This page will share some details for those helping with the repair of the Allegra transmission.
Details:
Engine – Yanmar 4JH3(B)E
Transmission – Kanzaki KBW20-1 Serial Number 09026
Information from Chat GPT
Thanks for the detailed description and photos — that helps a lot. Based on what you described and what I can see, this failure pattern is very typical for the Kanzaki KBW20 / Yanmar KM2P family transmissions used on many Beneteau boats.
What your symptoms likely mean
Your key symptoms are:
- Gear lever spins freely
- No detents for F/N/R
- Transmission stuck in reverse
- Cable removed and tested directly at gearbox
That combination almost always means the shift cam or detent mechanism inside the shift cover has failed or broken.
The component in your photo is the external shift cover / cam assembly. Inside that cover:
- There is a shift cam plate
- A detent ball + spring
- A selector shaft
If the cam or detent pin shears, the lever spins and the gearbox stays in the last gear (in your case reverse).
The good news:
This failure is often repairable without replacing the entire transmission.
Many times you only need:
- Shift cam
- detent spring
- detent ball
- or the entire shift cover assembly
This can be changed without removing the transmission from the boat.
First thing to try (important)
Before ordering a transmission, try this quick test:
- Remove the shift cover assembly (the part in your photo).
- Look at the selector shaft inside the gearbox.
- Using vise-grips, rotate the selector shaft manually.
You should feel 3 positions:
- Forward
- Neutral
- Reverse
If you can shift the internal shaft, the transmission itself is probably fine and you only need the shift cover assembly.
If the internal shaft will not move, then internal gears failed and replacement is required.
Parts you may need
For your engine (Yanmar 4JH3E with Kanzaki KBW20):
Equivalent transmission family:
- Kanzaki KBW20
- Yanmar KM2P
Common replacement parts:
Shift cover assembly
- Yanmar part: 128170-13200
or sometimes
- 128170-13201
Cost typically:
- $200–400
A full rebuilt transmission:
- KM2P / KBW20 rebuilt
- $1,200 – $2,000
Best vendors that can ship quickly to Bahamas
These suppliers are reliable with Yanmar parts and marine transmissions.
1️⃣ Mastry Engine Center (BEST OPTION)
Mastry Engine Center
They are the largest Yanmar distributor in the U.S.
- Very familiar with KM2P / KBW20
- Can ship same day
- Often have rebuilt units in stock
Phone
+1 727-576-4000
Ask for:
Yanmar KM2P / Kanzaki KBW20 transmission for 4JH3E
Website
They regularly ship to Bahamas.
2️⃣ Torresen Marine
Torresen Marine
Excellent Yanmar parts lookup system.
Website
Phone
+1 231-759-8596
They can confirm the exact part numbers from your serial.
3️⃣ Mack Boring
Mack Boring & Parts Company
Another major Yanmar distributor.
Phone
+1 732-919-7777
Website
Mechanics near Great Harbour Cay / Nassau
Getting a mechanic to Great Harbour Cay is difficult but possible from Nassau.
Good contacts:
Bradford Marine Nassau
Bradford Marine Bahamas
They have Yanmar mechanics.
Phone
+1 242-323-2222
Nassau Marine Repair
Nassau Marine Services
Often works on cruising boats.
Most realistic scenario:
1️⃣ Order parts or rebuilt transmission from Florida
2️⃣ Ship next day air to Nassau
3️⃣ Ferry or charter flight to Great Harbour Cay
4️⃣ Either install yourself or fly mechanic in
Installation difficulty
Replacing the entire transmission on your boat is moderate difficulty:
Typical time:
- 3–5 hours
Steps:
- Remove prop shaft coupling
- Remove transmission bolts
- Slide transmission off engine
- Install replacement
- Re-align shaft
It can be done in a marina slip.
Important diagnostic question
Before ordering anything:
Can you tell me:
1️⃣ Does the selector shaft inside the gearbox rotate by hand when the cover is removed?
2️⃣ When the failure happened did you hear:
- a pop
- grinding
- or nothing
This will tell me 90% certainty whether you need a $300 repair or a $1500 gearbox.
If you want — I can also help with
- A step-by-step gearbox removal guide
- A parts diagram for KBW20
- Emergency fix to get the boat into neutral so you can move it
- Bahamas shipping strategies (very important)
This is actually a very common cruising boat problem, and there’s a good chance you don’t need a full transmission.
