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#683683 - 02/04/17 2:53 pm Sealed Bearing on the Gearbox Main Shaft?  
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leon bee Offline
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arkansas
Working on a basket A65. We have on hand a new sealed bearing for the mainshaft. Don't know where it came from. Now I have used a shielded bearing in there on other engines, but I removed the shield on the inner side.

So, my inclination is to try to dig out the seal on the inside, but haven't tried yet.

I think this bearing came from one of our well known parts suppliers. but not sure about that. Does anyone think it was intended to be left sealed and run that way? And is that a good idea?

Thanks for any thoughts on this!

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#683750 - 02/05/17 2:31 am Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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DMadigan Online content
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The seals in bearings are for grease, not oil. Better to remove the seal and let the external seal do the proper job.
The oil will wash the grease out of the bearing and limit the fresh oil from getting to it.

#683756 - 02/05/17 4:01 am Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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Thanks, Dave. I was just now reading about this and I guess those seals come out easy. I hadn't inspected it closely and thought that seal might be some kind of hard plastic I might have to really get down on to get it out of there.

#683794 - 02/05/17 11:26 am Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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My experience is any ball bearing one buys now will come with both sides sealed, either with plastic sort of seals or metal seals. In either case they are easy to pick out. Go to a bearing supplier and ask for a non-sealed ball bearing (at least high quality ones) and they will look at you like you are weird. There might actually be a reason to have sealed bearings. Just wondering if there is actual quantitative evidence about the pros and cons of leaving the seals in when rebuilding a motor like those in our vintage bikes? Intuition says remove the inner seal but intuition is not always correct.


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#683804 - 02/05/17 1:08 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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I remember when they first came out--they were marketed as "sealed for life".
My intuition is also to remove the inner seal--but like Peter I wonder if that is wise.
If the inner seal is removed then the bearing is open to the bulk gearbox oil--which itself has to be changed regularly in colder climates at least in order to avoid "mayonnaise" in the oil.
Rather than the bearing being subjected to this perhaps it would be better if the bearing ran in its own totally enclosed lubrication "room"?--- that is--the two seals left in place.
Just thinking aloud.

#683809 - 02/05/17 1:44 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: DMadigan]  
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Originally Posted By DMadigan
The seals in bearings are for grease, not oil. Better to remove the seal and let the external seal do the proper job.
The oil will wash the grease out of the bearing and limit the fresh oil from getting to it.


I agree... And gear oil is a better lubricant for rolling element bearings than grease...


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#683811 - 02/05/17 2:15 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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I think I'll pull it out. I can see maybe a sealed wheel bearing, but this is a lot bigger deal.

#683813 - 02/05/17 2:31 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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I've been obsessed with bearings recently and as a result have a shelf filled with modern and 'ancient' bearing catalogs. Although there's way too much relevant information on the topic of oil vs. grease to extract very much of it here, I'll hit the high points.

Basically, the advantages of oil are that it carries heat away from the bearings and carries away particulate matter that gets inside. Of course, with a sealed bearing it's harder for particulate matter to get inside (but, if it does, it stays there, along with the heat). Applications mentioned in a modern Torrington catalog where sealed bearings are used are low speed operation in the food industry where "grease might be injurious" and in mechanisms where "relubrication is impossible or would be a hazard to satisfactory use." Neither situation applies to us.

Lubrication is important enough that the Torrington catalog spends pages in the "Engineering" section discussing the properties of the various choices. Importantly, it notes that "there is no known universal anti-friction bearing grease," and then goes on to list the properties of a half-dozen greases and the applications where each should be used. A summary sentence is "The successful use of lubricating greases in rolling bearings depends on the physical and chemical properties of the lubricant as they pertain to the bearing, its application, installation, and general environmental factors."

As can be seen from the above, it's more complicated than just sealed vs. non-sealed. Do you even know the composition of the grease in the sealed bearing you have and whether it is appropriate for the conditions it will face in a gearbox? For what it's worth, all my replacement bearings will continue to be naked.

