Author Topic: Gearbox oil leak  (Read 1438 times)

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Bles31

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Gearbox oil leak
« on: 24 April, 2020, 10:49:27 »
In the current lockdown I decided to revisit my gearbox oil leak. I pulled the clutch etc off and the final drive sprocket, exposing the gearbox. By measurement at both sides of the box I have found that when I fill the gearbox (B & M group plunger 1938-63 on the Draganfly website) to the bottom edge of the filler port, the oil level is:
12 mm above the lip seal where it sits on the drive sprocket
9mm above the splines between the sprocket and the output gear
5mm above the bush between the mainshaft and sleeve gear (items 97 and 98 on the dragonfly parts list/diagram). The bush, item 103 seems a good fit.
I filled the gearbox to the bottom of the filler port then sat and watched. Cold oil, Duckams 20-50, seeped out of the splines at the sprocket and from the bush/shaft interface
Slipping the sprocket into place and nipping the nut up seemed to sort the splines seepage. I expect it might seep thin hot oil, but hopefully not to any great messy extent ( or am I wrong?)
Currently I'm thinking my biggest leak is from the bush area, which is predictable as there has to be some clearance there and hot oil will find it. My question (eventually) is whether the felt and cork  sealing rings which sit in that area when the bike is assembled actually prevent leakage, or  is the leak inevitable? It seems a pretty crude seal system given that it sits flooded when the gearbox is properly filled. Am I missing a  trick somewhere? I can  run the bike with 10 mm less  oil in the gearbox as I only do short cafe runs at present, but I would like to achieve better than that.
Any advice welcome as this is a major pain as I don't like to park up and drip oil around the place.
Thanks.

Ian C

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Re: Gearbox oil leak
« Reply #1 on: 24 April, 2020, 12:56:20 »
The gearbox oil capacity as far as I know is around 1 pint or 570ml for sake of argument.. Further to this I use single grade 40 in my M20 gearbox.. HTH
« Last Edit: 24 April, 2020, 13:08:03 by Ian Clifton »

Jim S

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Re: Gearbox oil leak
« Reply #2 on: 24 April, 2020, 14:19:55 »
I have a 1949 B33 and a 1957 A7.
All documents that I can find for the B33 indicate that the gearbox capacity is 1 pint or about 570ml. If I fill my gearbox with 1 pint I get significant oil on the ground and your measurements demonstrate why. Your measurements are probably with the gearbox sitting horizontal with the bike on the centre stand. They would be even worse with the bike on the side stand.

For the A7 there is conflicting information. Some manuals and service sheets say 1 pint and some say 400ml. In the Haynes manual for example on page 10 for gearbox lubrication it says "1 pint (570 cc) (actual capacity 398 cc)" which implies that if you put in 1 pint, you can expect to have 170 cc leak out. I put 400 ml in the A7.

In summary, I think 570 ml is too much oil for the B33. I overfill it with 500 ml of oil, let it find its level by running the bike and check the level frequently using a tie wrap as a dipstick in the filler hole to ensure the level has stabilized.

Since you seem to have a method to measure the internal levels, it would be interesting to know what the internal levels are with 400 ml of oil or what volume of oil is required to bring the internal level to the bottom of the output shaft?

Jim

JulianS

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Re: Gearbox oil leak
« Reply #3 on: 24 April, 2020, 15:19:10 »
Suggest you try a thicker oil - factory recommended SAE 50 and 30 winter.

Or try a non EP classic gear oil.

I use Morris AG90 non EP in my A10 box.

https://www.morrislubricantsonline.co.uk/golden-film-ag-90-gear-oil.html

Bles31

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Re: Gearbox oil leak
« Reply #4 on: 24 April, 2020, 15:48:26 »
Thanks for replies so far.
Jim - no clever measuring system. I just measured the height of the filler plug from the garage floor then went round to the other side of the bike, with clutch etc removed and measured heights of lip seal, splines bush etc. Then I compared the two. I finished off by removing the sprocket from the gearbox and let the oil drain out until level with the lip seal. This equates to 12mm below bottom edge of filler port. I don't know what volume this equates to.
Thanks Julian - I will consider that, have a look at the link you sent.
For information - Actual measurements are
Height from floor to bottom of filler port - 285mm ( note my centre stand is worn and the bike sits a bit low)
Height to bottom edge of lip seal housing - 266mm
Height to lowest point of seal lip - 273mm
Height to  low point of splines - 276mm
Height to bush on output shaft - 280mm
Done with a steel rule from a concrete floor, but fairly accurate.

Rog1

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Re: Gearbox oil leak
« Reply #5 on: 25 April, 2020, 12:25:55 »
I have found in the past (at least with Jap bikes, but using Haynes manuals) that given oil capacities seem to be for when the thing's been apart and cleaned out before reassembly. It always seems that less oil is needed than they say, on a normal oil change.

