Mercury 90 lower unit troubles

[baltica]

" I am having trouble with my

" I am having trouble with my engine (a 1986 Merc 90), I think the lower unit is messed up. I just bought the boat this summer (a 16 foot 1970 Whaler), and it ran fine the first time or two, but then the problems started.
The engine runs well in neutral, even at high rpm, but has trouble getting up to higher speeds when its in forward gear.
Sometimes, it will not go above 7-8 mph, other times it maxes out at around 25 mph, well below its capacity. You can hear the transmission struggline to get it on.
So I pulled the plug on the lower unit, and out came stinking greyish oil- a real mess. Obviously water had seeped in. On top of this, the magnetic lower plug had some fine metal shavings on it (not lots, but enough to make me worried). I changed the lower unit oil, and ran the boat hoping this might help, but the problem is still there- she runs fine at trolling speeds but can't get above 20-24 mph on plane.
So my questions are-
1) is the lower unit finished, or is there hope that I might be able to fix it?
2) Can I fix it myself, or is this a job for an expert? I've checked, and the cost of a replacement lower unit is over $1000....
3) given the age of the engine (1985), should I be thinking another whole engine? Since I just just bought this boat (my first Whaler), I'm relunctant to blow a wad on expensive repairs if this engine's days are numbered...
I need advice- any suggestions? "

 

[tonyob]

"Baltica,

The water in the

"Baltica,

The water in the lower unit is probably getting in through the prop shaft seals. The drive shaft and shift rod seals are other, less likely possibilities. These problems can be fixed rather inexpensively. Removing ( and replacing ) the bearing carrier is where you will run into trouble. The assembly is held in place by a large ring nut that threads into the casing. You can break the old one to remove it, but you will still need a special tool to install a new one properly. I think the tool costs about $60 from Mercury. You have to remove this assembly to replace the prop shaft seals.

The loss of power may be a separate problem. Start by checking compression and spark.

"

 

[KJ]

" Also, check the carbs. I kn

" Also, check the carbs. I know my 1978 JOhnson 70 sounded like a champ in neutral and on the hose muffs but was an absolute dog until I got my carb problem fixed. Your problem could very well be solved by dimantling the carbs, cleanig the bowls & jets, and installing a new float & gaskets.

Old lower unit oil will look grey & nasty. A true sign of water infiltration is a more chocolate/foamy texture to the oil. Have you checked the oil since you changed it out? What you replaced was quite possibly the original lower unit oil. That's not out of the realm of possibility! I would suggest draining the oil and filing it again if the oil you first removed was that nasty.

Was the metal on the plug filings (slivers) or was it more powdery. A powder/fine pieces is not uncommon on an old motor, slivers of metal are VERY bad however. Check this again when you swap out the oil. You might also consider using a synthetic lower unit lube. I haven't done this myself, but I'm told synthetics do a better job of conditioning seals. "