Strange Noise After Full N55 Engine Replacement on BMW F10 535i
2026/06/16
Latest company blog about Strange Noise After Full N55 Engine Replacement on BMW F10 535i

Malfunction Symptom

Abnormal engine noise

Repair Process

1. Inspection revealed the loudest abnormal noise originates at the joint of the engine and transmission, suspected to be caused by the flywheel.


2. After removing the transmission for inspection, cracks were found on the flywheel. Only one locating pin was installed, the locating pin holes had rough surfaces, and wear marks were present on the lower crankcase skirt.

Strange Noise After Full N55 Engine Replacement on BMW F10 535i

3.After communicating with the customer, we learned that the vehicle’s engine assembly, flywheel, transmission center housing, as well as transmission and engine mounts had been replaced following a collision accident. Combined with the actual on-site fault conditions, the issue was suspected to be caused by improper assembly.

4. After replacing the flywheel and installing the two missing locating pins, we found that the transmission could not fully mate with the engine during reassembly. We initially suspected deformation of the transmission housing.

5.Maintenance personnel measured the center-to-center distance between the transmission positioning holes as 35 cm, and the center-to-center distance between the positioning holes of the lower crankcase skirt was 35.2 cm. The flatness warpage of the lower crankcase skirt was 0.45 mm (Figure 1), while the flatness warpage of the transmission was 1.2 mm (Figure 2). Based on these measurements, the preliminary conclusion is that the transmission front housing was deformed due to the collision accident.
Strange Noise After Full N55 Engine Replacement on BMW F10 535i

6.Replace the transmission front housing, install all missing locating pins completely, then reassemble the vehicle properly. The fault was eliminated afterward.


Solution

Replace the transmission front housing and install locating pins.

Case Summary

1.Before assembling the transmission to the engine, you must check whether the two locating pins of the engine and transmission are missing. Any missing pins must be refitted, and any deformed pins must be replaced; otherwise, flywheel cracking will occur.


2.When handling collision accidents involving transmissions or engines, thorough inspection for deformation of the transmission, engine and torque converter is mandatory. Failure to do so will lead to faults such as abnormal noise, flywheel cracking and abnormal wear of crankshaft bearings.