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BF 225 Lower Unit Corrosion

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dang_it

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New to Forum. Just purchased a 2005 Honda 225 (350 hrs) on pontoon boat and used only in a freshwater lake, South Texas. Lower unit is severely corroded, skeg (leading edge) is 20% eaten away. Body housing below cavitation plate pitted. No Leaks (yet). Appears lower unit below Cavitation plate rested in water and anodes were not in water. Plan to replace lower unit in couple of months. Desire Forum's thoughts concerning corrosion on / inside block or where? No water intrusion in engine oil. Just got this rig at decent price (scares me) and have not dived into exhaust / water jackets etc. Thanks in advance...
 
you could pull the thermostat and get an idea of the condition of the inside of the engine, which is fairly easy. I doubt the lower unit being in water has anything to do with the condition of the engine especially being in freshwater.
 
Plan to pull both thermostates snd inspect the block area. With T’states removed do a chemical flush of block and reinstall T’states after testing.
 
Stray electrical current can cause electrolysis, if it’s eaten away, there must have been something happening. But checking areas above the lower unit is the only way to know what was damaged, ie pulling thermostats and going further if you find any damage. How do the anodes look?
 
Anodes on lower unit in good shape. Appears the area below cavitation plate was submerged in freshwater lake. Unit never in salt water. I was not able to get to lower unit to get depth reading of pitting.
 

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Those anodes could be toast, I weigh mine to compare old and new.

I had a 63 Pontiac, due to electrolysis from the backup light in the bumper, the bumper had been eaten away where it mounted to the bumper brackets, part of the bracket was eaten away and part on the frame was gone too. This was all heavy steel and a stock chrome bumper, I’ve seen many old car bumpers on cars rotted into the ground, no bumper rotted like this from what I assume was a wire problem with the light.

Was this boat spending time on a dock plugged in to shore power? I’ve not seen a lower unit pitted like that and I’m a salt water only guy.
 
That looks like damage from hitting rocks and gravel- unless the casting is very inconsistent, it shouldn't erode that much in any single area.

Do a continuity test from each part to the battery- if you don't see low DC resistance, your continuity wires may not be intact and the bolts/mating surfaces for the anodes in place may be corroded.

Is this brackish water, or inland? Those anodes don't look good- most have an even appearance and those are very crusty. YOU may not leave it in the water, but it seems that the previous owner did- even the stainless prop has stuff on it that shouldn't be there. Where was this used before you bought it?
 
chawk_man said:
One other thing. The large anode on the forward part of the engine bracket should have a ground wire attached to the swivel case. That allows the anode to protect the lower unit. It's missing or not connected on a lot of these engines. See part 5 at...
Click to expand...
That's a continuity wire, as I mentioned. I would imagine a lot of repairs are made and the wires are lost or ignored- similar to the bonding cables or straps on cars & trucks, but those are used to prevent RF escaping the engine compartment and affecting other nearby vehicles.
 
Thanks to all for the feedback, great forum!
. I have pulled the thermostats and very little corrosion detected within housing and on thermostats. I was hoping to run borescope into exhaust manifold, but too much interference. I'm going to wait and possibly pull manifold later.
. Appears continuity wire from engine to frame anode is missing. Hard to get to since boat is in hoist and lower part of engine is not accessible. Lower unit is out of water.
. Glad I saw the thread on timing belt tension and should be checked / adjusted every 200 hrs. This belt needs adjusting, I can turn tensioner pulley by hand! Have about 3/8" flex of belt from crankshaft to tensioner pulley.
 
dang_it said:
Thanks to all for the feedback, great forum!
. I have pulled the thermostats and very little corrosion detected within housing and on thermostats. I was hoping to run borescope into exhaust manifold, but too much interference. I'm going to wait and possibly pull manifold later.
. Appears continuity wire from engine to frame anode is missing. Hard to get to since boat is in hoist and lower part of engine is not accessible. Lower unit is out of water.
. Glad I saw the thread on timing belt tension and should be checked / adjusted every 200 hrs. This belt needs adjusting, I can turn tensioner pulley by hand! Have about 3/8" flex of belt from crankshaft to tensioner pulley.
Click to expand...
I just recently purchased an OEM shop manual for my Honda outboard and there’s a procedure for the timing belt tightening. If you want I will post that page for reference. Just let me know.
 
need advise on repaired / filling pitted areas on lower unit of BF 225. Leaning towards using West Systems G Flex or possibly JB Weld. No holes completely through housing.
 
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