How the lower unit is coupled to the upper Honda BF40

R

rogerbum

New member
Does anyone have (an) image(s) (from a service manual perhaps) that they can post that will show me how the lower unit on a Honda BF 40 is coupled to the upper unit? My question stems from the problem I experienced on my boat over the weekend after work had been done on it at a local dealer. In brief, the work that was done was 100 hr service plus a change of the impeller. The engine ran fine for 2-3 hours and then wouldn't shift into gear. Fortunately, I have twins so I could make it back to port without a tow.

I took the boat back to the repair shop and they have fixed it. They indicated that there is a shaft the runs from the upper unit to the lower unit and that some bolts that hold it in place came loose. Without a diagram to know what is reallly inside, I assume the shaft runs through some retainer with a bearing in it that is bolted in place. Anyway, they indicated that they added locktite to the fasteners and re-tightened them and also disassemble the 2nd engine to do the same so that the problem wouldn't re-occurr.

What concerns me is the potential for additional damage being caused whenever this came loose so I'd like to understand in more detail how the damn thing works. I never heard any bad noises, the thing just quit shifting into gear so I hope there was no damage. However, I'm thinking I may still drain the oil on the lower unit and run it through a coffee filter to look for metal pieces.

Any comments/thoughts from the marine mechanics in the crowd?
 
Roger,

The shift rod in an o/b lower unit moves either up and down or it rotates to perform the shifting. I am not sure which motion your Honda has. Sometimes a portion of the shift rod is visible and you can confirm the motion. That rod has to be disconnected to remove the lower unit for the impeller change. If the re-connection was not done properly, the upper shift rod could disconnect from the lower resulting in no shifting.

If you didn't hear any ratcheting or grinding sounds, most likely there was no damage to the shifter. You could drain the lower unit and check for metal particles. If you do, be sure to use new gaskets on the drain and vent plugs and refill with the correct new oil from the bottom.

If you learn how to do the gear case oil change, you are on your way to doing your own services! Knowing that the shop blew it the first time around is not reassuring.

Have you considered buying a shop manual for your motor? Even if you do not do your own work, it would help you understand what the shop is or is not doing.
 
Larry,

Thanks for the reply. I will be buying a service manual in the next few days for the very reasons you suggest. While I haven't worked on my own boat engines to date, I'm afraid I'm going to have to start learning if I want to have things done right.... I certainly can learn how - I've done a good bit of automotive work in the past (even took automotive machining in community college many years ago - turn valves, honed cylinder, etc). I'm still hoping I can find someplace I really trust as the reality of my present life is that I can make more $'s/hour doing what I know well than it should cost to have someone else handle the mechanical work.
 
This is thrilling for me, mechanical dolt that I am, to actually be able to contribute to this discussion! The shift linkage on your BF40 is visible on the forward, leading edge of your lower unit near where it joins the rest of the engine. It's about a quarter-inch, two-piece rod joined together by a couple of jam nuts. If these aren't joined correctly, or come loose, your shift linkage fails. I've dropped my lower units several times and simply observe how much thread is showing on the lower rod to aid in accurate reattachment. So far so good.
Al
 
Four Gold Stars! :D Moose has it right.

For lack of a better term the upper shift rod and the lower shift rod are held together with a "turnbuckle" nut (it's a solid piece with wrench flats on it and fairly long). The nut above it and the one below it are locking nuts; once you have the turnbuckle nut adjusted properly hold it with a wrench (10mm comes to mind) while you tighten the upper and lower nuts against it.

The easiest way to adjust the turnbuckle nut is to put it back in the same location it started in; I usually mark the lower shift shaft threads with a Sharpie or such. If it's moved and you don't know the original location then what you're trying to accomplish is to make sure the prop freewheels when the shift lever is in neutral and that there is equal "throw" (lever movement) to engage forward and reverse. That's as technical as it gets. It helps to have one person moving the shift lever and one spinning the prop by hand and adjusting the turnbuckle nut. You can do it by yourself if you get water to the engine and start it; then you can tell when forward and reverse engage quite easily. FOR GOODNESS SAKE...make sure and take all the safety precautions...make sure the hose won't get whacked by the prop, don't let anybody stand near the engine, and don't even THINK about adjusting the turnbuckle nut without shutting down the engine first.

This is not an exacting adjustment; as long as the prop spins freely in neutral and you have roughly equal throw of the shift lever into forward or reverse you're good to go. Only personal preference and fussiness will demand more.
 
Roger, shoot me your e-mail address via PM and I'll send you two scans of the lower unit from my Honda manual. It's good for the 35/40/45/50 HP engines. The advise you got is right but a pix is worth 1000 words, as they say. The site won't let me post a .jpg file in the tech section.

Charlie
 
Roger:

Please look in the Photo Tech Section, I think I added the pages you want. If more informations is needed, let me know

Best regards.,
Rollie/C-batical
 
OK, Help. I am getting ready to remove the impeller and clean something out of water passages that is impeding flow on one of my BF40's. I have removed the lower unit before and have the shop manual for my BF40. There are five bolts plus the shift linkage to deal with. I have disconnected the linkage, removed the zinc under the cavitation plate to get at the bolt it hides, removed it and the four bolts connecting the lower unit to the engine. I should then be able to get the lower unit off but no luck. the engine is in neutral. It acts like there is another bolt somewhere. I have tapped it hard with a rubber mallet. no luck. What am I missing?
 
https://sites.google.com/site/bf50impellernotes/


form BF 50

impellerws.jpg
 
Thanks Brent, good info. However, I have done as it suggests, i.e. removed the bolt under the zinc, removed the four larger bolts, disconnected the shift linkage and still nothing. The unit seems tightly held as if there is another bolt somewhere. The engine is a 2006.
 
The shift control in the cabin was in neutral, I'm done for the night, I'll try tomorrow, Also I did not have then engine fully raised, that may have something to do with it. Thanks.
 
just did my 45, just need to tap on it a little harder. there is a couple alignment pins that can be fairly tight. can lay 2x4 on fins/ cavitation plate and tap on also. just hang on to it cause once 1/8 - 3/16 apart you'll be loose
 
just did my 45, just need to tap on it a little harder. there is a couple alignment pins that can be fairly tight. can lay 2x4 on fins/ cavitation plate and tap on also. just hang on to it cause once 1/8 - 3/16 apart you'll be loose
 
Got it off. Just tight. The two alignment pins were the issue. I'm putting anti-seize compound on them so it'll be easier next time. The impeller was toast. Blew out all the water tubes, the intakes, etc. good air flow so water should get through ok.

Thanks for the help.
 
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