Model A & B

Ford Garage

Babbitt Main Bearing Align Boring Bar Fixtures

Kwik-Way & Tobin-Arp

Kwik-Way

Pictured above is a pair of Kwik-Way main bearing align boring bar centering fixtures positioned on the pan rail and bearing saddles of a Model A engine block. These fixtures are used to properly locate the boring bar centerline for machining the poured babbitt main bearings for the Model A and B crankshaft.

The fixtures have (near) net locating pin holes for various Ford blocks including Model A, Model B, early flathead V8, and Fordson tractor. There is a front locating fixture and a rear fixture which are similar, but different.

The locating fixtures are used to center the 1-1/4 inch diameter main bearing boring bar in the bearing saddles, and place the boring bar centerline at the pan rail datum plane.

The Kwik-Way fixtures can also be used to position the LEMPCO boring frame on a block, instead of using the LEMPCO camshaft bore locators. Both Kwik-Way and LEMPCO use a 1-1/4 inch diameter boring bar.

The main bearing boring bar itself is supported by the adjustable Kwik-Way boring bar bearings and support bridges.

The bar locating fixtures are removed after the Kwik-Way bar bearings and support bridges are fastened in place, and then the bearing caps are bolted to the block for subsequent align boring.

Shown above is the boring bar rear locating fixture positioned in place and pin-located to the main bearing cap bolt hole.

Shown above is the boring bar front locating fixture positioned in place and pin-located to the main bearing cap bolt hole.

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When used on vintage Fords, the Kwik-Way boring bar locating system relies on the integrity of the pan rail datum surface, and on the position of the main bearing cap bolt holes.

It does not 'know' or account for the location of the camshaft directly, or make use of the camshaft bores, or utilize a false cam for alignment.

The concept of locating the main bearing boring bar independent of the camshaft centerline position is a little bit unintuitive in a non-timing chain engine like a Model A, but Ford did originally use the main bearing bolt holes as the net datum features for all subsequent critical block machining operations as shown above, so it follows the original production method.
Check your work!


Tobin-Arp

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 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 cam and crank 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 this links below on Ford Garage for information about establishing and maintaining proper crankshaft and camshaft timing gear engagement and clearances.


More Bearing Tool Links 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 Lempco Main Bearing Boring Bar Fixture
  4. Kwik-Way Line Boring Machine Operating Instructions
  5. Kwik-Way Line Boring Machine Parts List

December 2009