Cracked! - Need a lower unit for Honda BF40 (1997)

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Wood Zeppelin

New member
I have a crack in the housing around the propeller shaft.

The first question is: Does anyone know how/why this happens?

The second question, where do I find an affordable replacement (used?).
 
The first question is: Does anyone know how/why this happens?
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There multiple causes from hitting a structure, to fishing line around the shaft, ruining the seals, to other causes of water in the lower gear case, leaking gear case oil, over heating of the gear case etc.

What does the oil look like when. you drain it?

There are both replacements: used (E Bay) or factory new. I could not find a SEI replacement for the 40/50 hp Honda series. (SEI makes new units for many outboards and stern drives, but Honda not listed on their web site.
 
thataway":2ie0euu5 said:
The first question is: Does anyone know how/why this happens?
Click to expand...

There multiple causes from hitting a structure, to fishing line around the shaft, ruining the seals, to other causes of water in the lower gear case, leaking gear case oil, over heating of the gear case etc.

What does the oil look like when. you drain it?

There are both replacements: used (E Bay) or factory new. I could not find a SEI replacement for the 40/50 hp Honda series. (SEI makes new units for many outboards and stern drives, but Honda not listed on their web site.
Click to expand...

Would you replace the whole lower unit as an assembly. Or would you look for just a housing, and put the existing parts into the replacement housing?
 
Wood Zeppelin":3l3huvyv said:
Could it be welded?

What about JB Weld and a SS hose clamp to keep it from propagating in the meantime?
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When I had a damaged lower unit, I got a whole good used lower unit. Theoretically you could take gears out, but the tolerances may be out of factory specs in a new case. The entire lower unit would be as expensive as just the outer case. No one makes just an outer case that I know of.

Welding is very likely to cause heat distortion at the best, and ruin seals at the worse. Some places, like repair of a damaged lower skeg can be done with adequate cooling of the gear case.

I did use JB weld to get the RIB back to our boat, and had a lower hp motor aboard to use (25 hp lower unit damaged, 15 hp often used on the rib when carrying less weight and passengers. In this case JB weld is. just a bandaid, and not a permanent repair. I would never trust it again. (My "kit" when going a long distance in the RIB (up to 30 miles or more) included JB Weld, a dinghy repair kit for the tubes, amount spare prop, nut washers etc. I also carried a 3.5 hp two stroke and oil for it, (that was the motor I usually used on the second soft dinghy. /when in remote areas there needs to be redundancy and ingenuity. Once I had to make a new diaphragm for an outboard fuel pump out of dingy Hypalon. It worked fine, until I could get the proper fuel pump diaphragm.
 
James, approximately 14 years ago in about 2009, I had a damaged lower unit housing on a 1999 Honda 40 hp from the process of replacing the seal. A new housing at that time was $600 & if available, I imagine much more now. Lots of those motors made, so probably E Bay or the like, the best bet. That motor with new gear housing was still going strong, when the motor was replaced by new Honda 60’s in 2019.

As far as the JB Weld, it is amazing, so a possible option, but it would be a gamble, which I did take on a 1984 Ford F250 with the 6.9 L diesel engine in 1991. A 2.5 inch crack formed out of the hole in the block, where the cold weather block heater was inserted. The truck at that time was 7 years old & the block replacement or removal to have special welding done, cost prohibiting for us at that time, so I ground out about half way down through the crack it’s length & drilled a small hole in the end of the crack, then inserted a metal screw in the hole coated with JB Weld to stop the crack from further growth. I then, filled the ground out part of the crack with JB weld. Even under the coolant pressure & the crack originating in a pressure point from the inserted block heater, the JB Weld prevented leaking for about three years. I ran that truck for another 20 years & 150,000 + miles by replacing the JB Weld at about three year intervals. If it weren’t for where the crack originated, the JB Weld may not have had to be replaced.

Jay
 
I would replace the whole assembly. It's not cheap....but you get to start out new. As far as what happened to yours? So many things could have happened....but if you haven't hit anything with it, it would not be the first one that corroded where the packing nut that threads into case (the one you remove to change the seal) caused the crack to form. The nut, the case, and the shaft all have different metallurgic properties and interact with one another. After a long enough time, well.....the threaded nut going into the case sort of expands and then you get a crack in that spot. It will eventually fail catastrophically one day.....It really isn't the best design in my opinion. I'm sorry it's your turn to deal with it. BTW....they can be TIG welded in the right hands, but everything must be disassembled...expensive.
 
Wood Zeppelin":288f2f6o said:
Thanks for the thoughtful responses guys!

