Honda 50hp Lower Unit failure

Lower Unit Failure

Taken from

In chronological order.  My Honda 50 hp lower unit had an oil leak somewhere.  It turned out to be at the water pump seals around the drive shaft.  But because I am a DIY'r without scruples I tried to remove the lower unit first.  It did have nasty looking corrosion around the threads of the locking nut so I figured it was due for maintenance anyway.  As of today when I write this, March 28, 2010, all is very well and very tight.


Re: Lower Unit Failure - BF50A

Postby opie » Sat Mar 21, 2009 11:01 am

The threads holding in the prop shaft retaining nut came loose (not the prop nut, but a big 3 or 4 inch nut inside the lower unit.) The threads had corrosion which started the whole repair issue. Everything closed today and tomorrow, but here at the Isle of Palms Marina we are happily using the amenities including showers, sauna and restaurant. Dockmasters Ryan and Chase could not be nicer. I'll order a newlower unit Monday and while waiting, rent a car and visit downtown Charleston. (To answer the question one had above about changing the impeller, I'll leave it up to you, but that is a skill I think is important to be able to do if necessary.) As I said, it could have been worse. After 4 days of 5200 hundred RPM, 9.5 avg speed, top speed 14.3 knots, going south for 161.4 NM, the gears came loose when we were were only 2 nm away from entering large and busy Charleston harbor, with freighters and all. Someone upstairs looked after us......

Postby opie » Fri Mar 20, 2009 9:00 pm

My fault. Late today, on the water, in 15 to 20 kts, my lower unit popped loose. If the moderators see fit, I suggest they take my previous multiposting pompous verbage about my self-repair of this lower unit gear case and delete the thread altogether. Amateurs should not work do major repairs on such important parts of the propulsion system. As it was, heaven above found an old crumbling wooden dock for us to drift into and we got a tow to a marina. It could have been worse.

On edit, many months later on 12/17/09 I can say that all is fine for now and I do not feel so bad. The boat is fine. I tapped the lower unit and put in SS bolts and nyloc nuts right thru the bearing carrier and lock nut.  The nut could not be tightened without slipping threads.  I guess threads can not be repaired to take the torque necessary.  It looks bad but all is well.  It has held together thru many miles of use.  There is NO OIL in the vicinity of the weld.  The oil seal is 2 inches or so to the right of the weld.

Postby opie » Sun Dec 07, 2008 11:52 am

(Let's start off by my expecting the response of the majority of those sane members here who want to tell me to take my problem lowerunit to a Honda dealer. I won't. I am a stubborn fool.)

I need to replace the lower unit prop shaft oil seals on my Honda 50HP (1999) outboard. I have a Seloc manual that is either worthless or great depending on how lucky you get with the subject and model since Seloc can not possibly cover all models for 20 years like they say on the cover.
 And I have not spent the $89 for a proper shop manual. So here goes my question for anyone who has replaced their own seals.

My lower unit comes off easily since I had to replace the water pump and vertical drive shaft oil seals successfully last summer.

On the bench, I removed the prop, the two washers and exposed the leaking seals on the prop shaft. I thought about "picking" the seals out with some sort of puller device. Any advice on that being a possibility?

Next, I find the bearing carrier (around the prop shaft) that is held in with a 3" (or so) large threaded washer with about 16 'dogs' on it that would 
seem to need a tool to remove. I probably can rig a garage tool of some kind to engage the dogs and move it counterclockwise unless it is frozen into the threads by 10 years of sitting there.

That's where I am at this point. I am in no rush. Anybody out there that has been successful (or failed) in a DIY manner? :?: :?

Postby Luke » Sun Dec 07, 2008 2:28 pm


Last January I experienced your issue with my 1999 Honda 50.
The seals are a serious maintenance issue many of us overlook until we discover that the seals have failed. By the time the seals have failed, water 
has entered the lower end and has ruined the bearings and gears.

I do 99% of the maintenance on my Honda, and I was certain that I could R&R the prop shaft seals and bearings myself. My Honda factory service manual was helpful.

“On the bench, I removed the prop, the two washers and exposed the leaking seals on the prop shaft. I thought about "picking" the seals out with some sort of puller device. Any advice on that being a possibility?"

Next, I find the bearing carrier (around the prop shaft) that is held in with a 3" (or so) large threaded washer with about 16 'dogs' on it that would seem to need a tool to remove. I probably can rig a garage tool of some kind to engage the dogs and move it counter clockwise unless it is frozen into the threads by 10 years of sitting there.”

