This video documents the in-depth diagnosis of a BMW M57 E91 engine that unexpectedly became extremely difficult to turn by hand, despite the vehicle operating normally until recently. The initial investigation, prompted by a planned transmission upgrade, ruled out external components and ancillary systems. Systematic disassembly of the engine revealed a severely bent crankshaft, described as being warped "like a banana," exhibiting substantial runout. The primary cause of the engine's stiffness was identified as the "wandering" or shifting of the main bearing caps, evidenced by aluminum material transfer from the engine block onto the steel caps, and micro-deformations on the block itself ("cellulite"). The presenter hypothesizes this damage is a consequence of the bent crankshaft, an imbalance, or a pre-existing warp in the main bearing bore. The crankshaft will be sent for professional balancing and precise runout testing to further determine the exact primary cause.
Exploring a BMW M57 Engine's Mysterious Stiffness and Bearing Damage
0:00 - 0:50: The video begins with the planned upgrade of a BMW 335i (M57 E91) transmission, necessitated by common issues like worn bushings and oil pressure problems in the 4.5g gearbox.
0:50 - 1:30: During the transmission removal, a baffling discovery is made: the engine cannot be turned by hand, despite the car having been driven into the workshop and covering 2,000-3,000 km recently without any noticeable performance issues or symptoms.
1:30 - 2:35: Initial troubleshooting involves removing external components like the belt drive and high-pressure fuel pump (suspected due to HVO fuel usage), but the engine remains extremely difficult to rotate, confirming an internal issue.
2:35 - 3:55: Further disassembly, including auxiliary components, glow plugs, and injectors, reveals that the camshafts rotate freely. This indicates the problem lies within the lower engine, likely involving the main bearings or pistons. The surprising absence of engine noise, increased engine braking, or metal shavings in the oil is highlighted.
3:55 - 4:18: Hypotheses for the engine's stiffness are discussed, including past "flood damage" from a faulty water-methanol injection (WMI) check valve or an instance of excessive WMI. The team decides to fully dismantle the engine to uncover the root cause.
4:27 - 4:57: After the initial engine teardown, a visual inspection of piston pins, bearing surfaces, and camshafts does not immediately reveal any issues. The oil pump also appears to be functioning correctly.
5:48 - 6:53: The crankshaft is removed and inspected on a lathe. It is found to be significantly bent ("like a banana"), exhibiting substantial runout, with measurements showing up to 0.5mm deformation.
6:53 - 7:47: The main cause is identified: the main bearing caps ("Hauptlagerböcke") have "wandered" or shifted, evident by aluminum transfer from the engine block onto the steel caps. The engine block itself shows micro-deformations, described as "cellulite."
7:47 - 8:10: The presenter speculates that the wandering bearing caps are a consequence of the bent crankshaft, an imbalance, or a pre-existing warp in the main bearing bore. Despite the damage, the main bearing screws were found to be tight, and bearing clearance was within specifications.
Key Takeaway: The severe engine stiffness was caused by a significantly bent crankshaft leading to the shifting of the main bearing caps and micro-deformations in the engine block.
Next Steps: The crankshaft will be sent for professional balancing and precise runout testing to confirm the full extent of the damage and help determine the exact primary cause of the failure.