1973 402 twin cyl. lower unit serial numbers

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mcguyvermike

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Dec 14, 2006
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I have a 40 hp twin with a bad lower unit. Looking for a replacement, as a rebiuld costs @ $600. I have been told that the lower unit that I have will fit a variety of H.P. motors. How can one tell from the seriar numbers witch one fits what ? Mine has serial number 1643-6037. The ones on ebay say they will fit 40-60 HP but the serial number is different. Can I go off the number of splines on the shafts along with the length? or is there more to it ?Any suggestions MIKE
 
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Laddies

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Sep 10, 2004
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Re: 1973 402 twin cyl. lower unit serial numbers

To start with you need the casting number of thier unit, and know that they a both long or short shafts,it will probaly fit, you can ck on parts sites like BAM Marine if you have the casting numbers or the serial numbers for interchange
 
WillyBWright

WillyBWright

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Dec 29, 2003
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Re: 1973 402 twin cyl. lower unit serial numbers

Models that fit include 35 and 40 twins. 40, 45, and 50 inline-4's. 50-70 triples look alike but will not fit. Roughly from the 1960s through the 1990s
 
Chinewalker

Chinewalker

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Re: 1973 402 twin cyl. lower unit serial numbers

Actually, some of the 3-cylinder model units WILL fit, BUT they are a different gear ratio and propping it to work correctly can be a pain...
- Scott
 
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mcguyvermike

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Re: 1973 402 twin cyl. lower unit serial numbers

Thank you for the help!! I'll se what I can find en ebay, and hope for the best.
 
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