Are you hearing strange noises coming from your BMW N55 engine? The cause could very well be related to the pulley and belt system, and one of the common “culprits” is the idler pulley. This article from Xe Tải Mỹ Đình will help you understand idler pulleys on cars, from the signs of failure to how to replace them yourself, helping your BMW run smoothly again.
The original article mentioned repairing BMW N55 engine noise by replacing the tensioner and idler pulley, along with the main belt. We will delve deeper into the role of the idler pulley on cars, the signs that it needs replacing, and detailed instructions on the replacement process, empowering you to confidently do it at home.
Engine noise, especially in turbocharged BMW N54 and N55 models, often originates from the accessory drive system. The belt tensioner, idler pulley, and serpentine belt work together harmoniously to ensure components like the alternator, power steering pump, and air conditioning compressor operate smoothly. When one of these components malfunctions, especially the idler pulley, unpleasant noise will appear.
The idler pulley on cars plays a crucial role in routing the serpentine belt. On the N54 and N55 engines, there are two idler pulleys tasked with redirecting the belt, preventing it from bending sharply as it moves around the front of the engine. Age and harsh operating conditions can cause the bearings of the idler pulley to wear out and dry up, leading to annoying squealing noises.
Idler pulley and its location on the BMW N55 engine
Besides the idler pulley, the main serpentine belt is also a cause of noise. An aging serpentine belt can become stretched and slip on the pulleys, creating a squeaking sound, especially noticeable when the engine is cold or just started. However, pinpointing the exact source of the noise can sometimes be difficult due to sound echoing from various components.
To thoroughly resolve BMW N55 engine noise, especially when suspected to be related to the idler pulley, the best approach is to replace the serpentine belt, belt tensioner, and idler pulley simultaneously. This is an effective solution that eliminates noise and ensures the accessory drive system operates reliably.
Replacing the serpentine belt, belt tensioner, and idler pulley on the BMW N54/N55 engine is not overly complicated. The idler pulleys are located in easily accessible positions, and the serpentine belt can also be replaced without removing many other components. Below are detailed instructions to guide you through the process yourself.
Preparing Parts and Tools for Idler Pulley Replacement
1. Necessary Parts
– Main Serpentine Belt: BMW N54/N55 engines use a single serpentine belt for all accessories. Choose a quality OEM belt to ensure durability and performance.
- Main Serpentine Belt – Continental 11287628653 – N54 and N55 engines 1, 3, 5 and X1-series
- Main Serpentine Belt – Genuine BMW 11287628653 – N54 and N55 engines 1, 3, 5 and X1-series
– Belt Tensioner: There are two different types of belt tensioners depending on whether it is an N54 or N55 engine. Check your vehicle information via VIN to choose the correct type.
- Belt Tensioner – INA 11287582946 – N55 engines 1, 3 and X1-series
- Belt Tensioner – Genuine BMW 11287582946 – N55 engines 1, 3 and X1-series
- Belt Tensioner – INA 11287563927 – N54 engines 1, 3, 5 and X1-series
- Belt Tensioner – Genuine BMW 11287563927 – N54 engines 1, 3, 5 and X1-series
– Idler Pulleys (guide pulleys): The N54/N55 engine has two idler pulleys, one upper and one lower. Both should be replaced simultaneously. Similar to the belt tensioner, check your vehicle VIN to choose the correct type of idler pulley.
- Idler Pulley (upper) – INA 11287556251 – N54 engines 1, 3, 5 and X1-series
- Idler Pulley (lower) – INA 11287556251 – N54 engines 1, 3, 5 and X1-series
- Idler Pulley (upper) – INA 11287578675 – N55 engines 1, 3 and X1-series
- Idler Pulley (lower) – INA 11287578674 – N54 engines 1, 3, 5 and X1-series
2. Necessary Tools
- Torx T50 socket
- Torx T60 socket
- Torque wrench
- Flexible head torque wrench
Idler Pulley and Serpentine Belt Replacement Procedure for BMW N55 Engine
Part 1 – Removing the Belt and Pulleys from the BMW Engine
The serpentine belt and idler pulley replacement procedure on the N54 or N55 engine is quite simple. You can easily access these components from above the engine without lifting the car or removing the cooling fan.
- Remove the two bolts securing the air intake snorkel to the hood. Open the air intake snorkel from the silencer box and remove it from the vehicle.
Removing the air intake snorkel from the BMW N55 engine
Location of the air intake snorkel and bolts to be removed
- Identify the locations of the belt tensioner, upper and lower idler pulleys, and the main serpentine belt on the front of the engine. Note that the belt tensioner on the N54/N55 engine also has two pulleys.
Location of the belt tensioner, idler pulleys, and serpentine belt on the BMW N55 engine
- Using a Torx T60 socket, rotate the belt tensioner clockwise to reduce tension on the serpentine belt.
Using a T60 socket to rotate the belt tensioner
- When the tension is reduced, use your hand to pull the serpentine belt off the tensioner idler pulley.
Pulling the serpentine belt off the tensioner pulley
- Continue to remove the serpentine belt from the remaining pulleys and take the belt out of the vehicle.
Completely removing the serpentine belt
The serpentine belt has been removed
- Use a small flat-head screwdriver or metal pick to pry open the protective cap of the upper idler pulley on the tensioner assembly. Using a T50 socket, remove the upper idler pulley from the tensioner assembly. Removing this idler pulley first will make removing the tensioner assembly easier.
Opening the protective cap of the upper idler pulley on the tensioner assembly
Location of the idler pulley protective cap
Removing the upper idler pulley from the tensioner assembly with a T50 socket
The upper idler pulley on the tensioner assembly has been removed
- Hold the belt tensioner firmly and remove it from the engine.
Removing the belt tensioner from the engine
- Next, open the protective cap of the upper idler pulley and use a T50 socket to remove it.
Opening the protective cap of the upper idler pulley
Removing the upper idler pulley with a T50 socket
- Finally, repeat the step above with the lower idler pulley and remove it.
Removing the lower idler pulley
The lower idler pulley has been removed
Part 2 – Assembling the BMW Engine
Install the new idler pulleys and serpentine belt into the BMW N54/N55 engine in the reverse order of the removal steps. Ensure the serpentine belt is routed correctly around the pulleys according to the installation diagram.
BMW N55 Engine Idler Pulley and Serpentine Belt Assembly Checklist
Note: The following steps were performed on a 2011 335i, other models may have differences.
- Install the new lower idler pulley and tighten the bolt to 50 Nm (37 ft-lb).
- Install the new upper idler pulley and tighten the bolt to 50 Nm (37 ft-lb).
- Install the new belt tensioner (with only the lower pulley) onto the engine. Installing the belt tensioner in parts is usually easier.
- Install the upper idler pulley of the belt tensioner and tighten the bolt to 50 Nm (37 ft-lb).
- Install the new serpentine belt. Pay attention to routing the serpentine belt according to the correct diagram.
- Use a T60 socket to rotate the belt tensioner clockwise. Slip the new accessory serpentine belt onto the upper idler pulley of the belt tensioner.
- Reinstall the air intake snorkel into the engine.
Completed idler pulley and serpentine belt assembly
The process of repairing BMW N55 engine noise by replacing the idler pulley and serpentine belt is now complete.
Garatructuyen and Xe Tải Mỹ Đình wish you success and the ability to take care of your beloved BMW.
Compiled by: Xe Tải Mỹ Đình
