Insert Main Bearings

Designed for the Model A

Insert bearings provide durable and stronger bearings for the engine. As we drive longer times at higher speed the demand for updating the Model A engine is an essential part of rebuilding. Tri-metal lined bearings designed for the Model A block have holes drilled with integral oil groves to give more bearing surface with proper lubrication.


  • Insert main and rods work fine without any changes to oil system. Bearings work with or without pressure oil system.
  • Oil filter gives longer life but is not required. Change oil regularly with modern motor oil.
  • Contact oil seals are not necessary.
  • The block does require machining to install inserts the first time.
  • Main bearings are same OD and ID as MG bearings. Only 2 shells per journal instead of 4 or 6.
  • Available in STD as well as 010, 020, 030, 040, 060.

Main Bearing Instructions

Crankshaft size
Standard 1.6254/1.6259
010 Undersize 1.6154/1.6159
020 Undersize 1.6054/1.6059
030 Undersize 1.5954/1.5959
040 Undersize 1.5854/1.5859
060 Undersize 1.5654/4.5659

The block and caps installed with no shims will require align boring. The housing bore in block is to be 1.7705/1.7710. the finish 60-90 mico inches ra.

The back of the rear main bearing block and cap portions are to be counter bored 2.250 OD and .125 deep. Now remove cap and counter bore block only on front of rear main 2.250 OD and 125 deep.

Remove all caps and cut slots in block and caps for aligning lugs.

Place bearings in block and caps check that aligning lugs and oil holes fit correctly. Some blocks, mainly early 28, may require elongating oil holes in bearings. 80 percent alignment is good.

Fit thrust washers in block and cap. Now file any portion that extends higher than parting line. File large bevel on both edges of front thrust washer 1 only (the contact face of crankshaft thrust) A square edge will cause oil to be wiped from crankshaft. On the back of the rear main it recommended to use 2 thrust washers and 1 of the washers should be doweled to block or cap to prevent rotating. The counter bore holds washers in place, crankshaft keeps them in position. The dowel keeps the rear from rotating and the cap keeps front from rotating. Thrust washers are not to be secured to block or cap as this can cause end loading and premature wear. I recommend a small amount of RTV sealer be used on outside edges of rear main cap to prevent leaks.

Model A Main bearing set $93.50
Model A Thrust washer set $29.70