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Author Topic: Confession first... Question second  (Read 1883 times)
4onFloor
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« on: July 12, 2013, 10:01:16 AM »

     Confession first.  Hi, my name is John, (*everyone says "hi John"*) and I'm a Lurker.  I didn't intend for it to be that way, but every question I ever had has already been answered and every bit of advice I could give has been given, usually better than I could have pontificate on.  So, sad to say, I'm a Lurker.  Until today.

     Background before I get into my question.  While I was in Afghanistan my wife went to start the bus, but discovered the batteries were toast, so we agreed to buy a pair of group 31 AGM batteries.  I finished out the battery bay with fresh paint and new 3/0 wires to tidy things up.  When I got home I started the bus a few times to check for air leaks and to perform some much needed PMCS (preventive maintenance, checks and services) a few days before we were to depart for our new destination.  I went to start the bus on the day we were to leave and... nothing.  Just a slow depressing chug chug chug so slow that I might have been able to hand crank the engine just as fast.  So, I pulled the batteries and put two chargers on them to get them back up to speed because daylight was burning and we needed to leave on a schedule.

     After 3 hours, I attempted to get the bus (hereinafter known as Mr Bus) started but with the same results as before.  So I did what anybody with the motto “Overkill is Underrated” would do.  I took Spinal Tap’s philosophy of turning everything up to 11 and put the batteries back on... with the chargers on the batteries, and set the chargers to ‘start’.  This would definitely give me the amperage I needed to get Mr Bus going.  Wrong.  It took the last of my ether and several tries before we were started.  Whew.

     Once at our new site, we needed to move because the site we were at was promised to us as a 50 amp site, but it wasn't, it was 30 amps.  So, I tried to start Mr. Bus but he wouldnt start... AGAIN.  Even after an hour of driving I still had nothing, so I rewired for 30 amps (don’t ask, it's a story for a different post) and here we sit.

     I called Luke at U.S. Coach and he sent me a starter solenoid but that wasn't the issue.  I had 4/0 wire made to replace the crispy wires in the back, new solenoid, and Luke’s mechanic (Mike?) talked me through jumping the start solenoid in the breaker panel in the engine bay to rule it out as a cause.  nothing, nothing and nothing.  I replaced the batteries (under warranty) and that didn’t help, though I did get Mr Bus started with a generous squirt of ether.  I let him run for a bit, I know that I’m not supposed to idle the 8v71, but I wanted to recover some of the charge used to start the bus and let it warm up so that I could try a restart.  On the restart... nothing.  less even.  So, less than nothing?

     I took the starter apart yesterday to see if there were signs of obvious failure that would indicate where a problem might lie.  There were signs of rubbing on roter from the stators.  If the motor had shaft bearings, they don’t spin, all that was between the rotor and the housing was a brass bushing.  The brushes had a lot of material left over.  In all, it appeared that it should work.  I cleaned it up because there were a lot of contaminants on it like grease and oil and I reinstalled it.  On the restart the engine wouldn’t do a fraction of what it was doing before, and right before it started doing less than nothing I noticed a glowing orb off to the left of the engine.   That my friends was the grounding wire for the oil gauge which is mounted to the frame.  When I was starting the engine, and the starter was providing too much resistance, the grounding wire for the oil gauge in the engine bay was lighting up like a filament... instantly.  And then the starter died a horrible burning death.  No fire fortunately, but it smoked like the Deepwater Horizon for a few minutes and that was it. 

     So, now I obviously need a new starter, but more than that, I need to understand what the hell went wrong here and what i need to do to fix this problem right.

     I have full voltage at the rear of the bus when I throw the main switch, I only lose about .3v between the battery bay and the starter.  The solenoid is new, though it may be a little less than pristine at this point (to be taken apart soon).  Cables in the engine bay and battery bay are brand new...

- John

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Lin
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« Reply #1 on: July 12, 2013, 10:25:34 AM »

It would seem that there is a serious short that is turning your oil (pressure?) gauge ground to a hot wire.  First, just for information sake, I would disconnect that wire and see if it corrects the start issue.  In any case though, you will have to find and correct that short.
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bevans6
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« Reply #2 on: July 12, 2013, 10:29:35 AM »

I didn't see what kind of bus, what voltage the system is at, etc.  My MCI starter is itself grounded directly to chassis with a 4/0 cable.  Since you fried a little oil gauge wire you would seem to have a ground problem - the ground path for the starter shouldn't even be through the engine at all.  I would replace the ground cable to the start, or at the least take it off and give it a good talking to...  That, with your new starter will probably fix you up right.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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« Reply #3 on: July 12, 2013, 11:05:30 AM »

Well, there's your problem. That little filament wire you called an oil pressure wire just ain't gonna cut it for grounding a big starter.

