Quote:
Originally Posted by PaulGros
Hi Nik,
The shell variation is per shell, not per pair. Unfortunately we do not know how BMW graded the engine assembly or what criteria they applied on the selection of bearing shells. It would be normal for the component manufacturer to grade the parts. But we honestly do not know if this was the case.
It seems odd to use one of each grade on assembly as per the parts catalogue. This could have been achieved with a single grade part. Again, I have seen no data to prove or disprove what colour codes were fitted from the factory.
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Hmm, I clearly missunderstand something here but eager to learn. How can MAHLE quote a (theoretical) Max/Min clearance if they don't have BMW's shaft/housing spec's..?
Quote:
Originally Posted by PaulGros
Correct. The increase in clearance is mainly due to offering a single grade part to ensure it works at all extremes and the material MAHLE has selected to use. I think in the MAHLE document they used the phrase er on the side of caution :-)
What others are targeting is difficult to say. I see posts saying "we are targeting x clearance" for example, but no data to back this up. I know some are stating "real world" measurements, but for me the first stage has failed. How do we know the parts measured are the size the manufacturer intended i.e. are they in spec?
I know you kindly queried ACL on their tolerances so maybe I will use that data along with the MAHLE Motorsport data which will give us theoretical min / max as well as average clearance from drawing specs. Maybe BE will divulge their specs and we can add those too. I have asked king for the same information.
Maybe then we can start to build a clear picture of target Vs actual each bearing brand available.
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Which again would be theoretical simply using housing-shaft-2 x shell wall...no?
Quote:
Originally Posted by PaulGros
Ignoring the debate on OE shells and only looking at data, yes the OE shells should be fine.
We really need to define the "extended clearance" It is not unusual for aftermarket bearings to run marginally larger clearances. This is due to aftermarket parts only having a single grade V's OE multiple grades. It ensures the part stays within spec at the extremes of tolerances.
For me "extended clearance" for means parts that have additional clearance over the standard part from the same manufacturer. These commonly use an X in the part number (ACL / Clevite HX, King STDX). These parts typically have 0.025mm (.001") extra clearance over the standard part from the same company.
Anything else would be a standard part (even though technically they have a little extra clearance to OEM).
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From what I see most fabs are offering various extended clearance (vs OE), which seems to make sense as they otherwise would introducing the risk to go too tight. My wondering really is; would replacement with OE shells be a viable option without the possibility to measure cranch and shaft?