Engine Block Repair Basics - Spun Bearing Blues- Tech

Armed with misalignment data, the technician peened the block using a hardened chisel and 4- to 8-ounce hammer. The cap bolts were loosened (finger-tight), then strategically placed blows caused surface displacement of the block material that shifts the cap position. The cap fasteners were then torqued to specification, and the dial-bore gauge was used to measure progress. The goal is to make each cap fit tight in the block without being more than 0.003 inch off-center from side to side.

The chisel used during the block-peening operation must have a rounded tip; sharp tips will gouge the block.

After peening, the caps were in near-perfect alignment, and just as importantly, the press-fit between the caps and the block had been restored. While a 0.008-inch feeler was used to fit in this gap, after restoration, even a paper-thin 0.0015-inch gauge wouldn't fit.

The main cap machinework left a 0.005-inch step at both sides of the block parting line, a temporary result of the reduced id of the caps, and it would be addressed by the hone.

This Sunnen CH-100 horizontal hone is not a boring bar-instead of cutters, spring-loaded shoes abrade the metal to be removed. The main cap fasteners must be torqued during the align-hone operation.

The hone uses 200-grit shoes. Alcarez set up the honing bar prior to yield the desired bearing-housing id. The honing operation relies heavily on operator skill. Resistance decreases as the shoes remove block and cap material. As Alcarez says, "It takes a touch, but the feel is intuitive. When it smoothes out, you know it's time to take a measurement and increase the shoe preload to remove more metal if need be."

Frequently using the dial-bore gauge to check progress, no more than 0.003 inch was removed between checkups. Though the setup time is usually about two hours, the actual honing is finished in less than 20 minutes. After the desired id of 2.6406 inches was achieved, Alcarez left the block in the hone for 30 minutes to let it cool and then rechecked the diameters. He'd make a light "perfection pass" if warranted.

The restored caps and saddles were as good as new and could be returned to service using standard replacement bearings. When done properly, align-honing alters the crankshaft to camshaft distance by less than 0.003 inch, so that timing-chain tension is not impacted. Roughnecks using crude methods are responsible for giving block repairs of this type an undeserved reputation for causing timing chain slack-not so at JMS. CHP