Mark N

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Re: Gearbox oil leak
« Reply #6 on: 27 April, 2020, 13:10:55 »
Had my 1948 M21 gearbox rebuilt by a very experienced guy and I topped it up with the specified amount of oil and, yes, there is always a puddle underneath. Iím hoping that when it finds the correct level that it will stop leaking.
Never had a leak on a Burman......

A10 JWO

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Re: Gearbox oil leak
« Reply #7 on: 27 April, 2020, 15:51:38 »
Last year I sat with a huddle of British Bike Experts at the Saturday pub meet. They were the ones that passed their test in about 1960. They all spoke about oil quantities in gearboxes and concluded that the manufacturers set the levels too high. I put this to an ex Triumph mechanic who also worked for Team Heron Suzuki. He agreed that if you used the Triumph dip stick system built into the drain plug, you will get oil in the outer gearbox cover; too much oil in gear-box. Going on from there a chap from SRM told me that we are all putting too much in the chain cases, causing clutch problems, which helps to sell clutches. Keep safe everyone.

DAVE BRADY

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Re: Gearbox oil leak
« Reply #8 on: 27 April, 2020, 17:55:15 »
Hi,

Did the chap from SRM suggest by how much we are overfilling our chain cases?  I would think that most of us, when topping up primary and gearbox oil levels, use the level screws/plugs designed in by BSA.  If these are causing us to put too much in how do we work out how much is correct?

Dave.

A10 JWO

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Re: Gearbox oil leak
« Reply #9 on: 27 April, 2020, 18:53:54 »
Hi Dave. He suggested just enough to keep the chain lubricated and to splash the other components, not to flood them.

Jim S

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Re: Gearbox oil leak
« Reply #10 on: 27 April, 2020, 19:07:14 »
To reply to part of Dave's questions, the problem with the B33 gearbox is there is no level plug, at least not in mine.
I think a big contributor to Bles31's oil leak is he is putting in far too much oil. In the original post at the top he indicates filling the gearbox to the bottom of the fill port. That results in the bottom of the lip seal and the gap between the mainshaft and output shaft are submerged in oil in the static horizontal condition. Of course oil will flow out.
However, he has included some important information. When he removed the drive sprocket, exposing the lip seal, oil drained out over the lip seal. When the oil level reached the bottom of the lip, he measured the oil level to be 12 mm below the filler port with the bike horizontal on the centre stand.
In my opinion, I do not think any part of the ID of a lip seal should be submerged in oil in a static condition otherwise oil will seep out between the shaft and the lip. So 12 mm below the bottom edge of the filler port would be a good place to start for oil level provided that this does not exceed 570 ml. The next time I change gearbox oil I'll measure what volume this gives.
However, all this assumes the bike is horizontal on the centre stand. When the bike is put on the side stand, oil will submerge the lip and will put a mess on the floor again.

DAVE BRADY

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Re: Gearbox oil leak
« Reply #11 on: 27 April, 2020, 20:09:48 »
No level plugs does make it impossible to check levels and seems to require a complete drain and refill rather than a top up.  I wonder if BSA realised this and took steps by including a level plug on subsequent models.  The adoption of virtually the same gearbox for just about every pre-unit model and some plunger models must have been an ideal opportunity to make this improvement.  The drawing of the primary oil level in my A65 manual does show the oil level being over the height of the chain and critically very close to the plates.  Assuming accuracy of the drawing it makes the level of the oil quite critical.  Are some of us a bit impatient when topping up and do not allow any surplus to fully drain/drip out?  This could result in too high a level so a second cup of tea is needed to make sure the last drip has dropped.

Dave.

Bles31

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Re: Gearbox oil leak
« Reply #12 on: 28 April, 2020, 15:35:13 »
Thanks for the replies. I have a bit more information from some notes I have found from when I looked at this a couple of years ago. According to the notes I have dug out of the garage I had previously concluded that the way to reduce leakage was too keep the oil just below lip seal level, approximately 12mm below the bottom of the filler port. This, according to my old notes, equates to around 370cc of oil ( which answers your question in an earlier post, Jim). When I get a minute I am going to drain and refill, just to confirm this number. Why I have revisited this is because the 370cc is well below the recommended volume of 570cc. I have been trying to work out whether it is possible to get 570cc to actually stay in the gearbox, as I have been concerned about the consequences of running with the reduced volume.
Apologies for late addition of this information.

Bles31

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Re: Gearbox oil leak
« Reply #13 on: 28 April, 2020, 15:59:31 »
Right - just drained gearbox. 350 ml came out pretty quickly then became a slow dribble that I couldn't be bothered to wait for. So 370ml to the bottom of the lip seal seems about right. So theoretically underfill, or fill to 570cc and tolerate leaks?
Or find a way to have 570cc and no leaks.
Going for a brew!

Blackthou

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Re: Gearbox oil leak
« Reply #14 on: 28 April, 2020, 22:18:26 »
Enough to spalsh feed should be enough surely. As long as it cntacts moving parts it's got to be better than nowt.