In today's musclecar market where six-digit selling prices are commonplace, a numbers-matching drivetrain can equate to thousands of dollars. Because of such value, hobbyists oftentimes go to great lengths to salvage a vehicle's original components. No one knows this better than Steve Schappaugh of Lincoln, Nebraska.
He brought an SD-455-powered '73 Trans Am to us for tuning and, like countless other vehicles we've tuned before, the process included removing its distributor for recalibration. Reinstallation didn't, however, play out as planned.
Unbeknownst to us, the intermediate shaft that drives the oil pump didn't engage the distributor tang, which caused a chain reaction that ultimately forced the distributor upward, pushing it partially out of the block upon initial start-up.
The Incident
A few anxious moments passed as we gathered our thoughts and extracted the distributor from the engine for closer inspection. That's when we discovered the unthinkable-the loop cast into the block that otherwise retains the intermediate shaft had broken away, seemingly ruining the original Super-Duty block.
Painstakingly, we recounted each step during the otherwise routine procedure, searching for any possible cause that could result in the situation at hand. No matter how many ways we worked it over in theory, the only way to determine the actual cause, inspect for collateral damage, and attempt to save the numbers-matching block, was to remove the engine from the vehicle for complete teardown.
We expected to find the broken portion of the block lying somewhere within the engine or oil pan during disassembly, and hoped that it could be reattached in some manner. There wasn't any trace of it, however, indicating that the block's damage occurred previously in the engine's life, and wasn't the result of an oversight on our part.
With a newfound sense of relief, we quickly determined that since the block wasn't able to retain the intermediate shaft, it fell over and came to rest on the crankshaft's rearmost counter-weight when we removed the distributor. But because it completely cleared the distributor gear during distributor reinstallation, there wasn't any indication that the shaft was misaligned. It was then immediately thrust upward by the crankshaft while cranking over.
The Repair
No matter the cause, the Super-Duty block clearly needed repair, and veteran machinist Chuck Willard, of Willard Auto Machine in Omaha, Nebraska, was enlisted for assessment. Willard determined that little damage had occurred this time, but he found unmistakable evidence of at least one previous engine failure that was catastrophic, and felt that it likely caused the loop's failure. He was confident that the block was easily repairable, though.
"That area of the block isn't under much stress, and the loop's only purpose is to maintain intermediate shaft alignment while the distributor is out," he says. "Since the broken portion of the block wasn't available, we could have attached a small piece of shaped iron restoring the loop's function, but I felt a step-bushing, restoring the actual shape, was best in this instance."
Willard placed the Super-Duty block onto the mill and spot-faced it internally, creating a depression for a bushing to sit in. He then enlarged the inside diameter of what remained of the loop, and machined from nodular iron a piece that closely resembled the loop's original dimensions.
When inserting the bushing into the block, Willard says his options for retention were limited. "Welding isn't a good choice when making repairs of this type. Not only is the area tough to access, the preheating that's required to properly weld cast iron can sometimes create other issues, so we machined the block and bushing for an interference fit, and added a coating of industrial-strength epoxy to ensure that the bushing stays in place. It should be a permanent fix."