Model A & B

Ford Garage

AER Insert Main Bearings & Bronze Thrust Washers

Installation Data & Instructions

This page details the installation instructions of the main bearing inserts produced specifically for Model A & B Ford engines by Antique Engine Rebuilding (AER).

These modern insert bearing shells are specifically engineered and produced for the Model A and B engine and are not an adaptation of an existing bearing from another application. The bearing shells are steel backed and have modern aluminum (not Babbitt) bearing surfaces.

The insert bearings are manufactured for AER to precise dimensions by an OEM engine bearing manufacturer. The block, caps, and crankshaft are required to be prepared and sized to precise dimensions to receive the bearings. See the table and information below for AER's recommendations.

Model A:
Finished Journal
Min / Max
AER Bearing
Set Number
Block & Cap Bore
Diameter & Finish
60-90 µin Ra
Min / Max
1.622 / 1.624 ~ ~ Original Ford Crankshaft Dimensions
1.623 / 1.624 ~ ~ Burlington Crankshaft Dimensions
1.6254 / 1.6259 A Standard 1.7705 / 1.7710 For built-up journals?
1.6234 / 1.6239 A 002 Under 1.7705 / 1.7710 For new Burlington, and NOS Ford A crankshafts
1.6154 / 1.6159 A 010 Under 1.7705 / 1.7710
1.6054 / 1.6059 A 020 Under 1.7705 / 1.7710
1.5954 / 1.5959 A 030 Under 1.7705 / 1.7710
1.5854 / 1.5859 A 040 Under 1.7705 / 1.7710
1.5654 / 1.5659 A 060 Under 1.7705 / 1.7710
Model B:
Finished Journal
Min / Max
AER Bearing
Set Number
Block & Cap Bore
Diameter & Finish
60-90 µin Ra
Min / Max
1.998 / 1.999 ~ ~ Original Ford Crankshaft Dimensions
1.9985 / 1.9990 B Standard 2.1345 / 2.1350 For NOS Ford B crankshafts
1.9885 / 1.9890 B 010 Under 2.1345 / 2.1350
1.9785 / 1.9790 B 020 Under 2.1345 / 2.1350
1.9685 / 1.9690 B 030 Under 2.1345 / 2.1350
1.9585 / 1.9590 B 040 Under 2.1345 / 2.1350
1.9385 / 1.9390 B 060 Under 2.1345 / 2.1350

Dave Gerold of Jordan, Minnesota ( has considerable experience rebuilding over 180 engines using these AER main bearing inserts and has posted some valuable experience on internet message boards.

Dave's personal views and experiences are included here with his permission for the reader's consideration.

Though the recommended running clearance for the main bearings is 0.00175" per AER, Dave has slightly different recommendations. Dave has stated that AER's recommended clearances have not worked well for him on the rear main bearing inserts after AER switched the final surface of the insert shells from Trimetal Steel-Copper-Lead/Tin construction to the presently-produced Bimetal Steel-Aluminum construction.

Dave has related the following failure mode he has experienced with the aluminum-faced insert shells welding themselves to the crankshaft. The bearing to shaft clearance was likely too little and it was the lack of oil that heated up the surfaces to the point of rubbing and melting the bearing material to the crankshaft. The spinning of the insert in the block housing bore was the last thing that occurred as the engine locked up.

Dave has found that the currently supplied aluminum lined rear main bearing inserts should have 0.0020" to 0.0022" clearance to be reliable (meaning no lock-up) and to be leak free. He now hones the rear main bearing shells precisely using a honing mandrel and process recommended by Sunnen to increase the clearance to the aluminum-faced insert to allow for sufficient oil film.

The front and center main bearing inserts can be finished at 0.00175" to 0.0020" clearance and not create issues with running too tight.

Dave's clearance recommendations are highlighted in yellow above! Learn from his experience!

Block and Bearing Cap Bronze Thrust Washers

Additionally, Rich Fallucca and AER supplies machined bronze thrust 'washers' which are designed to work with his bearing inserts.

They can also be used in place of the original cast and machined Babbitt thrusts on the rear main journal when using cast Babbitt bearings.

These bronze thrust washer sets are recommended for use with modern insert bearing shells and can also be fitted to the rear main bearing block saddle and bearing cap when using cast Babbitt bearings. The same block and cap preparations for the bronze thrust washers are required for either application.

The original Ford rear main Babbitt bearing length was 2.993 / 2.995 inches between the front and rear Babbitt thrust faces, and centered about the block saddle per the Ford block machining drawing.

The original thickness of the Babbitt thrust was 0.125 inches thick front and rear. The replacement bronze thrust washers are each 0.250 inches thick, indicating a nominal 0.125 inches counterbore in the block and cap is required to properly place each bronze thrust washer face.

Bearing and/or Thrust Sets Cost (confirm)
Model A Insert Main Bearings (6 piece set) $85.00
Model A Bronze Thrust Washers (3 piece set) $27.00
Model B Insert Main Bearings (6 piece set) $90.00
Model B Bronze Thrust Washers (3 piece set) $30.00

To purchase insert bearing sets, bronze thrust washer sets, or complete engine rebuilding services, contact AER at:
(847) 674-6716

Model A Block and Bearing Cap Preparation Instructions

The block and bearing caps are to be assembled using no shims, then align bored, finished, and prepared to receive the main bearing inserts and bronze thrust washers.

Some blocks, mainly early 1928, may require elongating the oil feed holes in the block to align with the oil holes in the insert bearing shell.

