1958 mercury mark 58 thunderbolt four lower unit diagram

[homey58701]

anyone know where i can find a diagram/exploded view of the lower unit for my mark 58? i got the motor to turn over..but i think the lower unit is a bit rusty or something is going on...i wanna tear it down and inspect it but ive never had one of these apart so i dont know want to miss something

 

[Woodonglass]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

This oughta do the trick for ya...
http://www.marineengine.com/parts/mercury-mark-outboard-parts/mark-55ae-55am-58ae-58e/all

 

[homey58701]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

that helped for sure...at least i got a good idea..i gotta figure out where the oil port is..and the flush port on the lower unit..i think it didnt have much oil in it so its sticky and makes the motor hard to turn over

 

[Chinewalker]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

If it's "sticky", then it's likely the needle and ball bearings are rusted up. MUST come apart to be dealt with. If you're planning on doing it yourself, I would highly recommend getting the 1965 & prior Mercury shop manual.

 

[Texasmark]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

that helped for sure...at least i got a good idea..i gotta figure out where the oil port is..and the flush port on the lower unit..i think it didnt have much oil in it so its sticky and makes the motor hard to turn over

Forget the flush port. If the LU oil was low you have a leaking seal: Driveshaft under the water pump, LU shift shaft about 1" below the top of the shaft, prop shaft, no or leaking seals on your LU drain and vent screws.

Mark

 

[homey58701]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

the motor freed up..spins freely now..and started for the first time in years..the prop needs replaced and the nose cone will not come off!! also..where does the oil go in the lower unit?..what weight? and how much? how do you change it if need be?..im assuming this motor is a 2 stroke?..gas/oil mix ratio?..still looking online for an exploded view of the lower unit so i know how to take it apart...

 

[homey58701]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

thats just it...im not sure if theres any oil in there anymore..i got it freed up but i dont wanna run the thing without oil in the bottom end..

 

[Chinewalker]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

Drain screw on the very bottom of the gearcase, head is slotted, about the size of a dime. Vent screw is smaller, round head, up near the AV plate. Vent screw is NOT the same size as the drain screw on these motors. The slotted screw above the AV plate, on the port side, is for a flush adapter and has nothing to do with the oil drain.

 

[Texasmark]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

You remove both the drain screw and the vent screw and let what's in there drain out. Quicksilver LU oil is available at WW in a container with a pump....very nice vs squeezing a pint tube. I leave my engine vertical and screw in the fill adapter. Pump the oil into the LU until it comes out the vent hole. I like to let a little run out till most of the bubbles are gone.

Put in the top screw with a new seal (get it from your Merc dealer) and then, with the lower screw ready (with new seal also) unscrew the adapter and install your drain plug. Once in where the oil leakage stops you can tilt your engine up so that you can better access the drain screw for tightening. Use an appropriately sized screwdriver and tighten it as much as you can get with one hand.

Run the engine for an hour or two and look for leakage. If you didn't have screw seal problems the most likely spot would be the prop shaft seal. Removing the prop and inspecting the rubber seal will tell the story.

Then you might put 10 hrs on it or thereabouts and go back and check your oil level. Also the color. Let the engine sit without running for like a week. With the engine vertical (you can loosen the screw then set the engine vertical) carefully remove the drain screw and check the color of the oil. It should be the same color as what you put in and there can be NO water present in what comes out. If any it will come out first as oil floats on water. If it has any chocolate tint it is ingesting water and you definitely have a seal leaking.

Otherwise attempt to add oil using the filling process, only this time install the oil fill adapter from the oil container before you remove the top screw (vent). If you need none and the color is still blue black, you are good to go. Button her back up and go have some fun.

Mark

 

[homey58701]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

what weight is that lu oil?..ill try to find the screws..i havent looked that close yet

 

[Texasmark]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

what weight is that lu oil?..ill try to find the screws..i havent looked that close yet

I "dunno". You don't want just any oil, buy the oil designed for the application....says so on the container then you don't have to worry about what weight. The reason for this is that it has special additives that makes it stick to the metal and form a semipermanent film that resists washing off WHEN you have water in your LU. You only change it once a year and it's only a quart and costs about $5. Big deal.

HTH,
Mark

 

[Chinewalker]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

Sold as outboard motor lower unit or gear oil. NAPA, Wal-Mart, any marina will carry it...

 

[homey58701]

Re: 1958 mercury mark 58 thunderbolt four lower unit diagram

okie...thanks! ill change it out this weekend when its nice and get it running good...right now its nasty out and the wind is blowing at gusts over 60 mph...next would be the boat..ive never restored a boat..and im sure the wood in the keel and transom are rotted..