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Old 11-12-2009, 11:04 AM   #1
More_Miles OP
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Airhead R100 horrible smoke at cold start

Inmates! Opinions solicited!

Specs:
1983 R100RT
Stored overnight in the garage
On centre stand
Fuel valves off

Symptom: Left (when astride the bike) cylinder burns clean at start up but smokes FURIOUSLY after about 1-2 seconds of running. Right cylinder burns (relatively) clean upon start up.

If I was storing it over night on the side stand, I could buy the "oil lays in that cylinder" song. But I'm not, and it's sitting upright all night. It DOES clear, and if started up later on (i.e. warm start) no problem. This just started a few days ago. It also seems to be using a bit of oil. I know, it's a boxer, live with it...

My thoughts, and feel free to tell me what an idiot I am for this line of reasoning:

Over night, everything is cold, and a valve guide or valve stem contracts. This opens up a clearance into the cylinder. At start up, things are relatively dry and away it goes. Oil gets pumped into the top end (do boxers actually have "TOP" ends?) and out this opening into the combustion chamber. Smoke like hell... Warms up, things expand, seals back up and Bob's your uncle. Also, cold is in the -5 degree C range...

Tonight when I get home, I'm going to pull the plugs to take a look. I also should get a compression tester sometime. I'm wondering if at 107000 km with an unknown engine I'm due for a top end rebuild.
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Old 11-12-2009, 11:31 AM   #2
Pigford
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If you're lucky, it may only be the valve guide seals

Or at worse, the guides!
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Old 11-12-2009, 12:22 PM   #3
SOLO LOBO
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Quote:
Originally Posted by Pigford
If you're lucky, it may only be the valve guide seals

Or at worse, the guides!
No valve guide seals on boxers....
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Quote:
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your bike is suitably dirty. Well done.
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Old 11-12-2009, 12:49 PM   #4
Mista Vern
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This sounds too simple, but in many cases where there is a mix of cool weather and humidity and the bike has not been ridden enough to get all the moisture out of the exhaust system, it will blow smoke-like vapor like a sumbich until all the moisture in the mufflers is gone.

Odd thought, but could well be the case, especialy if this seems to be a brand new problem.
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Old 11-12-2009, 01:04 PM   #5
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That's a thought!

See if you can tell whether it is smoke, or steam. Though why one side would have more condensate than the other....

If it is oil, my guess is that it continues to burn the same amount on the left side, but when it is hot, the oil is burned up more, leaving less to "see"....

Your idea of pulling the plugs should give you additional clues/information..

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Old 11-12-2009, 01:07 PM   #6
outfit
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You only put oil in upto the halfway mark between bottom & top mark's on dip stick? Otherwise it'll just burn off any oil above.

Karl.
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Old 11-12-2009, 01:46 PM   #7
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Quote:
Originally Posted by outfit
You only put oil in upto the halfway mark between bottom & top mark's on dip stick? Otherwise it'll just burn off any oil above.

Karl.
Really? So I shouldn't have bothered just topping my oil up?
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Old 11-12-2009, 02:00 PM   #8
Mista Vern
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Quote:
Originally Posted by sharkojoints
Really? So I shouldn't have bothered just topping my oil up?
Doesn't hurt anything, but it will prolly gravitate down to where it wants to be below the full mark. Airheads are funny that way.
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Old 11-12-2009, 02:12 PM   #9
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Eh? Results of plug pull

Gentlemen and ladies,

Pictures to follow as soon as I can find my %!@#& cable for my camera... Card reader is still at work. Prior planning prevents piss poor performance I guess.

Verbal (textual?) description:

Left plug was somewhat brown, darker shade than lighter. I wouldn't consider it too bad but my prior experience has been with a 2 stroke that was running rich on the oil pump so I may be biased.

Right plug was lighter, had a grey/white patch on the outside of the bend of the electrode. Personally I would think it's running too lean on that side, but again my previous experience is probably biasing me.

So I set up the camera on the tripod, and started recording. Its always easier to SHOW what is happening than to describe it. The bike had sat for 22 hours from when I got home last night until just now when I tried to demo it. Of course, being a bike with "personality and character" it didn't do anything untoward....

Data point: It's been sitting in the unheated garage all day. Currently it's in the 10 degree C range, and considerably warmer than when it USUALLY manifests this behaviour. So, we're back to condensation... Possibly.

Think I might just live with the "personality" and take my ribbing when I smog out the parking lot in the spring and fall... If I can catch it tomorrow morning I'll post the results.

