By Joe Gresh
The stereotypical image of a Harley-Davidson motorcycle leaking oil has become a cultural icon. Dirty, unshaven and drunk riders astride seeping, smoking, rattling, home-built murdercycles were made popular in biker movies from the 1970’s and the image persists today.
How real is that image? I can’t say because my Buell was manufactured in 1995 but I hear new Harleys mostly don’t leak…much, if at all. My 30 year-old Buell leaked oil. Before we dive into the engine oil leak we have to get a few other leaks out of the way. .
You’ll remember all the trouble I had with the original Mikuni carburetor, the float needle leaked through various repair attempts and I thought I had the problem licked. The Buell ran good and got 50 miles to a gallon of gas. I took it out for a few rides and no carburetor leaks. Then I walked into the shed one day, straddled the Buell, hoisted it up straight and gas poured out the air cleaner. Like a lot of gas.
That was the final straw for the original Mikuni carburetor. I replaced the entire unit with a Chinese clone carb from Amazon and the bike has never run better and it doesn’t leak out of the carburetor or the air cleaner. Thanks, Global Trade!
But here’s my question: why did the old carburetor overflow at all? I had the fuel petcock off, where did the gas running out of the carb come from, you may well ask? Turns out the petcock was not completely shutting off as a steady drip of gasoline wormed its way past the 4-hole rubber seal in the petcock. Thus, the fuel shut-off was never really shut-off.
I took the petcock apart and flipped the 4-hole rubber seal around. That cured the fuel leaking to the carburetor in the off position but it created a bigger problem in that gas leaked out of the body of the petcock in all positions.
Finding a replacement rubber, 4-hole o-ring was uneventful as none were to be found. Instead, I bought a new petcock on Amazon and the new valve fixed the bypassing problem. But there was another gas leak.
The Buell has a roto-cast plastic gas tank under that pretty, race-bike inspired, but heavy, fiberglass bodywork. An aluminum gas cap flange screws onto the tank with a rubber gasket. This joint weeped gas when riding the bike. Not a lot, but annoying and enough to leave streaks of fuel mungus down the side of the gas tank.
Dismantling the flange, I discovered a check valve under the tank vent that needed to be removed before the flange would come off.
The valve must have something to do with emissions control as it only let air into the tank. I’m sure this added to the float needle issue as the tank was under slight pressure just sitting in the warm New Mexico sun.
Fixing the flange leak was as easy as cleaning off the gasket. Blasting it with a little Permatex high-tack and reassembling the mess. I omitted the check valve to equalize the pressure between the tank and the Earth’s atmosphere. Of course now when the bike falls over it will leak gas like every other old motorcycle I own.
With the gas leaks sorted I turned my attention to the oil leaks. The rear rocker cover was dribbling oil down the cylinder where turbulent air whisked it onto the battery and all points south. It wasn’t a huge leak but let’s just say the back of the Buell is not likely to rust anytime soon.
Luckily Erik built the S2 so that the rocker covers are removable without dropping the engine. I did have to cut an Allen wrench short to clear the frame tube, but it was an easy job all things considered.
With the new rocker cover gaskets, I took the bike out for a spin and the rear cylinder puked oil as badly as ever. I figured the oil must be leaking from under the rocker box. I’m nothing if not persistent so I took the rocker covers back off and then the rocker boxes. (This year Sportster engine has 3-piece rocker assemblies)
The paper gasket is under the rear rocker box was brittle and broken. I replaced both front and rear gaskets with a metal version of the paper gasket. I knew for sure I had the leak fixed.
On the test run the reassembled rear rocker leaked as bad as ever. Back to the shed and everything came apart again for the third time. I was pretty much out of ideas.
Studying the situation over the course of several days I observed the rear umbrella valve (a nickel-sized, round flapper-type deal in the rocker cover) was much harder than the front umbrella valve. Like hard plastic instead of soft rubber. I swapped both umbrella valves with new ones. Then assembled the mess thinking no way it could be those little valves.
I test rode the Buell 200 miles and no oil leaked out the rear cylinder. The battery area and aft sections were dry. Look, I’m not complaining. I can’t pin this on Harley’s image. 30-year old motorcycles are going to leak oil. Seals harden, gaskets dry up and split, 0-rings lose their O-ness and umbrella valves aren’t going to bounce. Besides, I enjoy working on the Buell. It’s a weird, wonderful machine that fits no known stereotype.
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