Mysterious crack in lower unit, 1986 175 BMax

[dingbat]

I went over to adjust the cover on the boat this weekend and found a mysterious crack on the side of the lower unit. The crack looks like an inverted J about 2 ½” in length that is back about 5” back from the front, (prop end) and 1 ½” up from the CL of the prop. The crack does not appear to be leaking at this time, at least at atmospheric pressure but the inside of the “j” is about a thumbnails thickness above the opposing surface. <br /><br />I know I’ve not hit anything and LU unit still seems to run fine so I’m kind of at a loss. I guess the question is has anyone seen this before and can this be repaired by welding.

 

[jrampey]

Re: Mysterious crack in lower unit, 1986 175 BMax

This could be ugly... I would drain and replace the lower unit oil - carefully inspecting the old oil for water. If milky then water has penetrated the seals and may have frozen over the winter.<br /><br />Does the prop spin freely?

 

[dingbat]

Re: Mysterious crack in lower unit, 1986 175 BMax

I changed the fluid when i put it away the first of Januray so I doubht that it's freeze damage. I've put maybe 70-80 hours on it since the end of March so I find it hard to beleive that I didn't notice it before but who knows. <br /><br />I checked the fluid and it was full with no sign of water whatsoever. I even dropped it in gear and it sound fine, at least stiing in the driveway.<br /><br />I'm stumped.

 

[Capt Ken]

Re: Mysterious crack in lower unit, 1986 175 BMax

Mercurys and Mercruisers are bad about that when they get some age on them. Caused by many years of use in salt water. Corrosion builds up between the bearing carrier's retaining nut and the outer shell of the gearhousing and splits the housing. Never seen it get bad enough to get into the gear area but anything is possible. Some folks will have the crack welded in place but don't ever plan on disassembling that unit for repairs.

 

[studlymandingo]

Re: Mysterious crack in lower unit, 1986 175 BMax

I think as everyone has said, it would be prudent to check the fluid for moisture. I don't see any reason not to weld the crack, it should seal up any leaks that might be there, and prevent any further movement of the crack.<br /><br />Good luck and keep us posted!

 

[LubeDude]

Re: Mysterious crack in lower unit, 1986 175 BMax

Bet you stored it in the tilted position over the winter and the area around the prop filled with rainwater and froze.

 

[dingbat]

Re: Mysterious crack in lower unit, 1986 175 BMax

Originally posted by Bassin' Fever AKA LubeDude:<br /> Bet you stored it in the tilted position over the winter and the area around the prop filled with rainwater and froze.

Only one problem with that theory, the crack is behind the carrier bearing and is comma shaped. Not the type of fracture you'd associate with your scenario. Shape alone would suggest some kind of an impact fracture more so than a stress fracture.<br /><br />Still scratching my head.