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1998 BF90 suspect lower unit needs rebuild/replacement.......looking for advice!

R

rvasak

New member
Greetings,

As the subject line says, I have a 1998 BF 90 that came on a boat I recently purchased. Based on the condition of the spare props that came with the boat, I suspect that the previous users hit some rocks while piloting in shallow waters.

I have used the boat quite a bit this summer, and all was well until a couple of days ago. The motor had been shifting fine, but all of a sudden would not go into reverse. Forward and neutral still work fine however. I checked the shift and throttle cables at the motor, and then detached the cables at the motor and tried to shift into reverse while a helper rotated the prop. I can see the shift rod rotate into position, but the prop will not rotate.

I then checked the gear case oil drain plug and found metal powder and one metal chunk about the size of a grain of rice. At this point I am guessing that either the clutch dog or teeth from one of the gears has sheared off. I am not very familiar with the innards of the gearcase, so perhaps the metal I saw is from some other component?

The questions I have are: 1) Am I on the right track, or
missing something here? 2) If I decide to rebuild te lower unit, where is a good place to purchase parts? 3) How technical is rebuilding the gearcase? I know that is a subjective question, but...... 4) Would I be better off buying a Honda lower unit and putting it onto this motor? I believe I can do that with a new shift rod and some other new parts.

Thanks in in advance for any replies. Hoping to get back on the water soon!

-Ryan
 
Yes your on the right track.Parts availability not sure,hondadude can help out there! I believe some special tools are required for disassembly & assembly, I would think it would be cheaper to find a used l/u than rebuilding existing unit,to much$$$, But you never know what your going to get with a used one! keep us posted on your decision.
 
Well, I took the lower unit off, pulled the carrier bearing housing, and poked around a bit. What I found is that the part at the bottom of the lower shift rod, which I believe is called a shift cam or shift cam control, is chipped! Certainly explains the metal bits on the drain plug.

To my novice eyes, the teeth of the gears and the clutch dogs look good and are not rounded, as far as I can tell. The shift bullet looks ok too. I am going to take the prop assembly etc. to a Honda tech and him put his eyeballs on the parts.

Best case scenario is that the shift cam is the only part needing replacement. But, why did the cam chip in the first place? That is the question that has me worried...... @hondadude.
 
Took the shift and reverse gear, clutch dogs, etc. to the Honda tech yesterday. His assessment was that everything but the shift cam and "shift bullet" loomed really really good. His only thought was that perhaps the previous users had backed into rocks, or the shift cam was weakened by the boat being driven I reverse and pulling against something for a while. Tech said he has seen the shift cam worn do own and weakened, but not chipped before. Strange.
 
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Yes, your image is not opening.

The link below is the transmission parts page from boats.net
This may be the Merc trans because I have rebuilt a few of the smaller (20 hp on down) Honda transmissions but I don't recognize this one. Item #4 doesn't look like the little "bullet pin" I'm accustomed to seeing in those. Does this one look like yours? Or, does yours just have a pin that looks like a long 25 cal. bullet?

While you're in there, look VERY CAREFULLY at the clutch (item #1) and reverse gear (item #7). The squared off sections (engagement "dogs") MUST be cleanly squared off and well defined at the edges....almost knife sharp at the edges. If they get rounded off, the trans will balk at going into gear. They wear over time, of course, but they can also be made to wear extremely fast if the transmission isn't shifted correctly.

Pulling the shift selector slowly and having the dogs chatter against each other will wear them out quickly.

The trans should be put in gear with a crisp, quick motion so that it "snaps" into gear. Always shift at idle, from neutral, after having given the trans time to coast to a stop. It should be:
Forward-neutral...wait a sec...reverse. And then vice versa if going from reverse to forward.

I know this can't always be done when maneuvering around a dock or other obstacles but it should be practiced whenever possible.

Anyway, check out the parts link and get back with your thoughts.


http://www.boats.net/parts/search/Honda/Outboard Engine/1998/BF90AW LRTA/PROPELLER (1)/parts.html
 
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