Mercury 3.3 Gearbox

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Ken20101

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I drained the gerbox of my engine without a problem but I am having difficulty refilling. There is significant pressure building up when I squeeze in the oil from the lower drain plug hole and no air vents from the upper drain plug hole. I've tried squeezing in oil from the top hole to try to dislodge any blockage but to no avail. Has anybody else had this problem and can provide a suggestion to fix it. Since the oil ran out easily when I drained the system I assumed that there were no very narrow oil ways that could become blocked is this the case?
 
Take the gearbox end plate off and refill it from there
Ken20101 said:
I drained the gerbox of my engine without a problem but I am having difficulty refilling. There is significant pressure building up when I squeeze in the oil from the lower drain plug hole and no air vents from the upper drain plug hole. I've tried squeezing in oil from the top hole to try to dislodge any blockage but to no avail. Has anybody else had this problem and can provide a suggestion to fix it. Since the oil ran out easily when I drained the system I assumed that there were no very narrow oil ways that could become blocked is this the case?
Click to expand...
 
Edit. Comments below refer to Mariner 3.3. I think it is identical ...

Not much help to you I'm afraid, but I have changed my gearbox oil many times and never had that problem. It is a simple self contained structure with no obscure oilways that I am aware of. I can't see how it could get pressurised if both filler screws have been removed.

Trying to think laterally about how it could happen...
Can you blow air through from one hole to the other? I am thinking that if the oil drained out there can't be a vacuum.
Can you poke a rod into each hole?
I have the service manual online somewhere and I will check, but from memory the gear just runs in a simple casing, so I can't see where there might some internal blockage.
Could the blockage actually be in the nozzle or the tube you are using to fill with?

It is relatively easy to dismantle the gearbox to have a look, if you really need to. You might remove the propeller then ease the the plate behind it to take a peek. I think there are just two cogs, one attached to the drive shaft and one to the prop.

If you have removed the gear box from the leg, for example to change the impeller, the top tip is to keep it right way up, otherwise a gear can drop off the shaft and you will have to take it apart.

It is a bit of a fiddle getting the drive shaft, gear change and water pipe to slip into place when reassembling the leg after changing the impeller.

Good luck. Please let us know how you get on.
 
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I normally refill the gearbox by replacing the lower, drain, plug; lean the engine slightly then dribble oil into the upper hole. Turn the propeller by hand a little to ensure no air bubbles. Stand vertical and allow any excess oil to drain out of the upper hole.
 
alahol2 said:
I normally refill the gearbox by replacing the lower, drain, plug; lean the engine slightly then dribble oil into the upper hole. Turn the propeller by hand a little to ensure no air bubbles. Stand vertical and allow any excess oil to drain out of the upper hole.
Click to expand...
+1
That is also the only way I've ever been able to make it work....
 
Thanks to everybody with their responses. Perhaps an additional piece of info I should have added with my original post was that I had also changed the impeller after draining the gearbox and during that operation the waterpump base was removed. In doing that, the drive shaft lifted about 1cm before I pushed it back down again. I know that the gear can drop off the shaft if it is lifted too high, but I dont think that happened as now the gear engages properly and the shaft/prop rotates when the engine is turned. The only additional concern I now have is that, in putting back the pump body, the top oil filler hole has been obscured. I don't know where the top hole is in relation to the bearing that sits immediately beneath the water pump base. Could the oil seal in the pump base that sits above the bearing have covered the hole somehow? The pump base can only go on one way and the seal was not removed from the base during repair of the pump.The base went fully down with only reasonable pressure when reassembling. Following davidbfox reply I have probed the holes. I can push a wire into the top hole about 2cm before it meets something hard. I can push a wire about 8 cm into the bottom hole, clearly into the bottom gear chamber and way above the level of the prop shaft. I have obvioulsly managed to get some oil in, as the gear chamber seems to be full. The blockage seems to be to do with the top hole and uncertainty about the level of oil makes me worry about the lubrication reaching top bering. I suppose that if I elevated the prop end for a while and let any air bubles escape before topping up the oil I could assume the lower leg was full. However if anybody thinks I might have inadvertantly blocked the top hole when replacing the pump base I'd like to hear. I know I could always remove the leg, disassemble the pump, investigate from the inside and start again, but it is such a faff to get shaft gerlinkage and water tube lined up on reassembly, it would be nice not to have to do this!
 
