Mercury 850 thunderbolt 1974 gearbox check

[Legend850]

Morning all from New Zealand. I tried the search function, couldn't find anything.

I bought a trailer. It had a boat and motor sitting on it, so I have decided to get it all working.

I started at the bottom, let the gearbox oil out.

The gearbox was full of water, looks like the fibre washer wasn't replaced on the top screw.

I took the prop off, sprayed the seal in "snoop" gas leak fluid, and puffed a bit of air into the box - no bubbles so I dont think the seal is had it. But there was no lubricating oil, so I am thinking its prudent to inspect the innards before I spend any more on the motor, which I know has other issues.

Does the bearing carrier come out by rotating the entire assembly with the castellated edges anti clockwise ? Any tip or tricks ?

Thank you,

Dave

 

[1960 Starflite]

Morning all from New Zealand. I tried the search function, couldn't find anything.

I bought a trailer. It had a boat and motor sitting on it, so I have decided to get it all working.

I started at the bottom, let the gearbox oil out.

The gearbox was full of water, looks like the fibre washer wasn't replaced on the top screw.

I took the prop off, sprayed the seal in "snoop" gas leak fluid, and puffed a bit of air into the box - no bubbles so I dont think the seal is had it. But there was no lubricating oil, so I am thinking its prudent to inspect the innards before I spend any more on the motor, which I know has other issues.

Does the bearing carrier come out by rotating the entire assembly with the castellated edges anti clockwise ? Any tip or tricks ?

Thank you,

Dave

Look around the housing inside. You'll find a external lock washer, 3 1/2" +/- in diameter. Pry lock tab out of nut. Trim/lift engine full up, penetrating oil around nut, hammer and punch gently on face of nut. More penetrating oil. Let it sit overnight, repeat. The nut is a right hand thread. Lefty Loosey. The bearing carrier will need to then removed with a puller. Don't lose the small key on bottom of carrier. Good luck, most that old are stuck GOOD.

 

[racerone]

No----That is a nut.-----Remove it ( cut it if you have to ) and bearing carrier pulls out.

 

[Legend850]

Look around the housing inside. You'll find a external lock washer, 3 1/2" +/- in diameter. Pry lock tab out of nut. Trim/lift engine full up, penetrating oil around nut, hammer and punch gently on face of nut. More penetrating oil. Let it sit overnight, repeat. The nut is a right hand thread. Lefty Loosey. The bearing carrier will need to then removed with a puller. Don't lose the small key on bottom of carrier. Good luck, most that old are stuck GOOD.

Thanks, I will go and have a look. The prop took some removing thats for sure. I used a hydraulic puller, and I had it creaking...

 

[Chris1956]

If the gearbox was full of water, the gears and bearings are likely bad. Fixing them takes special tools and expensive parts.

If the engine runs well, you might look for a new (used) gearbox.

 

[Legend850]

Look around the housing inside. You'll find a external lock washer, 3 1/2" +/- in diameter. Pry lock tab out of nut. Trim/lift engine full up, penetrating oil around nut, hammer and punch gently on face of nut. More penetrating oil. Let it sit overnight, repeat. The nut is a right hand thread. Lefty Loosey. The bearing carrier will need to then removed with a puller. Don't lose the small key on bottom of carrier. Good luck, most that old are stuck GOOD.

Yes, perfect instructions thank you.
its stuck pretty good. So as I am reasonably sure the prop seal is OK, I will go to plan B. I will replace the water pump, and check the seals on the top of the gearbox. If they are OK, I will just use it, see how the gearbox goes, and check the magnet bung in a few hours, see if it has any scary lumps of metal, and that the oil is on the inside and the water is on the outside. Plenty more to do on this engine, wiring loom is rotten, choke solenoid doesnt work, and I a havent done a compression check. And as it runs OK, I am not sure I will. Dont need to lift too many lids looking for trouble, cos I might find some.

 

[Legend850]

If the gearbox was full of water, the gears and bearings are likely bad. Fixing them takes special tools and expensive parts.

