Model A & B

Ford Garage

Tobin-Arp Boring Bar Locating Fixtures

Babbitt Main Bearing Align Boring

Shown above is a pair of Tobin-Arp B-138 main bearing boring bar locating fixtures for use when align boring the crankshaft main bearings in the Model A and B Ford engine block.

The Tobin-Arp uses a 1-1/8" diameter boring bar, whereas the Kwik-Way and the LEMPCO use a 1-1/4" bar. These fixtures are used with both the TA-14 and TA-15 Tobin-Arp machines.

These locating fixtures insert into the cam bearing bores at the front and rear of the engine block to locate and support the boring bar centerline, according to the camshaft bore centerline location, and the pan rail datum surface.

In this way, the Tobin-Arp fixtures directly locate and control the centerline dimension between the engine camshaft and crankshaft, which is important to maintain proper timing gear engagement and clearances.

The Tobin-Arp boring bar locating fixtures also do not interfere or obstruct the main bearing caps and bolts on the Model A and B cylinder block.

In theory, this is a reliable enough strategy for locating the main bearing boring bar (to the camshaft) in an engine design like a Model A Ford having a direct camshaft and crankshaft gear engagement. However, the cam and crank alignment and engagement could be compromised when using this strategy to set up on a worn block.

If the block has excessive wear in either the front or rear camshaft bores, this method of locating off of the camshaft bores can introduce error in the proper placement of the boring bar in the block. This condition is often found on the front bore on Model A's and B's.

Measure cam bores for egg shape. Check your work carefully and confirm position before cutting.

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

More related information on Ford Garage:

  1. Model A & B Camshaft to Crankshaft Gear Alignment
  2. Model A & B Proper Crankshaft and Camshaft Positioning
  3. Model A & B Kwik-Way LBM Main Bearing Boring Bar Fixtures
  4. Model A & B LEMPCO FSU Main Bearing Line Boring Machine
  5. Kwik-Way Line Boring Machine Operating Instructions
  6. Kwik-Way Line Boring Machine Parts List
  7. Model A & B AER Insert Main Bearing Data & Instructions

December 2009