Dabney's Mysterious Oil Leak
It was a day like most days around Dabney's garage. He was leaning over the engine of his fully-restored 1954 Jaguar XK120 Fixed Head Coupe and mumbling to himself as the Doctor tapped him on the shoulder.
"Hey Dabney," said Dr. Crankshaft, as he walked into Dabney's garage. "When
did you get this spiffy XK120?"
"Oh, I got it a couple weeks ago, Doc. I've always loved the looks of these coupes. They look very much like a 1930s Bugatti. Unfortunately they don't have a lot of head room inside and outward visibility is downright dangerous, but it sure looks great. I have a problem with it that's a whole lot worse than comfort, though."
"What's that," asked the Doctor. "It stands nice and straight and everything looks in order. That interior wood trim looks better than my library!"
"I might have bought a pig-in-a-poke with this one, Doc," replied Dabney. "The engine runs fine but once it warms up it starts leaking oil out of both the front and rear crankshaft ends. I could live with the front leak but it pours out of the rear and sooner or later the clutch is going to get saturated. Oddly enough, it doesn't leak when it's cold."
"Very Interesting!" said the Doctor, mimicking a character from a '60 TV comedy show. "Now that is a puzzler. Are you running the correct weight oil? I happen to know these old Jags need 30-weight and they all leaked a little."
"I just changed the oil to straight 30, and thought I'd take it for a spin to warm it up. Wanna go along?" said Dabney.
"Let's do it," replied the Doctor, and off they went with Dabney at the wheel.
"Man, this thing is a brute to drive," said Dabney. "The steering shaft is nearly 6 feet long, and I've seen large earth movers that are easier to turn than this."
"That's no surprise, Dab," said the Doctor, "These things were considered great sports cars back at the beginning of the 1950s, but bear in mind what they were compared against. For its time the XK120 was a pretty nimble car, but it still had a pitifully small master brake cylinder, manual linkage clutch and that big, heavy XK engine out there in front. It was work to drive all right, but it was the only thing on the road that could do 120 mph, hence its name."
"I can't imagine driving this car 120 mph. You'd be lucky to come out alive. You sure know a lot of history about cars, Doc." said Dabney, "I hope you can figure out what's going wrong with the engine, because there's a thin trail of oil following us down the road. Let's go back to the garage and put it on the lift."
That they did, and when they looked up at the bottom of the engine they could clearly see oil streaming out of the rear and front main bearing areas. It wouldn't drain with the engine off, but starting it up caused the oil to flow.
"This isn't good, Dabney old buddy," said the Doctor.
"I was afraid you'd say that," said Dabney. "I get the feeling we're going to have to take this engine out and see if the seals are missing."
"Not so fast," said the Doctor. "First of all, these engines didn't have a rear oil seal. They had an oil "slinger" that sits just around the crankshaft a few thousandths away. They sort of "screw" the oil back into the sump as the shaft turns. It's possible the slinger is in backwards, and I think we can see if that's the case by removing the oil pan and the rear bearing cap. Let's take her apart."
It was a fairly simple operation to remove the 20, or so, screws holding the oil pan in, plus the few steering linkages in the way. Once the pan was off they put a temporary jack (made out of a 2x4) under the crankshaft and removed the rear bearing cap. To their dismay the oil slinger was there and correctly fitted. In fact, the bearing cap and engine block had been machined with an oil seal groove (a popular fix done back in those days when rebuilding engines) and a rope seal installed.
"Now we have a situation," mused Dr. Crankshaft. "We have a good seal at the back and still leak from there and the front seal. Better get a big pry bar."
Dabney looked at Doc with a funny look. "What're you going to pry?" He was starting to get a bad feeling about this.
"Well, my boy, I think we just might have us a thrust problem and I need the pry bar to prove it," said the Doctor a little irritated with Dabney's lack of trust.
"I'm not sure what you're getting at, Doc," said Dabney. "What thrust are you talking about/"
"The crankshaft thrust, dagnabbit!" said Dr. Crankshaft starting to show his irritation. "We need to see how much the shaft moves forward and backward. There's a specification for every engine on how many thousandths the crankshaft should slide in that direction when cold. The spec allows for linear expansion of the crankshaft so that it doesn't push against the block ends when it gets hot. I suspect that's what our problem is. I bet there's no thrust and the block is expanding at the ends, allowing the oil to gush out. That would explain all the symptoms."
True to his prediction they found no crankshaft end thrust at all. "Where's your service manual for this thing? Doc asked.
"Here," said Dabney, handing the manual to the Doctor.
Consulting the Jaguar service manual they found it should have been 8 to 12 thousanths. "Well," said the Doctor, "Looks like the engine's going to have to come out and get torn apart."
"You know, Doc, I don't think I'm going to do that," replied Dabney looking like he'd just had a revelation. "After driving the car and realizing that it's uncomfortable, relatively dangerous to drive — marginal brakes, lousy visibility and poor steering response — I think it's not worth the effort. It's a work of art, though, both in the exterior styling and interior trim.
"So what do you want to do?" asked a puzzled Dr. Crankshaft.
"Well, you know I have that big gaming room up at the Big House (as Dabney referred to the Dufus estate) and it's already decorated with automobilia. I'm going to move the car into the game room and use it as a conversation piece. It is a rolling piece of art, after all," replied Dabney.
"Whatever, Dabney." mumbled the Doctor as he walked out of the garage shaking his head.