Can't refill outboard gearbox!

As I mentioned above the old oil is not milky just darker with no obvious particles or sludge.

This model has the impeller in a housing at the top of the box instead of behind the propeller.
So instead of removing that top impeller housing to gain access which from an initial attempt to chisel the gasket proved difficult I shall have a go to examine the workings inside by removing the prop housing.

Thanks again gents.

 

Never heard of removing the water pump to get to the gearbox. There is only the shaft hole and water passage under there. I would go with sukis idea and pull rear bearing cover out then you can clean it properly.

 

Seems like a lot of trouble for simply removing some sludge, which solvents will do pretty quickly.

 

Very strange business !

 

The gearbox is a separate part from the impeller, in terms of the two mechanisms. The impeller is pretty much always mounted on the top of the gearbox housing. To remove the impeller, undo the 4 bolts with a good 6 point socket set and gently tap with a wood/plastic block the housing up the driveshaft. Do NOT lose the keyway - a pin or Woodruff key, depending on model/year etc. So best done over a clean bench or floor.... A new impeller has to be keyed on using this and there is a specific set to the blades of the impellor, do not assume the one in there is correct!

The gearbox is accessed by removing the prop, shear pin and then the back housing. Expect to possibly find stuff like fishing line, sea weed, that may be wrapped around the prop shaft behind what you can see prior to removal. Once you have undone the two bolts of the housing the gears should separate as you pull the housing with prop shaft off. It's very simple as you will see. Check for bearing wear, and that the gear teeth are undamaged, clean out and reassemble. Then refill as per normal ie squeeze or pump from bottom until oil just drips from tetop hole. Put in top screw, the vacuum then holds the oil enough for you to get the lower screw in, without too much dripping out.

When you put the gearbox assembly back on the motor ensure the water pump outlet pipe from the impellor housing fits to the water tube in the bottom leg of the motor correctly. If you don't the water is going nowhere....

The 'worst' aassemblies IMHO to reassemble fast are the Mariner 3.5/4/6 four strokes, but once you've done a few the 'technique' for these is not too bad. They're just a bit tricky to get everything lined up just so. Part of it is that wretched gear link under the rubber grommet. Good fun starting one without it in place....

 

Is there any chance that the top hole was not through drilled all the way, then tapped.
At the manufacturing level, there is no reason to assume that they fill the gear case using the two drain holes. Ie maybe they just put in the lube before they put the lower housing together as it would be faster
So as Mr E said, blow some air into the bottom and see if any air comes out the top. Then blow some air down the top hole. If no air goes in, I would take a small thin wire and poke it into the top hole and see if the wire goes past the threads and into the gear case. If not, then the top hole was not drilled all the way into the case

 

Good thinking Barry.

As mentioned I poked a thin wire into the top hole and it would not go right through. Which is why, in my ignorance, wondered whether there was a non valve inside it to create the vacuum.

I have tried low pressure air in the bottom hole without any through flow. Which is where my frustration started - 'why won't the oil go in?'
I really do not think there is any debris/detritus inside the box. It is a very small 3.5 Tohatsu unit with very small water inlet holes.

The top hole certainly does not have a clear through passage - which is why I wondered if there is a valve at the end. I shall blow into the top hole . . .

 

Barry may be right, the top hole may not have been drilled through. Yikes.

 

You would think having a tapped hole would mean it had been drilled.

 

Depending on the depth of the thread, I suppose. Hard to imagine that would get past quality inspection.

 

Thats what i was thinking. The gearbox housing is quite thin. It would be hard not to drill right through.

 

One would think so but if the two holes were open to the common gear case, then the oil should flow through, or air as the op has tried.

I expect that the thickness of the gear housing is quite thin over the rest of the housing. In order for a parallel thread plug, an assumption on my part, to have enough thread length to work, the casting needs to be thicker in the plug area.

The NC milling center, again another assumption, used to
drill and tap the holes, would have the drill depth preprogrammed. If for some reason the drill did not penetrate the gear case wall and the tap was a bottoming tap, there is a chance that there is no access to the gear case through the top plug.

 

Three seconds on google got me the workshop manual,shows 3.5 hp.

Page 165 or so

http://www.tecnomar.cl/pdf/pdf_servicemanual/2t/Service Manual_1-2 Cylinder 2-Stroke.pdf

Maybe you can find a blow up drawing,hope this helps.

 

Should not be hard to establish whether this is the case, with a strong light.

 

Thank you for the manual westvanhan, now on my desktop.

The water pump is at the top of the gear housing on this model.
I've separated it from the leg and removed the water pump base (along with impeller, drive shaft, gear shift)

In the underside of this water pump base is the drive shaft ball race with its rubber oil seal.
When all reassembled this oil seal is directly in the passageway of the top oil level plug. And it blocks the air flow (or oil flow) through the top oil level plug.

Bloody marvelous eh!