What should I do with this? (pics) lower unit

[Doobienaq]

My 2005 Yamaha 90hp has been making a odd rattling sound (only while running) the last two or three trips out. I decided to check it out today and found this. I have no idea how it happened because I haven't hit anything that I can remember in quite a few years - the anodes seem to be working, so I don't think it's from electrolysis. I'm not sure how long it's been like this, but apparently the lower unit is only being held on by one bolt. Can anyone tell me why two heads would break off of the bolts on one side and crack the other? My dad is an aluminum welder with over 30 years experience, so can this be fixed with by welding? Anything to watch out for in trying to repair?

image1 by Lyle Naquin, on Flickr

image3 by Lyle Naquin, on Flickr

[DennisG01]

***, that's a weird one for sure!

EDIT: ^^^ Why can't I say W O W (without the spaces)?

This is, of course, just a guess but... Maybe after the last impeller change (or for whatever reason the lower unit was removed) the nuts weren't put back on all the way. That could of allowed for the unit to twist and tilt, especially with the torque of the prop. The whale tail would have likely increased the issue.

Eventually, the lower unit twisting caused the two studs to snap off and the casing to break on the other side. I don't see any excessive corrosion on the bolts to warrant that being a cause.

I'm not sure if this would have caused any problems to the drive shaft coupling area, but it would be good to get that checked.

Obviously, hindsight is 20/20, but when you hear something that doesn't sound right, check it out right away. Weird noises don't usually mean "everything is OK", you know?

[mjf_1955]

Looks to me that you at least need a new housing. As the parts are moved to the new housing, each part must be checked tonmake sure they are usable.
I think it is beyond welding.

[TownsendsFJR1300]

Agreed with both posts above.

There's no visible corrosion there and the foil puts a whole lot more pressure on the lower unit.

My moneys on the bolts (bolts on the below model as I don't know your model) loosening up or not fully tightened to start with.

2005 F90TJRD Yamaha Outboard LOWER CASING DRIVE 2 Diagram and Parts

I gather the boat is left in the water trimmed down??

[Doobienaq]

Yes, hind sight is definitely 20/20 - wish I would have looked into it sooner, but to be honest, I wouldn't have even known to look to tighten those bolts. I've had the boat for a few years and have never dropped the lower unit because I've never had any problems with overheating or the water pump. I've never been told, or read, that it was necessary, so I didn't know - lesson learned

Dad has already welded it back together, so we'll be putting it back together. Is there anything that I should look for to make sure that it's in good shape to put into use? Would you suggest taking the fin off? Or do you think it was more than likely the loose bolts more than the fin?

Btw, the boat is shed kept - it doesn't sit in the water, but I am aware of the water marks on the motor (I was told that it's probably from the lack of alignment between the foot and upper casing while this mess was happening). Is that accurate?

[pstephens46]

Try running without fin. See how it does. I would think without would put less pressure on the damaged area. You may still have to replace parts. Consider replacing water pump if it has been several years.

[Doobienaq]

I have all of the parts on order - water pump kit; lower housing of the water pump (it was very corroded and cracked on extraction); both the seal and gasket that is under the lower housing of the water pump; and the bolts to put it all back together since the old ones were a little corroded.

I don't think the boat was ever set up correctly - I think it would need a jack plate to lower the motor. Since I've been having it, it cavitates even in small turns; this is why I put the whale tail. I'm thinking I'll just have to deal with the cavitation until I can afford to put a jack plate and installation.

[DennisG01]

Those fins can often CAUSE cavitation (actually, it's ventilation in this case). It can both disrupt the water flow and also lift the prop slightly higher out of the water. Trimming too high during a turn can do it, too. I take it there are no holes available in the bracket to lower the motor?