Just keep telling myself that personality and character is good in a bike. Otherwise it's a Tupperware clad two wheeled refrigerator...
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Old 11-12-2009, 02:15 PM   #10
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Quote:
Originally Posted by outfit
You only put oil in upto the halfway mark between bottom & top mark's on dip stick? Otherwise it'll just burn off any oil above.

Karl.
I should have mentioned that the oil level is just above the low marker on the dipstick and due for a change. It's getting that and a filter tomorrow. Almost time to put it up.
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Old 11-12-2009, 03:02 PM   #11
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Just thinking out loud here...

You have a '83 which has the "new" style airbox, right?
The breather might be different, but I'm wondering about the crankcase check valve and breather hose(s).

The older style motors (with the round air filter) used a fiber washer and coil spring style check valve for the breather. These could get tired and allow excess crankcase vapor to be vented thru the breather hose(s) and into the airbox. This check valve was updated, at some point, to a reed valve which works much better.

I also think the standard models used one breather hose which was routed into only one intake tube, while the S and RS models had a "T" and twin hoses - one into each intake tube.

This might explain why only one side smokes.

In any event, the check valve is located under the starter cover and is fairly easy to access.

_jay
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Old 11-12-2009, 04:04 PM   #12
Mista Vern
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Quote:
Originally Posted by More_Miles
Gentlemen and ladies,


Left plug was somewhat brown, darker shade than lighter. I wouldn't consider it too bad but my prior experience has been with a 2 stroke that was running rich on the oil pump so I may be biased.

Right plug was lighter, had a grey/white patch on the outside of the bend of the electrode. Personally I would think it's running too lean on that side, but again my previous experience is probably biasing me.

...
That sounds fairly normal - slight discoloration could be anything from synching to plug gap, carbs, etc.

I really think you need to take the bike for a longish (20 mile) ride and blow the snot out of it, put it on the center stand and see if the problem repeats. If it is as bad as you say the area should reek of oil; thus I am still betting on condensation. It takes a long time to get everything heated up enough to completly get the moisture out of the muflers (actually, you can't ever get them totally dry, but you get the idea).
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Old 11-12-2009, 04:55 PM   #13
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So it looks like no one asked...

What color is your smoke?

Also, FWIW, the stock BMW vavle guides on the early 80's bikes are soft garbage... my exhaust guides were totally played out at 20,000 miles!
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Quote:
Originally Posted by Stagehand
your bike is suitably dirty. Well done.
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Old 11-12-2009, 04:56 PM   #14
SOLO LOBO
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Quote:
Originally Posted by word1
I also think the standard models used one breather hose which was routed into only one intake tube, while the S and RS models had a "T" and twin hoses - one into each intake tube.
My '81 G/S has twin hoses...
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Quote:
Originally Posted by Stagehand
your bike is suitably dirty. Well done.
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Old 11-12-2009, 05:21 PM   #15
More_Miles OP
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Quote:
Originally Posted by word1
Just thinking out loud here...
You have a '83 which has the "new" style airbox, right?
Yes, the new style air box. I'm going to dig in and look at it shortly.

Quote:
Originally Posted by Mista Vern
I really think you need to take the bike for a longish (20 mile) ride and blow the snot out of it, put it on the center stand and see if the problem repeats. If it is as bad as you say the area should reek of oil; thus I am still betting on condensation.
Well, I ran the snot out of it yesterday (4 hours plus, all at 110 km/h and higher) then let it sit while had dinner with friends. About 5 hours that. Heavy frost on the bike, cranked it up and drove everyone inside... But when warmish, no problems. More on smell and colour momentarily...

Quote:
Originally Posted by SOLO LOBO
So it looks like no one asked...

What color is your smoke?

Also, FWIW, the stock BMW vavle guides on the early 80's bikes are soft garbage... my exhaust guides were totally played out at 20,000 miles!
Smoke is whiteish grey. The more I think of it, it doesn't LOOK or SMELL all that much like burning oil. So I'm leaning to condensation. One of the reasons I am worrying about this is that I know that the guides are shite on this era engine, and it's a mystery to me maintenance wise. But why does it always come from the left cylinder? Enricher maladjustment? Worn or clogged jets?

I dropped the bowl's on the carbs tonight just to see if there was anything settled in there. There wasn't actually. I'm really leaning more towards "it's the way the bike acts when it has better sense than the rider does about cold" kind of answer.
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