white smoke right cylinder after standing for weeks

DaveW · Feb 5, 2014

I started my 750 commando the other day after it had been standing for a number of weeks on the centre stand.
It smoked after starting on the right cylinder only, settling down but more smoke on revving.
Once it was hot, it was ok.
does anyone have any ideas what may be causing this?

PS The right cylinder does pop on tickover as well.

Many thanks, Dave

Brooking 850 · Feb 5, 2014

Badly tuned carb , also check for an airleak between the carb and the manifold and the manifold and the head on that side. (popping)Sounds like unburnt fuel.
have you checked the spark and ignition, compare the strangth of the spark on either side, swap plugs from one side to the other to discount dodgy plug
Regards mike

Rohan · Feb 5, 2014

Did the white smoke smell like petrol, or oil ?

Could also be where the oil drained down from your tank into the sump - sometimes only one cylinder will smoke.
Did you check the oil level in your oil tank before starting it, and after it had been run for a while
- when all the oil should have made its way into the oil tank.

dave M · Feb 5, 2014

It is more likely to be due to wet-sumping if the bike was parked for a period of time, they often smoke more on one side than the other until the oil is scavenged back into the tank, if it stopped smoking after a few minutes then you shouldn't worry about it.

pierodn · Feb 6, 2014

Me too.
The right manifold was broken.
Ciao.
Piero

B+Bogus · Feb 6, 2014

My Combat 750 does this, but my 850 doesn't. They both wet-sump from standing.
Previous threads have discussed drilling holes in the crankcase web low down in the timing case...
Presumably oil fills the timing chest with standing, and then dumps it through the RH main bearing into the RH pot when it's fired up.
Late 750 cases seem to need quite a few bits of metal removed to solve a number of issues, but this is one I didn't do on mine.
It's almost worth pulling it down to get it sorted.
Almost :roll:

Has anyone experienced this issue with an 850?

rvich · Feb 6, 2014

B+Bogus said:
My Combat 750 does this, but my 850 doesn't. They both wet-sump from standing.
Previous threads have discussed drilling holes in the crankcase web low down in the timing case...
Presumably oil fills the timing chest with standing, and then dumps it through the RH main bearing into the RH pot when it's fired up.
Late 750 cases seem to need quite a few bits of metal removed to solve a number of issues, but this is one I didn't do on mine.
It's almost worth pulling it down to get it sorted.
Almost :roll:

Has anyone experienced this issue with an 850?

I am a pretty diligent reader, but I missed this one. So forgive me for asking the obvious. The right side main bearing is at the crank. How does that translate to oil in the pot?

Thanks
Russ

vintner · Feb 7, 2014

Dave,
Had this happen on my Mk3 but on LH cylinder. Once warm nothing to note so for a long time I just put it down to general wear and tear. Eventaully I overhauled the top end and found a broken ring on the LH piston, the ring was in 5 pieces and part of it had actaully overlapped i.e. one piece of ring above the other. Obviuosly the ring groove had worn over time to allow this to happen. The standard size bores was in good condition so I gave them a light hone and fitted JP pistons (produced here in Australia). These were 1 oz. heavier than standard and I wish I'd never used them but that's another story. Hopefully you smoking is caused by something much simpler to rectify.
Cheers, Simon

B+Bogus · Feb 7, 2014

rvich said:
B+Bogus said:

My Combat 750 does this, but my 850 doesn't. They both wet-sump from standing.
Previous threads have discussed drilling holes in the crankcase web low down in the timing case...
Presumably oil fills the timing chest with standing, and then dumps it through the RH main bearing into the RH pot when it's fired up.
Late 750 cases seem to need quite a few bits of metal removed to solve a number of issues, but this is one I didn't do on mine.
It's almost worth pulling it down to get it sorted.
Almost :roll:

Has anyone experienced this issue with an 850?

Click to expand...

I am a pretty diligent reader, but I missed this one. So forgive me for asking the obvious. The right side main bearing is at the crank. How does that translate to oil in the pot?

Thanks
Russ

Russ.

Please note I caveat my comments with 'presumed'!
My hypothesis is oil gets from the timing chest past the main bearing and is then flung into the cylinder off the crank web.
That's the only reason I can think for folks to drill relief holes low down in the timing chest... :?:

rvich · Feb 7, 2014

Like Comnoz says we need Scotty's recipe for clear aluminium!

B+Bogus · Feb 8, 2014

rvich said:
Like Comnoz says we need Scotty's recipe for clear aluminium!

:mrgreen:

DaveW · Feb 10, 2014

Thanks to all of you who replied with some great answers.

Once I can get in the garage I'll take a look.

DaveW · Apr 2, 2017

More on this guys.
With the sump oil drained back into the tank and the bike started from cold, after a few seconds it smokes from the right exhaust. I can't tell if it's blue or white smoke, smells oily so let's say, blue.
Also I can see oil coming out the exhaust pipe nut at the cylinder after a run. It's been dripping down onto the rhs crank casing.

Any ideas what the problem might be? I've done the valve seals btw.

Dave

o0norton0o · Apr 2, 2017

One of your wristpin circlips popped out and has scored the crap out of the cylinder wall. Now you have some ridges in one of your jugs which the rings glide right over allowing oil to enter your combustion chamber....

At least 20 years ago right after a rebuild, I was doing about 60mph and I got a pop and puff of blue smoke out of one pipe. I shut the bike off and got my van to haul the bike home. I pulled the head and jugs and sure enough, a circlip had popped loose and scored the cylinder wall. The circlips were the "bent wire" type, which look like cheap crap if you ask me. I replaced them on the rebuild with circlips cut from flat steel and had no trouble with them since...

DaveW · Apr 2, 2017

I'm wondering if these are two separate problems, one being the push rod tunnel leaking and looking as though it's coming from the exhaust nut. As for the smoking exhaust on startup, could this be leaking valve guides? The problem where the outside of the guide leaks oil due to poor drillings? The compression tests come out the same on both sides by the way.

Just a thought.

o0norton0o · Apr 2, 2017

What does the spark plug look like on the smoking cylinder side? Perhaps the pop is a misfire that pumps unburnt fuel into the hot exhaust pipe then ignites it on the next power stroke...

Regardless of the cause, it seems you have 2 choices.

1) Pull the head off and take a look. IF it is the pushrod tunnel leaking into the head, you'll see it. IF you roll the engine over so the pistons go down, you'll see if it's a misplaced circlip without pulling the barrels off. It sucks to go backwards and disassemble,... but that's the only way to fix stuff. Go backwards far enough to correct what is broken, then rebuild.

2) Ride it as it is...

DaveW · Apr 3, 2017

Many thanks - option2 for now.
Perhaps break it down in the Autumn?

white smoke right cylinder after standing for weeks

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