BMW M3 Forum
BMW M3 Forum BMW M3 Gallery BMW M3 Reviews BMW M3 Social Groups BMW M3 Chat M3Forum Sponsors >>

Mobile M3forum
Go Back   BMW M3 (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X) > BMW M3 Discussions > E90 M3 (Sedan) | E92 M3 (Coupe) | E93 M3 (Convertible) (2008-2013)
Tire Rack Buy Winter Tires Now!
Not a member? Register Now!
Register Gallery All Albums Garage Search Today's Posts Mark Forums Read Calendar FAQ

E90 M3 (Sedan) | E92 M3 (Coupe) | E93 M3 (Convertible) (2008-2013) {Engine: S65 - Max Hp: 414 hp (420 hp Euro) at 8,300 rpm / 295 lb/ft at 3,900 rpm}

Thread Tools Display Modes
Old Mon, Jun-11-2018, 01:34:48 AM   #1
2008 M3 - Red
Join Date: May 2008
Posts: 846
Reputation: 0 PencilGeek is on a distinguished road

United States

Default Official ACL Rod Bearing Measurements

ACL Bearings

ACL Race Bearing Catalog:
Wiki: Full Technical Specifications
Photo Blog: About 100 full resolution photos

ACL Bearings has a long history in the automotive and racing bearing market. They are the latest company to throw their hat in the ring of S65 aftermarket bearings. ACL markets these bearings as extra clearance. The measurements below will show them to have a little extra clearance over stock bearings.


At first glance, the ACL bearings look worn and/or damaged. To the untrained eye, they might look like they just came out of an engine showing excessive bearing wear. Don't let the looks deceive you. This is normal appearance for ACL race bearings. ACL addresses this issue in their catalog with a lengthy description of their appearance. (See "Picture Description" below for a direct citation from the ACL bearing manual.)

Tools and Calibration

All measurements are performed on new "virgin" connecting rods and "virgin" connecting rod bolts. These rods and bolts have never been used in any engine. Using virgin rods and bolts is an essential step for obtaining reliable and calibrated results. After use, every connecting rod big-end is deformed with extra diameter. Using virgin rods and bolts ensures that the measurements obtained will be the same reference as a new factory engine. It's the only way we know to ensure repeatable and reliable results.

The image above shows the tools used for this job:
  • * Two virgin connecting rods (P/N: 11247838623)
    * Snapon electronic torque wrench (P/N: ATECH3FR250B)
    * Mitutoyo data-logging drop indicator (accurate to 0.00002 inch) (P/N: 543-562ACAL)
    * SPI bore gauge (accurate to 0.00005 inch)
    * 2-inch calibration ring
    * SPI gage blocks

The Mitutoyo drop indicator is used to measure each bearing thickness. It's a very pricey tool that is accurate to 0.00005 inch. It features the ability to data log to computer, categorize the results with go/no-go screen colors, and it's the same tool used by BE Bearings to measure each and every bearing shell thickness.

Before beginning to measure thickness, the instrument must be calibrated. The SPI gage blocks are used to set the proper instrument calibration.

The bore gauge used to measure the bearing clearance and eccentricity must be calibrated as well. The 2-inch bore gage shown in the picture is accurate to 0.00004 inch.

Production and Composition
Manufacturer: ACL

Composition: Trimetal steel/lead/copper

Coating: None

Part Number: 8B1580H (STD), 8B1580HX (+0.25 mm)

Target Market: OEM replacement market; Minimal increase in clearance over OEM rod bearings

ACL Bearings are a full custom rod bearing designed and manufactured by ACL. ACL manufactures the bearings to their own custom specifications.The composition is a standard lead/copper bearing. The bearing does not contain a low-friction coating.

Set Numbering
ACL RACE Series bearing sets are identified by the ‘H’ after the set number e.g. 8B663H-Std. Most ACL RACE Series bearings are also produced in a ‘HX’ version e.g. 8B663HX-Std. The ‘X’ signifies the set will give an extra .001” (.025mm) oil clearance on a standard size shaft when compared to the H-STD set. The wall size of these HX-STD bearings is .0005” (.013mm) thinner than the H-STD Bearings, in all other respects the HX set is identical to the H-STD set. There are selected con rod bearing sets that are manufactured with a dowel hole in the lower shell, to suit a dowel location in the con rod cap. These are designated with a ‘D’ in the set numbering e.g. 8B663HD-Std or 8B663HXD-Std etc.

