Gearbox vent 1971 B25T

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Gearbox vent 1971 B25T

Post by madmac » Tue Aug 11, 2020 5:54 pm

Just spotted this little hole in the inner timing cover, I did have bother with the dipstick filler venting oil before i blocked it maybe it would be better to block this little hole, any thoughts from the colective
b25 vent.jpg
Also the oil in the gearbox seems very black more like engine oil? looked in the holes for gear spring retainer and the gear selector shaft couldent see any faults

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Re: Gearbox vent 1971 B25T

Post by minetymenace » Wed Aug 12, 2020 9:48 am

This is the gearbox breather, gearbox warms up, stuff expands and it cools down, this little hole allows the pressures to equalise. I surprised you say the gearbox is venting (over full? it only takes a splash), and you say the oil is black, have you got a leak between crank and gearbox?
There is no evidence to support the notion that life is serious.
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Re: Gearbox vent 1971 B25T

Post by beat » Wed Aug 12, 2020 9:42 pm

minetymenace wrote:
Wed Aug 12, 2020 9:48 am
a leak between crank and gearbox?
there is a thread to something the like in a topic here........ <216

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Re: Gearbox vent 1971 B25T

Post by madmac » Wed Aug 12, 2020 10:12 pm

Thanks for the replies Mighty and Beat, I understand the gearbox needs venting but its vented on the pressure side of the breather circuit so this will give the gearbox a positive pressure? (or so I thought) and that's when I had oil coming out of the dipstick not a lot but enough to be annoying
Yes alarm bells rang when I drained the box and it was black, just drained the box new oil filled will give it a week and see what comes out
Yes Beat I have seen something about holes being drilled too deep but can't remember where?? feel a engine strip comming on :shock:

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Re: Gearbox vent 1971 B25T

Post by minetymenace » Thu Aug 13, 2020 8:14 am

The void between the inner and outer cover is a sort of plenum chamber and also serves as a condenser to trap (and then return) the oil mist from the engine breather back to the engine. There should be another small hole through the inner cover to provide a path for the oil back into the sump, this hole is small so that it doesn't short circuit (too much) the engine breather. This void breaths to the outside world through the short stubby pipe next to the bulge that retains the clutch cable outer.

kommando posted here
kommando wrote:
There's oil coming from the gear shift
Sounds like the small oil return hole in the inner timing cover is blocked so breathed out oil instead of draining back into the crankcase gets stuck between the inner and out timing covers, once it gets as high as the gear lever it leaks out. If it gets higher then it can get into the points chamber and mess up the points depending on what version cover you have and how the LT cable enters the points chamber.
and beat posted here
beat wrote:
koncretekid wrote:You stated leaks from " clutch arm, kick start, gear lever", all which originate from the gearbox, not the crankcase.
this sounds for me as the space between the outer and the inner timing cover is overfilled by oil .

- maybe the small tiny hole is clogged ?
beat <201
Some clues perhaps...

There is a picture somewhere of the little holes, but can't find it at the moment (Anyone?)....
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Re: Gearbox vent 1971 B25T

Post by koncretekid » Thu Aug 13, 2020 12:12 pm

Clutch oil gets very black. Is it possible that the bushing in the sleeve gear is worn enough that clutch oil is contaminating the gearbox oil? This would be quite possible if neither of the primary cover access covers is vented and the timing access cover is well sealed on the non-primary vented covers, allowing primary to be pressurized when hot, of if main seal is leaking compression into the primary. That could also explain leakage at the gearbox dipstick if the small hole into the inner timing cover is plugged.

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Re: Gearbox vent 1971 B25T

Post by eebtr7 » Thu Aug 13, 2020 1:59 pm

Also, let us not forget when the engine has set for several months, the wet sumping fills the 'plenum' allowing the engine oil to drip out thru the shift shaft onto your concrete floor. Apon draining the sump in June, (after it setting for about 7 months), an honest 1 1/3 quarts of fresh engine oil collected in the drain pan.

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Re: Gearbox vent 1971 B25T

Post by Jeff K » Thu Aug 13, 2020 2:03 pm

The newer Gear oils contain Sulfur that can eat away at anything that has brass in it, like bushings. This will in time turn the oil dark. I think that you want a GL4 rated oil and not the GL5.
Jeff

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Re: Gearbox vent 1971 B25T

Post by JB » Fri Aug 14, 2020 11:30 am

Jeff K wrote:
Thu Aug 13, 2020 2:03 pm
you want a GL4 rated oil and not the GL5.
Jeff
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Re: Gearbox vent 1971 B25T

Post by madmac » Fri Aug 14, 2020 3:39 pm

Hi all thanks for the input, The little hole is clear, So will leave the little vent hole in the timing cover alone sure BSA knew what they were doing.
was out on Sunday did 116miles and only stripped it to sort a persistent problem with the second gear not selecting that's when I found the black oil, Might be the primary oil as the case was empty when it was checked :oops: so could be that
While it was stripped I noticed the oil feed to the crank had a drip so I think the oil pump is passing oil
The wet sumping is a problem so the oil getting back along the gearchange shaft might be the source as the bike has been standing for some months
never thought of the gearchange shaft :idea:
Gear change now sorted revised gear change plate fitted
Thanks again It helps to pass ideas or even just read others
Ian

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