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Honda 50 Lower unit Crack

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lakeguy

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"My Honda 50(1999) has

"My Honda 50(1999) has a piece of the gearcase missing(clamshell shaped) fron the back edge of the case and runds forward about 3.5"s. It is and 90 degree arc at the back edge and runs out just forward of the bearing retainer rear section. The retainer nut is cracked just behind the prop. The moter runs fine at low speeds, the propshaft part stack is tight axially and doesn't wobble. At about 5000 it makes a cavitating noise.
Any thoughts on why this happened and is it a common Honda problem?
Thanks"
 
"Yeah, what he said. Pictures

"Yeah, what he said. Pictures.

From your description through, damage sounds like it could have been several things. Bad casting, prop hit something, handling damage.

My guess is that at 5000 RPM, the casting is expanding slighlty due to dynamic oil pressure from the shaft rotating. This results in the bearings drifting a bit more, and wobbling the shaft. But without pics, thats just a total guess.

Could also be cavitation induced by the missing piece. In which case, you could probably just smooth it out with some metal epoxy. Again, a total guess without pictures."
 
"O'k I have got this one,

"O'k I have got this one, for sure. Have had 4 Honda's 50 for the last 10 years all at about 4 or 5 years have had same prob. Diff. metal in lower unit causes rust and swelling. On advice of my h guy filed on inc. and I am real sure I must have it some under water object"
 
Sounds like this is the corros

Sounds like this is the corrosion problem affecting many BF50 motors. According to a Honda mechanic corrosion builds up under the threads of the retaining nut. Then the corrosion swells which puts pressure on the gearcase causing small cracks to develop. You can see them just forward of the prop hub. The cracks propogate causing large piece(s) to break off. See my post on Dec 10. The mechanic said this can even happen in fresh water where the engines are flushed with well water as well water can contain contaminants i.e. if your coffee tastes bad you had better check the lower unit for corrosion.
 
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