Topic: White smoke after valve adjustment...

[brentnclemson]

I've read through several white smoke posts, but I'm still hung up on a few things w/ my 76 CB750...here's the background...

Bike ran fine before, at worst (after not riding for 2-3 weeks) it would smoke for a couple minutes while warming up.  Tore it down a little last week to do some work...valve adjustment, oil/filter change (w/ Honda 15W-40...previous oil was Mobil1 15-40 automotive, hence the change), cosmetic changes.  While adjusting the valves, all were pretty close exept for #4 intake...it was missing the locking nut.  Replaced the nut, never found the old one.

I finally started it up after several days of work and white smoke is billowing out of the exhaust along w/ a good spray/drip of oil.  For some reason, the oil coming out of the exhaust is jet black.  The old oil in the engine was only in for about 1k miles and was still new-looking...can't figure out where this black oil would be coming from, unless it's running through the cylinders and is blackened during combustion.

The engine runs much better than before, there's a noticeable difference in acceleration after adjusting the bad intake valve...but the smoke is pretty bad...  How could it have gotten this bad so quickly??

[brentnclemson]

The next step is checking the plugs and checking compression.  What should I do before checking plugs, any particular operating conditions the engine should see before removing to read the plugs??

Thanks!

[DRam]

Are you sure it's oil dripping from the exhaust and not condensation?  Or unburned gas?  Post back and let us know what the plugs look like, as well as what your compression is.  I'd be a bit worried about that lock nut floating around inside the engine.  While it may be innocently sitting on the bottom of your oil pan, it may also be in a position to do some damage.

[brentnclemson]

The fluid coming out of the exhaust is very black and oily, so I'm pretty sure it's oil.  I searched a while for the lock nut...as much as possible under the valve cover w/out actually removing it.  I also dropped the oil pan, but didn't find anything...

[DRam]

Better find the nut.  If it isn't in the pan it could be in a good position to cause harm.  If you're lucky it's just sitting somewhere on top of the head.  It's amazing how well those things can hide among the various little recesses up there.  Dropped one once while working on my CBR.  Not only did I hear it, I saw which direction it went.  Took me forever to find it hiding behind a valve spring the next cylinder over.

Let us know how the plugs look and compression check comes out.

[brentnclemson]

Here are the spark plugs (1-4 L-R).  For the most part, they're dry and black, but #3 was a little oily.  This is after the engine sat for several hours, would I get different results pulling them immediately after running (hard accel, immediately cut off engine)??

No compression gauge, will work on that this afternoon.

[UnCrash]

I lost a locknut as well.

I couldn't find it by looking through the tappet covers, and it wasn't in the pan when I dropped that.

So I lifted up the valve cover as much as you can in a 750 without removing the engine and found it nestled in a deep little nook.  My trusty flexible magnetic grabber fished it out for me.

If it unlodges from wherever it settles and is up at the top end, it do some damage to the top end.

[brentnclemson]

I'll try and remove the valve cover as much as possible...I had some issues with the Phillip's head screws last time I tried that...  What style gasket is beneath the valve cover??  Is it paper?  If so, I'm assuming I should go ahead and order a new one...

[brentnclemson]

Any comment on the spark plugs from someone who knows more about it than I do?!  Thanks!

[upperlake04]

 Can't comment knowledgeably on the plugs.
  But about the locknut..  it would be prudent to know exactly where it is. You will never have 100% peace of mind riding your bike until you find it. Been there, the good news is when the engine is out, the mangled phillips head valve cover screws can be replaced and torqued easily.    Its a PIA, but probably less  than fixing the (possible) damage the loose nut could cause.

[Bob Wessner]

Have you checked this, might be worth a look.

http://www.dansmc.com/spark_plugs/spark_plugs_catalog.html

[DRam]

Black and dry indicates a rich condition, so #1 and #2 look like they're running rich.  #3 looks almost normal, and #4 could be running a little rich.  That reinforces the thought that what you're seeing dripping out of the exhaust isn't oil, but condensed water or gas vapor.  It would pick up carbon from the pipes on the way out and appear dark and oily.  White smoke is another clue - smoke from condensation is white.  Oil smoke is blue.  Also, if the bike is giving out clouds of smoke from burning oil you should be able to smell burned oil in the air.  Check out the intake side for airflow restrictions, and if there are none, you're probably looking at a carb rebuild.

[brentnclemson]

Thanks for the link, Bob.  The actual appearance looks like carbon fouling on most plugs w/ some oil fouling on 3 and possibly 1...both are a little "shiny".

I see what you're saying DRam about condensation, but I'm still pretty convinced it's oil.  I could be wrong, but the smell is very strong and the spatter/drips on the ground very slippery (don't ask...).  I'll still check the air side just to be sure there's no restriction.

I adjusted the valves again to be sure, all intake are .002", all exhaust are .003".  Also adjusted the cam chain for the first time, quick off-topic question: What's the best way to tell if the engine is 15* past #1 TDC??  There's no mark, so I estimated...

[mystic_1]

What's the best way to tell if the engine is 15* past #1 TDC??  There's no mark, so I estimated...

The manuals say to put the engine at #1 TDC, then continue to turn the engine until the spring post of the advancer is just past the timing mark.

mystic_1

[TwoTired]

Black and dry indicates a rich condition, so #1 and #2 look like they're running rich.  #3 looks almost normal, and #4 could be running a little rich.  That reinforces the thought that what you're seeing dripping out of the exhaust isn't oil, but condensed water or gas vapor.  It would pick up carbon from the pipes on the way out and appear dark and oily.  White smoke is another clue - smoke from condensation is white.  Oil smoke is blue.  Also, if the bike is giving out clouds of smoke from burning oil you should be able to smell burned oil in the air. 

