In-Chassis rebuilds on older engines; we always try to do an in-chassis rebuild vs. an out of chassis because of the time element and the added expense. However, this past week two Caterpillar engines came into our shop for in-chassis rebuilds, and during the disassembly of the engines the main bearing caps fell out of the engine block. The main bearing caps are an interference fit and should be snug in the block. When they are loose the engine must be removed from the truck, completely disassembled, and the block and crankshaft must be sent to the machine shop. Sometimes a new main bearing cap is machined and fitted to the block, other times a small bead of weld is applied to the main bearing cap, then machined to once again be snug in the engine block. Once all of the bearing caps are tight, the crankshaft bore is then machined and the deck surface of the block is also machined. Next, the crankshaft is magnafluxed, straightened, and polished. Once the crankshaft is placed in the new main bearings, main bearing caps tightened to the proper torque, a man can turn the 400 pound crankshaft with one hand. At that point you know the machine work was properly performed.
There is another way to tell if the line bore in the block is OK without removing the engine from the chassis, and that is by a visual inspection of the bottom half of the main bearings. The wear across the bearing should be equal on both sides. If copper and the majority of the wear is on one side of the bearing than the line bore is out and the block must be removed from the truck and sent off to a good machine shop. The positive outcome is the Owner-Operator ends up with a great engine, maybe even better than when it was new. Unfortunately, the cost increases by about $12,000. A Signature rebuild on a Caterpillar 3406-E or C-15 with all of the performance parts we have to offer is about $38,000 plus the labor to remove and replace the engine back into the truck. Once the engine is out, now is the time to replace cab mounts, fuel lines, air lines, and brake lines. Total cost for all of the parts and labor can reach $45,000. The fuel mileage improvement over a stock engine will be 1.5 miles per gallon, which in turn will pay for the rebuild in about 2.5 years. It pays to have great credit, set aside 10 cents per mile into a maintenance account, have high limits on a few credit cards, or be good friends with your banker. The cost of parts and labor increases each year, I sure hope your freight rates do also.
Written by: Bruce Mallinson
Many of the articles compiled here where written by Bruce Mallinson. Attribution to other contributors is given in the specific articles.