Ken20101 said:
Thanks to everybody with their responses. Perhaps an additional piece of info I should have added with my original post was that I had also changed the impeller after draining the gearbox and during that operation the waterpump base was removed. In doing that, the drive shaft lifted about 1cm before I pushed it back down again. I know that the gear can drop off the shaft if it is lifted too high, but I dont think that happened as now the gear engages properly and the shaft/prop rotates when the engine is turned. The only additional concern I now have is that, in putting back the pump body, the top oil filler hole has been obscured. I don't know where the top hole is in relation to the bearing that sits immediately beneath the water pump base. Could the oil seal in the pump base that sits above the bearing have covered the hole somehow? The pump base can only go on one way and the seal was not removed from the base during repair of the pump.The base went fully down with only reasonable pressure when reassembling. Following davidbfox reply I have probed the holes. I can push a wire into the top hole about 2cm before it meets something hard. I can push a wire about 8 cm into the bottom hole, clearly into the bottom gear chamber and way above the level of the prop shaft. I have obvioulsly managed to get some oil in, as the gear chamber seems to be full. The blockage seems to be to do with the top hole and uncertainty about the level of oil makes me worry about the lubrication reaching top bering. I suppose that if I elevated the prop end for a while and let any air bubles escape before topping up the oil I could assume the lower leg was full. However if anybody thinks I might have inadvertantly blocked the top hole when replacing the pump base I'd like to hear. I know I could always remove the leg, disassemble the pump, investigate from the inside and start again, but it is such a faff to get shaft gerlinkage and water tube lined up on reassembly, it would be nice not to have to do this!
Click to expand...

there are two bearings with a spacer between them and an oil seal below the pump housing. I cannot think of anyway in which you could blank off the level hole unless you had removed the seal, upper bearing and spacer and then omitted the spacer on reassembly. Since you apparently did not remove the drive shaft that seems unlikely ....... unless ..... someone has been in there previously and reassembled it incorrectly.
 
neale said:
Not teaching to suck eggs and all that, but it is definitely these two holes that you are working with.
Click to expand...

I wondered that but AFAICS there are no other screws that could be confused with the oil drain and level plugs !
 
I would try blowing compressed air through either the top hole of bottom with the other open and see what happens.

Not too much pressure as it could damage the shaft oil seals.
 
The only seal I lifted was the one that sits immediately below the pump base, which was retained in the pump base when I removed it. The upper bearing below this remained in place. Do you know whether the internal entrance to the top oil drain hole lies below the level of the upper bearing or above it? I didn't notice when I dissassembled the pump. If it is above the bearing could there be a possiblity that the oil seal has not seated properly when I put the pump base back and blocked the hole internally? The exploded parts diagram unfortunately doesn't make the position of the drain hole in relation to the pump base clear.

Today I inverted the engine and opened the bottom filler screw to see if any air came out (turned the prop a few time whilst doing this). The chamber seems to be full and no air bubbles appeared. I'll try some gentle pressure with the holes open tomorrow just in case some crud has become lodged. I am wary of doing this though as I dont want to damage the oil seals.
 
In the event than anyone returns to this 6 yo thread with the same issue, I'd like to chip in some recent experience, having just had the same problem.
I found first of all that beneath the level screw was a great deal of fairly solid gunk. I carefully excavated this and blew out loose debris. Using a small endoscope I deduce that the level hole emerges into the gearbox such that it is the top of the top bearing and the bottom of the oil seal that we see in the attached picture

In my case they are in contact. In this condition it is possible to blow air into the level hole and out of the drain, but not vice-versa. Evidently the geometry of the bottom of the oil seal acts as a very effective check valve, against the edge of the bearing.

I don't know whether the fact that there's no space between the bearing and the seal means that the seal has moved downward within the water pump housing (aka top of gearbox). Probing beside the drive shaft, measuring and comparing with photos of housings with the oil seal in situ suggests not. There's no possibility that the bearing is higher than it should be as the bottom of the housing has a "landing" for it.

Having said that I suppose it's not IMPOSSIBLE that the fairly soft alloy housing has worn, if at some time in its life the bearing seized, though it clearly turns freely now, and that seems unlikely.

I'm very reluctant to remove the housing, as a) it's clearly pretty firmly stuck, and b) given the age and general condition of the unit, disturbing anything is likely to lead to more work/extra cost than its worth. It works now and I want to leave well alone.
So, to conclude. I was able to blow all the oil out. To get the new oil in, I pushed a fine stiff wire between the bearing and the seal and continuosly giggled it. This allowed air to escape as oil was introduced at the drain. Slow but worked.
All closed up and running now. Fingers crossed for a few more years.

( We now only really use this engine for a short run to the mooring and back, so when it dies it dies, and it won't be mourned all that much)level hole.jpg
For scale, the bottom of the hole is about 4mm across.
 
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