Wires crossed. Why did the exhaust get oiled? confusing logic...

[MarkT]

What do you suppose would happen if you crossed the wires for two spark plugs?  Say #4 and #6?
Yep this happened.  I was installing larger coils on George.  Had to move several parts to make room - it's very cramped in there with the carburator, blower, velocity stack and air cleaner, Pingel, coils, air horn and some other device that hangs off the back of the blower manifold, don't know what it is.  You can't see the wires routing with a flashlight even with the tank off - have to push and pull and observe wire movement to ID them.  Can't read the number labels on the wires under the outer insulation sleeves. Easy to FUBAR.  Thought I was good to go.  Fired it up and he started but it wasn't right.  Smoked a LOT but I had just done a wet (oiled) compression test so expected smoke.  Backfired quite a bit, missing I said Whiskey Tango Foxtrot.

Ran it for a few minutes as George wasn't making self-destruct noises, enough to warm him up while I diagnosed what's the problem.

Got out the temp gun and checked the exhausts as I was working on the ignition, we might have a crossed wires issue.  Normal hot except 4 & 6 cold.  Hmm.  Inspected closely and yep, they were crossed.  And there is a LOT of oil running out the exhaust.  Oops.  I put the wires back correctly - actually had to reassign the coils for the back 4 as the wire to #4 wouldn't reach with the moved coils.

Now I'm worried where did all that oil come from?  Ran a compression test and it's normal - that is, wet test 165-180# on all cylinders so the pistons aren't holed and I suspect rings not broken.  

Then I got to thinking, what actually happened for the few minutes I ran it?  Here's my analysis.

There are 3 coils, each fires 2 cylinders and fires each engine revolution - half the sparks are ignored as they happen on the other cylinder 360° off from the TDC (approx, call it that for easy explain) firing moment of the current power cylinder.  The coils are assigned, 1&2, 3&4, and 5&6.  My wire swap put them at 1&2, 3&6, and 5&4.  The firing order is 145236.  

I made a table to look at the logic.

Say a snapshot when #1 fires looks like this, cylinders in firing order, crank rotate clockwise (here and from rider's position).

  Cyl spark  Fn (stroke)      crank pos.  ° on crank (approx)
    1    ҈       Firing                  ↑                0
    4           Compression        ←              600
    5           Intake                →              480
    2    ҈       both closed          ↑              360
    3           Exhaust              ←              240
    6           Power                 →             120

Now swap wires 4 & 6, put 4 at TDC, observe which cylinders get a spark and what might happen

    4           Firing                  ↑                0
    5           Compression        ←              600
    2           Intake                →              480
    3    ҈       both closed          ↑              360       Normal Fn, spark ignored
    6    ҈       Exhaust              ←              240       60° after BDC exhaust stroke, backfire into exhaust
    1           Power                 →             120

put 3 at TDC, observe which cylinders get a spark and what might happen

    3    ҈       Firing                  ↑                0       Normal Fn, Power
    6    ҈       Compression        ←              600     60° after BDC on comp stroke, WAY advanced, might break piston, conn rod, rings
    1           Intake                →              480
    4           both closed          ↑              360
    5           Exhaust              ←              240
    2           Power                 →             120

put 6 at TDC, observe which cylinders get a spark and what might happen

    6           Firing                  ↑                0
    1           Compression        ←              600
    4    ҈       Intake                →              480       120° after TDC on intake, negative compr, might not ignite, mixture to exhaust
    5    ҈       both closed          ↑              360       Normal Fn, spark ignored
    2           Exhaust              ←              240      
    3           Power                 →             120

put 5 at TDC, observe which cylinders get a spark and what might happen

    5    ҈       Firing                  ↑                0         Normal Fn, Power
    2           Compression        ←              600
    3           Intake                →              480      
    6           both closed          ↑              360
    1           Exhaust              ←              240      
    4    ҈       Power                 →             120        120° after TDC on Power stroke, may backfire or mixture to exhaust

I don't think I damaged George with my brain fart.  Other than soaking the innards of my custom exhaust with oil.  Yet I'm concerned, I haven't figured out WHY the result was a LOT of oil getting in the exhaust.  Seems the worst of the above tables is #6 getting spark when 60° into the compression stroke.  Like I said - no big noises and compression indicates no apparent lower end damage.  I'm thinking a ride this weekend will burn out most or all of the oil in the exhaust.  The dipstick doesn't indicate it's low - but it was dripping out of the pipes.

Why do you suppose this resulted in oiling the exhaust?

[Jess from VA]

Why do you suppose this resulted in oiling the exhaust?

