Smoke gets in your eyes... Or how I spent my morning...

[bevans6]

So I've been getting my bus ready for it's first official Nova Scotia DOT inspection, and everything is perfect.  Batteries are about ready to get changed but bus starts OK, all lights are working all at the same time (almost a first for this bus), brakes are perfect, tire pressures are good, air doesn't leak down too fast, etc.  So I pull out of the driveway to go to the mechanic's shop and notice the speedo isn't working.  Odd I sez, and carry on.  Half a mile later there is smoke from under the dash.  I am on a steep but short hill, so I start looking for a spot to pull over.  See a great spot about 200 yards on, so I kill the engine and start to roll, pull over and stop, but smoke is still coming!  Leap out, run to the bay and throw the master switch.  Smoke stops.  Panic over, but what the heck do I do now?

I find a screw driver and pull the dash.  I turn on the power, and smoke is coming from the wiring to the master switch.  Power off.  I wonder if it runs.  Power on, start engine, turn off, power off (all this requires running up and down the stairs and back to the bay to hit the master switch).  But it runs fine.  Now I know that the bus will run all day long with no power, so I turn it on, start the engine, and am about to hit the master switch when I remember the alternator - the alternator might free-run if I disconnect the batteries while it's running.  I run back into the bus, which is smoking, turn off the engine, and run back and turn off the master switch.  Now, how do you make the alternator not run?  I thought of pulling a relay but without my manual I don't know which one.  I do know that without belts the alternator doesn't run, so I decide to pull the belts.  Three trips back home for different tools (only on the last trip do I bring double handfuls of wrenches and a couple of socket sets, duh...).  Now I wrestle with the DN50 and the four belts, and 15 minutes later I have them off.  I gotta figure out a better way to do that, it involves undoing two brackets and loosening the adjusting bar and is a PITA.  Now I am golden - I start the bus, throw the master switch, no smoke but the engine dies.  I forgot the shut-down lever with the air cylinder - the Skinner valve is open when voltage is off, so as soon as I disconnect the master switch the air cylinder pushes the lever and shuts down the engine.  I pull the shut-down lever off the governor and start the engine, throw the master switch off and the engine is still running.  Good to go.

Now, I stopped at the crest of a hill by a really nice wide driveway with an up-hill approach..  I plan my attack - drive up the driveway, turn around up top, come down, drive home.  Three quarters of a mile I can do with no lights or turn signals.  Then I remember the reverse solenoid - no electricity, no reverse.  Now the hill on the driveway becomes very important.  My wife will stop traffic while I drive up the hill into the driveway, and roll back down to turn around on the main road.  Done, and home... ain't it nice that old fashioned Detroits run with no electricity?

So that's how I spent my morning.  Back home, pull the steering wheel off, get the dashboard up and survey the mess.  LGI (Last Guy In) did a horrible job of rewiring the master switch, one leg of the little bus bar that distributes power is melted right off, two wires are melted off, but it is definitely fixable.  So that's what I did this afternoon....  I thought this whole thing was hilarious, in retrospect having fixed the bus, so I thought I would share...

Brian

[Ralph7]

          Glad you have a good outlook on the bus, made my laugh, Thanks!  Have a great day!

[Cary and Don]

Well,,,,, ours comes in threes.  That's one.  Hopefully, you are luckier than us.


It is funny,  after it's fixed.


Don and Cary

[bansil]

Good show,great story

Good ending! safe at home

[Oonrahnjay]

    I'm amazed that you were able to fix it so quickly.  Seeing smoke let out like that makes me think of melted wiring harnesses and major rebuilds!

BH    NC    USA

[Scott & Heather]

Sounds like my kind of day. Love your positive humor filled outlook.


Sent from iPhone via Tapatalk

[bevans6]

The root cause was faulty workmanship coupled with dodgy design, and the melting was highly localized.  Part of why I was happy is that I know all too well how trying to find an electrical short can be the work of ages.  The MCI master switch in the dash is a fairly heavy duty 4 pole single throw toggle switch.  It switches two power sources to two basic loads - the small one is the headlights, and the big one is everything else that is powered up through the master switch.  It uses two copper bus bars connected to the screw terminals on each side of the switch to put the three gangs in parallel - they effectively become one switch with three times the ampacity.  What happened, probably long ago, is the bus bar touched the side of the windshield washer valve and would intermittantly ground out, and eventually melted the bus bar corner off.  Problem one.  It had been "corrected" in the past by someone putting some plastic from a bucket in there as insulation, the sharp corner of the bus bar wore through the plastic.  Problem two was simple loose connections.  These connections are heavy wire, the breaker is a 30 amp auto-reset, and loose connections heat up.  The plastic sheaths on the ring terminals melted off, the connectors touched things, smoke ensued.  All I had to do was replace a couple of connectors, put on some heat shrink, remove a few connections to things no longer in use, fix the little bus bar and put it all back together again.  I have no idea why it decided to let the smoke out when it did but at least I was there to fix it.  As you with MCI's know a lot of the bus is not controlled through that master switch, like turn signals, clearance lights, etc, so there is always power there if the battery master disconnect is on.  My new habit is going to be to throw the battery master if I am not actively going to run the bus.

Brian

[Oonrahnjay]

... Problem one.  It had been "corrected" in the past by someone putting some plastic from a bucket in there as insulation, the sharp corner of the bus bar wore through the plastic. 

    Oh, noooo!  In that case, I'm guessing that you were lucky that it wasn't a problem before (like late on a snowy night, when you're far from home and you really need to be somewhere in the AM) but that's just BAD!

As you with MCI's know a lot of the bus is not controlled through that master switch, like turn signals, clearance lights, etc, so there is always power there if the battery master disconnect is on.  My new habit is going to be to throw the battery master if I am not actively going to run the bus.
Brian 

     For what are good reasons in "transit" service, my battery master is the only switch for a number of loads (i.e. when the master is on, some lights are burning and some other circuits are 'hot'), so throwing that switch off is mandatory procedure for me even in normal operation, but it's a good point to consider as part of ordinary protection against problems.

     Again, I'm glad that it wasn't a bigger problem for you.    BH    NC    USA