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1969 mercury 110 9.8 hp lower unit interchangeably

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DuckhunterJoe

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I have a 1969 mercury 110 9.8 HP, it is stuck in reverse and I can’t get the prop off of it to see what’s broken inside the lower unit. So I was wondering what interchange there is for this particular motor to replace the lower unit. I found a 6 hp that I can get for cheap, it looks to match the 9.8 I have, will the lower unit swap between the two motors?
 
First, how long has it been like this? Second, what's the gear oil look like? Third, has it been used in salt water? Fourth, have you ever had it apart before? Fifth, what year or serial number is the 6 horse? Be same unit if it's a model 60. Last suggestion, make sure the 60 has a good lower unit. Seems they often go bad. Why? Driveshafts leak under water pump, trading good grease for water.....Why? Shafts are NOT STAINLESS STEEL.....they rust at the seal there.
 
Last edited:
Lots of interchangeability between 6, 7.5 and 9.8 hp Mercs of that period.

As Tim said, drain the LU and see what comes out. If it's water, start looking around for another LU.

Jeff
 
timguy said:
First, how long has it been like this? Second, what's the gear oil look like? Third, has it been used in salt water? Fourth, have you ever had it apart before? Fifth, what year or serial number is the 6 horse? Be same unit if it's a model 60. Last suggestion, make sure the 60 has a good lower unit. Seems they often go bad. Why? Driveshafts leak under water pump, trading good grease for water.....Why? Shafts are NOT STAINLESS STEEL.....they rust at the seal there.
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Thanks, This LU tied up years ago and I never really got much into it after not being able to remove the prop no matter what I tried, if I remember right the gear oil might have been milky, it’s never seen salt water as I live in the Great Lakes region, and I put a new impeller in the water pump and had the LU off for that but I’ve never had the gear case apart.
 
fastjeff said:
Lots of interchangeability between 6, 7.5 and 9.8 hp Mercs of that period.

As Tim said, drain the LU and see what comes out. If it's water, start looking around for another LU.

Jeff
Click to expand...


Thanks that the info I was looking for, I’m hoping the LU from the 6hp will just slide righ in and I’ll be good to go.
 
Yes, the black steel shafts rust out here too. Might want to replace aforementioned seal on the 60, as well as the pump. If you can set the new seal slightly deeper, below the old groove and pitting (if there is any), that is my suggestion. Use anti seize on fasteners and splines.
 
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