Opie, your “bearing carrier” is a retaining ring facing you as you observe shaft entering the lower end. This carrier has to be removed for servicing 
the seals and bearings. I tried to rotate the ring counter clockwise by pounding on the “dogs” with a wooden rod. I could not rotate the ring, so I 
took the lower end to a Honda dealer. The Honda dealer explained that Honda Marine has a special tool used for this purpose. The special tool is 
made to fit into the recesses in the dogs in the retaining ring. No, they absolutely would not sell me that tool—something about their dealer 
franchise contract specifically stating they are not allowed to sell special tools to the public @#$!!
I left the lower end with the dealer. Six weeks later they gave it back to me with new seals and bearings. Their Honda tool broke while they were trying to remove the retaining ring. The ring had “frozen into the threads by 10 years of sitting there”. The Honda shop took the lowerend to a machinist shop. The machinist shop somehow removed the retaining ring by cutting it out of the lower end. The machine shop bill was $80.00. 
When I have to do this job again, I will take the lower end to the machine shop for the carrier ring removal and then I will install new seals and 
bearing myself. 


Postby opie » Sun Dec 07, 2008 2:58 pm

Thanks for the advice. It makes perfect sense that the dogged ring holding the bearing carrier was frozen as I am sure mine is. Fortunately, in my 
other life, I have an excellent machine shop in mind that just did a valve job in my 1960 TR3A engine block. I will have my Honda lowerunit in his 
shop tomorrow morning. You saved my screwdriver from damage as I probably would have banged the hexx out it on the dogged ring tomorrow if I tried to remove it. More news tomorrow.....

Luke, and others with BF30/40/50A engines from Honda:
In my research on-line today, in preparation for my trip to the machine shop tomorrow, I found several sources of Honda owners that complained that the retaining bearing carrier nut had corroded so bad that the lower unit cracked under the pressure of corrosion outward! They said that the nut should be removed, cleaned, oiled, and the threads on the nut and the threads on the lower unit should be cleaned before reassembly. It should be part of regular maintenance. But, as Luke says, the tool to remove it and re-torque it back is not sold by Honda. More later..... 
Image this is the wrench
Image this is the nut
Image and this is the possible crack if the nut gets really corroded, which would be a 
bummer I did not even think about on top of the difficulty of reaching the bearings and seals though the hard-to-get-off nut.

Postby opie » Mon Dec 08, 2008 5:17 pm

My tears are dried now. And not tears of joy.

I did not go to the machine shop. I figured, why not do it myself?

I had my hammer and screwdriver. I unlocked the locking washer. See pic.
I banged away.
I cracked the housing. Exactly like the pic I posted yesterday. The bad karma was strong.... And there was more than one tab locked down, so the 
nut could not move to come off. I just missed the tab. A Honda dealer would not have missed it.

So, now I need find a "shell" of a lower unit that I can place all my good gears and shafts into. Any suggestions?

As for the lesson learned? I think taking it and leaving it with a dealer, as Luke did, was a stroke of genius. Hundred's of $$$ for him and thousands of $$$ for me if I can not find a shell.

Postby Luke » Tue Dec 09, 2008 9:24 am

Opie I am sorry for your misfortune. 
The Honda mechanic warned me that I would probably crack the housing, as you did, if I tried to remove the nut myself using a hammer. He 
explained that the lower end is known to crack, and he told me that his local machine shop repairs cracked lower ends. I believe he told that if the crack is not too wide, the machine shop can weld it.

Other options:
Purchase a new lower end. This is very expensive.
Purchase a used lower end on eBay. These are available several times a year. The Honda mechanic told me that those available on eBay are usually ruined from water intrusion past failed seals.

Below is the contact information for the dealer I used.
I believe the mechanic’s name is “John”.
John can advise you on your options.

Gulfstar Marine, Inc.
Contact Us
Call us at:


Postby opie » Fri Dec 12, 2008 12:06 pm

Luke and others.....

I have been to a Honda dealer and talked to many people and searched the web. I know this thread is getting like a personal blog, but there may be a newbie (or oldie) here that may oneday need this info.