#683826 - 02/05/17 4:32 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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I once fitted a so called "sealed for life" bearing to the sleeve gear of the Commando gearbox, it did not take long before the bearing started to produce grinding noises, so I learned the hard way, and removed the seal on the inside of the bearing ever since.


Peter.
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#683846 - 02/05/17 6:59 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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I have been picking out the inner seal but have never been certain of if I was just being overly nervous. I like the thought of heat dissipation with access to the oil.


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#683859 - 02/05/17 9:44 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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"Applications mentioned in a modern Torrington catalog where sealed bearings are used are low speed operation in the food industry where "grease might be injurious" and in mechanisms where "relubrication is impossible or would be a hazard to satisfactory use." Neither situation applies to us."--from MMans post.
There are standards for food processing machinery which prohibit the use of open bearings.
This from my time in UK when I ran a company making machinery which dispensed yoghurt cups, put in a fruit bottom then filled with yoghurt, applied and sealed the lid and date stamped it at the rate of 25,000 per hour.
The use of sealed bearings in this application is not just advantageous but mandatory.
No one wants a glob of solidified grease in their yoghurt!
However this does not necessarily mean that sealed bearings are disadvantageous for other applications such as our old clunkers--such as wheel hub bearings and gearbox bearings.
"Ah!" but you say "it is hot in the gearbox--not like in a wheel hub".
"Not so" say I.
Another piece of personal experience:
In 1967 four of us were in the Isle of Man for TT week.
I was riding a 1954 BSA A7 500cc twin.
That year A7 had the very good 8" single sided front brake.
On one of the non race days we decided to go round the race course for about 3/4 of the way (the course is about 37 3/4 miles around)and stop at the Greg-Ny-Ba pub, trying to get there as fast as possible. We went flat out and braking hard at the last moment all the way round.
We got to the pub, went in and were enjoying the first pint when a guy came rushing into the bar shouting "Whose is the BSA twin--it is on fire".
I rushed out to find the front brake emitting clouds of smoke which turned out to be the front wheel grease heated up by the repeated heavy braking.
So in my book I reckon a gearbox bearing sees about the same duty cycle as a wheel hub bearing--so if bearings with grease in them--sealed or unsealed--are OK for wheel bearings then they are also for gearbox bearings-sealed or unsealed.
Just to complete the Isle of Man story--what did we do about the front wheel bearing?
After much deliberation we decided to have another pint and give it more time to cool down.
The bike did many thousands of miles after that with no ill effects.
I guess that next time MMan builds a gearbox there will be no seals on the bearings.
When I do the same there will be seals on the bearings.
Which will last longest?
I suspect that we will never know as we will be both pushing up the daisies long before the gearboxes give problems.
As ever--just my two centsworth.

#683869 - 02/05/17 11:37 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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The bearing catalogs have different limit speeds for grease and oil.
The seals installed on bearings are not lipped with spring as replaceable oil seals. They sit in grooves in the races so are not as tight sealing. They are usually a thin steel disc with a rubber coating.
Porsche's Boxster changed from a double row ball bearing on the intermediate shaft to a single row bearing. Both are sealed (although they are inside the motor the design did not allow for pressure oiling). The single row bearing is prone to failing (almost 10% failure rate) which basically takes out the motor. Although higher loaded than the two row bearing they surmise the problem stems from the oil washing out the grease and contaminants get in but the seals keep them from getting out again which causes the balls to impact the contaminants into the race and eventually destroying the bearing.
They recommend replacing the bearing without the inside seal.
I am not sure why the same would not happen to the double row bearing.

#683879 - 02/06/17 12:33 am Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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Interesting, David.
However I cannot quite see how the seal lets contaminants get in but not out.
In an unsealed bearing those same contaminants would be in the oil that "lubricates" the bearing.
I guess that this is one of those questions to which we will never know a definitive answer.
Again--just my two centsworth.

#683889 - 02/06/17 3:36 am Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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I bought a shielded bearing for my a65, the cage is nylon! So this didn't stay on for long. Abnormal race with a SKF seal and I don't have any leaks.


beerchug
#683918 - 02/06/17 10:40 am Re: Sealed Bearing on the Gearbox Main Shaft? [Re: Tridentman]  
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Originally Posted By Tridentman

So in my book I reckon a gearbox bearing sees about the same duty cycle as a wheel hub bearing--.


