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Repair Summary
This article gives detailed instructions on replacing the tensioner pulley, idler pulleys and main accessory (serpentine) belt in a BMW vehicle with the N54/N55 turbocharged engine. Even though we used a 2011 335i to perform this repair, this article can be applied to all 1,3,5 and X1 vehicles with either the N54 or N55 turbocharged engine with minor modifications to the repair steps.
See all vehicles this article applies to
E88 1 Series 135i
E82 1 Series 135i
F20 1 Series M135iX
F20 1 Series M135i
F20N 1 Series M135iX
F20N 1 Series M135i
F21 1 Series M135iX
F21 1 Series M135i
F21N 1 Series M135iX
F21N 1 Series M135i
F22 2 Series M235iX
F22 2 Series M235i
F87 2 Series M2
F87N 2 Series M2
F23 2 Series M235iX
F23 2 Series M235i
E90N 3 Series 335xi
E90N 3 Series 335i
E91N 3 Series 335xi
E91N 3 Series 335i
E92N 3 Series 335xi
E92N 3 Series 335i
E93N 3 Series 335i
F30 3 Series Hybrid 3
F30 3 Series 335iX
F30 3 Series 335i
F31 3 Series 335iX
F31 3 Series 335i
F34 3 Series 335iX
F34 3 Series 335i
F35 3 Series 335Li
F35N 3 Series 335Li
F32 4 Series 435iX
F32 4 Series 435i
F33 4 Series 435i
F33 4 Series 435iX
F36 4 Series 435i
F36 4 Series 435iX
F07 5 Series 535i
F07 5 Series 535iX
F07N 5 Series 535i
F07N 5 Series 535iX
F10 5 Series Hybrid 5
F10 5 Series 535iX
F10 5 Series 535i
F10N 5 Series Hybrid 5
F10N 5 Series 535iX
F10N 5 Series 535i
F11 5 Series 535iX
F11 5 Series 535i
F11N 5 Series 535iX
F11N 5 Series 535i
F18 5 Series 535Li
F18N 5 Series 535Li
F06 6 Series 640iX
F06 6 Series 640i
F06N 6 Series 640iX
F06N 6 Series 640i
F12 6 Series 640i
F12 6 Series 640iX
F12N 6 Series 640iX
F12N 6 Series 640i
F13 6 Series 640iX
F13 6 Series 640i
F13N 6 Series 640iX
F13N 6 Series 640i
F01N 7 Series Hybrid 7
F01N 7 Series 740i
F02N 7 Series Hybrid 7L
F02N 7 Series 740LiX
F02N 7 Series 740Li
E84 X1 Series X1 35iX
F25 X3 Series X3 35iX
F26 X4 Series X4 M40iX
F26 X4 Series X4 35iX
E70N X5 Series X5 40iX
E70N X5 Series X5 35iX
F15 X5 Series X5 35iX
F15 X5 Series X5 35i
E71 X6 Series X6 40iX
E71 X6 Series X6 35iX
F16 X6 Series X6 35iX
F16 X6 Series X6 35i
A BMW N55 engine squeal repair includes replacing the tensioner and idler pulleys, as well as the main accessory belt.
We continue to hold the belief here at the Repair Guide that the most annoying sound that is ever generated from the motors in our BMWs is engine squeal due to worn pulleys and/or drive belts. It is a nerve grating sound that is almost impossible to pinpoint due to all of the other ambient noise emanating from the engine. But if you are experiencing engine squeal in your N54/N55 turbocharged powerplant, it is most likely due to a failing belt tensioner, idler pulleys, or main accessory belt.
A BMW N55 engine squeal is usually caused by a failing belt tensioner or idler pulley. The belt tensioner does exactly as its name implies; it keeps pressure on the main accessory (serpentine) belt as it weaves its way through the alternator, power steering pump, and ac compressor. As the belt tensioner spring ages this pressure begins to decrease, allowing the belt to slip and cause a squeaking sound from the engine. The idler pulleys (there are two on the N54 and N55 engines) have the job of redirecting the main accessory belt so it doesn't get bound up as it travels around the front of the motor. Age also takes its toll on their bearings, causing them to squeal as they reach the end of their service life. The two belt tensioner pulleys are also susceptible to bearing failure.
The main accessory belt, also known as the serpentine belt, can be another source of BMW N55 engine squeal. As the belt ages, it can stretch, causing it to slip on the pulleys producing a chirping sound. This is most noticeable when the engine is cold, or when it is first started.
