Air leaking around spark plug?

[Hammer65]

Hey guys... Was firing up my bike earlier today and I looked down at the left side spark plug and noticed that when i was starting it, I saw bubbles coming from some oil that had gathered around the base of the spark plug (also where the hell is that oil coming from!)  I figure that's not normal...I'll try new spark plugs but I'm worried I may need new cylinders?

It's a 79 by the way.

[Barry]

It's not that unusual to have some oil in the cylinder possibly it's from the engine breather which seems to favour the left side. I wouldn't worry about the oil unless it's enough to foul the plug.  

It is unusual for a spark plug to leak even if slightly under torqued.  A new plug or crush washer should cure it.  

[Burt]

As Barry said.  Is it possible that the heat in the cylinder is boiling the pooled oil?  

[montmil]

Do you most often park your bike on the sidestand? What can happen is engine oil that would normally drain down the pushrod tubes and back into the sump is now collecting in the left side cylinder head. Some of that oil may pass into the combustion chamber via worn valve guides. An overfilled crankcase could also be a contributing factor. Many Airhead owners keep the oil level at a 'half full' indication on the dip stick. And parking the bike on the center stand is part of the BMW Airhead drill.

The troublesome "Jed Clampitt" oil bubbling up around the base of the spark plug could be indicative of either an under-torqued spark plug with a worn out sealing washer or even worse, stripped spark plug threads in the cylinder head. No real way for oil to accumulate in that area unless there is a mechanical issue.

Have you done a compression check on the engine? Cold engine and carb butterflies held full open by shimming the butterfly shaft arms.

Share what you find.

[Luca]

Leaking combustion gasses can create a nasty, oily looking goo.  Combustion gasses, unburnt fuel, and oil vapor in the cylinder are getting pushed past the spark plug gasket.  Normally this crap gets burnt off, but that doesn't happen when it gets outside of the cylinder/exhaust.  The leak that's causing the bubbling is probably also the source of the liquid.

Throw a new plug in there and be sure to clean around the plug hole when you do.  It's probably just your plug gasket; they can leak when the plug is tight if it has been reused (usually many times).

Don't fret unless the leak comes back.  Don't stress about the plug threads either.  If they were truly bad you probably would have seen the plug bouncing around as the engine was running.

[Hammer65]

I'll replace plugs.  To answer some of the questions, the bike often lives on a hill (vandals don't like climbing hills for some reason) and is parked on the sidestand (the center stand obviously wont work on this hill, its San Francisco!).  I still need to replace a few seals on the bike but I wanted to make sure this wasn't a huge issue.  The threads on the plugs seem cool and not stripped out.  I'll report back after further inspection tomorrow.

[montmil]

The up-side of living in hilly SanFran is that there's always a hill nearby to bump start an Airhead with a low battery. I've never truly mastered the Mike "The Bike" Hailwood run n' bump.

[Tony Smith]

The up-side of living in hilly SanFran is that there's always a hill nearby to bump start an Airhead with a low battery. I've never truly mastered the Mike "The Bike" Hailwood run n' bump.

I try not to bump-start airheads unless I absolutely cannot avoid it. My R100, a friend's R60 and wife's R65/80 all managed to spit the final drive flange off the gearbox output shaft whilst being bump started.

When you think about it, it is logical, lot's of torque, in the wrong direction, upsets the morse taper (how I hate BMW for inflicting that on us) and unwinds the tension nut. In the case of my R100 and the wife's R65/80 a check with Prussian blue indicated that after a clean up everything could be put back together with no "time bombs", the R60 needed quite a few hours of hand lapping the flange to the taper before Prussian blue indicated an acceptable contact area - looking back I wonder now if it was all that flash from the factory, we will never know now as the bike, and sadly its owner, are long gone.
 

[Luca]

I've never truly mastered the Mike "The Bike" Hailwood run n' bump.

neither have I, but I once pop started a nighthawk 650 whilst running alongside it.  I did get it running, but when the engine woke up the ibke nearly took off into the side of my roommate's Jetta.  I've become a fan of jump-starting

[Tony Smith]

I've never truly mastered the Mike "The Bike" Hailwood run n' bump.

Clearly never owned worn out English bikes or other questionable stuff. I was a master of bump starting the accursed Velocette I was once afflicted with - bumping it was a lot safer than kicking the thing when it was in "one of its moods", mind you I was  more than 40 years younger than I am now then and a lot fitter.

There was only one time I was ever proud of the horrid Velo (which was a Venom made as near a Thruxton as my wallet, my skill and my imagination would allow at the time) was when I participated in some sort of "lifestyle" display at the local showgrounds.

A ghastly long streak of misery with attitude came along and loudly announced that all British Bike owners were full of the proverbial and that he owned a Yamaha XT500 and HE could boot that thing into life anytime with none of the namby-pamby nonsense of finding compression, setting throttle or similar nonsense.

I invited him to give the evil Velo a prod in the guts.

Being half-smart he enquired as to technique, I told him to jiggle the little brass thingy on the side of the carb until fuel flowed over his fingers, then move that lever on the left all the way forward, give it about 75% throttle and go your hardest.

I was an evil sadistic bastard when I was young, I'd just set him up with a flooded Amal, full ignition advance and lots of throttle.

Well he leapt on that kick start lever from a great height with a stiffened leg, the evil Velo did about 3/4 of a rotation and backfired, just as I knew it would. Flame belched from the carb mouth and from the exhaust in equal measure and the young lad sailed through the air with the greatest of ease landing in a heap about 4' in front of the bike.

He limped quietly away, attended by his friends, with what I hoped was a new found respect for old British bikes.......

I gave the evil Velo a pat on the tank and said a silent "thanks old girl".


I have only been badly "bitten" once and that was by an innocuous, harmless Honda XL185 trail bike. I was only wearing sandals so the imprint of my own big toe-nail in my shin was silent evidence of how over-extended my ankle had been.

I limped for 6 months.

[skippyc]

Shifting to a Pazon ignition which kicks over at 1 or 2 degrees advance was the best thing i did to my BSA B50. Before it was kicker beware.

[georgesgiralt]

Tony,
I think the BMW design is there to save life, sometimes...
Think what would happen if the engine and/or gearbox seized at highway speed and you do not had a tapper at the gearbox output coupling... The rear wheel will seize for good.
With this "wonderful" design, the flange will slip and the rear wheel will continue to turn maybe saving you from a huge fall.. Maybe.
I've seen gearboxes seized good and the output shaft design saved the day. But not the gearbox.

[Hammer65]

Swapping in new plugs seemed to sort it out.  I definately need to replace some of the gaskets on the engine but for now it's not blowing oil bubbles!