Ok, I stand corrected. For long time BMW used mainly fully counterweighted cranks in its inline-6 engines which are as good as best aftermarket ones. Forging fully counterweighted inline-6 crank is pretty expensive so seems that newer engines are back to using partially counterweighted cranks.Kevin Johnson wrote: ↑Sat Mar 16, 2019 10:28 amYes, I walked out to my shed and inspected an Eta crank and it does have symmetrical counterweights but it is not correct that all BMW inline-6 engines have perfectly symmetrical counterweights.
Here is a link to an OEM BMW crankshaft for sale in Germany; note the asymmetrical counterweights:
https://www.ebay.de/itm/BMW-E46-M3-S54- ... 0009.m1982
BMW Kurbelwelle.jpg
That S54 crank is little in between one, it has full 12 counterweights but it still isn't fully counterweighted crank - japanese manufacturers did use those kind of designs in 4-cylinder engines in 70 and 80's but switched later to fully counterbalanced versions. Odd that BMW put partially counterbalanced crank in high revving, long stroke S54 when same time M52 versions got fully counterweighted cranks. Maybe they tried to lessen engine inertia but less counterweighting means more bending force to crank which leads unwanted torsional vibrations which greatly shortens all moving parts life.