+1   I concur with this written assessment.

More details:
When the black carbon buildup on the center insulator gets bad enough, you will begin to get misfires that worsen until it won't fire anymore at all.  You might consider new plugs, while you get the root problem(s) sorted.

The spark electrodes would not have oil on them if the cylinder was firing.  Oil burns too, and leaves a cream/brown colored crusty deposit over time.  If your plug tip feels oily, suspect that the cylinder isn't firing at all.

Have you checked the head pipe temps for even heating?

When were the carbs last synchronized?

What do you think that missing adjuster nut will do to the engine when it jams between some important bits in the engine?

Cheers,

[goon 1492]

I'm goin with #3 as the nicest/closest to optimal and my second vote is #4 and 1 & 2 need help....
I would buy plenty of extra plugs, good to keep at least three on the bike.
Also that is very well said Two tired. I enjoy your replies they are so thuro

[brentnclemson]

+1   I concur with this written assessment.

More details:
When the black carbon buildup on the center insulator gets bad enough, you will begin to get misfires that worsen until it won't fire anymore at all.  You might consider new plugs, while you get the root problem(s) sorted.

The spark electrodes would not have oil on them if the cylinder was firing.  Oil burns too, and leaves a cream/brown colored crusty deposit over time.  If your plug tip feels oily, suspect that the cylinder isn't firing at all.

Have you checked the head pipe temps for even heating?

When were the carbs last synchronized?

What do you think that missing adjuster nut will do to the engine when it jams between some important bits in the engine?

Cheers,

Quick answers...

There's no visible oil on the spark electrode, only what looks to be carbon fouling

Spark plugs will be replaced.

Will add pipe temp check to the list, and carb sync was to be the last step of this tune-up...not completed yet.

Again, the valve cover will be removed to search for the nut.  Is it likely I'll need a new gasket?  Is it paper or rubber?  I've never actually seen the lock nut on that valve.  Since buying the bike, this is the first time I've looked at the valves.  Not saying it's not in the engine, but I have no way of knowing if the PO removed it or not...

Also, the Timing mark was right past the spring post, just seems like there should be a better way to make this adjustment...

Thanks!

[brentnclemson]

Okay, update...compression results below.  All cylinders reached max pressure is 6-8 cycles (normal?).  I appreciate the help, guys!

#1: 145psi
#2: 145psi
#3: 145psi
#4: 160psi

Pulled the plugs after 10 minute warm up, there was a small amount of wetness (not sure if oil or water...) on 2 and 3.  If I scratch the carbon off the #4 plug, the metal is gold colored, others are silver colored.  #4 pipe was noticeably hotter than the others (by touch, no IR gun yet).

#4 has been running w/ no intake valve locknut for probably 2k miles.  Since I bought it (2k miles and 9 mos ago), the engine performance, sound, and vibration have not changed.  When discovered, the valve adjustment was probably .25-.5" out...it was hitting the tappet cover.  Should have checked it over more thoroughly when I first got the bike, but it was my first bike and I didn't.

I'm thinking that w/ #4 only getting half the fuel/air of the other cylinders, it hasn't been worked as hard and the rings are in better shape.  Who knows how long the nut has been missing!  There also could be some buildup (carbon, burnt oil, condensation?) inside that cylinder...perhaps that's what seeing coming out of the exhaust as smoke??

As far as the "oil" coming out of the exhaust pipe, I looked a little closer today.  It's definitely oily, but it certainly could be condensation, it has a "wattery" feel to it as well.  So thanks, DRam!

Any comments are certainly welcome!  I may pull the #4 wire this afternoon, run it, and see if the smoke goes down at all.

[mystic_1]

#1: 145psi
#2: 145psi
#3: 145psi
#4: 160psi

Well, obviously that compression reading on #4 is suspicious.  You may be right about carbon buildup in that cylinder.

When discovered, the valve adjustment was probably .25-.5" out...it was hitting the tappet cover.

That's a HUGE variation, considering that the stock intake clearance is 0.002".  With a HALF INCH of clearance, that valve probably wasn't opening at all, if it it was, just barely.


mystic_1

[brentnclemson]

Well, obviously that compression reading on #4 is suspicious.  You may be right about carbon buildup in that cylinder.

When discovered, the valve adjustment was probably .25-.5" out...it was hitting the tappet cover.

That's a HUGE variation, considering that the stock intake clearance is 0.002".  With a HALF INCH of clearance, that valve probably wasn't opening at all, if it it was, just barely.


mystic_1

Not sure about the #4, but I guess I'd rather have one cylinder w/ high compression than one w/ low compression...  One thing to note, before replacing the lock nut, there was never a noticeable difference b/w exhaust pipe temperatures after warming up (using the hand-o-meter, of course).

About the bad valve...I know!!!   I may have been exaggerating about 1/2", but it was at least 1/4" out.  There's literally a dent in the round cover, any longer and it proabably would have poked through! 

[brentnclemson]

Quick update...

Exhaust pipe temps (IR gun) were as follows after warming up for 5 min in driveway...
#1 - 498F
#2 - 573F
#3 - 185F (!!)
#4 - 541F

After riding for 10 minutes...
#1 - 283F
#2 - 293F
#3 - 301F
#4 - 301F

Smoke is still present but has gone down considerably.  Motor is much stronger and acceleration is much smoother, it's like a new bike!  Still need to find that nut (waiting for valve cover gasket) and sync the carbs.  I'll just keep watching the smoke, I'm guessing it was residue in that cylinder...