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FCP Euro LIQUI MOLY Sale

FCP Euro LIQUI MOLY Sale

BMW’s high-performance nature means that every one of their engines is built with strict tolerances. In the more mechanical days, engine builders carefully measured their clearances to get them right and knew the correct tolerances via a book. Nowadays, BMW publishes engine clearances and technical data via ISTA/AIR, a paid access portal. All engine builders must do is log online and match codes stamped into the block to see which bearings the engine will need.

 

BMW N55 Main Bearings

Main bearings are assigned on the engine block and the crankshaft itself. Upper main bearing assignments for positions 1-7 can be found on the engine block (code letters A, B, or C), while lower bearing assignments are etched into the crankshaft (code numbers 1, 2, or 3). These numbers represent a grinding stage for bearings, and a combination of these bearings creates the in-spec tolerance required per journal on the crankshaft.

Upper Main Bearings

Code letters on the engine block designate the bearing type and its position. This information can be found written vertically on the right side of the engine block directly to the right of the coolant feed pipe.  Below is an N55 engine block with the location of this information circled in red for reference and a close-up of what you'll read.

FCP_Euro_BMW_N55_Bearing_Clearances_Engine_Block
FCP_Euro_BMW_N55_Bearing_Clearances
  • Code letter A = bearing shell, yellow with lubricating groove.
  • Code letter B = bearing shell, green with lubricating groove.
  • Code letter C = bearing shell, red with lubricating groove.

Using the assignment from the second image above as an example:

*BBABABB

The asterisk denotes the front of the engine block (timing chain end). Left to right is the order of positions 1-7. In this case, this engine block requires the following colors/part numbers by position:

  1. B = Green = 11217627038
  2. B = Green = 11217627038
  3. A = Yellow = 11217627037
  4. B = Green = 11218605857
  5. A = Yellow = 11217627037
  6. B = Green = 11217627038
  7. B = Green = 11217627030

 

Part Numbers For Positions 1, 2, 3, 5, 6:

Code

Color

Part number

Sizing

A

Yellow

11217627037

55.989-55.983mm

B

Green

11217627038

55.982-55.977mm

C

Red

11217627039

55.976-55.970mm

 

Part Numbers For Position 4 (thrust bearing):

Code

Color

Part number

Sizing

A

Yellow

11218605858

55.989-55.983mm

B

Green

11218605857

55.982-55.977mm

C

Red

11218605856

55.976-55.970mm

 

Part Numbers For Position 7:

Code

Color

Part number

Sizing

A

Yellow

11217627029

64.999-64.993mm

B

Green

11217627030

64.992-64.987mm

C

Red

11217627031

64.986-64.980mm

 

Lower main bearings:

The lower main bearings are coded to the crankshaft itself using numbers. Similar to the system used on the engine block, these numbers correlate to a specific color, which in turn correlates to a specific grinding stage of the bearing, allowing for a precise tolerance between the bearings and the crankshaft main journals. 

The numbers on the crankshaft counterweight represent a color (grinding stage), coded by position to specific part numbers. The letters represent the following:

  • Coefficient 1 = bearing shell (2) yellow without lubricating groove.
  • Coefficient 2 = bearing shell (2) green without lubricating groove.
  • Coefficient 3 = bearing shell (2) red without lubricating groove.

 

Part numbers for positions 1, 2, 3, 4, 5, 6:

Code

Color

Part number

Sizing

1

Yellow

11217627033

55.989-55.983mm

2

Green

11217627034

55.982-55.977mm

3

Red

11217627035

55.976-55.970mm

 

Part numbers for position 7:

Code

Color

Part number

Sizing

1

Yellow

11217627025

64.999-64.993mm

2

Green

11217627026

64.992-64.987mm

3

Red

11217627027

64.986-64.980mm

 

Here is an example of the numbers on the crankshaft denoting main bearing assignments 1-7:

 

FCP_Euro_BMW_N55_Bearing_Clearances

An example of a main bearing assignment code on a crankshaft:

"2222233"

  1. 2 = Green = 11217627034
  2. 2 = Green = 11217627034
  3. 2 = Green = 11217627034
  4. 2 = Green = 11217627034
  5. 2 = Green = 11217627034
  6. 3 = Red = 11217627035
  7. 3 = Red = 11217627027

