50hp Mercury 500 lower unit swap

[16ftspecial]

I have a 1974 50hp Mercury 500 ser#4073302. My lower unit is locked up I have found one but it is listed as being from an early seventies red stripe 50hp with 11 splines on the drive shaft mine has 13 splines. I thought the redstripes were merc 500s also. If anyone could shed some light I would greatly appreciate it.

 

[GA_Boater]

Re: 50hp Mercury 500 lower unit swap

The stripe colors don't mean rated HP. More a year range. My Merc 500 has no stripe from '66. There are red stripes from 4 - 115 or so HP.

Some advice, even if it interchanges don't put an 11 spline lower on her. Parts are getting scarce and forget new props. I'm re-sealing my lower and and I have to buy the seals/gaskets individually because kits are non-existant. Costing more $$ than it should.

 

[16ftspecial]

Re: 50hp Mercury 500 lower unit swap

Thanks, I did not know if the difference in spline count would damage anything.

 

[GA_Boater]

Re: 50hp Mercury 500 lower unit swap

If it interchanges, it won't damage anything. Like I said - I just don't think it's a good choice. I don't know what you plan on paying but picking up a parts motor might be cheaper in the long run. I see those fairly cheap all the time.

 

[16ftspecial]

Re: 50hp Mercury 500 lower unit swap

They were only asking 75$ but I am disabled (colon cancer survivor) with limited funds and my boat is my salvation if any thing more were to go wrong i don't know what I would do. I want to make the best choice (within my means). I may just keep looking. I have seen your remarks on other posts and respect your knowledge and opinion. Thanks again.

 

[GA_Boater]

Re: 50hp Mercury 500 lower unit swap

Thanks, special. I'm just a shade tree guy but I try to help when I can. Can you turn the flywheel in neutral? Is the lower locked for sure? Just trying to gather info from afar.

I think, but not sure, the 40 (Merc 400) and maybe 35 (Merc 350) HP 11 spline lowers are the same. Like I said, I'm not 100% certain.

 

[16ftspecial]

Re: 50hp Mercury 500 lower unit swap

Yes, I was on the water everything was fine, ran smooth. The next day I took it out after about 15 mins of running the lower unit just locked up. I got it home and removed the lower unit and it was full of water. with the lower unit removed the fly wheel turns with no problems. The drive shaft and the prop shaft of the lower unit are frozen. I figured a bearing or gears locked up. Thought of using some mystery oil to see if it would come free but figured it may have messed up some of the gears inside.

 

[GA_Boater]

Re: 50hp Mercury 500 lower unit swap

If I remember, there are three bearings. Does anything turn if you put the lower into neutral?

 

[16ftspecial]

Re: 50hp Mercury 500 lower unit swap

shift shaft moves, drive shaft and prop shaft are frozen.