Lead/Copper, Tri-Metal design
Tri-Metal, lead/copper are considered the world's best bearings. The steel backing is coated with copper, then topped with a soft lead. The lead is embeddable, meaning small particles can embed themselves in the lead without causing any damage to the crankshaft. Look in the best automotive engines, and you're likely to find a Tri-Metal bearing design.

Oil Clearances
Oil clearances are most accurately measured using micrometres and bore gauges. Bearing wall thickness measurements are taken at 90 degrees to the parting line (i.e. at the crown of the bearing) using a micrometre with a ball anvil, for use on the curved ID of the bearing.

Vertical oil clearance is best measured by assembling the bearing in its housing, with bolts torqued to specification, then using a bore gauge measure the assembled ID of the bearings at 90 degrees to the parting faces. The mating crankshaft journal size is measured, and subtracting this measurement from the bearing ID bore size, gives the assembled oil clearance.

ACL RACE bearings can be assembled with .00075-.001” per 1” of journal diameter (0.020-0.025mm per 25mm of journal diameter) plus .0005” (0.013mm).

As an example for a 2.000” (50mm) journal diameter, 2.000 x .001= .002 + .0005 = .0025” (50/25 x 0.025= 0.050 + .013 = 0.063 mm) Bearings should not be polished with abrasive pads or paper, on the bearing surface, to change the oil clearance.
Picture Description
Questions about the appearance of the RACE Series bearings are quite common, as this series of trimetal copper lead bearings have a very different appearance to regular aftermarket “ACL Duraglide” trimetal bearings, which have a light silver /grey appearance.

The RACE Series performance bearings as manufactured have an appearance that is a dark tarnished colouration, which can vary from dark black/brown/blue colours. This colour comes from the electroplating which is the last manufacturing process. The electroplated overlay has copper as one part of its composition, which tarnishes to the dark colours described above. This tarnish colouration has negligible thickness, so once installed in the engine, the crankshaft journal contacting the bearing, will polish the bearing surface, removing the surface colour and leaving the bearings with a polished silver appearance.

Performance bearings do not start out with the silver grey appearance of regular aftermarket bearings, as there is no final silvery tin flash applied to these bearings. Not applying a silvery tin flash to these high performance bearings is a specific design feature. A silvery tin flash for appearance and long term corrosion protection, as applied to the regular aftermarket bearings, can under high loading and heat, move, with the plate migrating and causing high spots on the back of the shells, and distorting the bearing. For this reason the ACL RACE Series performance bearings do not have a cosmetic silvery tin flash applied, so there is no risk of any overlay plate movement on the backs of the shells, giving better bearing to housing contact and better bearing performance and function.

Standard (STD)

+0.250 MM, +0.010 INCH

Standard (STD)

+0.250 MM, +0.010 INCH
Bearing Clearance Specifications
Clearance Measurements
Eccentricity Measurements

Bearing Eccentricity: ACL Bearings vs. stock 702/703 rod bearings
Supporting photos


Last edited by PencilGeek; Mon, Jun-11-2018 at 01:57:45 AM.
Jump to top PencilGeek is offline   Reply With Quote
Sponsored Links
Register now and remove these ads


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT. The time now is 08:17:30 PM.

Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd. and is in no way sponsored, endorsed or affiliated by or with BMW NA / BMW AG or any of it's subsidiaries or vendors.
BMW and M3 (E90 M3 | E92 M3 | E93 M3 | E46 M3 | E36 M3 | E30 M3) are registered trademarks of BMW AG.
M3Forum Terms of Service
Copyright 1999-2017
Discussing Official ACL Rod Bearing Measurements in the E90 M3 (Sedan) | E92 M3 (Coupe) | E93 M3 (Convertible) (2008-2013) Forum - {Engine: S65 - Max Hp: 414 hp (420 hp Euro) at 8,300 rpm / 295 lb/ft at 3,900 rpm} at BMW M3 (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)