It looks like I have a few options:

https://www.ebay.com/b/Complete-Outboar ... rand=Honda
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Be sure that you are getting aa good gear case. Some suitable for the 20" 40hp look beat up. You want to be sure the runout on the prop shaft is true. That gears are not compromised. See if you and find the history of the full motor these came off of. For example, a motor which was submerged in fresh water will be fine. One where this lower unit was swapped for a new not;;;probably not good.
 
Looks like I have two options. I'm wondering what you guys think is best:

(1) I can get a used lower unit, but I take some risk not knowing the condition of the gears and prop shaft runout, etc.

(2) I can get NOS housing, and swap in the parts from my old one.

Question: Option 2 seems like a safer bet. But I have never done this job before. It is super hard and complex? Are special tools and techniques required?
 
There is a special wrench:" Lock Nut Wrench, 62 mm, 07LPA-ZV30100". this may have been superseded by a similar number but the last is ZV31010 They cost from $200 to one one $250.

Upon further reading it appears that many of these cracks stem from a design flaw and corrosion of the unit and carrier nut. The carrier nut should be removed once a year and threads greased, then put back in place.

The problem with welding is that thee is a good that the threads in the gear case That the carrier nut threads into will be damaged. In hat case you would have to find a machine shop to repair the threads....may be easier and cheaper to buy a new one.
 
thanks!

Yes, I am seeing on the internet that it is a known problem. I wonder if my 1998 BF40A is still covered by Honda?

Also, I have a 2006 Honda 50hp and 9.9hp. Does anyone know if this design flaw still existed in 2006?
 
Pretty unlikely that s 1998 motor would be covered by anything from Honda. On the more recent motor, I would pull the carrier nut and check for corrosion. I have a Seloc Manual (2002 to 2008) for Honda (2 to 225 hp). It is not as detailed as the full shop manual (which I had for the 150 series). Rebuilding the gear case is above my pay grade. Part of that is that I don't have the specialized tools, which are necessary.

When the assembly is out, then both check for corrosion and the threads, lightly grease before reassembly.

My impression is that Honda has more corrosion issues that the majority of outboards. (Based on owning both a number of Hondas, OMC, Suzuki and Yamaha outboards.). There are members on the forum who do rebuild some of these motors and hopefully they will weigh in.
 
No cracks around that area on my Honda 40’s with about a half of their 2400 hours usage in salt water, but when I needed to have the lower unit seals replaced on my then 1999 Honda 40’s, I found like Bob the price of the special tool to be $200 +, so I made the rare choice for me of towing it to a dealer 150 miles away to have the work done at about the same price for the special tool. They didn’t have any problem with the one lock nut, but the other was so corroded, the case was ruined getting the nut off. I chose to have a new case at the price of $600 at that time & they changed out the internals at no charge, which surprised me as if I had bought the special tool & did the job, no doubt, I too would have ruined the case, so in this instance, glad I chose to have the job done by a Honda Dealership.

At that time there was no mention of this being a known problem, but any of those bolts & nuts that spent a good percentage of their time in salt water were known to corrode, so I would grease when ever I took them apart. On my Honda 2019 Honda 60’s, when taking off the lower units to replace the water pumps, I noticed the bolts all had grease or anti seize on them from the factory. It wouldn’t surprise me to find the locking nut does now too.

My Honda 60’s have a lot of anodes to replace & I'm doing that with replacement perhaps to soon other than to late.
 
Wood Zeppelin":3o1rmx8w said:
How do I post photos here?
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The easiest way is to put the photo in your album. (You already have some there.)
Then you click on "Img" found above, Go to your album, get the address of the photo there, copy that, (in the Mac, it is Control Key) then paste it after "Img", then click on the "[/Img]". Do a preview to be sure it is OK. You can do the same for images on the internet. But anything you paste there had to have a "jpg" (standing for a photo graphic convention.). There are several other conventions which will work.
 
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So the crack has not made it to the gearcase oil cavity. I could:
- Drill a hole at the end of the crack to prevent further propagation...
- Grind the crack open a bit to expose more surface area for bonding
- JB weld the crack
- Then I'd like to put some kind of Stainless Steel bank around the housing, just before the flange at the end near the propeller.

Thoughts on this approach?
 
Freshwater vs Saltwater question..

I also plan to only run it in Freshwater (such as Lake Powell) for the foreseeable future. (it used to spend 2-3 weeks per year in Puget Sound).. Is it safe to say the "corrosion-expansion" that caused the crack will halt as long as it's not exposed to saltwater anymore?
 
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