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.

 

Why Choose Our Yamaha Lower Units?

• Unbeatable 3-Year Fault-Free Warranty: Enjoy the best warranty in the industry. Our lower units include a 3-year fault-free warranty, meaning any failure is covered – even if caused by accidents or debris. In contrast, most OEM Yamaha parts come with only a 1-year limited warranty (and won’t cover accidental damage). Our warranty truly keeps you protected, providing three years of total peace of mind on the water.

• Huge Savings vs. OEM: Our aftermarket Yamaha lower units cost significantly less than OEM replacements. You’ll typically pay 50-70% less compared to buying a brand new OEM gearcase. Boat owners on a budget and repair shops alike appreciate getting like-new performance without the inflated OEM price tag. Why spend thousands on dealer prices when an affordable aftermarket unit will do the job equally well or better?

• Brand New (Not Rebuilt): This is not a remanufactured or used unit – it’s a brand-new aftermarket part built from all new materials. Every gear, bearing, and seal is new and built to precise Yamaha specifications. You get the reliability of a new unit as opposed to the uncertainty of a used or rebuilt lower unit (which can have hidden wear). There’s no core charge or exchange required either – you keep your old lower unit for spare parts or proper recycling.

• OEM-Compatible Quality: Our Yamaha lower units are engineered by reputable manufacturers (such as Sterndrive Engineering SEI) who specialize in aftermarket marine parts. They are precision-manufactured to OEM specs for a perfect fit on your engine. The units are dyno and water-tested for performance and endurance, so you can trust them in real-world conditions. Many marine professionals and mechanics already use these aftermarket units because of their proven quality and durability. In practice, aftermarket lower units can perform on par with OEM parts – the only difference you’ll notice is the extra money in your pocket.

• Complete Assembly, Ready to Install: Each lower unit comes as a complete assembly, ready for installation. Included is a new water pump impeller and housing already installed in the unit to keep your engine running cool. (Note: units are shipped without gear oil, so you will add your preferred marine gear lube during installation.) The gearcase comes pre-filled with all internal components correctly set – no need to swap over gears or shafts from your old unit. Simply bolt on the new lower unit, fill it with gear oil, and it will shift smoothly through forward, neutral, and reverse like a factory part.

• Fast Shipping & Support: We know downtime is critical. Our units are in-stock and ship quickly (usually within 1-2 business days), getting you back on the water faster. We offer excellent customer support by boating experts who can help you select the correct unit, provide installation guidance, and quickly assist with any warranty claims. Our team is here to support boat owners, marine mechanics, and commercial operators – if you have any questions or issues, we’ll make it right.

• Trusted by Boat Owners and Pros: Our Yamaha lower units are ideal for a wide range of customers. Boat owners love the easy plug-and-play replacement and long-term reliability for weekend outings. Marine mechanics trust these units to satisfy their clients while keeping repair costs down and margins up. Commercial fishermen and charter captains rely on the durability and warranty – even under grueling daily use, they know we’ve got them covered if anything happens. No matter your use case, our lower units are up to the task.

• Better Than a Rebuild: Worried about a costly repair? Skip the complicated rebuild kits. A typical Yamaha lower unit rebuild kit can cost around $800 (not including the labor or time to install all those parts), and you’d still end up with older components in the mix. For only a bit more, you can get our complete new lower unit and be done with it. Instead of gambling on a rebuild’s longevity, you’ll have a brand-new assembly with a full warranty. It’s the smartest long-term choice for your outboard.

Wide Range of Models Covered (75HP to 300HP)

We carry aftermarket Yamaha lower units for a broad range of outboard models and horsepower ratings. Our inventory covers most Yamaha engines from mid-size to high-horsepower, including both older two-stroke models and newer four-stroke models. You can find the right replacement lower unit for engines such as:

• Yamaha 75–100 HP: Fits many 3- and 4-cylinder engines in the 75hp, 80hp, 90hp, and 100hp range (including popular two-stroke models and mid-range four-strokes). These units restore like-new performance to smaller outboards often used on bass boats and bay boats.

