white smoke and dripping from crankcase breather tube

When I park my bike at idle after a five-mile ride, there is a somewhat
wispy white smoke coming slowly from the breather tube. Also there is
something (presumedly water) dripping from the tube. I haven't noticed
such smoke or dripping until this year, after not running the bike for
13 years. The exhaust is utterly clear and colorless.

I wonder whether the smoke and dripping indicate a ring problem ... I
wonder how serious it is and whether I should plan on a ring job this
winter or maybe sooner.

CJ360T (1976, SOHC, inline twin, CV carbs, air cooled, 21K miles)

 

I'd better mention that I replaced the old tube with tubing from the
auto-parts store before I noticed the problem, although I don't see why
that would matter.

 

If you remove the breather cover (the cap bolted to the valve cover)
isn't there a wire mesh pad underneath the cover? These pads are part
of an oil
de-mister system found on most 4-stroke motorbikes. The hot oil vapors
hit the cooler mesh pad and condense most of the vapor which fall back
down to the crankcase as oil droplets. The hottest vapors won't
condense, they will go wherever the hose connects to and condense
there.

It's possible that you're seeing some water vapor, since water vapor
would be the visible sign of steam condensing. Your oil has probably
been heated to over 300 degrees by a reasonably long ride and you do
want any water to boil out of the oil.

Refinery engineers talk about "acid dew points". They try to keep their
steel pipes warmer than the acid dew point, which is where sulfur and
water combine to make sulfuric acid that eats away at steel parts.

Motorcycle oil and gasoline has *some* traces of sulfur in it, so you
want the water to boil out of the oil to avoid acid build up...

When you first turn a hot engine off, most of the oil that was up in
the top end of the engine drains down but whatever oil remains up there
in the head is going to be heated to around 350 degrees. That oil
smokes as it gets cooked by the residual heat of the head.

Have you checked the compression? I wouldn't bother to re-ring an
engine that had at least 135 to 140 pounds of cranking pressure. An
engine would have to go through a quart of oil every 300 miles and
smoke a lot before I would go into it.

 

Did the tube you replaced have a hump in it where it connects to the
engine? Some vent tubes curve up a couple inches then curve down to the
airbox, I think this design catches the condensation and keeps it from
running out the tube.

Like Krusty Kritter said, I wouldn't think about an overhaul unless it
was smoking real bad out the exhaust, or had low compression.

 

Okay, so maybe the engine was at a temperature where the vapor was
partly condensed and misty and opaque. Also maybe there was water in
the oil due to making several short trips. I suppose that if I were to
continue with a load on the engine, the top end including the breather
tube itself would heat up to where the vapor would not recondense and
there would be no liquid or mist.

Might one reasonably expect this behavior even on a new engine?

 

Well, apparently your breather system is open to the atmosphere, just
like the exhaust pipe. But, even though moisture will condense in your
exhaust pipe, the pipe heats up very quickly and evaporates it. It just
takes longer for the engine to heat up and evaporate any water out of
the oil. On modern bikes with breather systems that go into the air box
you would never see any vapor because it would get sucked into the
carburetor...

 

Yes, it's just a ca. 20 inch rubber hose that goes from a nipple on top
of the engine, goes down behind the engine, and is open at the bottom.
When the bike is moving, the wind at the mouth of the tube pulls the
vapors out. I believe automobile crankcases were vented that way in the
days before PCV.

Yes, the dripping reminds me of water dripping from the exhaust pipe of
a car idling in cold weather. The breather tube doesn't drip as much,
of course.

I suppose there is more blowby now that the bike has 21K miles. I know
I had a compression tester somewhere ...

 

The old tube seems not to have a hump big enough to cause the condensate
to fall back into the crankcase.

 

The old CJ vented its rocker breather to atmosphere. What you're seeing
is condensate. Not a problem.

If you see oil mist or vapour coming out, then it means the valve guides
are shot.

 

I just found my compression tester and measured a pressure close to 150
on each side using the kick starter when the engine is warm. Not bad
for such a neglected old machine. So I can stop wondering/worrying
about my rings and valves.

 

Here you go:

http://cgi.ebay.com/ebaymotors/ws/e...d=1,1&item=4566867159&sspagename=STRK:MEWA:IT
http://cgi.ebay.com/ebaymotors/ws/e...d=1,1&item=4566867831&sspagename=STRK:MEWA:IT

Just a quick plane trip to Chicago---take your wife---then a nice ride
back ...

These aren't mine though ...

 

Also no 6th gear. I don't miss the front disk brake or the starter, but
a 6th gear would be easier on the engine and the gas tank at 65 mph.