1975 Mercury 500 Thunderbolt Lower Unit Rebuild

SmartFish

Recruit
Joined
May 13, 2012
Messages
4
I have a 1975 Merc 500 Thunderbolt that needs help. I haven't used it in a few years and it is mounted on a project boat that I'd like to get fixed up. Prior to setting this motor aside, I had taken it into a marine repair shop to have them work on a shifting issue. As I recall, it had a hard time shifting to reverse. Anyway, the guy dis-assembled the lower unit then said he couldn't get it to go back together. I think he said something about gearing being worn or something? Gave it back in pieces, literally in a plastic bag. I actually got the lower unit pieced back together and back into place myself. I'm pretty sure it's not right. Lesson learned.
I'm a newbie to outboards so this seems like a great project to cut my teeth. The top end ran fine last time it was running, but the lower unit needs to be gone thru along with the prop kits, etc. I'm not sure exactly what will need replacing (or what may be missing), but a parts list for the lower unit and prop shaft would help me identify what I need to do. The SN is #4284415. I'd like to do this myself and not break the bank on an old motor, but it's a shame to leave it sitting around when I'm pretty sure it's serviceable. Any help would be appreciated. Thanks in advance.
 

carholme

Rear Admiral
Joined
Sep 4, 2010
Messages
4,845
Re: 1975 Mercury 500 Thunderbolt Lower Unit Rebuild

Here is the parts listing for your s/n:

http://www.crowleymarine.com/mercury-outboard/471.cfm

See GEAR HOUSING ASSEMBLY, COMPLETE (PAGE 1)
GEAR HOUSING ASSEMBLY, COMPLETE (PAGE 2)

If you don't have a Mercury service manual the P/N is: 90-75512

In the interim, here is a link to a condensed version of the Clymer manual, which will help. Let the page load for several seconds and then download to your computer soonest as the link is short lived.

http://web.ebscohost.com/serrc/pdf?sid=9b70ad60-caf8-409f-9d14-57d09469b86d@sessionmgr15&vid=4&hid=8

Gerry
 

SmartFish

Recruit
Joined
May 13, 2012
Messages
4
Re: 1975 Mercury 500 Thunderbolt Lower Unit Rebuild

Thanks. I'll try to dig into this soon and see what I have and what I need. Any direction on the correct cable attachment to the throttle shiftbox on an 82 Merc 50 HP (SN 6098078)? I have that motor on the pontoon and when the shifter is in the forward position, the motor is actually in reverse gear, and when shifter to the rear the motor is in forward. I read something on this forum that directed to change the cable positions at the throttle, but haven't found the thread again. I really appreciate all the help.
 
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