Lower unit identification?

[sutor623]

Hey motor guru's. I bought a 1967 Mercury 650 4 cylinder and the lower unit is bad, but the seller gave me a good unit from a junkyard. Only problem is I dont know if it is interchangeable or not. Can anyone identify which series motor this came off of and if it is interchangeable? The serial # on the unit that came on the motor is 1623-2460, and the # on the other unit is 1623-0051. Thanks!!

 

[sutor623]

Re: Lower unit identification?

In the first pic, the unit on the left is the unknown, and on the right is the 650. Picture two, driveshaft on left is the 650, both have 8 teeth. Pic three is the bearing holder of the unknown motor, pic 4 is the bearing holder of the 650 (and it is cracked, so unfortunately that is the main reason that I cant use that unit). In the final pic. you can see that the gearcase farthest away has a longer fin, that is the unknown case, and it had a much larger prop than did the 650. Obviously, this is from a bigger motor, but which one????

 

[Faztbullet]

Re: Lower unit identification?

Place a mark on the propshaft and count how many driveshaft turns to make 1 prop revolution as that will give you gear ratio,if its not 2:3:1 it wont work. It looks to be off a mid 70"s inline motor.

 

[ThumbPkr]

Re: Lower unit identification?

One concern will be the driveshaft length of course if you plan to use the new unit whole.Another is that the newer driveshafts have an "0" ring on the top spline that has to match the spline on the crankshaft.I have heard that you can create the grooves on the driveshaft with a die cutter etc if needed.
The manuals say that the housings should fit the 650/150 engines from '63 until '86,that is they will bolt up but the gear ratios etc might be different.The gear ratio should be 2.3:1 for your engine as said but I ran my 650 for many years at 2:1.I did not know it at the time but it did seem a little tall coming out of the hole.I was running a two blade 19" pitch bronze prop most of the time on it.I just rebuilt mine with the correct ratios so the difference remains to be seen.
The part number on my lower unit was for a 150 engine which would have been the 2:1 ratio.
The pinion/gear tooth ratio for the 2:1 is 15/30 and the ratio for the 2.3:1 will be 13/28.Ron G

 

[sutor623]

Re: Lower unit identification?

Thanks! You guys are awesome man. Thanks for sharing the experiences Thumb, and thanks for the test method Fazt. This is exactly what I wanted to know. So check it out, I checked the gear ratio and it is in fact 2:1. So I think I will cut the groove in the main driveshaft to allow for the o-ring to seat for now. I just want to get back on the water. Ill be keeping my eyes open on E-bay.