If the engine runs well, you might look for a new (used) gearbox.

Yes, I am not really wanting to spend too much on this, we posted at the same time so have a look at my cunning Plan B.

 

[Chris1956]

Be aware that your cunning plan B can leave you stranded on the water, when/if the gearbox fail under use.

 

[merc850]

Here's the LU diagram
and the bearing carrier tool which might be still available from Merc

this is used to undo/do the nut and tork it properly. Look fopr corrosion on the housing where the nut is - soak it for a while with penetrating oil.
Usually a slide hammer is used to pull the carrier assembly or clamp the propshaft in a vise between 2 pieces of wood and tap on the case with a rubber mallet.

 

[racerone]

Perhaps drain the gear oil.-----Flush the lower unit.------Perhaps one of those " new cameras " that adapt to a phone can look at gears through oil drain hole .

 

[Legend850]

Thanks for the diagram. I see how it all goes together now. I could soon make a tool up to get the retaining nut out I think. I certainly appreciate there is the risk of gearbox failure if its not checked, and repaired as necessary. Any 45 year old motor comes with risk of break down, the reality is if I had endless money I would simply have a 45 day old motor ! The box goes in and out of gear fine, doesn't seem to have excessive backlash. The bearings dont have any detectable free play. I will make up a tool and see if I can do a proper inspection, without having to do anything irreversible like cutting nuts off, or using heat. If I cant, I will run it for some hours in safe waters where I can get home on my Aux without issues. I'll do regular oil chnges, look for metal shavings, changes in the gear box behavior or noise.

 

[Legend850]

Perhaps drain the gear oil.-----Flush the lower unit.------Perhaps one of those " new cameras " that adapt to a phone can look at gears through oil drain hole .

Now thats good thinking ! I was thinking about getting one of those anyway.

 

[racerone]

Post a picture of that big nut.----If motor was used in fresh water ( I know there is lots of salty water in your area ) it might be an easy venture.

 

[Legend850]

As much as you can trust any seller of anything, its done a lot of fresh water work, he says he bought the boat in Taupo, which is all fresh. So only its last few months has been in salt. But the prop was well seized on. I made a puller tool, and used a small Sykes Hydraulic pump. (I welded 4 lengths of steel together to form a collar behind the prop). Everything was squawking pretty hard before the prop came off. There was about 1/2 inch of compression on the props rubber damper before it finally moved.

 

[Legend850]

 

[Legend850]

And to show I have a sense of humour, here is the condition of the wiring loom inside the engine. I will fix this by cutting away the rubber around the internal plug, drilling out the wires, and soldering in brand new wires. I will do all those that dont go via this section of loom at the same time. I will post photos if its of interest here.

 

[racerone]

That plug is not needed at all.----A convenience item.-----Just go straight to a terminal strip.---- and battery cables straight to solenoid and ground.---- Do not forget to check wires inside the control box.

 

[Legend850]

That plug is not needed at all.----A convenience item.-----Just go straight to a terminal strip.---- and battery cables straight to solenoid and ground.---- Do not forget to check wires inside the control box.

Yeah I did consider just running the cables through a 40mm electrical gland and not using the plug. If I ever need to disconnect it I can easily just cut the cable somewhere inside the hull, and use a strip connector - or even a 5 or 7 way trailer plug for the smaller wires. Its out of the weather and water there. I think I will take your advice on that, its a lot of work to rebuild that connector, and a connector is never as good as a direct cable any way.

 

[Chris1956]

Those engine harnesses are available on the web. Of course you could make your own with 7 different color wires and some ring terminals.

Check the wires that go to the distributor. They also go bad. The rotor is non-removeable, fragile and $240+USD to buy. You need to install it then. The trigger is also about that cost. The distributor cap is also about the price, but they last a real long time.

The rectifier can be replaced by any 10A or more full wave bridge rectifier.

 

[merc850]

That LU looks serviceable but apply lots of penetrating oil first. Another piece that needs to be looked at is the alternator stator under the flywheel, the wires might be corroded they are yellow and run down the stbd. side of the block.