• Yamaha 115–150 HP: We stock lower units for the ever-popular Yamaha 115 HP and 150 HP outboards (including the F115 and F150 four-stroke, and older 115–150 two-stroke models). These are among the most common Yamaha engines, and our replacements are a perfect fit for all applicable years. The 150hp unit (SEI part 90-416) is a direct replacement with correct gear ratio and driveshaft length options.

• Yamaha V6 200–225 HP: Our lineup includes V6 lower units for Yamaha 200 HP and 225 HP outboards, including High Pressure Direct Injection (HPDI) two-strokes and equivalent four-stroke versions. For example, the 2.6L 90-degree V6 engines (such as older carbureted or EFI 200hp) and the later 3.1L/3.3L 76-degree V6 engines (like the HPDI 200-250hp) are all covered by our aftermarket units. We offer standard rotation and counter rotation models to suit single or twin-engine setups.

• Yamaha 250–300 HP: Need a replacement for a big block Yamaha outboard? We have lower units for 250 HP and 300 HP Yamaha V6 outboards as well. This includes units for the 3.3L HPDI 250, the 4.2L V6 four-stroke 250/300, and other popular configurations up to 300hp. These heavy-duty gearcases are built to handle the high torque of larger engines, making them suitable for offshore boats and commercial vessels requiring top reliability.

Standard & Counter Rotation: We supply both standard (right-hand rotation) lower units and counter rotation units (for twin-engine boats that require one prop to spin opposite for balanced steering). Simply choose the appropriate rotation, gear ratio, and shaft length for your engine. We have multiple shaft length options – 20-inch (long shaft), 25-inch (extra-long shaft), and 30-inch (extra-extra-long shaft) models – to match your outboard’s configuration. Each unit’s gear ratio is matched to Yamaha’s specifications (for example, 1.86:1 or 2.00:1 gear ratios for different engines) so you’ll get the same performance in speed and acceleration as the original.

Not sure which model fits your motor? No problem – we’re here to help. Yamaha model codes can be confusing (for instance, an “F” at the beginning of the model number denotes a four-stroke, and “L” can indicate counter-clockwise rotation). If you’re unsure, simply contact our team with your outboard’s model number or serial number and we’ll quickly identify the exact lower unit you need. We make it easy to get the correct part the first time, so you can avoid any guesswork or compatibility issues.

OEM vs. Aftermarket Lower Units – Comparison

How do our aftermarket lower units stack up against Yamaha OEM parts or rebuilt units? Below is a comparison of key factors that matter to boaters and mechanics:

Aspect	Our Aftermarket Lower Unit	OEM Yamaha Lower Unit	Rebuilt/Used Unit
Cost	$$ – Typically 50% or more lower cost than OEM. Extremely cost-effective for the same functionality.	$$$$ – Highest cost. You pay premium pricing for the Yamaha brand name.	$-$$ – Initial price is lower than new, but rebuilds have hidden costs (labor, downtime) and uncertain value.
Warranty Coverage	3-Year Fault-Free Warranty. Covers any failure, even damage from impacts or mishaps. Truly worry-free coverage for 36 months.	1-Year Limited Warranty. Covers manufacturing defects only. No coverage for accidents (you’re on your own if you hit a rock).	Varies (30 days to 1 year, if any). Many used or rebuilt units have very limited warranty, often only covering workmanship and not covering normal use failures.
Quality & Condition	Brand New. All-new parts manufactured to OEM specs, zero hours of use. Fully tested for performance. Equivalent or superior to new OEM quality.	Brand New. Genuine Yamaha factory part. Top quality, but you’re paying a steep premium.	Mixed Condition. Combines refurbished old parts and some new replacements. Wear history is uncertain, and performance may not equal a new unit.
Reliability	High Reliability. Proven in thousands of installations. Designed for long service life; backed by replacement guarantee if anything goes wrong. Ideal for both leisure and commercial use.	High Reliability. Original equipment designed by Yamaha. Reliable, but if it fails outside of warranty, replacement is very expensive.	Uncertain Reliability. Could last years or fail quickly depending on rebuild quality and prior damage. Greater risk of early failure, which can end up costing more in the long run.
Availability	Immediate Availability. Aftermarket units for popular Yamaha models are usually in-stock and ship out quickly, minimizing your downtime. No need to wait for factory order.	Potential Wait Times. OEM parts might need to be ordered via dealers – can be backordered for weeks, especially for older models. Limited availability outside dealer networks.	Variable. You must locate a suitable used unit or wait for a rebuild service. Finding the exact match (year, model, ratio) can be time-consuming. If rebuilding yours, your boat will be down during the rebuild process.
Installation	Bolt-On Convenience. Ships fully assembled with new water pump – just add oil. No core return needed. Install is straightforward, identical to OEM process. Support available if you have questions.	Bolt-On. OEM part will install fine but may not include minor parts (pump kits or hardware) – and you’ll have to return your core for some dealer reman programs.	More Involved. A rebuilt unit may require you to send in your old core first or swap over some parts. If it’s a used unit, it might need new seals or impeller before use. Expect extra steps to ensure it’s seaworthy.

