1958 mercury mark 58 thunderbolt four lower unit removal

[homey58701]

can anyone tell me how to remove the lower unit on this motor so i can replace the impeller and put new seals in it?...the motor runs great but doesnt seem to be spittin out any water so i dont think that the impeller is working..which way does the nosecone turn to remove it?..

 

[Chinewalker]

Re: 1958 mercury mark 58 thunderbolt four lower unit removal

Lower unit held on by four bolts/studs. One on either side under the secondary AV plate, one centered above the prop, one hidden inside the exhaust outlet (allen head bolt). Unit should then drop.

I believe the rear gearcase cover and waterpump cover are both righthand thread, but it's been awhile since I've had one apart. I would highly recommend getting a manual if you're planning on getting into the lower unit...

 

[Texasmark]

Re: 1958 mercury mark 58 thunderbolt four lower unit removal

You can buy manuals right here. I have the Seloc and the OEM and prefer the Seloc.

Mark

 

[homey58701]

Re: 1958 mercury mark 58 thunderbolt four lower unit removal

what about the nosecone for the prop? is that right hand thread or left hand thread?..if its a normal left hand to loosen, im in trouble cuz it is stuck stuck stuck on there...

 

[Chinewalker]

Re: 1958 mercury mark 58 thunderbolt four lower unit removal

Yes, the prop nut is normal lefty-loosey righty-tighty... Make sure all the lock tabs are bent back.

 

[homey58701]

Re: 1958 mercury mark 58 thunderbolt four lower unit removal

if thats the case..im in trouble cuz that damn thing will not move..its stuck rusted solid...

 

[Texasmark]

Re: 1958 mercury mark 58 thunderbolt four lower unit removal

Not surprised. Alum cone on ss shaft and in 50+ years no telling how long it has been on there and probably was installed without grease. Get some really good penetrating oil and work it over, letting it sit for several days.

Impact is a wonderful thing. As I recall the nut had a hole in it whereby you stuck something (screwdriver) in it to get it off. What you might do is get a high quality Phillips, like a #3 and a 2-3# hammer and whack it over and over. The impact torque is much higher than the twisting force you can put on it normally.

If worse comes to worse, cut it off. Being alum that will be somewhat of a problem as the alum will gall and plug up your saw or file but you can take a wire brush and keep the tools clean.

Once you get the nut off your next challenge will be to get the prop off. Buttt they usually have a bronze spline and the bronze and SS shaft are a pretty good match.

Good luck,
Mark

 

[homey58701]

Re: 1958 mercury mark 58 thunderbolt four lower unit removal

yeah its gonna be fun..almost seems like steel threads in a fiberglass nosecone..but im gonna have to do what you said and let it soak for like 5 yrs before itll move...

 

[Texasmark]

Re: 1958 mercury mark 58 thunderbolt four lower unit removal

yeah its gonna be fun..almost seems like steel threads in a fiberglass nosecone..but im gonna have to do what you said and let it soak for like 5 yrs before itll move...

PB Blaster brand penetrating oil in the spray can is readily available around here and an excellent tool. Kroil is an industrial oil and is excellent too but not readily available....can get it online under the name.

Mark

 

[homey58701]

Re: 1958 mercury mark 58 thunderbolt four lower unit removal

we have pb around here...ill try that if its not sold first..its up for sale right now so we'll see

 

[Texasmark]

Re: 1958 mercury mark 58 thunderbolt four lower unit removal

we have pb around here...ill try that if its not sold first..its up for sale right now so we'll see

Sounds like a plan. Grin