1. The local Honda dealer says 5 or 6 lower units per year come in to him (could I interpolate that to 500 in the US per year?) with cracked lower 
units. He says it is cheaper to get a new lower unit than rebuild it. So I am talking to Santa.
2. Welding may or may not work. The seal of the "O" ring on the bearing carrier (see pic below) may not retain the oil if the shell of thelower unit is cracked and therefore perhaps warped a bit even though the crack is before the oil area.
3. The cracking can come from, a) leaving the lower unit tilted up and letting rain fall into it and then freezing with the ice expansion cracking the lower unit shell, b) aluminum corrosion stress cracking, where the corrosion expands and cracks the shell at the nut area. c) the nut may be 
corroded so badly into the lower unit that the two are mated for good and crack may occur when trying to separate them.
4. The board has a shouting match among Honda owners about whether this is a inherent design flaw in Honda lower units or if poor maintenance is the problem. (My opinion is 20% former - 80% latter).
5. Even if the nut comes out, the bearing carrier may be corroded in the lower unit and break when trying to remove it. Google searches turn up 
the trick of putting the lower unit in a warm bath or using a propane torch to heat it gently to expand the shell of the lower unitand perhaps 
loosen the bearing carrier.
6. I ordered a shop manual for my engine. In the meantime, my local library had a Johnson/Evenrude shop manual that said their nut and bearing 
carrier should be removed and cleaned and anti-seized with compound and returned to the lower unit ANNUALLY. haha - who does that? (I will.....when this episode is completed.)
7. Another owner I found says that he religiously washes out the lower unit behind the prop every time and then uses salt-away solution, and 
rinses again, and his lower unit is pristine.
8. Let's go for a moment to common sense part of this. True, the regular cleaning sounds like the answer, but I bet the average Joe never gives this area a thought. 5-10-20 years and the lower unit is corroded together, but so what, if there is no crack or oil leak. Or even if there is a crack, weld it or JB weld it, as long as there is no oil leak? And a bicycle pump and 3 to 4 # of pressure will reveal the source of the leak, says some on the web.
9. And there is the school of thought I found that unless you open the lower unit oil plug and see the milkshake indication of water intrusion, never touch the lower unit except to change oil. And if you do find water intrusion, only panic if your get actual water out of the lowerunit. If it is milky, just capture it and let the milky oil sit in a jar for a day and see if it separates. If it does not, don't worry. One guy said his lower unit oil has been milky for years.
10. Bottom line............ I think good maintenance will keep outboards going for years and years. Some can (and want to) do that maintenance themselves and others use a dealer. Either way, the Honda can last forever, I think, if maintained properly. [This whole thing of cracks has to apply to Johnson and Evenrude motors as well since they have a indentical bearing carrier and nut. I don't know about other makes.]


Postby temall00 » Wed Dec 17, 2008 11:35 am

The "special" tool that they would not sell to you is "07LPA-ZV30100" available at ... 30100.html for a 
painful $86. 

Quite a bit for a tool you use for 4 minutes a year...

Stay warm!!


Re: The "special tool"

Postby Luke » Wed Dec 17, 2008 11:57 am

Tim, than you for finding the source for the tool.
I will buy one.
On a related note: The Honda dealers would not sell me a set of Honda carb synchronization gauges.
They quoted their Honda franchise agreement and stated that they are not allowed to sell Honda tools to the public.
So I bought the same gauge set from a Honda motorcycle dealer.

Opie, have you purchase a new lower end?

Postby opie » Fri Dec 19, 2008 7:38 am

My tale continues:

At this point, my lower unit gear case was cracked but the carrier lock nut was out (in pieces)......

-- Reading and looking at the Honda shop manual closely I figured out that the proper way to remove the bearing carrier is to pull on the prop shaft. 
(If you only pull on the weak ears of the bearing carrier it will break.) They suggest a special tool. However, the tool just puts a spacer between the gear case and the prop castellated nut (the one on the end of the prop shaft.) So I put the prop back on the prop shaft, put hard wood strips (pine wood did not work, it just got crushed) between the prop and gear case and tightened the castellated nut on a washer on the prop shaft onto the propeller as a spacer. The bearing carrier and prop shaft "popped" loose.

-- I removed the assembly and separated the bearing carrier from the propeller shaft. (Be careful, there is a small washer on the end of the reverse gear, a shift pin and ball bearing at the end of the prop shaft, and reverse gear shims (I had 2) that are "loose" and will fall to the ground if you are 
not careful to catch them first.) All looked good except the two oil seals. I found fishing line in them. There was corrosion on the mating surfaces of the carrier, the "O" ring had junk under it, and there was grunge in the outer chamber, where the exhaust gases go out.

