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Old 11-03-2012, 01:11 PM   #3550
Cam Killer
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Joined: Jun 2005
Location: SF Bay Area
Oddometer: 7,615
Originally Posted by markjenn View Post
I've always wondered why BMW hasn't tried eliminating the offset (and presumably the rocking couple vibration) by using a forked conrod on one side with bearings on either side of the other side's bearings so that the two cylinders could be aligned.

- Mark
The wethead reduces the cylinder offset according to this:

The crankshaft is now much more compact, thanks to the reduced width of the connecting rods and consequent reduced parallel misalignment of the opposing cylinder. This was possible thanks to the enlarged diameter of the crank journals, from 48mm to 50, which increased the load capacity of the related bearings, thus reducing their width. The main journal diameters were reduced from 60mm to 55. The new crankshaft is more rigid and lighter. The reduced misalignment of the cylinders causes less rocking imbalance and related vibrations, and favors the much-higher rotational speed needed to produce the new level of power.
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