DD alternator horror story

[JohnEd]

Lin offered me a righteous deal on a DH-50(?) for the 8V92 and other DD's.  Well, I don't need one and I wanted to be helpful(to Lin) and also I thought my Bud in the truck alt rebuild bidness (that's Texan) might have interest.  Got a little education of sorts and I am positive others can amplify/correct what I learned.

Rick has been in the alt rebuilding racket since graduating HS and he is in his mid forties.  He makes no claim to knowing it all but he has probably forgotten more that most here will ever learn.  He isn't all that mouthy but he is principled in that he will try to stop you if you are making a mistake.  Nice guy.  I mentioned the alternator and he motioned to a shop cart with a "brandy new" rebuilt on it.  He said that his rebuild charge for that one was $1200.  As far as the price that Lin quoted, the core charge alone was nearly twice what Lin wanted for his REBUILT.  Lin is indelibly in my mind as a good guy and generous beyond the call.

NOW HERE IS THE IMPORTANT PART(POOP): I learned that the gear driven alt can completely ruin a DD in a New York minute.   The bearings seize up and take out the gear train and that lets the cams operate independent of the crank and that is confusing to both.  Rick said that DD recommends that the alt be rebuilt at 100 or 125 K mile intervals.  With such catastrophic consequences I truly wonder that I haven't heard that mentioned....and re-mentioned.  If it is the alt bearings that do all the damage then why not remove the thing at 90K and replace the bearings as a PM. 

What say the experts about this latest dose of scuttlebut?

John

[luvrbus]

JohnEd, it will happen and not a pretty sight to see there is nothing left when that happens no way will I run a gear driven alternator and then again it may never happen but with me it would LOL.
Fwiw they have a backlash adjustment on the engine and folks never check it till it is to late. 
You know the drill here if not broken don't fix it 



good luck

[JohnEd]

Clifford,

Thanks for the confirmation.  I guess Rick wouldn't know about the backlash adjust.  Superb info for all.

I suspect that there will be a serious flurry of activity in the alt area thanks to your confirmation.  This is a case where What You Don't Know can cost you $25K and ruin a weekend outing.

Thank you Clifford,

John

[zubzub]

For sure the gear driven alt is a potential weak link in a DD.  Personally I am still trying to set up a belt driven alt for mine....maybe even with  an air tensioner....since I have one around

[roadrunnertex]

It's called a 50-DN alternator.
For most part these type oil cooled alternators are very trouble free.
At one time I owned a 1960 PD4104 serial number 5025 that had the 50-DN as a option from the factory never had a problem with it as long as I owned the coach.
I now own a P8M5905A and it has the 50-DN oil cooed alternator 24 volt never has been a problem.
These 50-DN alternators were put on all of the GMC intercity coaches from the PD4106's through the H8H649's.
Greyhound put them on the PD-4501's Scenicruisers the MC-8 and the 9's and later model MCI had them.
I sure would not remove it for a belt driven alternator.
But to each his own!
jlv

[white-eagle]

where is this backlash adjustment thing?  after hearing you two and knowing i have about 140k on my engine (according to PO and Heartland in Arcadia), i think i need to adjust mine now! 

[zubzub]

I sure would not remove it for a belt driven alternator.
But to each his own!
jlv

I probably wouldn't have removed it either, but my 67- had a dead split field generator, and the mountin configuration on the 671 is such that I can't install the (free for me) alts on the 6-92 I have access to.
BTW does anyone know?  on the 671 the gear drive and mounting flange for the alt are in line with each other and on the 6-92 they are off set....so you can't mount a 6-92's alt on a 6-71. 
My ? are the 6V71 and 8V71, alt drives offset or direct.

[JohnEd]

White Eagle,

I am told that replacing the roller bearings in the 50 DN is required by DD at 100K miles.  Clifford has a valid point in that there is precious little that can go wrong with a DD that will destroy the engine in its entirety.  The gear driven 50 DN is that single point of failure.  I also agree that the thing is over designed and extremely reliable if properly maintained.  Gears are less maint and sap far less power than belts, any day.  Given the choice I think I would go with Clifford unless I did the overhaul and KNEW the gear train was new and properly adjusted and the 50 DN was also in like new condition.  Now just figure the odds on my not checking the bearings with a stethoscope OFTEN.

INMHO and that really humble,
John

[Chopper Scott]

Glad mine is belt driven! I have a buddy who owns a wrecking yard and one of his Case loaders with a Cummin's had the gear driven compressor lock up, sheared off the shaft, and did some major damage that resulted in a major rebuild. Probably not something that is limited to the DD's.

[wal1809]

I have a 6v92. Is it gear driven like y'all are talking about?  Mine has a ujointed shaft from he engine to a gear box.  It has a shaft that goes 90 degrees to the left side of the bus where it runs the alternator.  Belts from the alternator run the radiator fan.  On the other side of the gear box was another shaft that ran the air conditioner when I had one.

Anyhow is this the same kind y'all are talking about?

[luvrbus]

No Wayne that is the standard mitre box setup for a Eagle the miter box shaft goes to a pillar block then the fan and alternator run from the pillar block make sure to grease the pillar block.


good luck

[wal1809]

Hello Clifford!!  Thank the lord and all that is holy.  $1200 for a rebuild is not what I need right now.  I did grease that block for I had a squeal backthere on start up when I bought it.  I started greasing all zirks I could find.  That bad squeak is now a chirp on start up so I guess I got it.

[Barn Owl]

For real?   Now all the gear guys are going to be biting their nails off.    If only I could rack up the 100k miles to even think about it......then again, I need a rebuild anyway.   Life is real good if we only have a geared, or non-geared 50dn to worry about. For me, I love the geared version.   Of all of the problems I have ever read about in the bus conversion world, I haven't seen this to be one of them. Time and money would be better spent on items that have proven to be real show stoppers. My very late night, shouldn't be posting, opinion of course!

[busshawg]

so when I want to eliminate my gear driven alt completely,  do I simply make a plate with a gasket to cover the hole where it was mounted??

[Van]

Yup! stock cover or do your own if a stock one is not available.