Caution:

Per BMW’s technical documentation, yellow and red main bearings must not be mixed. If a yellow bearing is assigned on the block and a red bearing is assigned on the crankshaft for the same journal, you must use a green and upper bearing

The reason for this is pretty straightforward. Yellow and red-coded bearings are on the tighter end of the spectrum for clearance. If we take the maximum tolerance for each bearing shell (55.989-55.970, respectively), we could end up with a hypothetical clearance of 0.019mm, which is too tight and out of spec for the recommended main bearing clearance of 0.020-0.046mm.

 

A Complete BMW N55 Main Bearing Assignment Example:

Position

Code on the engine block

Part number for the upper bearing

Code on crankshaft

Part number for the lower bearing

1

B - Green

11217627038

2 - Green

11217627034

2

B - Green

11217627038

3 - Green

11217627034

3

A - Yellow

11217627037

4 - Green

11217627034

4

B - Green

11218605857

5 - Green

11217627034

5

A - Yellow

11217627037

6 - Green

11217627034

6

B - Green

11217627038

3 - Red

11217627035

7

B - Green

11217627030

3 - Red

11217627035

 

BMW N55 Connecting Rod Bearings

Connecting rod bearing assignments are located on the crankshaft. There are only two options for rod-bearing clearances on the crankshaft, with a lower and upper bearing shell needing to be installed in matched pairs. The two color options for the small end (connecting rod bearing cap) are red or blue, which is coded on the crankshaft as “r” or “b.” On the big end (connecting rod), the bearing shell color corresponds to the color used on the small end. Red on the small end matches with yellow on the big end, and blue on the small end fits with violet on the big end.

Here is an example of how connecting rod bearing assignments are ordered 

FCP_Euro_BMW_N55_Bearing_Clearances_Connecting_Rod

 

Code

Color

Part number (Cap End)

Sizing

r

Red

11247628034

49.9835-49.9930mm

b

Blue

11247628035

49.9730-49.9834mm

 

Code

Color

Part number (Big End)

Sizing

r

Yellow

11247576714

49.9835-49.9930mm

b

Violet

11247576715

49.9730-49.9834mm

An example of a code on a crankshaft and how part numbers are assigned:

"brrrrr"

  1. r = red = 11247628034 and 11247576714
  2. b = blue = 11247628035 and 11247576715
  3. b = blue = 11247628035 and 11247576715
  4. b = blue = 11247628035 and 11247576715
  5. b = blue = 11247628035 and 11247576715
  6. b = blue = 11247628035 and 11247576715

 

BMW N55 Clearance Specifications:

Measurement

Specification

Maximum runout at the main bearing journal

0.15mm

Crankshaft bearing radial play

0.020-0.046mm

Coefficient of friction of crankshaft

2-2.5Nm

Crankshaft side clearance

0.060-0.250mm

Connecting rod radial play

0.025-0.071mm

Information in this article pertains to Genuine BMW factory bearings only. Aftermarket rod bearing and main bearing sets include upper and lower in an entire package. They’re ground somewhere in the middle of the spectrum so that a standard set can apply to almost all engine block/connecting rod and crankshaft combinations. The factory bearing tolerances are tight, and if you’re looking to build an engine according to BMW’s engineers, Genuine bearings are your only option.

 If you use an aftermarket bearing set, FCP Euro recommends checking clearances during engine assembly. Plastigauge PG1 (green) is the recommended method by BMW for a quick check, as the tolerances are machined from the factory. However, more accurate options are available to you if performing a complete rebuild where the block or crankshaft has had machine work.

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Written by :
Gareth Foley

Gareth is the BMW Make Level Marketer for FCP Euro and has been with the company since 2012. Gareth's BMW obsession started with a hand me down E39 528i when he was 17. From this car he learned how to do his own repair work while also learning more about BMW. When Gareth was at CCSU studying Marketing he had the opportunity to go to SEMA with the college car club. This is where he developed his love of the automotive industry. Since joining FCP in 2012 Gareth has sought out to develop one of the broadest and most accurate BMW replacement parts catalog. he can be reached at gareth1@fcpeuro.com


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