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Tiny metal flakes on the drain plug -- should I be worried about my transmission?

FWIW, I order the Mahle oil, air, and fuel filters for my Oilhead from RockAuto. I usually order a year of maintenance parts in one order which brings the shipping cost down to a fairly reasonable per item cost. I order my Airhead maintenance parts with the same order.
Looks to be a car part seller, do you order by bmw part numbers?
 
Looks to be a car part seller, do you order by bmw part numbers?

I'm not m_stock but I was able to find the filters by Mahle part numbers: air filter LX578 (though it's out of stock at the moment), oil filter OC91, and fuel filter ML145. They also carry Autolite 3923 spark plugs for dirt cheap, bulbs by generic part numbers (H4, 7506 and 7528), and loads of compatible alternator belts in a lot of different part numbers (Dayco 5040240, Bando 4PK610, Gates K040245, Continental 4040245).
 
Looks to be a car part seller, do you order by bmw part numbers?

The search engine on RockAuto will return the compatible parts when you enter the BMW part number. I have ordered other Mahle parts for riding buddies with K bikes too. The OC91 is just the Mahle oil filter. The OC91D is equivalent to the BMW filter kit, with the plastic bag of crush washers.
 
Minor update: I have ordered ACDelco part number 93368564 from RockAuto. In theory, it should be an NSK TM-series bearing that's 25x52x15mm (if I'm remembering right), the same as the clean bearing on the back end of M97 input shafts.

It was about $44 with shipping and tax. When it arrives I'll post pictures for you folks. Fingers crossed that it's a good source for this one weird bearing.

Edit: I'm not 100% sure exactly which bearing is which. The other bearing on M97 shafts is a 20x52x15, which is much harder to find anywhere. Guess I'll have to open up my transmission to really know. Will probably just order one of each beforehand if I can find the oddball one.
 
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So I got the bearing, it arrived in only 5 days. And...

It's a genuine NSK TM205-. So that part is good. With tax and shipping I believe it was cheaper than ordering it from BMW. It would definitely arrive a lot faster at the very least. My last BMW order took 4 weeks to get.

IMG_20211217_1308308.jpg

The problem is I forgot which bearing was the hard one to find, and this isn't it. A quick search shows that the NSK TM205 can be found in a decent number of places, even on Ebay for around $51 (though it has to be ordered from Europe).
The other bearing, the 20x52x15, is the one that's impossible to find anywhere but BMW. I believe it's NSK part number TM304.

The good news in my case is that based on info on NSK's website as well as seeing this bearing in person, I can make a guess at a decent substitute.
This doesn't look like a contact seal to me in either the diagrams or in person; it looks like a labyrinth-style non-contact seal, or perhaps a light-contact seal. That means while NSK's seal geometry may be unique, the design basis is not unique and almost every bearing maker offers the same type. An NTN 6304LLBC3, for example, can be had for less than $20. Labyrinth-seal non-contact bearings of any brand would, in theory, perform the exact same function of allowing gear oil to pass through the seal but catching small gear chips and flakes. The filtration efficiency would likely vary with seal design and NSK's does seem to be one of the best.

However, things got more confusing when I started looking on Ebay based on BMW's part numbers. BMW's "input shaft repair kit", part number 23002325604, can be had for about $200 here: https://www.ebay.com/itm/114870965810
Look closely and that is very much not an NSK TM-series bearing. It's an NTN LLU-series contact-sealed bearing, meant to only be lubricated by its factory grease.
I found the exact same thing when looking for part number 23122325518, which is supposedly the 25x52x15 bearing I just ordered from RockAuto. See here: https://www.ebay.com/itm/203628449194
Again, that is very much not a TM205. It's an NTN 6205 LLU double-contact-sealed bearing.
Both of these listings show the products in their original BMW bags with the original part number on them, but they are not the clean-sealed NSK bearings they're supposed to be. I don't know why. Apparently at some point BMW thought that using fully sealed bearings in our transmissions was just fine. I also saw a few transmission rebuild threads on ADVRider where transmissions had a mix of NSK TM and NTN LU bearings, which is even more confusing.


Baffling research aside, I'm taking a bit of a risk and going with NTN labyrinth non-contact sealed bearings of their LLB type. I have ordered a 6205LLBC3 and a 6304LLBC3 for my input shaft. These bearings cost a combined total of $33 and are very commonly available. My transmission has likely already shed most of the break-in gear chips it's going to make, and I'm willing to be a guinea pig for the sake of research and saving other folks money and time.

Consider this an experiment. Once I do the work, fix the input shaft wear issue, and get the transmission back in, I plan to keep documenting how things go. At the very least I expect these bearings will have much better life than open bearings.
I will, of course, also document what bearings are original to my transmission. I'm very curious as to what I'll find in there.
 
