lower unit commonality?

Bsquared

Seaman Apprentice
Joined
Aug 30, 2007
Messages
39
Can I change a lower unit from a '77 75 hp 3 cyl with one from a '95 115 V4? Do they use the same ratio? The older unit is deepley corroded, and I have been unable to remove the drain plug. I'm afraid using more forceful methods will mess up the whole casting. Meanwhile, I have a free V4 unit just sitting here..

Thanks!
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: lower unit commonality?

I guess you could if you wanted to make adaptors but it's not a direct swap and the gear ratio is different. Try using an impact driver. If you don't have one take it to a dealer -- they'll have one.
 

Bsquared

Seaman Apprentice
Joined
Aug 30, 2007
Messages
39
Re: lower unit /drain plug removal

Re: lower unit /drain plug removal

Just a long-overdue followup. No luck on the drain plug with heat, impact driver, penetrating oil, etc. Got some good drill bits and drilled it for an extractor. Went too small to start with and broke off the extractor. Not good. Fortunately had drilled the plug all the way through, so I was able to punch the broken-off end into the gear case. Not good, either. Drilled out the plug larger; to less than 1/8" wall thickness (some of the threads were actually cut through and the whole screw head fell off). With some cranking, the bigger extractor finally pulled out the remnant. Looked like a small ring :)
Drained the oil. Went through the oil pan and couldn't find my broken-off tip, so I took a coat hanger, attached a big magnet, and went fishing in the gear case. Found it!! Very nice not having to buy another new lower unit...
Flushed the gear case with some oil, added new oil, new plug and gasket, and been working great ever since. Old lube was BLACK :-( No water, but the threads of the old plug definitely had a little corrosion.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: lower unit /drain plug removal

Re: lower unit /drain plug removal

Glad it all worked out! Thanks for the follow-up!
 
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