At this point, you could say this project is struggling. If you read Part 1, you know I blew up the motor in our ZR-1 project car during its first dynamometer test. Nothing like a jinx right out of the box, eh? This wasn't just any ordinary engine failure, either. When I blow motors, I make sure they're really expensive ones. A ZR-1's LT5 costs about 25 grand, new, and probably a third of that to overhaul.
But, we're comin' back strong. This month, our Purple Project C4 gets an engine overhaul. Then, we'll move on with a brake upgrade and some transmission work.
Getting Back On The Road
The intention of Part One's test was to verify our C4 project's advertised performance. Testing was on a Dynojet, inertia-type chassis dynamometer, which is about as abusive as accelerating on a slight downgrade. The engine failed at 6,400 rpm, well below its 7,072-rpm rev limit. Considering the test's lack of severity along with the performance, reliability, and durability standards to which General Motors stated the LT5 engine was built, it should not have failed.
Fortunately, when this happened back in '96, the car was still under warranty. Jim Van Dorn, whom I'd met via the "ZR1 Net" electronic mail list, owns Automasters, one of the few Corvette service shops in the western U.S. doing LT5 overhauls. A few Chevrolet dealers in southern California sublet Corvette warranty work to Automasters. Can you see where we're going, here?
One of those dealers, Mac McGruder Chevrolet in Palm Springs, was reasonably close to the dyno test venue, so I had the car flatbedded there. I never told them a magazine article was underway. To them, I was just another customer. The people at McGruder processed the warranty claim and the following week the car was moved to Automasters' shop in nearby Palm Desert for the overhaul. A week or so went by and Jim Van Dorn telephoned. "We got it out. Come down and we'll pull it apart."
I arrived the following Saturday to find Van Dorn and one of his service techs, Joe Delara, starting the tear down. By lunch, the top of the motor was spread out on the bench. It didn't look good at all. The upper structure of the right cylinder head was fractured in numerous locations around the #4 cylinder's intake valves. The primary intake was stuck in its guide and the intake camshaft and the #4 primary intake valve lifter, locks, retainer, and valve spring were destroyed. The #4 piston top was damaged. Sitting in a little cup on the bench was a pile of mangled debris that came out of the oil pan and the top of the head.
"Because we couldn't find all of what's left of the valve gear for number four," Jim said in his office after lunch, "it's hard to be sure what caused the failure. It's interesting that it blew up at such a low rpm. If it was a split lock or a retainer that broke, even down at 6,400, the results will be what you saw in your motor. You're lucky it didn't suck that intake and get torn up even more."
That afternoon, as I watched Automasters disassemble the bottom end, I was dismayed to find: 1) the rear main bearing was very worn, considering the 27,000 miles on the engine at the time of failure, and 2) the rubber sleeve that seals the oil pickup tube in the block had been improperly installed at the factory. It is possible the sleeve had not been sealing at high rpm when there was a significant pressure differential between the oil pump intake and the oil pan. That might have caused air to enter the oiling system through the improperly installed seal. Aerated oil could have caused the seriously worn bearings. Even if the engine hadn't blown up, maybe an overhaul was a good thing.
For a couple of reasons, it took a few months to get the engine back in the car. "Take all the time you need, guys," I told the folks at McGruder Chevy. I wanted no cut corners due to an impatient customer. Also, Chevrolet and I had an exchange of views on what parts were to be replaced during the overhaul. That took a week or so to resolve. Chevy felt it should only replace the #4 piston and liner. My view was, since the engine had near 30,000 miles on it, the right way to repair it and have it running at its optimum after the job was done was to replace all eight piston/liner sets. Eventually, Chevrolet agreed. In the end, the major parts replacements were all eight pistons and liners, a new right cylinder head, its intake camshaft and valve gear, a set of bearings, and an oil pump. By the middle of the winter, the car was back on the road. The people at McGruder Chevrolet and Automasters did a good job.