Dabney's Smoking Engine
The other day our friend the Doctor was taking his usual stroll down the street and passed Dabney's cavernous garage. From under the partially-open door of one of the bays was emanating a thick, blue cloud of smoke that simply couldn't go unnoticed. He stepped in and found Dabney hunched over his engine test stand...
Just to be annoying, the Doc started coughing and hacking loudly. "Hey, Dabney, what's the matter with this engine?" asked the Doctor
After shutting off the engine and disconnecting the fuel pump, Dabney looked up at the Doctor, saying "I just finished rebuilding this old Hemi engine from that 1955 Chrysler Imperial over there in the corner. The car only has 40,000 original miles, but the old Hemi's valves were eaten away. I took the whole engine down and installed rings, bearings and new valves."
"From the look of the amount of smoke coming out, the first thing I'd ask is whether you remembered to install the valve seals," replied the Doctor.
"I sure did, Doc," said Dabney, "that's the first thing I thought about too and I went back to my digital photos to make sure I did. This photo clearly shows the new valve seals in place."
The Doctor looked and, sure enough, the photo didn't lie. The valve seals had been installed. "Hmmm," he said, "there's always the chance the new rings haven't seated themselves properly, but that's a lot of smoke. Why not run the engine for about 15 minutes and see if the smoke gradually lessens?"
Dabney agreed and the two set the engine stand for another run. The engine fired right up and, after they ran it for 15 minutes or so, continued to smoke badly. In fact, they agreed that it was getting worse.
More fake coughing and hacking and the Doc said, "Time to take it back apart.
"Yeah, I suppose that's the case," replied Dabney. "Let's take off the heads and see if there's oil leakage around the valve guides.
They did, and there wasn't. With that, they had to go through the effort of removing the oil pan and pump and then removing the pistons. They did all this carefully because all the parts were new and they didn't want to unnecessarily replace items that could be reassembled later. They observed the cylinder bores and noted that none looked scratched or oil-soaked.
They removed the first rod's end cap and tapped off the bearing insert. It was clean, bright and showed no sign of wear, as expected with a newly-assembled engine, but still a relief to both of them.
"Let's remove one piston and see what we see," said Dabney, "so maybe we won't have to remove any more. I think it will tell us what might be the problem."
"Okay, but it only takes one piston to fail for an engine to smoke," replied the Doctor.
They removed the piston and the rings looked clean and fine. There was no obvious problem with that one, so they carefully removed all the others on that side of the engine block, being extra cautious so as not to scratch the crankshaft journals with the rod studs. The three other pistons and rings looked fine.
"Well, it's on to the other side," said Dabney. The Doctor agreed and they turned the engine block over to the other side and proceeded to remove the pistons.
"Well looky here," said the Doctor. As they removed a piston from the other cylinder bank the Doctor immediately noticed that the ring gaps were lined up with one another. "What's this, Dabney," he said, "you certainly know better than that."
"You're right, Doc, I do. I can't believe I didn't space the ring gaps around the piston," he said, "and I hope this is the only one."
It wasn't. All four pistons on that side had in-line ring gaps. Dabney was embarrassed and the Doctor was incredulous. "What were you thinking when you put these rings on and installed these four pistons?"
"I can't explain it, Doc, but I must have been concentrating on something else," said Dabney.
"Well, this explains our oil burning pretty well," said the Doctor, "and don't feel so bad. I don't know anyone who hasn't done this at least once, including me."
Dabney did feel better, although he'd always wonder if the Doctor was just trying to make him feel less embarrassed.