In summary, our aftermarket Yamaha lower units offer the best value and convenience. You get like-new quality and superior warranty coverage at a far lower price. OEM units are excellent but extremely costly, while used or rebuilt units are a gamble. With our product, you make no compromises – you’ll save money and enjoy worry-free boating.

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.

  

  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.

  Does SKU 90-422-B25F lower unit works for model number F250HET  Serial : 6DX-1010950 / Model Year 2019?

  It's an international model and we don't have that usually but 90-422 would work. If It's 25" drive shaft then 90-422-B25F should work.

  I'm looking for Low unit for a 2007 V150TLR in reading my manual its discussing shimming is this already completed? All I'd need to do is install the low unit and add gear oil and prop What about gasket to bolt back up? Also there is a rubber plug over the top bolt will that come with or do i need to order both of these items?

  Shimming is completed and you are correct. Install lower unit, fill gear lube, and complete break in process. No rubber plug, you will have to reuse old one or order a replacement. No gaskets required, any rubber exhaust rings can be reused as long as they are in good condition.

Are aftermarket Yamaha lower units as reliable as OEM parts?

Yes – our aftermarket lower units are engineered to be just as reliable as genuine Yamaha parts. They are manufactured to meet or exceed OEM specifications for fit, materials, and performance. In fact, they undergo stringent quality control and testing to ensure reliability (including pressure testing for leaks and running tests for proper gear function). Many boaters are successfully using these units for years in both recreational and commercial applications. With proper installation and maintenance, an aftermarket unit can perform indistinguishably from an OEM unit – and our 3-year warranty further guarantees your reliability and satisfaction.

What does the 3-year fault-free warranty cover?

Our 3-Year Fault-Free Warranty is an exceptionally comprehensive coverage. It means we will repair or replace your lower unit if it fails **for any reason within three years of purchase. This warranty covers manufacturing issues and accidental damage. For example, if you hit a submerged object, damage the lower unit from debris or fishing line, or experience any kind of failure that renders the unit inoperable, you’re covered – no questions asked. Simply contact us if you ever encounter an issue. We’ll guide you through a quick warranty claim and get you a replacement unit or the necessary parts to fix the problem at no cost to you. This hassle-free coverage is a big reason many customers choose our units over others. (Regular wear items like routine maintenance seals or oil changes aren’t covered, but any major failure or breakage is included under the fault-free policy.)

How do I choose the correct lower unit for my Yamaha outboard?

Selecting the right lower unit is important for proper fit and performance. The good news is we make it easy to get the correct unit. First, identify your Yamaha outboard’s model details. Locate the model number or serial number plate on your engine (usually on the transom bracket). This model code will tell us the horsepower, year, shaft length, and rotation of your motor. For example, a code like “F150TXR” breaks down to a 150 HP Four-Stroke, with 25” shaft (X) and Right-hand rotation (standard). A code starting with “L” (like L200) would indicate a left-hand counter-rotation model, and codes with “F” denote four-stroke engines. If you’re unsure how to decode it, just provide us the model code. Contact our team via phone, email, or chat with that information, and we will confirm exactly which replacement unit you need (including the correct gear ratio and driveshaft length). We have cross-reference charts to match our units to Yamaha OEM part numbers and models. We’re happy to do the legwork so you get the right part the first time.

Should I rebuild my damaged lower unit or replace it with a new one?