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Look closely and that is very much not an NSK TM-series bearing. It's an NTN LLU-series contact-sealed bearing, meant to only be lubricated by its factory grease.
I found the exact same thing when looking for part number 23122325518, which is supposedly the 25x52x15 bearing I just ordered from RockAuto. See here: https://www.ebay.com/itm/203628449194
Again, that is very much not a TM205. It's an NTN 6205 LLU double-contact-sealed bearing.
Both of these listings show the products in their original BMW bags with the original part number on them, but they are not the clean-sealed NSK bearings they're supposed to be. I don't know why. Apparently at some point BMW thought that using fully sealed bearings in our transmissions was just fine.

If readers go back to my earlier post # 32, they will find that indeed there was a period when BMW was using sealed, greased bearings. I don't know the years but it was some Oilhead bikes. These are the ones where the grease eventually washed out, usually with synthetic gear oil, turning the oil a muddy brown.

If I read GSAddict correctly they discontinued these sealed, greased bearings at some point to use a different type to again use geaar oil but to keep early manufacturing swarf from damaging the bearing.

BMW does not always document these running changes very well and sometimes even reuses part numbers.
 
You're right, I missed that little detail you posted. That makes sense.
What I find very odd is the pictures of some transmissions that had a mixture of both types; my best guess is that at one point during manufacture of M97's Getrag didn't have enough of one bearing type in a specific size, purchased a lot of the other type, and mixed them together when assembling some transmissions.

I'm no expert but I think having a bearing that allows a continuous supply of gear oil to pass through smoothly would be better than a sealed bearing only letting gear oil leak in, and then resisting letting it out.
 
I'm no expert but I think having a bearing that allows a continuous supply of gear oil to pass through smoothly would be better than a sealed bearing only letting gear oil leak in, and then resisting letting it out.

The issue BMW was trying to deal with at the time was that metal particles associated with manufacturing of the transmissions and break-in of the gearsets were damaging the bearings early in the life of the transmissions. So they wanted to keep metal contaminants in the oil from entering the bearings. Thus the use of grease filled sealed bearings. These were at the time called "clean bearings."

It appears from what GSAddict has shown that sometime later they devised another method to keep metal particles out of the bearings while at the same time allowing gear oil to lubricate the bearings.

When this first was going on I was writing my monthly Benchwrenching column in the BMW Owners News. I wrote an article in which I scoffed at the notion that it was necessary to use sealed greased bearing in a gearbox full of lubricating oil. In response I received quite a bit of information from techs and others about why the sealed greased bearings kept the early swarf out of the bearings and eliminated a lot of the early bearing failures. While I initially laughed at the greased bearings I finally agreed that it made sense. Then I personally ran across a few cases where the oil turned muddy brown from bearing grease washed out of the bearings.
 
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That also makes perfect sense; hardened gears making very abrasive dust and chips wreak havoc on open bearings.

To be clear I'm not disputing the use of sealed bearings with the sentence you quoted; they are used in lots of places and are a good solution for preventing that kind of short bearing life.

What I'm referring to is a specific scenario: if one of the two seals in a contact-sealed bearing eventually fails to keep gear oil out and the factory grease gets diluted and possibly washed out, it would, I'm guessing, be worse for the subsequent reliability of the bearing than if it were meant to pass gear oil through one seal and out the other seal. Contact seals aren't designed for that purpose, so it seems to me they'd be worse in that situation by restricting the flow of gear oil. Obviously not an immediate transmission-ending difference but I'm guessing some kind of reduction in remaining service life.

When you've seen the muddy brown gear oil problem, have you noticed any bearing noises or failures in those transmissions afterwards?
 
When you've seen the muddy brown gear oil problem, have you noticed any bearing noises or failures in those transmissions afterwards?

No, but I never had any long term followup with the owners. The longest was the bike that did about 12,000 miles in the next 11 days, and then 2,000 or so home after the Iron Butt Rally. That was the bike where he put in synthetic gear oil for the first time, and then when he changed it right before the IBR he panicked. He had a used gearbox on the way and we arranged for a garage to swap the transmissions. But after he explained everything, the dealer bringing the transmission, a couple of other certified techs, and I were convinced he just had bearing grease in the oil. We did not swap transmissions and up to 14,000 miles later there was no calamity.
 
That certainly sounds like those seals being compromised wasn't an issue, then. It's probably reasonable to assume that if synthetic gear oil can get through one of a bearing's seals, it can probably get through the other one too and thus keep a steady supply of oil going through a bearing.
My hypothetical of just one seal failing out of a pair probably isn't very likely. On top of that, I also just realized I've been mentally overestimating the amount of oil a bearing needs to keep running smoothly. One of the hobbies I eventually hope to get into is machining, and I have learned from watching videos on it that some machine tool bearings are fine with rotating for hours on just a squirt of oil.

