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Author Topic: Confession first... Question second  (Read 1989 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

[ ----- enter advice here ----- ]
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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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« 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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« 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.
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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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Seangie
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« Reply #15 on: July 12, 2013, 02:20:34 PM »

Hi John!

I recently had my starter rebuilt and before doing so it took a few turns and sometimes tries before it would start.  After rebuilding and replacing wires it starts up on a half turn of the key.  Id definitely guess starter here.  Trace all your wires out (labeling as you go) it takes time but after doing so it makes it much easier to troubleshoot and there is no more guess work.  Many wires I have seen on my bus worn through where the wire touches a surface.

Also - curious as to how easy it starts up once you get it going?  Does it run right off or chug up to full speed?

Welcome to the club!

-Sean


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4onFloor
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« Reply #16 on: July 12, 2013, 02:42:11 PM »

it starts up quite nice and goes to high idle within a minute.  

I'm looking for starters now... if anyone has one located in central Texas, send me a msg and I'll send you a beer.  Just don't drink it out of the box, put it in the freezer for a few min first.

It's too bad the one in Southbend is too far away. 
« Last Edit: July 12, 2013, 02:43:45 PM by 4onFloor » Logged
Lin
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« Reply #17 on: July 12, 2013, 03:36:37 PM »

See if there are any auto electric shops around that can rebuild it if you can't find another one.
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« Reply #18 on: July 12, 2013, 04:02:34 PM »

I love it when someone says Central Texas not like it a square mile but anyway if you are around Killeen try Kings, Car Quest in Killeen may have that starter in stock or can order it 

To bad you couldn't borrow one from Ft Hood they have thousands of the 24 volt MT 42 starters setting on shelf's there   
« Last Edit: July 12, 2013, 04:08:34 PM by luvrbus » Logged

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« Reply #19 on: July 12, 2013, 06:08:32 PM »

John, I don't where your located but I have a ex

Richardtra starter. I,m about 20 miles N. of San Antonio.
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« Reply #20 on: July 12, 2013, 06:47:57 PM »

John,

I had mine rebuilt at an alternator repair shop.  They had all the parts and pieces and did an outstanding job and were done same day.  Cost me 250.00.

-Sean


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« Reply #21 on: July 12, 2013, 07:43:10 PM »

Thanks for the great advice all!

I'm in the Temple area so I can check out Kings.  I thought about going up to Western Star or Freightliner too.  The Napa in Killeen says they aren't a medium truck shop, so they don't have any in stock.  There's a salvage yard south of Belton that has a few buses in their yard that I thought looked promising...

I'm sure there's a motor sergeant on Ft Hood that could part with a starter or two Wink

(p.s. NSA, I was kidding about that.  please don't monitor my phone now)

so far rdbishop is in the lead for that warm beer!
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rdbishop
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« Reply #22 on: July 12, 2013, 10:02:18 PM »

John, I'll take $50 for this starter if you want it. Call me 1- 830-6 two 5- one 696. There's some good deals on E-bay also.............

Richard

I also have my wreaked 68 mc-7 you might find some parts you can't live without!!!!
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4onFloor
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« Reply #23 on: July 13, 2013, 09:44:43 PM »

***Update***

Mr Bus runs! 

Thank you Richard for the starter, it was a tight fit, but it works like a champ!  The "new" starter is noticeably bigger than the original one.  The old one has four stators, where the new one has five.  The housing is bigger too.  Unfortunately the teeth on the new starter showed some serious wear on the leading edge, so I swapped the old starter's teeth in... kinda like borrowing dentures...  The new starter's housing almost keeps it from aligning with the facing on the engine but with some serious encouragement it's in there.  I also had to swap out the dog gear housing on the tip of the starter, the new one was a few thousands too big.  Other than that, it was just the solution I needed.  It appears the old starter was fried to the point that it was grounding out internally and sending the voltage through the engine block.

Big thanks to everyone for your input!

John
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« Reply #24 on: July 13, 2013, 11:41:48 PM »

Glad you got Mr . Bus going. Sorry it didn't go easy, it did come off a 8-92. Maybe someone can tell us the difference..........Really enjoyed the visit. you need come again soon.........

Richard
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« Reply #25 on: July 14, 2013, 01:25:45 PM »

Glad you got your starter sorted still FWIW your engine should still be grounded properly so that various gages etc work properly.  A hot wire from the the oil pressure sensor to the chassis is not how that is usually done.  Most engines have a ground strap somewhere, and they get neglected.... not hard to invent one if yours is gone.
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