While rebuilding a lower unit is possible, it often makes more sense to replace it with a new complete unit – especially when an affordable, warrantied option like ours is available. Rebuilding requires tearing down the entire gearcase, diagnosing every bad component, and replacing multiple expensive parts (gears, shafts, bearings, seals, etc.). The labor costs can be high, or if you DIY, it’s time-consuming and technically complex (special tools are needed to set bearing preload, shimming gears, etc.). Even after investing in a rebuild kit, you might end up with some old parts still in use, and typically you’d get at best a short warranty on the rebuild work. By contrast, buying our new aftermarket lower unit gets you all-new parts and a fresh start. You eliminate the risk of missing an unseen issue in the old unit. For only slightly more cost than a rebuild, you get a zero-hour unit with a 3-year warranty. In short, if your lower unit has major damage, replacing it outright is the fastest and most reliable way to fix your outboard. Many mechanics will agree that a new unit is often more cost-effective when you factor in all the variables.

What are the signs that my Yamaha lower unit needs to be replaced?

There are a few telltale symptoms that your outboard’s lower unit may be failing or damaged beyond repair. Common signs of a bad lower unit include:

• Milky or water-contaminated gear oil: If you check your lower unit oil and it appears milky white or creamy, that means water is leaking into the gearbox (often through a bad seal). Water in the oil can lead to inadequate lubrication and internal damage. This is a strong sign to inspect the lower unit – it may need new seals or full replacement if gears are rusted or pitted.

• Grinding, whining, or knocking noises: Unusual noises from the lower unit while running (especially a grinding gear sound or loud whine in gear) often indicate internal wear or gear damage. A chipped gear tooth or worn bearing can cause these noises and usually requires a rebuild or replacement of the unit.

• Difficulty shifting gears: If you experience trouble shifting into forward or reverse, or the engine slips out of gear, the lower unit could be at fault. This might be due to a bent shift fork, worn clutch dog, or other internal issues. Consistent shifting problems often warrant replacing the lower unit, since these internal parts come pre-set in our new assembly.

• Visible damage or cracks: Any visible crack in the gearcase housing, a broken skeg (the fin at the bottom), or other external damage can allow water in or misalign internal components. Running with a cracked housing is risky – it’s generally safer to replace the whole lower unit in that case. Similarly, if you’ve hit a rock or log and the impact was severe, internal damage might not be visible, but it can shear gears or shafts (often evidenced by immediate failure or noise).

• Overheating or lack of water flow: If your engine is overheating because no water is circulating, the issue could be a failed water pump impeller (which lives in the lower unit). While an impeller alone can be replaced, severe overheating can also warp the gearcase or damage bearings. If a new impeller doesn’t solve the issue, the entire lower unit may have suffered damage. (Rest assured, our replacement units come with a brand-new water pump installed to restore proper cooling.)

If you notice one or more of these issues, it’s time to take action. Continuing to run an impaired lower unit can lead to further engine damage. It’s best to address the problem early – and in many cases, installing a new lower unit is the most straightforward and reliable fix. You’ll start fresh and protect your engine’s health.

Does the new lower unit come with a water pump and gear oil?

Each of our Yamaha lower unit assemblies comes with a new water pump kit pre-installed. That includes the impeller, pump housing, gaskets – everything needed to ensure proper cooling. You do not need to purchase a separate water pump repair kit; it’s already taken care of in our unit. However, the lower unit is shipped without gear oil for safety during transit (no oil means no messy leaks in the box). During installation, you will fill the gearcase with fresh marine gear lube. We recommend using Yamaha’s Yamalube Marine Gear Oil or any good-quality 80W-90 outboard gear oil. It typically takes about a quart (liter) of gear oil to fill a Yamaha lower unit, but always fill to the level indicated in your service manual. With a new impeller in place and proper oil fill, your replacement lower unit will be ready for dependable service from day one.

Can I install the lower unit myself, or should I hire a mechanic?

Our Yamaha lower units are designed for bolt-on installation, and many mechanically inclined boat owners do handle the replacement themselves. The unit installs in the same way as an OEM lower unit – you’ll need to remove the old lower unit and simply slide the new one into place, aligning the driveshaft and shift shaft splines with the powerhead, then bolt it up. That said, there are some technical aspects to be mindful of: proper torque on the mounting bolts, ensuring the shift linkage is adjusted correctly, and filling/venting the gear oil properly. If you have a service manual and moderate experience with outboard maintenance, you can likely perform the swap at home with common tools. We include basic installation and break-in instructions with the unit to help you through the process.