I did find something interesting in my bearing research that I just remembered; NTN's "bearing selection guide" and a couple of other places mentioned that full-contact seals have a finite life span. What eventually happens with all full-contact sealed bearings is that the friction wears away the seals and opens them up, turning it into the equivalent of a shielded bearing. NTN mentions this in their literature as a very bad thing for manufacturing because it'll cause bearing failure quickly in dusty and humid environments, and then advertises how their LLU seals are designed to compensate for the friction wear and last longer.

I'd hypothesize that in a manual transmission full of oil, this kind of wear-induced seal failure would most likely happen to the original bearings long after the worst of the break-in grit and gear chips have been removed with oil changes.
 
I'd hypothesize that in a manual transmission full of oil, this kind of wear-induced seal failure would most likely happen to the original bearings long after the worst of the break-in grit and gear chips have been removed with oil changes.

It is my understanding that was BMW's intent. Early protection until the early debris is washed out with a few oil changes.
 
It is my understanding that was BMW's intent. Early protection until the early debris is washed out with a few oil changes.

With that in mind, my selection of rubber shielded, but not contact-sealed, bearings to replace the originals should be just fine in my 36,000+ mile transmission. Especially since I'm replacing the wavy washer with a solid spacer to eliminate the source of shiny metal flakes.

Piece by piece I'm ordering parts for the rebuild. Seals and bearings have been ordered, along with a used gear and input shaft (if needed). Some things just can't be known until I pop open the transmission, like exactly how to fit a spacer and whether I need to order one that's commercially made or modify the spring perch myself to make a BMW one fit.

My favorite song to sing to myself lately, to the tune of "If I Only Had a Brain" from The Wizard of Oz, has been "If I only had a lathe..." as there are a whole bunch of parts I could make instead of buying in my vehicle work escapades if I had one. A spacer to replace that wavy washer and fit on the existing spring perch would be easy to turn. Darn these lathes for being so expensive.
 
With that in mind, my selection of rubber shielded, but not contact-sealed, bearings to replace the originals should be just fine in my 36,000+ mile transmission. Especially since I'm replacing the wavy washer with a solid spacer to eliminate the source of shiny metal flakes.

I would agree with that.
 
I do not understand the argument for or against sealed or open bearings.
Manual car and truck transmissions have been around 100 years and those bearings hardly ever fail.

What did Getrag/BMW do that deviated from established engineering practice, and why?
 
I do not understand the argument for or against sealed or open bearings.
Manual car and truck transmissions have been around 100 years and those bearings hardly ever fail.

What did Getrag/BMW do that deviated from established engineering practice, and why?

All manufacturers have gone this way not just BMW.
Open bearings are passe.

I have seen/had open bearing failures on earlier transmissions of all types.
 
GSAddict is right. Owners of M93 Oilhead transmissions and high-mileage Airheads would be able to provide you with a lot of very good, real-world examples of why open bearings are outdated for transmission use. They wear out more quickly than sealed bearings because nothing prevents abrasive grit and chips of hardened gears from getting into them, and this is most pronounced during the early life of the transmission. The traditional open tapered roller bearings are also noisier and less efficient than sealed ball bearings.

Open bearings would theoretically last much longer if transmissions had a more complex lubrication system that included an oil filter, but the design of transmissions for most cars and motorcycles hasn't really changed much because oil-bath lubrication works just fine and is cheaper to make than its alternatives. (There are vehicles, mostly heavier-duty ones, that have these kinds of lubrication systems in their transmissions, with oil pumps and coolers and filters, but this is very uncommon in the car and motorcycle world.)

That ACDelco part I ordered and posted a picture of earlier in the thread (that turned out to be a genuine NSK TM205 bearing) fits a whole bunch of GM cars made from the 1980's to the 2010's, which is a good example of how the entire automotive industry has moved to sealed (or shielded/filtered) bearings and not just Getrag.
 
Another minor update: learned a valuable lesson yesterday about ordering bearings from trustworthy suppliers.

I had ordered two "NTN" bearings from Ebay. Got them both in the mail, and one looked especially suspicious, with no NTN embossed in either of its rubber seals. Went to NTN's website to check and they are likely BOTH counterfeits! The one that had correct-looking seals had tangible axial play despite being "new in the package" and claimed to have been made last year, in the US, despite having a plain sticker and not the fancy holographic one NTN says it should have if made after 2017. I used the World Bearing Association's phone app to scan the barcodes on both packages and they both flagged as fakes.

Started a return for both of them, and the seller of the obvious fake refunded me immediately. Likely that seller knew it was a fake when sending it to me in the first place. The other one wants it back and I'll be sending it back.

Too cheap to be real is often the case on Ebay. I'll be re-ordering from Grainger -- which I can pick up locally in Nashville. I'll wait until have my transmission open to buy it; that way I know for sure which bearing needs to be replaced.
 
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