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03-14-2024, 07:21 AM | #2729 | |
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While measuring, binning and matching shells imo is great and certainly reduce the actual clearance variation. |
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03-14-2024, 11:48 AM | #2730 | |
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03-14-2024, 12:26 PM | #2731 | |
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But sure, what clearance this result in is obviously completely depedning on the surrounding hardware. From what I understand the housing is known (13um variation?) while the shaft is estimated (I believe ACL use 0.016um and BE measured 0.010 variation). So a (theoretical) clearance variation is in my mind not possible to quote while confirmed combined shell thickness is tightening it down a bit. I'm assuming that MAHLE have BMWs shaft/housing tolerances? |
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03-14-2024, 02:45 PM | #2732 | |
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I do have the original figures for the shaft and housing, but it is somewhay academic. As long as you use the same figures to calculate all parts then you can compare. Maybe I am misunderstanding the way the data is presented (it's been a long week!). There is shaft size measurements (which correspond very closely with BMW average) but no housing size data. There is measurements once bearings are in the rod for each part and a clearance figure given. You can take this data and back calculate to an average housing size as you have shaft size, clearance and wall thickness. But this isn't adding up, I'm seeing theorutical differences of 30um. So either the data is wrong, I'm misunderstanding the data or I've transposed the data incorrectly. This is why I believe we need manufacturer data on shell thickness, we can then use a standard housing and crank figure and calculate theoritocal clearances. This can then be compared to measured shell thickness and calculate with the same crnak and housing size. This shoukd give us two data points. What the bearing manufacturer is targeting and what they are actually achieving. |
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03-14-2024, 03:24 PM | #2733 | |||
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While for the shaft spec: ACL use Max 51,991, Min 51,975 and BE I believe use Max 51,9887 and Min 51,9786 i.e. a tad tigher. Quote:
Anyways, great if BE took part in the discussion. |
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03-14-2024, 03:41 PM | #2734 | |
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03-14-2024, 04:17 PM | #2735 |
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FWIW, sure thing mate...
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03-14-2024, 06:45 PM | #2736 | |
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http://wiki.rcollins.org/core/index..../%2B025_shells |
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03-14-2024, 07:05 PM | #2737 | ||||
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03-15-2024, 03:48 AM | #2738 |
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03-15-2024, 08:39 AM | #2739 |
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03-15-2024, 10:18 AM | #2740 | |
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03-15-2024, 11:46 AM | #2741 | |
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Put it another way if you kept increasing the RB clearance towards infinity would the oil flow through the mains be affected at any time. |
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03-15-2024, 11:51 AM | #2742 | ||
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Std Bearing = 1.9812 - 1.9939 +0.025 Bearing = 1.9939 - 2.0066 So we get a theoretical total wall min max as follows Min - 1.9812 + 1.9939 = 3.9751mm max - 1.9939 2.0066 + 1.9812 = 4.0005mm then take the measurements from rod 1 with bearing fitted 2.0494" = 52.055mm minus the shaft size 2.065" = 51.9811mm Gives a clearance of .0029" = 0.0737mm BUT if I take the following housing size - 56.013mm Upper Min Wall - 1.9939mm Lower min Wall - 1.9812mm Crank - 51.9811mm I get a theoretical max clearance of 0.0568mm It's been a long week and I'm jumping in and out of the data, hence why I said maybe I'm missing something, or misunderstanding something? |
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03-16-2024, 06:01 AM | #2743 |
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03-16-2024, 06:02 AM | #2744 | |
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03-16-2024, 07:04 AM | #2745 | |
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Its my understanding that a fluid will always tend to flow fastest through the point of least resistance. Is it not the case that the oil feed to the mains is the same oil feed to the rod bearings...albeit with the feed arriving at the mains first. Does the analogy I posted earlier not hold true? If you have a pressurised pipe with two holes in it, one represents the feed to the mains and the second the feed to the RBs. If you increase the size of the second hole, fluid will flow faster through the second hole and slower through the first hole all else being equal? |
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03-16-2024, 07:32 AM | #2746 | |
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03-16-2024, 10:43 AM | #2747 | |
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This is incorrect. Assuming constant pressure in your pipe, the mass flow rate must be equal. The mass flow rate of the fluid is function of the velocity and area (size of the hole), when you REDUCE the area of the cross section, the velocity INCREASES, thus maintaining the overall flow rate. This is fundamental fluid mechanics. This is how your garden hose works when you put a nozzle on it, or just your thumb over the end. |
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03-16-2024, 04:02 PM | #2748 | ||
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IIRC what they do is over stock on the bearings so that they have spare to be able to match and measure, then sell sets of hand measured shells within a very tight tolerance, negating any variances from the factory. So they have no need to ask the factory for a specified wall thickness. Re laser measuring, yes but they couldn't afford to bin or hold onto loads of shells could they? I'm sure you mentioned something like that if the tolerances were tightened right up. Quote:
Each main bearing has it's own feed from the main oil gallery, then each main goes onto feed one pair of RBs This diagram shows what I mean (even though it's not a BMW engine ) http://www.grumpysperformance.com/SBCOilingnew.png So assuming their was not a variable vol pump, their would be a drop off of mains pressure with larger RB clearances, but nowhere near as much as if they all had individual parallel feeds.
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Oil analysis for finding wearing rod bearings?. Collation of oil analysis reports with some rod bearing photos for the M3's S65. My categorisation of pulled rod bearings in the rod bearing condition thread. My updated 'Blown engines' list. Last edited by Assimilator1; 03-16-2024 at 10:02 PM.. |
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03-16-2024, 10:00 PM | #2749 |
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Added to the list, thanks mate.
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Oil analysis for finding wearing rod bearings?. Collation of oil analysis reports with some rod bearing photos for the M3's S65. My categorisation of pulled rod bearings in the rod bearing condition thread. My updated 'Blown engines' list. |
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03-17-2024, 08:30 AM | #2750 |
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And another S65 failure , posted at the UKM3V8 group - https://www.facebook.com/groups/bmwm...3606372017292/
What we do know is that it had the rod bearings replaced 10k miles ago, but we don't know what type. No details yet as he hasn't had it stripped down. Thanks to Smuler at m3cutters for alerting me to this one. **************************************** Btw, I'm contemplating starting an entirely new thread for this as I recently found out that a very regular member here wasn't aware of my clean up and categorisation of the ops list, even though it's linked in the op and in my sig. Is/was anyone else not aware of it?
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Oil analysis for finding wearing rod bearings?. Collation of oil analysis reports with some rod bearing photos for the M3's S65. My categorisation of pulled rod bearings in the rod bearing condition thread. My updated 'Blown engines' list. |
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