Corrosion of lower unit at impeller housing (Honda BF100)

[Wild Oar]

Howdy all,
As my first post to IBOATS, I need help! I hope to repay the favor as I gain more experience working on motors.

Here's the deal:
I have an old Honda BF100 (pre-1997, but not sure exact year) 10HP outboard. Bought it last year along with a 14' MirroCraft and it has been running very well. However, from the beginning I've noticed that the cooling pee stream is relatively week compared with other motors i've run. So, recently I pulled off the lower unit to inspect the impeller & housing. Turns out the impeller is in great shape, but I found significant corrosion in other places--mainly where the lower unit meets the impeller housing and "key-shaped cover". There is major corrosion just under the impeller adjacent to the shift linkage and also where one of the bolts screws in. See attached photos. Note that I've run this motor in salt water quite a bit, but have always flushed it with fresh water.

Being a novice boat mechanic, I have the following questions:
(1) Could the corroded-gap under the impeller housing be causing the water pump to lose power, thus the weak pee stream? It seems like the pump would be drawing air from the gap, thus decreasing water draw.
(2) What other problems, in any, could it be causing?
(3) Is the lower unit effectively screwed due to this corrosion, or can I clean it up and plug that gap with silicone (or something else)? Eventually, I'm going to buy a new motor, but would like to use this one for at least one more season since it runs like a champ.
(4) If the lower unit is screwed, does anybody know where I could find a replacement? Used is fine. Roughly, how much would it run? Couldn't find any on the internet, but have yet to check with my local Honda dealer.
(5) A rubber gasket where the impeller housing meets the lower unit is also degraded, but I can't find that part online? (see 1st photo) Does anybody know how to find the Honda part number on that? What is that gasket called?

Thanks in advance for your help,
Wild Oar

 

[Wild Oar]

Re: Corrosion of lower unit at impeller housing (Honda BF100)

Anybody? Throw me a bone!!! D:facepalm:

Howdy all,
As my first post to IBOATS, I need help! I hope to repay the favor as I gain more experience working on motors.

Here's the deal:
I have an old Honda BF100 (pre-1997, but not sure exact year) 10HP outboard. Bought it last year along with a 14' MirroCraft and it has been running very well. However, from the beginning I've noticed that the cooling pee stream is relatively week compared with other motors i've run. So, recently I pulled off the lower unit to inspect the impeller & housing. Turns out the impeller is in great shape, but I found significant corrosion in other places--mainly where the lower unit meets the impeller housing and "key-shaped cover". There is major corrosion just under the impeller adjacent to the shift linkage and also where one of the bolts screws in. See attached photos. Note that I've run this motor in salt water quite a bit, but have always flushed it with fresh water.

Being a novice boat mechanic, I have the following questions:
(1) Could the corroded-gap under the impeller housing be causing the water pump to lose power, thus the weak pee stream? It seems like the pump would be drawing air from the gap, thus decreasing water draw.
(2) What other problems, in any, could it be causing?
(3) Is the lower unit effectively screwed due to this corrosion, or can I clean it up and plug that gap with silicone (or something else)? Eventually, I'm going to buy a new motor, but would like to use this one for at least one more season since it runs like a champ.
(4) If the lower unit is screwed, does anybody know where I could find a replacement? Used is fine. Roughly, how much would it run? Couldn't find any on the internet, but have yet to check with my local Honda dealer.
(5) A rubber gasket where the impeller housing meets the lower unit is also degraded, but I can't find that part online? (see 1st photo) Does anybody know how to find the Honda part number on that? What is that gasket called?

Thanks in advance for your help,
Wild Oar

View attachment 202586View attachment 202587View attachment 202588View attachment 202589

 

[edmo]

Re: Corrosion of lower unit at impeller housing (Honda BF100)

Ok, but not much of a bone. I am your senior in posts by single digits I think. If It's a problem from salt water corrosion I know nothing, my closest association with salt water is nasal rinse.

Basic question. Did you notice if the engine was overly warm to the touch when your pee stream was weak? I had the same issue with a different brand of motor on the first day of a trip to Canada. Thought the vacation was toast until I inspected the pee stream plumbing. A bit of grass or something got in there and reduced it to a rapid drip. Might check yours to see if there is a separate little plumbing system for your indicator stream. And I guess there could also be some salt water crud there to look for. Probably no help, but a bone nonetheless.

 

[Wild Oar]

Re: Corrosion of lower unit at impeller housing (Honda BF100)

Thanks for the bone, I may be able to get some marrow out of there. I have inspected the pee stream plumbing and it does not appear to be clogged. Have a good one,
Wild Oar

Ok, but not much of a bone. I am your senior in posts by single digits I think. If It's a problem from salt water corrosion I know nothing, my closest association with salt water is nasal rinse.

Basic question. Did you notice if the engine was overly warm to the touch when your pee stream was weak? I had the same issue with a different brand of motor on the first day of a trip to Canada. Thought the vacation was toast until I inspected the pee stream plumbing. A bit of grass or something got in there and reduced it to a rapid drip. Might check yours to see if there is a separate little plumbing system for your indicator stream. And I guess there could also be some salt water crud there to look for. Probably no help, but a bone nonetheless.

 

[isaksp00]

Re: Corrosion of lower unit at impeller housing (Honda BF100)

I would buy a new set of gaskets and the metal impeller cover (looks like these 3 things are still sandwiched together in photo 4). If this is the same as my 8HP, the water gets sucked up into the impeller from the arch-shaped slot over to the left of photo 4, and is pulled up from the cavity in the lower unit surrounding the pinion shaft (the rod sticking straight up in pic 1). I think the path is something like: in the water intake screen at the bottom of the LU, up the cavity in the leg, up through the rear hole in the impeller cover (the one to the right in pic 4), into the "cover holder", down the other hole in the impeller cover, into the chamber surrounding where the pinion shaft is, and then up into the impeller housing.

You may also want a new impeller housing, if the inside of the old one looks bad. Maybe not if you will get rid of it in a year.

So wherever corrosion gaps would let the suction pull from outside that path, like the one in pic 1, could reduce flow. Given this is short term, you may want to try one of those epoxies that are like metal on these gaps, and get the top surface nice and flat. A new gasket set with impeller cover might then be good enough, and is not a costly repair to experiment with. Also as stated make sure the pee hole itself and its hose is not blocked - stick a stiff wire, like aluminum, up there. Bottom line, if the water is flowing enough to keep the engine cool, you are probably OK for a year or so.

Putting the leg back can be a little tricky. Make sure the upper part of the impeller housing fits properly into the water tube above (the 1st time I tried, it missed and no water was going to the engine). Put a little grease around the sides of the vertical shaft splines at the top, but not on the very top of the shaft (you don't want grease keeping it from seating upwards). You managed to get the rod joint at the top of the shift rod totally off; I never did that, I just pulled the LU low enough to get at the impeller.

I don't recall the gasket arrangement around the pinion shaft, pic 1. I think that seals water from getting in the gear system below, so verify that your gear oil is OK (not milky). If it is fine, I am not sure I'd do anything there, unless this is a longer term affair.