Case of the Month: Engine Rebuild

Aug 1, 2016 by

The 1968 Chevrolet Nova was taken in for body and paint work. While it was at the body shop, it suffered an engine failure. The engine was removed and disassembled for inspection and repair by an engine rebuilding shop. They provided a repair estimate to the insurance company prior to authorization to begin the repairs. GEI was hired to review the situation and advise on the reasonableness of the proposed repairs.

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The ‘68 Nova was originally offered with a variety of engine options, from the base model 90 hp, 153 cubic inch straight 4 to small block V8s to big block V8s. The engine installed in this particular vehicle was a modified 427 cubic inch V8 putting out over 500 hp. Before the vehicle was taken to the body shop, smaller wheels and tires were placed on the vehicle to protect the expensive aftermarket wheels from damage at the body shop.

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The replacement of the larger wheels and tires with smaller temporary replacement wheels and tires would allow the engine to immediately over-rev with the least loss of traction, such as could occur in the body shop environment due to water and/or dust on the floor. The body shop reported the vehicle had been driven and moved around the shop prior to the engine’s failure. This indicated that the engine was undamaged when it was brought in for body and paint work.

When we inspected the disassembled engine, we observed the following: the head of the intake valve of the number four cylinder was broken off of its valve stem.

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The valve head was bent prior to the fracture. The sequence of events occurred as follows: The engine was over-revved; the push rod guide plate was broken off; the rocker arm rotated on its stand and held the valve spring partially compressed; the piston traveled upward and pushed the valve into the cylinder head. When this occurred the valve keepers were allowed to fall out. The now-loose valve fell downward as the piston traveled down the cylinder; when the piston returned on its upward stroke, it pushed the edge of the valve, bent the head, and broke the head of the valve off of the valve stem. The head of the valve bounced around in the combustion chamber and damaged the cylinder head and spark plug.

The aluminum piston came in contact with the steel valve head, which punched a hole in the top of the piston.

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The engine had to have been turning at a great rate of speed during the failure in order for a piece of debris to travel from one side of the engine into an intake runner on the other side of the engine. This precludes the failure from occurring at an idle or low engine speed.

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However, although the engine was not able to run in its current condition, all of the listed components in the repair estimate did not have to be replaced in order to bring the engine back to its proper operational condition. Most of the components listed on the repair estimate appeared, hopefully, as a “worst-case” scenario prior to the engine being disassembled.

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At the time of the inspection, when the actual damages could be observed, the only repairs needed to the engine were the replacement of the damaged piston and rings, honing the cylinder walls, polishing the crankshaft, repairing the cylinder heads, replacing one valve, one spark plug, and a thorough cleaning and reassembly of the engine. Any other repairs and/or replacement components were unnecessary.

The original repair estimate included sublet items of $519, labor of $2,150 and parts of $5,639. Our expert concluded that the parts that actually needed to be replaced would cost $555. The original repair estimate for the entire engine was overzealous and was not needed to bring the engine back to its pre-loss condition.

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