Topic: Sudden white smoke from cam cover breather and exhaust

[Jonm99]

 Hi guys,

Was doing a little work on the bike (cb750 k7), new plugs and new airbox filter. Went out for a ride and noticed excessive white smoke from the cam cover breather and exhaust, simultaneously. Bike starts easy, idles fine, and rides well (although it was a very short ride, came back as soon as I saw the smoke). Oil level is within spec, noticed quite a bit of smoke inside the oil tank when I opened it to check the level. Have never seen that before (and I have opened it plenty right after a ride).

Attaching a couple of videos. Am I looking at a broken ring? Top end starvation? Any less catastrophic possibilities? If it was condensation, I suppose I wouldn't see it from the breather AND exhaust?  Happened shortly after topping up the bike with a full tank of gas.

https://photos.app.goo.gl/HExbFJxohCWz32R78
https://photos.app.goo.gl/xneQ8gcdsxM4gpHL8

[BenelliSEI]

White smoke is usually steam more than oil. On a car it’s sign of a blown headgasket, allowing coolant where it shouldn’t be….. obviously not in this case. Water in your fuel?

[Jonm99]

Well, come to think of it, this happened right after filling the tank with fuel. Bad fuel? Watered down?

[scottly]

Hi guys,

Was doing a little work on the bike (cb750 k7), new plugs and new airbox filter. Went out for a ride and noticed excessive white smoke from the crankcase breather

The drain tube in the bottom of the oil tank should be connected to the spigot on the back of the crankcase. Oil from the oil/air separator in the oil tank drains back to the crankcase through it. It should Not be open to atmosphere. The actual breather is the tube from the cam cover. Did you change the plumbing when you had the airbox apart to change the filter?? 

[Jonm99]

Ooooh, you are right! The smoking tube we see in the video  is indeed the breather from the cam cover, not crankcase! I'll edit the original post to correct that.

Oil tank drain tube is (and was) routed to the spigot on the crankcase.

Thanks

[scottly]

Well, come to think of it, this happened right after filling the tank with fuel. Bad fuel? Watered down?

Diesel instead of gasoline??

[Jonm99]

99% sure that is not the case. But, if it was, would this be the symptom?

One more thing to note, I have lately been taking the bike out only once a week or so for a very short ride, so, I suppose this could be an accumulation of condensation? Still strange that it would manifest itself so abruptly and excessively. Anyway, if that is the case, I could take it out for a long ride to see if that helps. But what if it's not condensation, then I'm killing the engine for good...

[BenelliSEI]

Dump that fuel in your truck or car and put something different in there. At the very least, dump a small can of gas line anti freeze
 to help mix the water in with the fuel.

[grcamna2]

I think your condensation trap/breather might be full and need to be drained.

[Jonm99]

I think your condensation trap/breather might be full and need to be drained.

It's not installed, cam breather vents to atmosphere.

[Jonm99]

Dump that fuel in your truck or car and put something different in there. At the very least, dump a small can of gas line anti freeze
 to help mix the water in with the fuel.

Yeah, just concerned with what I'm doing to the engine by running it if that's not the issue...

[scottly]

Is it smoke, or vapor? Vapor will dissipate, while smoke lingers. It's hard to tell from the video.
It might not be a bad idea to inspect the spark plugs?

[jgger]

Is it smoke, or vapor? Vapor will dissipate, while smoke lingers. It's hard to tell from the video.
It might not be a bad idea to inspect the spark plugs?

 

That would be the first thing I would have done. Plus looking for mustard on the oil filler cap. Really does sound like condensation in the oil could be a big part of it. If its only from 1 pipe check the drain holes on the exhaust.

[TwoTired]

Internal engine condensation can be “boiled off” with an engine power run of 15- 20 minutes AFTER the reaches full operating temperature.  If it is still spewing vapor after that, then you might have a blow by issue.

[HondaMan]

I don't think it will 'hurt' anything to run it a while longer to see if some heat will change things. When I have taken mine for the Spring ride it often shows white puffs from the exhaust for the first several rides (not less than 9 miles to work, etc.) of the season. Sometimes this might be attributed to temperatures (like 40 degrees and an itch to ride), but it is pretty consistent year-to-year. If the oil isn't showing whitish blobs or streaks then it isn't enough condensation to affect oil performance: if you see such marks in the oil, then it was gotten 'wet' with moisture and should be changed before it has a chance to rust the oil pump rotors or the crankshaft's journals if it sits long enough. I often find rusted rotors in oil pumps that sat for long periods with old, wet oil in them.