Diagnosing the exact culprit of your BMW N55 engine squeal is very difficult due to all of the background noise going on around the pulleys and the belt. Failing pulleys and belts can squeal when cold, hot, or anywhere in between. Trying to pinpoint exactly which component is failing is usually an exercise in futility. The best plan of action in curing your BMWs engine squeal is to replace all of the pulleys and the belt together in one repair.
Replacing the serpentine belt, tensioner, and idler pulleys in your N54/N55 turbocharged engine is actually quite simple and can be done by any home mechanic with average ability. The pulleys are easily accessed from the top of the engine and the belt can be replaced without having to remove any major components. It is a great money-saving repair that avoids an expensive trip to the dealership or local foreign repair shop.
View the detailed parts diagram for this repair.
Includes detailed part diagrams, part numbers and links to purchase all of the required components needed to complete this repair.
Before starting this repair, you must have the following required parts.
All E90 and E92 models with N55 engine
Continental Serpentine Belts come in a wide range of sizes and are designed to be oil-resistant and temperature-stable from -22ï½F to 176ï½F (-30ï½C to 80ï½C). Continental Serpentine Belts deliver 98% power efficiency. While a lower profile design easily handles higher engine revs, reducing noise and providing cooler running temperatures. High performance construction features include polychloroprene rubber cover and body, polyester fiber tensile members, and a ribbed belt design.
N54 and N55 engine - 1,3,5 and X1 models
This is the same factory accessory belt that would be installed at the BMW dealership.
N55 engine - 1,3,and X1 models
If you are replacing your accessory belt, you should also replace this tensioner assembly. By doing so, you ensure your belt drive system is going to work as it should and you won't be inconvenienced with lack of A/C and power steering.
Section 1 - Removing the Belt and Pulleys
As discussed at the beginning of this article, replacing the belts and pulleys on your N54 or N55 turbocharged engine is actually quite simple compared to other BMW models. The belt and pulleys are easily accessible from the top of the engine without any need to raise the vehicle or remove the cooling fan. It is a little bit of a tight squeeze getting the new belt on the lower pulleys so exercise patience during this step.- Remove the two torx bolts anchoring the intake duct to the suction hood at the front of the car. Unsnap the intake duct from intake muffler and remove it from the vehicle.
- Identify the belt tensioner, the upper and lower idler pulleys and the main accessory belt on the front of the engine. Note that the belt tensioner on the N54/N55 engine also has two pulleys.
- Using a T60 Torx bit, rotate the belt tensioner clockwise to release the pressure on the main accessory belt.
- With the pressure off of the belt, reach down and pull the belt off of the belt tensioner pulley.
- Pull the belt free from the rest of the pulleys and remove it from the vehicle.
- Use a small flat blade screwdriver or metal pick to remove the protective cap off of the top belt tensioner pulley. Using a T50 torx bit, remove the top pulley from the belt tensioner. It is easier to extract the main belt tensioner unit from the engine if you remove the top pulley first.
- Grasp the belt tensioner unit and remove it from the vehicle.
- Next, unsnap the protective cap off of the upper idler pulley and use a T50 torx bit to remove it from the vehicle.
- Finally, repeat the above step on the lower idler pulley and remove it from the vehicle.
Section 2 - Vehicle Reassembly
Installing the new pulleys and accessory belt in your BMW N54/N55 turbocharged engine is simply the above steps in reverse with no special procedures. Take your time installing the new belt ensuring it is routed correctly around the pulleys (see routing diagram below). We have provided a handy checklist below with the exact reassembly steps along with important torque values for the pulley bolts.BMW N55 Engine Squeal Reassembly Checklist
***The following steps were performed on a 2011 335i...other models may vary.- Install the new lower idler pulley and torque its mounting bolt to 50 Nm (37 ft-lb).
- Install the new upper idler pulley and torque its mounting bolt to 50 Nm (37 ft-lb).
- Install the new belt tensioner (with its lower pulley only) into the engine. Remember that due to clearance issues, its usually easier to install the belt tensioner in separate pieces.
- Install the belt tensioners upper pulley and torque its mounting bolt to 50 Nm (37 ft-lb).
- Install the new accessory belt. Pay careful attention to how it sits in the pulleys...you want to make sure that its ribs are lines up correctly.
- Use a T60 torx bit to turn the belt tensioner clockwise. Slip the new accessory belt onto the top belt tensioner pulley.
- Replace the intake duct back into the engine.
BMW N55 Engine Squeal Repair Finished
