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Author Topic: 50DN fell off?  (Read 4128 times)
brando4905
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« on: February 13, 2012, 01:55:59 PM »

I've heard of the gear driven 50dn horror stories, but I didn't think it happened like this? The "head" of the alternator fell off taking the oil line and some wiring with it. I don't think "head" is the proper term, but it is the bulk of the 50dn, not the part attached to the engine, if that makes any since. At least this happened while at home and not on the road. Can't get a hold of my mechanic today, and I'm fairly certain that I don't have the skills to fix this, but I was hoping someone would come along and give me an idea of what happened here? Thanks guys.



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1980 GMC H8H-649  8V71/V730 Marion,NC

"The highway is for gamblers, better use your sense" -Dylan
gus
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« Reply #1 on: February 13, 2012, 02:56:07 PM »

Brando,

It sounds to me like the cover over the diodes which keeps oil circulating around them has fallen off. As I remember this is held on by a few bolts or screws and just needs to be fastened back on with a new gasket so it doesn't leak.

I can't tell much from your photos, the second one looks like all is well?

To me the first one shows everything normal?

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PD4107-152
PD4104-1274
Ash Flat, AR
brando4905
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« Reply #2 on: February 13, 2012, 04:26:08 PM »

I wish it was just the cover, Gus. I know it's hard to tell from those pics, but the "bulk" of the alt. has come loose. The part that bolts to the engine is still there, but the "rest" of the alternator slides in and out on the shaft. When it broke loose, it severed the braided oil line to it and cut several wires. Look closely in the second photo, you can see the gap between the alt. and piece that bolts to engine. You can see the gap in the first one too, it's just behind those wires.
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1980 GMC H8H-649  8V71/V730 Marion,NC

"The highway is for gamblers, better use your sense" -Dylan
luvrbus
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« Reply #3 on: February 13, 2012, 06:33:52 PM »

You are one lucky guy most of the time when one freezes up it take the gear train on the engine yours took the 1/4 inch bolts.I have a 12 volt but no 24 volts for the 4905  

good luck
« Last Edit: February 13, 2012, 07:24:04 PM by luvrbus » Logged

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NoRivets
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« Reply #4 on: February 13, 2012, 06:54:55 PM »

I've heard about these causing problems as well.

Good luck. Hope your repair is reasonable $$.

Wondering how often this type of thing happens and whether I should remove mine and install an 24v truck alt.(belt driven).

Just thinking  Undecided


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AZ
1980- RTS - 8v71N w/N-65 A-timed/ 4:10 gears
towing a Jeep Wrangler.  99.9% completed (15th Yr)
rampeyboy
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« Reply #5 on: February 13, 2012, 07:53:24 PM »

"yours took the 1/4 inch bolts"

luvrbus, makes me wonder if itwouldn't be a terrible thing to have the 1/4 inch bolts act as the sacrificial part...??


Boyce
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Boyce Rampey
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« Reply #6 on: February 13, 2012, 08:54:55 PM »

I've got a 24v one if you need it.
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rdbishop
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« Reply #7 on: February 13, 2012, 09:11:53 PM »

brando,

There are 2 for sell on the MCI board for 200. each.

Richard
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Boomer
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« Reply #8 on: February 13, 2012, 09:53:29 PM »

Obviously it was running when it came apart.  When you get it off I would inspect the drive gear and flywheel housing VERY carefully.  If any debris dropped down into the gear train it can cause engine destruction in a big way.  The good news is that if that happened you would for sure know it.  Not a big deal changing out the alt, expecially on a GM but the wiring repair doesn't look like fun.  If the drive gear has to come off it must be replaced by using a special alignment tool.  Very important.  I would not consider putting another alt on without overhauling it first or you could suffer the same fate again, or worse.
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buswarrior
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« Reply #9 on: February 14, 2012, 12:04:12 AM »

The most fortunate thing is that there hasn't been a fire...yet.

Disconnect the battery, pronto, if you haven't yet!!!

happy coaching!
buswarrior
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brando4905
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« Reply #10 on: February 14, 2012, 02:45:41 AM »

It was running when it fell off, hopefully I'm not looking at gear train failure again, just had that happen two years ago. But it did shut down with a grinding noise. Replaced the gear train failure engine with a used one, broke a liner on that engine, then in-framed this one last year. If it is what it seems it might me, my bus days are over for good.

I'm on my way out there now to try and get the alt. off. If I get it off and don't see broken gears, can I cover the hole with cardboard and plug the oil line that was feeding the alt to get it in the shop?
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1980 GMC H8H-649  8V71/V730 Marion,NC

"The highway is for gamblers, better use your sense" -Dylan
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« Reply #11 on: February 14, 2012, 03:39:54 AM »

If you just had an Inframe a year ago, it would seem to me that someone else might be responsible for this plus it looks like a lot of oil covering the engine for just being rebuilt! You might want to go visit the mechanic or shop that did the work and ask what's up even if it's past their warranty stage!
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Ace Rossi
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brando4905
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« Reply #12 on: February 14, 2012, 03:55:04 AM »

The oil is from the feed line to alt., it was severed when it broke loose from the engine, spraying 40wt all over. I definitely have questions as to why this happened, but not placing any blame yet.

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1980 GMC H8H-649  8V71/V730 Marion,NC

"The highway is for gamblers, better use your sense" -Dylan
brando4905
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« Reply #13 on: February 14, 2012, 04:31:11 AM »

Here's a few pics of what it looks like now. Only one of the 1/4" bolts that held the head on was present, and it was backed all the way out. Doesn't appear to me that they broke, looks like they all worked their way out somehow?





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1980 GMC H8H-649  8V71/V730 Marion,NC

"The highway is for gamblers, better use your sense" -Dylan
luvrbus
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« Reply #14 on: February 14, 2012, 05:03:50 AM »

Brandon, that had to happen all at one time a loose bolt those things leak and you would have noticed it, check your drive careful I hope no one just installed a drive on a standard cam and mickey moused the drive those need to be installed right  
I preached to this choir here before about the 50D it is a bomb waiting to explode if not taken care of,Boomer will give you good advice as I remember every 100,000 mile they did a inspection and maintenance pulling alternator and changing the drive think I read that from him.

I don't see where the guy that did the inframe could have anything to do with that it would be no reason for him to be in that area unless he did a parts swap from your other engine

.Hope it not a hard fix and no damage to the gear train you can tell  when you remove the rest of the alternator fwiw every time you shut the engine off the alternator gets a back lash it's the nature of the beast sometime it breaks the cam

good luck
« Last Edit: February 14, 2012, 05:08:13 AM by luvrbus » Logged

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