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The IMS bearing is only submerged in oil when the engine is not running and all of the oil has drained into the sump, assuming normal oil fill levels.
With all my respect, I don`t understand the logic behind that. Why would that be? At max level on the dipstick, oil level is close to the top of the shaft. Why would the oil level change so drastically when the engine is running? And if it changes, by how much? A liter? That would mean that one third of the shaft is still submerged in oil. When the engine stops, most of the oil that has been circulating will not flow back to the sump but will stay in the oil galleries, otherwise the proper and immediate oil pressure in the crank bearings could not be ensured right after start up. And we are talking about at least a liter of oil that should disappear upon engine start. Where?
Once running, only a mist of oil kicked up by the crank surrounds the bearings while the engine runs.
Has anybody looked at that experimentally? I read this statement everywhere but I still don`t get what it`s based on.
The reason the shaft is full of oil during an extraction is because the seals have hardened and shrunk, allowing the oil to get into the shaft. The fact that the oil found during an extraction is usually rancid is because it has been in there for some time because it cannot drain out when the level in the sump rises after the engine shuts down.
Yes, that`s one reason, the other is that pressure builds up in the shaft due to the rise in temperature, which then forces air through the seals, which then builds up vacuum in the shaft when the engine cools down, and oil seeps back to the shaft through the seals. After a few hundred cycles the shaft will be filled with oil.
And having extracted a few LN bearings over the years, there was no oil to speak of trapped in the shafts.
Yes, those are not sealed bearings so I assume oil just drains off the shaft when you drain the oil from the sump. I agree, removing the seals is a good idea, I still don`t understand why the Germans placed sealed bearings there in the first place and never changed that over the years.
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