-- To remove the prop shaft oil seals I went to Autozone and used their loaner tools, in this case their Slide Hammer Kit. The medium ring puller attachment fit the oil seals perfectly and the seals came out of the bearing carrier. (Do not use a screwdriver or "pry" device, as the carrier is made 
of "pot" metal and will deform on the lip.) I should mention that the "O" ring is deep in the gear case and any "out-of-round" in the upper flange area near the prop shaft due to corrosion or mess-up under the carrier nut will have little effect on the "O" ring sealing.

-- I ordered 2 oil seals ($6 ea) and the "O" ring ($10) and carrier nut ($10)

-- I took the lower unit, w/o the carrier in it to a marine welder. It took about an hour and the gear case crack was repaired excellently. They do it 
all the time. While there I also had them add a bit to my skeg which was partly broken off in a loading ramp mistake last season. You can't tell where the new skeg piece was welded, they did such a good job.

-- When my parts come in and when I get back from a Christmas trip I will let you know how the assembled lower gear unit works on the water at WOT.

-- Caveat...... I am not recommending that anyone else try all this.

Re: How do you replace the lower unit propeller shaft oil seals?

Postby opie » Sun Jan 11, 2009 8:25 am

Well, here is the conclusion to my blog about putting in new oil seals... (same warning, this procedure may not work for you..)

The threads in the lower case, as seen above, were corroded and damaged. To clean and reshape them I used a cut-off disk on a dremel tool and 
went around every thread very carefully. Extreme caution taken not to cut out of thread lines. Steady hands are a must in doing this. Then, finding the 3" gear nut to be harder than the aluminum of the threads, I went in-and-out very slowly with the nut, using the nut as a 'tap' to clean out the threads. I had to sand some high edges down to produce exact roundness of the cavity. To drive the nut evenly, I made a tool from a TR3A car old oil canister.

I cut three tabs in a 3" steel oil canister and bent them to fit the tabs in the gear nut (about 2.75 inch diameter for canister tab circle). I used hand torque at first and later used a 'chain-pipe wrench" around the canister to get the 89 ftlbs required to drive the nut down.

Above is the prop shaft and bearing carrier. The shift 'dog' on the prop shaft (the round thing on the shaft about 2" long) is what engages the forward and reverse pinion gears when the shift lever pushes up and down on the shift pin, seen at right end of prop shaft.

Note that the crack I made in the lower unit was the shape of a large "J", but the marine welder figured out that there were propagation lines that weakened the case and following them he welded a large "U" on the case. I think it is as strong as original and the case is plumb and not contorted in any way. Good welding job!

After getting the 89 ftlbs on the nut and finishing up, I applied a pressure test at 9.5 psi and it held for 10 minutes without leaking. The 8mm oil 
fitting was from a Yamaha oil filler kit ($9) ( I had to file the edges off a little to clear the case.) The hand pump was from a home blood pressure test kit. 

I shifted the gears by hand and rotated the vertical drive shaft clockwise and found forward-neutral-reverse gears to be A-OK. I consider the job complete and my savage DIY attitude is intact. 8)

On edit - Dec 17, 2009. It has been many months of use, so I am brave enough to sneak this image of my lower unit. The large ring holding the gears 
in came loose and I guess you can NOT repair those threads like I tried to do. So I tapped the lower unit and put in SS bolts and nyloc nuts on all 
sides to hold it in. As I said it seems fine now after many months of usage.


by puggsy » Tue Feb 10, 2009 11:52 pm
In my mining days, i came across a product called anti-seize....a bit like a grey gritty paint....we smeared it on nuts and bolts that were at times...for months...under running water....And we could always undo them...It will not wash off in water.
If the stuck threads on these outboards had been coated with this prior to assembly, there would not have been the same problems...
The next time my lower end has to be serviced, i will demand they use a similar preparation for the NEXT time...
Note. the product has to be compatible
with the alloy of the motor...

Postby Compromise » Tue Feb 10, 2009 10:00 pm

Thanks for this thread Opie. The pics are invaluable.
I have a question, how did you become aware of the need to replace the seals in the first place?
Was there an obvious oil leak? Oil in the water, propeller?...
Thanks again

Postby Don T » Sun Jan 11, 2009 6:09 pm

Looks good, from one DIY guy to another.............we are a dying breed.