Model A Block and Cap Preparation:
  1. Bearing Inserts: Carefully inspect the main bearing caps and the block mating surfaces for damage or disruption. Ensure the caps fit precisely to the block surface without wobble, gap, or variation before proceeding further.
  2. Mark and identify the front and center main bearing caps for repeatable location and orientation on the block. The chosen cap, position, and orientation should be maintained throughout all machining and subsequent assembly and future service procedures.
  3. Assemble the main bearing caps to the block with no shims.
  4. Align bore and hone the block and bearing caps to the size and finish indicated in the table above.
  5. Remove all caps and cut slots in the block bearing saddles and bearing caps for the aligning lugs on the insert bearing shells. Confirm the alignment of the oil supply passage in the block with the oil feed hole in the insert bearing shell before cutting the block relief for the aligning lugs.
  6. Place bearing inserts in the block saddles and caps, and check that the aligning lugs and oil holes fit and align correctly.
  7. Using Prussian Blue, there should be at least 80% contact of the bluing on all bearing inserts to the block and caps.
  8. Thrust Washers: Counterbore the rear of the block rear main bearing saddle and bearing cap 2.250 inch OD and 0.125 inches deep to receive two semi-circular 0.250 inches thick bronze thrust washers. This will replicate the placement of the original rear Babbitt thrust surfaces.

    However if the crankshaft has been ground larger between the rear main journal cheeks it may be advisable to not sink the rear counterbores in the saddle and cap quite as much. Measure the crankshaft and do the math!
  9. Remove the rear main cap and counterbore the front (only) of the rear main saddle in the block 0.125 inches deep for a single 0.250 inches thick bronze thrust washer. This will replicate the placement of the original front Babbitt thrust surface.
  10. It is recommended to use two thrust washers on the back of the rear main, and one of the washers should be dowel-located to the block or cap to prevent rotation.
  11. The counterbore holds the two rear thrust washers in place, and the crankshaft keeps them in position.
  12. The dowel keeps the rear thrust washers from rotating, and the cap keeps the single front thrust washer from rotating.
  13. Thrust washers are not to be rigidly secured or attached to the block or cap as this can cause end loading and premature wear.
  14. Fit the thrust washers in the block and rear bearing cap.
  15. File any portion of the thrust washer that extends beyond the block-to-cap parting line.
  16. File a large bevel on both edges of the front thrust washer only (the contact face of crankshaft thrust). Leaving a square edge on the thrust would cause oil to be wiped from the crankshaft.
  17. A small amount of RTV sealer is recommended to be used on the outside edges of the rear main cap to prevent oil leaks at the rear.

Model B Block and Bearing Cap Preparation Instructions

The Model B instructions are the same as for the Model A above, except for the larger diameters of the bronze thrust washers and the bearing inserts. Refer to the Model B table above for block and cap bore sizes for the insert bearing shells.

The rear of the Model B block rear main bearing saddle and cap are both to be counterbored to 2.875 inch OD and 0.125 inches deep to receive bronze thrust washers.

Remove the rear main cap and counterbore the front of the Model B rear main saddle (only) in the block to 2.875 inch OD and 0.125 inches deep to receive a single bronze thrust washer.

Shown above is a 1932 Model B counterweighted crankshaft and a Starrett V-Anvil micrometer. This type of three-point micrometer is designed to measure shaft diameters very accurately and repeatably, compared to other tools such as conventional micrometers or vernier/digital calipers.

Highlights of attributes of aluminum-faced bi-metal bearing inserts versus lead/Babbitt-faced TriMetal™ bearing inserts, quoted from Clevite literature:
Engineering quality engine bearings involves a number of interdependent factors. Here is how Clevite 77’s TriMetal™ cast copper lead material compares to bi-metal bearings on the most important of these factors:

Seizure Resistance: TriMetal™ bearings have significantly greater seizure resistance than bi-metal bearings, by as much as 40%.

Load Capacity: TriMetal™ bearings can withstand much higher loads for longer periods of time as compared to bi-metal bearings, over 60% higher.

Embedability & Conformability: The overlay on a TriMetal™ bearing offers a far more forgiving surface than bi-metal bearings. These features may not be as critical during OE assembly as they once were, but they do offer additional protection that can be extremely beneficial in an engine that is poorly maintained.

Durability: TriMetal™ bearings not only exceed light vehicle OE durability requirements of 150,000 miles, they also exceed heavy vehicle OE durability requirements of 300,000 miles.

Tolerances: Because the surface layer of a TriMetal™ bearing adds an additional manufacturing step, we regularly hold wall sizes to within 0.0005” as compared to a bi- metal that can be held to within 0.0003”. This stack up of tolerances has nothing to do with quality, suitability, or service life.

Wear Resistance: While the silicon in the bi-metal material does contribute to slightly improved wear resistance as compared to the Babbitt surface layer of a TriMetal™ material, it’s at the direct expense of embedability and conformability.

Visit the links below for more information on Ford Garage about establishing and maintaining proper crankshaft position and camshaft timing gear engagement and clearances.

More related information on Ford Garage:

  1. For more Model A & B related information, use the Site Search box at the top or bottom of this page.
  2. Model A Burlington Forged Counterweighted Crankshaft
  3. Model BB Ford-Köln G28T-6303-B2 Counterweighted Crankshaft  
  4. Model A & B Proper Crankshaft and Camshaft Positioning
  5. Model A & B Camshaft to Crankshaft Gear Alignment
  6. Model A & B Rear Main Bearing Caps
  7. Model A & B Kwik-Way LBM Main Bearing Boring Bar Fixtures
  8. Model A & B Tobin-Arp Main Bearing Boring Bar Fixtures
  9. Model A & B LEMPCO FSU Main Bearing Line Boring Machine
  10. Model A & B J&M Machine Company Engine Rebuilding Videos

April 2017