lower unit swap

[gspig]

As I posted earlier, I destroyed the lower unit on my outdrive. My outdrive is marked 165hp and is a pre-alpha. I have an entire outdrive marked 145hp and is also a pre-alpha. I am uncertain of the condition of the replacement outboard, so I thought I would just swap lower units. After much frustration, I noticed that the input shafts are splined differently. Is it possible to swap input shafts without completely dismantaling the lower unit?

 

[Bondo]

Re: lower unit swap

Nope..........<br />You've got to Dig Real Deep to Change the Input Shaft.........<br />If you swap out the complete drives,<br />Your Gear Ratio is going to be Wrong.....<br />You'll need a Big Prop to avoid over reving.......<br />It's the Upper Gears that determine the Over-all Ratio........<br />Good Luck.........

 

[gspig]

Re: lower unit swap

Got a manual on order. Will the input shaft come out when the lower carrier bearing and prop shaft is removed?<br />The parts diagrams don't show anything that looks like a retainer on the input shaft. I can't figure out how its held in place.

 

[achris]

Re: lower unit swap

gspig<br /><br />What are you calling the input shaft? The shaft at the top of the leg (outdrive) that goes into the back of the engine or the shaft sticking out of the top of the lower half of the leg, the driveshaft?<br /><br />I don't recall Mercruiser ever making a 145.<br /><br />Chris.........

 

[gspig]

Re: lower unit swap

The shaft I'm talking about is the vertical shaft going into the bottom half of the outdrive. The shaft 90 degrees to the prop shaft the one the water pump impeller is on.

 

[achris]

Re: lower unit swap

That's called the driveshaft. <br />

Is it possible to swap input shafts without completely dismantaling the lower unit?

No. To remove it is a full stripdown of the box. To fit it to another box requires re-shimming. Impossible without the Merc special tools. <br /><br />I'm curious about the '145hp' leg. Does it have a serial number on it anywhere?<br /><br />Chris...........

 

[gspig]

Re: lower unit swap

Thanks for the bad news. I guess I'll change the upper that my lower matches. Didn't want to do that, but maybe the gearing won't be badly affected and hopefully won't over power the 145hp leg. I'll post the serial# on the 145hp leg tonight when I get home.

 

[gspig]

Re: lower unit swap

The correct tag for the "145hp" leg is Model MC 120/140. The manufacture dates for that model indicates to me that this drive may be the original drive ('67-73). The drive on the boat is a Model 80 ('66-69) is the one I damaged. The boat is a '72 Winner. The driveshaft to the lower units are the same length and same diameter and both have the spring pin on the end, the difference is the number of splines. <br /><br />I am now at a loss as what to do. Local shops can't get to the gear swap in the lower units in time for Labor day weekend. I can put the good lower back on the 120/140 upper, but if this is the original drive, there must be something wrong with it. Why would someone spend the money for a complete outdrive if they didn't need to? Coincidentally, the driveshafts from the engine to upper units on both outdrives are identical, same diameter, length, overall length, and splines.