Quote:
Originally Posted by PaulGros
Bearings is a technical subject, more so than many realise :-)
OEM specs are almost double what has been quoted ( 0.0254mm / .001" quoted vs 0.046mm / .0018")
In fact, if you run the data from the BE WIKI on the shells they have measured you will find ALL currently available bearings including OEM are remarkably close in clearance at around 2um (.00008") variation.
Now, I'm deliberately using the wiki data as this is often where people are pointed so there is consistency in comparisons.
Given the smallest part tolerance that is proven is the OEM parts at 6um (.0002") you begin to understand how small the difference is on all of these parts.
The only time we see a larger deviation on clearance is when you run theoretical min / max clearances between the parts. The problem is here that the largest measured deviation on some parts is over 12um (.00047") where others are deviating only 1um (.00004"). This then shows the parts with the largest measured size deviation will show a larger theoretical clearance. Theoretical clearances based on min / max is only relevant when absolute min / max sizes are known, including production tolerance. We don't have this data for all parts.
For reference here are the production tolerances that are known.
OEM 6um total - source original drawing
MAHLE 9um total - source original drawing
ACL 8um total - source email to ACL
King currently unknown, data requested
BE currently unknown
In short, the differences between bearings available are as follows:
1. Eccentricity (is this by design or wider tolerance? Without drawings it's unknown)
2. Material specification
3. Brand
4. production tolerances
So choose your bearings based on the above, local availability, price or preference of the person doing the job. All will have clearances within spec based on published data.
And staggering bearing sets or using extra clearance (ACL HX for eg) is perfectly OK. but if it were me, I would only use after shaft and housing measurements are checked to prove the extra clearance was required or desirable.
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Hi again Paul!
Again I’m aware of that you are not employed by MAHLE and I don’t expect you to know all answers. Still curious of your (and possibly other – initiated - peoples) view here:
Quick question on the BMW OE shells
As the shaft and housing variation together is 0.030 on its own (according to the specs I’ve seen?), I still don’t quite get how BMW clearance variance can be as tight as 33um (0.062 – 0.029mm), with a shell variation of apparently 0.006 on top. There are a couple of different shell thicknesses to play around with but doesn’t help really if surrounding HW isn’t known. So each shafts and houses are measured during assembly of the engine where after matched with the shells?
MAHLE
MAHLE’s target extended clearance (54um vs OE 46um) from what I understand to avoid getting too tight/lose in the ends due to overall variation (rather than increasing the oil film)?
Others
The various “extended” shells seems to all target around 55-60um clearance, i.e. similar to MAHLE?
So...
should my understanding be that 1) Originally installed OE bearings should theoretically be fine “for ever”, obviously assuming the engine is maintained/treated correctly. 2) If one for whatever reason (tons of miles, 10th owner etc) want to replace the RBs it should be with extended clearance due to mentioned tolerance stack up?
Thanks,
Nik