Yep, what Brian said. You need a ground from your starter to your batteries. Somewhere along the way, your starter is not grounded, and it's finding that little gauge wire to use. 

Start tracing your ground wire from the batteries to the starter. There should be one continuous path of 4/0 cable that's not corroded inside or at the connections.


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Craig Shepard
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4onFloor
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« Reply #4 on: July 12, 2013, 11:35:02 AM »

Okay, just to clarify what i said in paragraph 5, the wires to the starter (from the lug in the engine bay "hot" to to motor and from the motor to the chassis) were replaced with 4/0 wire.    and by motor i mean the electrical kind, not engine (internal combustion type).  I agree that there might be a short somewhere, but as to where, i'm totally confused.  Accessing the wires in the tunnel is a real PITA... maybe I need to start at the front and work my way back by taking the access panels out?  The water bay will be a real challenge since the tanks are in there pretty good...

sorry i forgot to put what kind of bus ect... I typed that post twice since my computer decided that it was time to restart and update when I was almost done.

I have a '70 MC-7 at 24v with a 8v71NA
« Last Edit: July 12, 2013, 11:37:30 AM by 4onFloor » Logged
Lin
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« Reply #5 on: July 12, 2013, 11:54:30 AM »

Before taking things apart, you could just run a cable from the batteries to the starter outside the bus.  If that takes care of the problem, it might be easier to just run a new cable and abandon the old one entirely. 
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bevans6
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« Reply #6 on: July 12, 2013, 11:56:38 AM »

In that case maybe part of the starter motor failure included the connection to it's ground lug.  Logic dictates that if that little wire had a melt-down the current came from the starter which sent it there instead of to it's ground connection.  I would start with the new motor and see if it works properly - it probably will.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
challenger440
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« Reply #7 on: July 12, 2013, 12:01:36 PM »

Starter on my 7 is grounded with a large cable from the back of the starter to the frame.  John M.
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John M.
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« Reply #8 on: July 12, 2013, 12:02:38 PM »

frame connection.
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John M.
Helena, Mt
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4onFloor
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« Reply #9 on: July 12, 2013, 12:11:45 PM »

yup, mine looks like that too, cept yours may be a little cleaner. 
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challenger440
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« Reply #10 on: July 12, 2013, 12:38:26 PM »

weird deal.  With that big fat ground wire it's hard to imagine the starter is grounding elsewhere.   Could that cable be bad? j
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John M.
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« Reply #11 on: July 12, 2013, 01:05:18 PM »

I'm in agreement that the starter is not properly grounded. I would ensure that the "new" ground cable is contacting clean  unpainted surface and you are not using stainless steel washers or bolt.

Thanks,

Jack
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4onFloor
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« Reply #12 on: July 12, 2013, 01:07:35 PM »

I hope not!  I had to buy it at a welding supply house.  It's one of those with a nice bendy rubber coating.  Both the ground wire and the hot wire have huge lugs on them too.  

The only wires I haven't replaced are the ones that go from the hot terminal in the engine bay to the battery box switch.  I may have to just rip it all apart and start from scratch.  I was hoping that someone had a similar issue and it would be an easy "oh, all you need to do is __________ and that should solve it" kind-of-thing.
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4onFloor
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« Reply #13 on: July 12, 2013, 01:08:48 PM »

okay, I'll get the wire wheel out and scrub the heck out of that grounding post.  I'll double check my washers too.
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Ralph7
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« Reply #14 on: July 12, 2013, 01:27:31 PM »

         NOW remove the ground at the frame and clean it. If you can get a copper washer install it after you install the wire end  to the frame then the lock washer. High Amp  need super good ground.  
        I relocated the batteries to the old AC compressor location and ran the ground to the to the frame lug where the starter ground is located.
        Do not use a lock washer in contact with the wire end(lug).  Lock washers seem to corrode over time.
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