I have no idea Mark, but I'm impressed (as always) with your technical skills.  

Reading this post (and trying but failing to understand it), it reminded me of Dr. Frankenstein building a man out of random body parts.  I mean, Frankenstein lived but he wasn't exactly right.  (In a later version of the movie, his brain was from Abby Normal.)  

With regard to oiling, did you check the drool tube?  If that tube (quickly) reached capacity, would that result in the exhaust oiling?

Is the oil down enough to notice on the dipstick?

When one or more spark plug wires are crossed, the timing of fuel/air compression does not align with the delivery of the spark.  This causes cylinder misfires, and the unburned fuel usually flows out the exhaust.  I think this can blow a head gasket too.

Now a blower increases compression no?  So a misfire with higher compression blows oil (and unburned fuel) past the rings in exhaust stroke?

Would it be prudent to carry a fire extinguisher on your shake down ride? (not trying to be a smart ass)    

[Itinifni]

Where does the crankcase vent with the blower installed?

I would think the cylinder with the advanced ignition timing would exhibit very high cylinder pressure resulting in excessive blow by into the crankcase.

The usual place for the crank to vent is into the air cleaner but not sure on a blown bike.

Just a thought.

edited for a correction.

[RWhitehouse]

Another thought, the "oil" could have been a little oil from the compression check and a lot of dirty condensate water from the swapped wire misfiring. water is a byproduct of the combustion process, and misfiring can cause a lot more (liquid) of it, as those cylinders aren't burning hot enough to vaporize it as normal.

Oil soaked into the packing can take a while to burn off, calls for an old fashioned Italian tune up.

[MarkT]

Thanks for your comments.

Why do you suppose this resulted in oiling the exhaust?


With regard to oiling, did you check the drool tube?  If that tube (quickly) reached capacity, would that result in the exhaust oiling?

Is the oil down enough to notice on the dipstick?

When one or more spark plug wires are crossed, the timing of fuel/air compression does not align with the delivery of the spark.  This causes cylinder misfires, and the unburned fuel usually flows out the exhaust.  I think this can blow a head gasket too.

Now a blower increases compression no?  So a misfire with higher compression blows oil (and unburned fuel) past the rings in exhaust stroke?

Would it be prudent to carry a fire extinguisher on your shake down ride? (not trying to be a smart ass)    

There's no drool tube.  Or airbox.  Entire ingress system is replaced with a carb, blower and manifold.
I suspect that the spark on #6 while in compression probably fired, that one could damage the engine.  The others put unburned mixture into the exhaust and caused backfires, I'm thinking.

Oil is not visibly down on the dipstick.  Blown head gasket should show up in other ways, like lost compression.  Typically coolant in crank oil, oil in coolant.  Didn't see those yet.  The oil dripping from exhaust is very black while oil in crankcase is very fresh.  But then the exhaust is full of soot so no surprise.

Don't know about the oil moving past the rings on exhaust stroke.  It's somehow getting in the exhaust and it seems this may be the only path though I don't understand that.  How did there get to be pressure moving the oil?  The crankcase is vented.

Not concerned about a fire inside the exhaust.  Just shutting the engine off should deprive that of oxygen. But I have a small extinguisher I could put inside my jacket.  

Where does the crankcase vent with the blower installed?

I would think the cylinder with the advanced ignition timing would exhibit very high cylinder pressure resulting in excessive blow by into the crankcase.

The usual place for the crank to vent is into the air cleaner but not sure on a blown bike.

It has a separate crank breather vent to atmosphere like an old car.  Not returned to the air inlet.

Another thought, the "oil" could have been a little oil from the compression check and a lot of dirty condensate water from the swapped wire misfiring. water is a byproduct of the combustion process, and misfiring can cause a lot more (liquid) of it, as those cylinders aren't burning hot enough to vaporize it as normal.

Oil soaked into the packing can take a while to burn off, calls for an old fashioned Italian tune up.

Much more oil than what I squirted into cylinders 4 & 6.  It is extremely black however.  The glasspacks are handmade, glass and stainless steel wool hybrids, built angled to follow the pipe's mandrel bend, with handmade smaller internal tube with holes, and crossover - which surprised me it was dripping oil too.  It's quieter than you might expect.  What's an "old fashioned Italian tune up"?

[Ricky-D]

Just a little observation but I would think if crossing the spark plug wires caused an ignition with the exhaust valve open even slightly it may cause a higher than normal pressure in  the exhaust that in turn would want to push out more thoroughly all the water and moisture that collected in the exhaust from the startup. It definitely would be black and oily and a considerable amount depending upon the relative temperatures of everything.

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