However, if you’re not comfortable or experienced with this type of work, it’s wise to have a professional marine mechanic do the install. A pro will ensure that everything is aligned and sealed correctly (for example, making sure the water pump tube engages properly and all seals are in place). Proper installation guarantees you get the best performance and it protects your warranty. In short, installation can be DIY, but don’t hesitate to seek professional help for peace of mind – especially for high-horsepower motors or if you don’t have the necessary equipment to lift and align the unit easily. Our customer support team can also provide guidance if you have questions during installation.

Are these aftermarket lower units suitable for commercial or heavy-duty use?

Absolutely. Our lower units are built to handle demanding conditions and continuous use, just like the OEM units. In fact, many commercial fishermen, charter boat captains, and marine rental operations use our aftermarket Yamaha lower units because of their combination of durability and low cost. The internal components (gears, shafts, bearings) are made from hardened marine-grade steel and quality alloys, designed to withstand high torque and long hours. We’ve had commercial users put hundreds of hours per year on these units in harsh saltwater environments. As long as you follow standard maintenance (like regular oil changes and replacing the impeller at routine intervals), our units hold up very well. And in the rare case of an issue, you have that 3-year fault-free warranty backing you up, which is especially valuable for commercial operators. So whether you’re running to offshore fishing grounds daily or using your boat for work, you can trust these replacement lower units to keep you operating with minimal downtime.

What other parts or accessories might I need when replacing a lower unit?

Because our lower unit package is so complete, you won’t need much else – but here are a few items to consider for a smooth replacement job:

• Gear Oil & Pump: As mentioned, you’ll need fresh gearcase oil to fill the new unit. Also, a simple hand pump attachment for the oil bottle is very helpful to pump oil up into the lower unit from the bottom drain hole. We offer marine gear lube and pump kits if you need them, or they’re available at any marine supply store.

• Installation Gasket/Seal Kit: When you drop your old lower unit, you may need a new gasket or o-ring where the unit meets the upper midsection (some motors use an o-ring on the driveshaft or a gasket on the mating surface). It’s a good idea to have a gearcase installation gasket kit on hand to ensure a water-tight seal to the exhaust housing. We can supply this if needed.

• Propeller or Hardware: This is a perfect time to inspect your propeller and prop shaft hardware. Our lower unit comes with a new prop shaft, but you’ll reuse your prop, thrust washer, prop nut, and cotter pin. Make sure these are in good shape. If your prop is damaged from the same incident that took out the lower unit, you might replace it as well. We carry a selection of propellers and prop hardware for Yamaha engines, so let us know if you need a new prop to go with your lower unit.

• Anodes: Your old lower unit likely had sacrificial anodes (zincs) attached. Our replacement units typically include new anodes installed, but if not, or if you boat in saltwater, ensure you attach the proper anodes to the new unit. These protect the aluminum housing from corrosion. We have Yamaha-compatible anode kits available.

• Service Manual: If you’re doing the install yourself, having the Yamaha service manual for your engine is extremely helpful. It will outline the bolt torques, any adjustments, and provide exploded views. Even though the process is straightforward, a manual ensures you don’t miss steps.

In most cases, though, you can simply swap the unit and go. We strive to make it as turn-key as possible so you can focus on boating, not hunting down extra parts.

Order Now – Get Back on the Water with Confidence!

Don’t let a broken or worn-out lower unit keep your boat sidelined. With our high-quality aftermarket Yamaha lower units, you’ll be back up and running stronger than ever – without breaking the bank. Enjoy the peace of mind that comes with our unmatched 3-year fault-free warranty and know that our team of marine experts is here to support you every step of the way.

Ready to restore your Yamaha outboard’s performance? Browse our selection of Yamaha lower units or contact us for personalized assistance. Our easy online ordering and fast shipping will have your new lower unit on its way to you in no time. Join countless satisfied boaters and professionals who have made the smart choice and upgrade your outboard with a reliable, cost-effective lower unit today. Order your Yamaha Lower Unit now and get back on the water with trust and savings – your boat (and your wallet) will thank you!