[Jonm99]

Ok, just took the bike out for a 30 minute ride.

Still smoking the same after 30 min from both exhaust and cam breather tube (new video here - https://photos.app.goo.gl/SkGZ3pHcCddu3s788).
Plug #1 is fouled (before and after this ride). Looks like oil to me, but hard to tell.
Plug#2, a little on the pale side, #3 looks good, plug #4 maybe a bit rich but nothing extreme? Attaching images of the plugs after the ride.

Other observations:
No white streaks or "mustard" in the oil tank.
Oil level is good.
When I opened the oil tank right after the ride, it was smoking from inside (see video here - https://photos.app.goo.gl/wAyeBizbH15zf2f78).
Engine does not seam abnormally hot.
No leaks anywhere.
Idles great, sounds great, and rides great except for one sputter mid-ride when I was at about 4k rpm (quickly recovered and did not repeat itself - nevertheless, that's never happened before).

Considering the above:
Can bad fuel still be a relevant culprit (I suspect that the bike wouldn't ride as well as it did for as long as it did if it was diesel or watered down fuel)?
Bad oil?
Valve guides?
Something else?

What next?
Flush the fuel and fill with a fresh tank?
Oil change?
Swap between the plugs (they are new and within spec: 25mm) to see if that changes anything?
Compression test? I don't have a compression gauge so would need to take it to a shop for that.
Dare I say, pull the engine and....then what? That would royally suck.

I will also note that the bike has less than 50 miles on it after installing a new cam shaft and camshaft holders after the right side oil gallery to the top end was blocked and caused those parts to literally melt (installation was done by the worst mechanic on the planet, took me almost a year to get the bike back, and I don't trust anything they did - anyway, it's a long story and it is what it is). So... where does that leave us? Maybe some bolts/nuts came loose? Or a seal that wasn't installed correctly? Although I suppose I would see a top end leak or hear some knocking if that was the case... no?

I am at a loss here.

Thanks!

[madmtnmotors]

My money is on blow-by from stuck/worn/damaged piston rings. Start with a compression test and go from there.

EZPZ

[TwoTired]

Appears that there is some sort of mechanical damage.  A compression test can tell you what cylinders are the problem.  A leak down test can tell you that, plus where the leaks are. Rings or guides.  Do you have a compressor?

An easier test is to use the clear tube method to verify the fuel level in the carbs isn’t to high forcing fuel vapor past piston rings into the crankcase.

Does someone following you notice “smoke” as you ride at speed?

[Jonm99]

Actually, there is LESS smoke at higher RPM (5-6k)... Not sure what that means?

[TwoTired]

Actually, there is LESS smoke at higher RPM (5-6k)... Not sure what that means?

Combustion chamber is burning more of the vapor due to more frequent firing cycles, higher cylinder temp average.  Do check carb fuel levels.  They could be a bit lower with higher engine use.  In theory…

[BenelliSEI]

I would also try a fresh tank of fuel (dump what ever is in there now) and change the oil before pulling out the motor.

[Floshenbarnical]

If it's any consolation, the bike/ smoke combination looks extremely cool. Strong Ghost Rider vibes. Hopefully you don't end up living the full Ghost Rider experience though.

[grcamna2]

If it's any consolation, the bike/ smoke combination looks extremely cool. Strong Ghost Rider vibes. Hopefully you don't end up living the full Ghost Rider experience though.

  

[scottly]

Plug #1 is fouled (before and after this ride). Looks like oil to me, but hard to tell.

If the plug was that fouled, it wasn't running on that cylinder.

[Jonm99]

Did a clear tube test - 2 and 4 were spot on, 3 a couple of mm under the bowl (which is weird because a pulled the carbs and leveled the floats less than 20 miles ago), and as for 1, dunno what to say - fuel doesn't even make its way up the tube to be parallel to the bottom of the bowl. When I agitate the tube with fast and light taps of a screwdriver, it starts pumping up the tube, and keeps going as long as I do that, higher than the carb itself?! Obviously I am doing something wrong, but can't figure out what. Usually just a flew flicks of the tube with my fingers gets the air bubbles out. Is the float too high? Too low?

Also did a compression test - 1=140, 2=150, 3=125, 4=150

Trying to get my hands on a compressor for a leak down test, will report back once I do that.

Haven't flushed the fuel for new fuel or replaced the oil yet, although at this point, not sure that will change anything.

Looks like a teardown...I suppose