Pictures
Thanks for the detailed description and photos — that helps a lot. Based on what you described and what I can see, this failure pattern is very typical for the Kanzaki KBW20 / Yanmar KM2P family transmissions used on many Beneteau boats.
What your symptoms likely mean
Your key symptoms are:
- Gear lever spins freely
- No detents for F/N/R
- Transmission stuck in reverse
- Cable removed and tested directly at gearbox
That combination almost always means the shift cam or detent mechanism inside the shift cover has failed or broken.
The component in your photo is the external shift cover / cam assembly. Inside that cover:
- There is a shift cam plate
- A detent ball + spring
- A selector shaft
If the cam or detent pin shears, the lever spins and the gearbox stays in the last gear (in your case reverse).
The good news:
This failure is often repairable without replacing the entire transmission.
Many times you only need:
- Shift cam
- detent spring
- detent ball
- or the entire shift cover assembly
This can be changed without removing the transmission from the boat.
First thing to try (important)
Before ordering a transmission, try this quick test:
- Remove the shift cover assembly (the part in your photo).
- Look at the selector shaft inside the gearbox.
- Using vise-grips, rotate the selector shaft manually.
You should feel 3 positions:
- Forward
- Neutral
- Reverse
If you can shift the internal shaft, the transmission itself is probably fine and you only need the shift cover assembly.
If the internal shaft will not move, then internal gears failed and replacement is required.
Parts you may need
For your engine (Yanmar 4JH3E with Kanzaki KBW20):
Equivalent transmission family:
- Kanzaki KBW20
- Yanmar KM2P
Common replacement parts:
Shift cover assembly
- Yanmar part: 128170-13200
or sometimes
- 128170-13201
Cost typically:
- $200–400
A full rebuilt transmission:
- KM2P / KBW20 rebuilt
- $1,200 – $2,000
Best vendors that can ship quickly to Bahamas
These suppliers are reliable with Yanmar parts and marine transmissions.
1️⃣ Mastry Engine Center (BEST OPTION)
Mastry Engine Center
They are the largest Yanmar distributor in the U.S.
- Very familiar with KM2P / KBW20
- Can ship same day
- Often have rebuilt units in stock
Phone
+1 727-576-4000
Ask for:
Yanmar KM2P / Kanzaki KBW20 transmission for 4JH3E
Website
They regularly ship to Bahamas.
2️⃣ Torresen Marine
Torresen Marine
Excellent Yanmar parts lookup system.
Website
Phone
+1 231-759-8596
They can confirm the exact part numbers from your serial.
3️⃣ Mack Boring
Mack Boring & Parts Company
Another major Yanmar distributor.
Phone
+1 732-919-7777
Website
Mechanics near Great Harbour Cay / Nassau
Getting a mechanic to Great Harbour Cay is difficult but possible from Nassau.
Good contacts:
Bradford Marine Nassau
Bradford Marine Bahamas
They have Yanmar mechanics.
Phone
+1 242-323-2222
Nassau Marine Repair
Nassau Marine Services
Often works on cruising boats.
Most realistic scenario:
1️⃣ Order parts or rebuilt transmission from Florida
2️⃣ Ship next day air to Nassau
3️⃣ Ferry or charter flight to Great Harbour Cay
4️⃣ Either install yourself or fly mechanic in
Installation difficulty
Replacing the entire transmission on your boat is moderate difficulty:
Typical time:
- 3–5 hours
Steps:
- Remove prop shaft coupling
- Remove transmission bolts
- Slide transmission off engine
- Install replacement
- Re-align shaft
It can be done in a marina slip.
Important diagnostic question
Before ordering anything:
Can you tell me:
1️⃣ Does the selector shaft inside the gearbox rotate by hand when the cover is removed?
2️⃣ When the failure happened did you hear:
- a pop
- grinding
- or nothing
This will tell me 90% certainty whether you need a $300 repair or a $1500 gearbox.
If you want — I can also help with
- A step-by-step gearbox removal guide
- A parts diagram for KBW20
- Emergency fix to get the boat into neutral so you can move it
- Bahamas shipping strategies (very important)
This is actually a very common cruising boat problem, and there’s a good chance you don’t need a full transmission.
PHOTOS
Vendors
Ace marine Diesel – Tim Vero Beach 772 564-7070
Allegra Sailing 