Design News for Mechanical and Design Engineers

Initially all right, after only a few hundred miles of operation, the rebuilt engine began making “rattling and growling” noises that grew louder with each mile until the owner ordered it stopped for repairs. Since the engine was still under warranty, the owner’s mechanic contacted the parts’ store for instructions to return the engine for exchange with another engine.

The store manager, without examining the engine or components, refused to honor the warranty, saying the automatic transmission torque convertor was improperly installed and excessive end thrust damaged the engine bearings. The fuming van owner’s lawyer retained me to determine the cause of the engine failure.

At my request, the engine was removed and placed on an engine stand for disassembly. The mechanic’s shop was a clean, well-equipped operation and the mechanic was NIASE-certified and enjoyed a busy trade with his many apparently satisfied local customers.

With the engine oil drained and the pan removed, I began a visual inspection of the engine. I saw immediately the re-manufacturer had mixed the main bearing caps during assembly, as two of the caps did not match the other caps in appearance or in positional numbering. I also observed the presence of severe gouges and scars at the front of the engine block from what may have been a catastrophic timing chain failure and very likely the reason the engine was rebuilt. The number one main bearing cap did not have matching scars and I suspected it was replaced due to severe damage. Inspection showed all of the eight connecting rods and their rod caps seemed to be in correct order and position.

As I lined up all of the rod and main bearing caps and inserts for an overall view, I noticed the rod bearing inserts as well as the main bearing inserts appeared to be scuffed in a curious pattern. The scuff marks described the circumferences of circles whose centers were off-axis from the crankshaft centerline. To assure correct bearing inserts were used, I measured the crankshaft main and rod journal diameters. I checked the part number of each main bearing upper and lower shell against the manufacturer’s part number for that crank journal undersize. Both main and rod bearings were correct.

While checking the bearing inserts for part number and size, I saw the number five (rearmost) main bearing upper and lower inserts had severely scored and worn the thrust surfaces on the left side. I pushed the crankshaft back and forth, using a dial indicator to measure endplay. I measured 0.080-inch axial movement of the crankshaft, well past the limit of .002- to .006-inch endplay for this engine. All these signs pointed to the crankshaft being off-axis causing the crankshaft thrust flange to gouge one side of the bearing thrust face.

To determine if transmission installation was a factor, I had the torque convertor inspected by its supplier. Their technician said the convertor and its drive lugs were in perfect working order and it appeared to have been correctly installed.

Typically, when main caps are installed, it is necessary to line bore the crankshaft journals. Because none of the five caps or the engine block journals showed signs of fresh machining on any of the curved surfaces, I suspected line boring was not done.

My report noted the evidence of improper engine assembly and I concluded the rattling and growling were caused by excessive endplay of the off-axis crankshaft. The engine supplier not only paid for an engine replacement, but also part of the mechanic’s labor.