replacement or repairing of the unit. Your outdrive is always covered and looks like one of the best warranty in marine outdrive industry. SEI tries to go extra mile to give their customers a peace of mind while they are over the water.

    Are these Lower Units Tested? It’s a responsibility of Quality Control department of every company to ensure the quality of every product produced and same goes to this company. They test all parts aggressively to make sure that all parts from shafts, gears, bearings to other wear parts are of high standard and long lasting.

    So if you’re looking for yamaha outboard lower unit rebuild then why not consider aftermarket yamaha lower unit, especially when it comes with three year fault-free warranty and you can interchange the parts with OEM? SEI produces aftermarket replacement lower unit. They have Yamaha gearcase for V6 outboards that includes two stroke and four stroke.

    Aftermarket Lower Units


    There are two options available either to repair your outboard motor after an accident or to replace worn-out parts of the outboard motor. The options are OEM parts and aftermarket parts. Both of the options are good but what kind of parts are best and you want to be used in your outboard motor to get best results. So for this purpose we have made some comparisons, listed below, between these two part types to help you to arrive at right decision.

    OEM parts: OEM stands for Original Equipment Manufacturer so it's clear from name that these are the parts directly made by outboard motor's manufacturer and not by third party. So these parts fits to the specification of the model of outboard motor in your use. So these parts provide you the same performance as the replacing ones and provides you a peace of mind, and also most of the manufacturers provide these parts with a one year warranty. But with such benefits there are some cons about them, which are that they are much expensive as compared to the aftermarket parts. Although there are many other ways to buy them, like (eBay, online wholesalers), but most of the people will buy them from the dealer because it takes longer to get your outboard motor repaired by ordering them online, thus limited number of places you can buy them from. And you have paid more for OEM parts doesn't mean that they are better than aftermarket parts, sometimes aftermarket parts are equal to OEM parts or even better in some cases. So you might pay extra only for the brand name.

    Aftermarket parts: Those parts for the outboard motor which are supplied by manufacturers other than your outboard motor manufacturer are called as aftermarket parts means parts which are sourced from third party. They are manufactured at a high volume and may fits to the requirements of different models of outboard motor, not the specific make or model. They are similar to OEM parts in kind but may not be perfect for use. So you should deal with right mechanic to provide you with high quality parts. But they are much cheaper than OEM parts and sometime you may get a better quality part. In this case you have more variety to choose from and wider price range as many manufacturers are making same thing. But to keep cost down they may not come with warranty.

    Frequently Asked Questions

    How do I know correct lower unit I need?

    If you are not sure about the lower unit you need then we need to know the engine model number to suggest you the correct lower unit you need. It starts with a letter, followed by horse power and some alphabets for example LF250TXR. If It's four stroke then you will see 'F' in the beginning like F250TXR. If It's counter rotating then there will be 'L' in the beginning like L250TXR. And If It's counter rotation as well as four stroke then It starts with 'LF' like 'LF250TXR'. You can use search bar to enter the model number or just send us the model number through offline message, Text message, contact form and we will get back to you with correct lower end you need.

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    What is the difference between 90 degree and 76 degree?

    90 degree is for 2.6 liter engine and 76 degree is 3.1 & 3.3 liter engine. These numbers like 2.6, 3.1 and 3.3 refer to the size of the engine. Specially the volume of air that It displaces on the basis of the number of cylinders.

    What gear lubricant do you recommend to fill in with and how much will it require to fill in lower unit?

    You can order SEI marine grade lubricant from our website or you can use a 80/90 weight, semi synthetic blend. You should be able to find it locally. You can use the quick silver brand at Walmart. Based on your lower unit, you may need a little over a quart.

    Where can I find the motor serial number?

    It’s located on transom assembly either on the port side or starboard side. There will be a little sticker showing this information. Following picture shows how this sticker looks like.
    Yamaha Outboard Serial Number

    How to measure the correct shaft length?

    Remove the lower unit, measure from the top where the splines are and pass the water pump until the base where it connects with the power head. If It's 20" shaft you will measure 23" and If It's 25" you will measure 27". In other words, If you are measuring from the top of the driveshaft down to the mating surface, past the water pump housing it will be around 23" for a 20" driveshaft.

    My motor is F250XA and mind shaft measures from the matting surface to the top of the shaft is 28 inches. The gears are striped out. I can't tell you what gear ratio is. How do I know the correct shaft length and gear ratio?

    The X indicates a 25 inch shaft which would have a 28 inch measurement. And as far the gear ratio, that model number (422-B25F) is a direct replacement, gear ratio and all.

    How would a 25 inch shaft have a 28-inch measurement?

    There is a standard across the Marine industry of driveshaft sizes. It will either be 20 inches, 25 inches or 30 inches. This is across the different OEM manufacturers. This is the standard. The actual length of the driveshafts across the OEM platforms are different. Examples are a 20 inch driveshaft for a Mercury outboard could actually measure 22 1/8”. This is considered a 20 inch driveshaft because it measures more than 20” but not enough for a 25” driveshaft. This is all because of the midsection lengths. That is the section between the motor and the lower unit. That midsection length is what determines the driveshaft length. I hope this explains the meaning of the different driveshaft sizes.

    Are these complete Yamaha lower units with drive shaft and water pump installed?

    Yes, these are complete lower units that come with drive shaft and water pump installed. Moreover, the shift shaft is also included.

    Do I have to buy Anode Kit separately?

    Yes, you have to buy Anode Kit. The lower unit does not come with the anode kit. Anode is not expensive. If you are looking to buy anode 90-421-05K, It will cost you $25 only.

    Do you also keep the 2018 model Complete Yamaha Gear Box like Yamaha F115 2018 and Yamaha F150 2018?

    We certainly do not have a unit for the 2018 F115. For the 150 hp, we have a few options. We need to know If it’s a VMAX. If so, we don’t offer that one. If it’s not a VMAX, it narrows down to the 416. However, we need to confirm if you have the short shift shaft.

    Are your outboard lower units come in black color and what If I need to change the paint?

    Yes, these lower units come in black color. It is a heat treated, powdered coat paint. If you want to paint it, you will just have to sand it down and then you can paint it to match the color of your outboard motor. We don't do that.

    I got the lower unit installed and it works perfectly. I went through the 10 hour break in period and wanted to go ahead and change the fluid. I noticed a small amount of metal on the plug magnet. Is this anything to worry about?

    Small metal shavings are okay. That is just the gears meshing together. There is nothing to worry about.

    Are the marine electrical parts such as starting motors, alternators, water pumps, power trim motors / pumps, hatch lifters, battery isolators, solenoids/relays, complete trim/tilt system, alternators follow SAE J1171 marine standard?

    Yes, they do follow SAE J1171 marine standard.

    Do you have yamaha 30" Left Hand V6 4.2 LITER?

    We need to find out the ratio and If It's a VMAX model. The one we sell is the low water pick up with the 2:1 ratio. We don't sell any other ratio such as European model 250DETX or USA model LF250UCA.

    My original lower unit has the dual water pickup. I would like to replace it with one with a single water pickup. Do you have one in stock that would work?

    We would only have the dual water pickups. Simplistically, our Yamaha outboard gearboxes are dual water pickups.

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