gearbox oil quantity

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Jan 3, 2021
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hi there,

a question about the gearbox oil quantity...
I`m a bit concerned about the correct quantity of gearbox oil....or its distribution inside of the box:
on my recently aquired commando 750 `72, doing the oilchange of the gearbox, after draining it I refilled the box till the fresh oil started pouring out of the orifice of the level screw.
re-checked the level some days after(looking inside the box with a torch from the filling orifice):
the level had stayed at the lower edge of the level screw.
used the bike for some kilometers, no issues with the gearchange.

now, doing another gearoil change, I was quite astonished, as only about 300ml left via the drain screw(did let it drain overnight).
and:
refilling the box with the "official" 420ml quantity, the level(checked by looking via the filling orifice) STAYS about 4mm ABOVE the upper edge of the level screw.
I know that the fresh oil needs some time to penetrate/distribute inside the box...

.....so I let it settle, used the bike.....now, same days later, the level stays still at exactly the same position...that means about 4mm ABOVE the upper edge of the level screw....

my explanation:
- the position of the thread of the level screw isn`t at the correct hight(quite improbable....)
- some issue with the distribution inside of the box(any orifice/passage blocked?)

any ideas?

thx a lot

chris
 
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I would venture that the 'official' 420ml is the amount needed when filling from 'dry', post rebuild etc....
A state the box will never return to unless stripped. The 'inner/outer' covers may well not drain totally, either.
I'd be happy the levels were consistent in both instances.
 
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Don't worry about the "correct" amount of oil per the spec. As noted, it is unlikely it will ever take that much. But regardless, on the center stand/level ground, level plug removed, add oil until it starts dripping from the level plug. When it quits dripping, replace the plug. If, when you remove the plug it immediately starts draining, do the same - let it drain until it quits, replace the plug. That is the proper amount of oil.
 

maylar

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It takes time for the oil to flow through gearbox and level out. I don't remove the level plug, I just look inside the fill hole with a flashlight. Add oil until it reaches the bottom of the level plug and wait a minute for it to settle before adding any more. Repeat as needed.
 
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It takes time for the oil to flow through gearbox and level out. I don't remove the level plug, I just look inside the fill hole with a flashlight. Add oil until it reaches the bottom of the level plug and wait a minute for it to settle before adding any more. Repeat as needed.
Yep, I check it that way! When I drain/fill, I use the other method.
 
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Have you checked the inner cover has a hole at 6 O'clock position, there was a case down under where a bike was serviced and it was found that the hole had not been drilled.
 
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thx, guys, for your advice.

meanwhile I`ve checked the communication between the outer and inner "chamber" of the gearbox by leaning the bike some 45 degrees to the right and to the left:
observing the oil level via the inspection hole confirms the flow from left to right and viceversa.

seems as if during a routine draining of the box a respectable amount stays inside...

but better "safe than sorry" :)
thx again for Your advice.
 
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Have you checked the inner cover has a hole at 6 O'clock position, there was a case down under where a bike was serviced and it was found that the hole had not been drilled.
I'm wondering what you're talking about here. I'm a new member with a '72 Combat, and a '74 850. Any chance you can elaborate some on this rather slim reference?
 
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There's no need to unscrew the oil level plug. Just one more thing to leak out oil. Unscrew the 2 inspection screws for the cap. Flashlight visualize the level at that oil level bolt point. It's way more important to have a layshaft bearing upgrade done first.
 
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I'm wondering what you're talking about here. I'm a new member with a '72 Combat, and a '74 850. Any chance you can elaborate some on this rather slim reference?
Yes, you pour oil in the outer cover, wait and it makes its way to the main gearbox shell via a hole in the inner cover. A bike was serviced in Australia that had less than a cup full of oil drain from the drain hole, the outer cover still contained oil. When the outer cover was removed it could seen that hole in the inner cover was missing.
 
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