I have a different book grin ,at 75 MPH the wheel bearing is rotating at about 900 or so RPM? The transmission bearings are spinning maybe three times that? The transmission bearings are subject to harmonics from the engine and changing loads...The wheel bearing, especially the front not so much.Wheel bearings are somewhat smaller the transmission bearings because of that.My 96 Ducati 900 has far more performance capability than any vintage Brit bike, yet the wheel bearings are the same size, well, it has three in the rear wheel. Same of the Buell I owned.Do any modern bikes or manual trans car or cars use sealed transmission bearings?

It was in the 1970's that heavy duty trucks went from grease lubricated non driving wheel bearings to sealed hubs using gear oil...bearing life doubled...


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#683930 - 02/06/17 12:43 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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The high gear bearing turns at almost half engine speed in top gear however he gearbox is a torque multiplier so higher load but lower speed than the wheel bearing.
Seals do not necessarily sit still as the shaft rotates. Small variations in the shaft or seal can cause them to vibrate which can move grease or oil past the seal.
I built a ball bearing inner primary for my triple by machining out the needle bearing support and bolting in a ball bearing support plate. I left the two seals in the bearing but it never effectively sealed and when opened later the grease was gone, presumably washed out. When I made new inner cases from plate for the ball bearing I made a provision for a lipped seal. No more leaking.

#683944 - 02/06/17 2:09 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: DMadigan]  
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On most Brit Bike transmissions the main shaft right side bearing spins at primary drive ratio. ..On a 650 Triumph for example that about 2100 rpm at 70 mph with typical 4.80 overall gearing, tire rpm is about 900 at 70 MPH...On automotive and Guzzi,BMW, the main shaft spins at engine rpm...
On my double engine Triumph LSR bike I used a modified Subaru wheel bearing hub for the jack shaft support on the primary drive. It's a 3 inch crowded race ball bearing spinning at 92% engine speed for about 30-60 seconds ( engines will see 7200 rpm.The bearing bub was grease lubricated so I converted it to gear oil...This is over three times the rpm original design.So far about 30 minutes use and it's fine..We will see how long it lasts... confused
Three made in USA 8000 rpm rated industrial greased bearings lasted about 15 minutes before getting severely galled...

Subaru bearing during development



Previous three bearing design..


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#684075 - 02/07/17 2:29 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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Well, I learned it takes about 3 seconds to pop those seals out. For some reason I though I'd have to get aggressive. You could even put it back if you wanted.

After a life time of packing wheel bearings, I was really surprised at how little grease was in this thing.

#684420 - 02/09/17 8:43 pm Re: Sealed Bearing on the Gearbox Main Shaft? [Re: leon bee]  
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A similar question came up in the Gold Star forum, re. sealed (or not) mainshaft bearings. In that case there are pumping pressures from the engine which is not the case in a separate gearbox (although I have seen breathers fitted on these). I have read that "modern transmissions" often have sealed bearings that run for 100,000 miles or more without attention.

I have a notion that with grease, when the bearing gets hot the grease liquifies to an oil-like state. As long as the seals work & it stays in the bearing all should be well.
I suspect that a modern transmission has the advantage of super slick gear changes with little crashing of gears. Compare that to a cranky old heavy Brit 'box that scrunches it's way through the gears & struggles to find them at times, then you have a recipe for a lot of metal "dust" in the oil acting as grinding paste everywhere in the box. Might be better if it didn't get into the bearings? Fit a magnet on the drain plug?
That said, I have always removed inner seals of wheel bearings in hubs with grease nipples, as some years ago I was made to feel paranoid about the inadequate amount of grease sometimes found (or not) in sealed bearings. Maybe that is an issue of bearing manuf. quality control. You gets what you pays for...
But... LB is working on an A65. TBH I don't know if this is a true unit motor or the gearbox is cast-in but separate. My ignorance knows no bounds!


na

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