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Author Topic: Internal trouble in a DD 8v92  (Read 3644 times)
Flatspot
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« Reply #15 on: April 20, 2011, 06:59:33 PM »

Now you guy's have me concerned. I've got an 8V92 with a 50D alternator. (Clifford I know how you feel about 50D alternators)The PO had it replaced at 160K miles with a brand spanking new one at a DD Shop in Atlanta. I've got the documentation. However the thing that has always bothered me with this engine is that I hear what sounds like gear train noise when the compressor is loaded. When the governor unloads it goes away. I don't hear this noise on the other 8V92's that I've been around but again they are running with out mufflers...
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Zuzax, New Mexico (Exit 178 I-40) 12mi East of Albuquerque

1956 PD4104 6-71T
1988 Eagle 15 CC Conversion
1983 Mack W Utility Bed Service Truck (road assistance in New Mexico)
happycamperbrat
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« Reply #16 on: April 21, 2011, 03:32:11 AM »

Oh geeze! Just a couple of weeks ago I was in a big discussion on the RTS yahoo group about these big alternators going off like grenades in our engines. The guys there are changing out to belt driven alternators and fabricating their own brackets for them....
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The Little GTO is a 102" wide and 40' long 1983 GMC RTS II and my name is Teresa in case I forgot to sign my post
Mike in GA
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« Reply #17 on: April 21, 2011, 07:48:21 AM »

Thanks for the interesting responses, fellow Bus Nuts! Today is test drive day for the repaired engine (with swapped in 5-speed and Jakes!). Results will be posted tomorrow.
    I was alarmed about the comments regarding the big alternator possibly being the culprit, so I went back to my mechanic and raised the question.
   He told me that 8v71s had a much worse track record with the alternator causing gear train failure, and in some cases they even destroyed camshafts. Yes, he said, many 8v71 owners removed their stock alternator, out of fear this may happen, and installed a belt driven truck one - as long as they had removed their over the road bus air.
   In the 8v92s the alternator problem was lessened, he said, through production improvements. Also, in my engine's case there are lash adjustments on the alternator housing that he did prior to buttoning it up that trued it up within several hundred thousands (if I understood correctly). That, plus new taper bearings on the idler gear, should have me set, he said.
   I'm not sure I have effectively translated this back, but I think I have it right. I do have sufficient peace of mind.
   Many of us repair only what's broken when faced with engine challenges, either out of economic reasons, or time savings, etc. I've gone a little beyond that. But how far should one go?
   A friend in the aircraft industry once explained that industry's technical description of an engine rebuild. Every part is disassembled and measured and miked for wear. Parts are then kept or replaced based on their industry tolerences for being "as new". Maybe overkill for engines in our kind of service, but great peace of mind.
Mike in GA
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Past President, Southeast Bus Nuts. Busin' for more than 14 years in a 1985 MC 96a3 with DD 8v92 and a 5 speed Allison c/r.
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« Reply #18 on: April 21, 2011, 08:37:41 AM »

The cam is different in a 92 series it has a bolt, thicker gear and not the nut on the end of the cam it has a different type locking ring and the gear bolts to cam gear and they use a vibration damper on the front of the cam shaft and no one ever changes that per DD 100,000 miles.
Mike glad your guy knew the 2 screws for adjustment was in the flange most don't. 
The 92 series will still break cams or the nut comes loose on the 50D,you never know I have saw engines run for 300,000+ miles on the factory adjustment seen them run for 200 miles on the backyard repairs 


good luck
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Mike in GA
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« Reply #19 on: April 22, 2011, 06:31:11 PM »

Picked up the bus this afternoon, and everything worked great! In addition to really liking the new 5-speed AT, I love the Jakes - can't wait to try them on the big hills. Also, the engine seems to have picked up a bit more power, and the smoking under heavy acceleration is gone.
    Ahhhhh = peace of mind!
    Thanks, board members, for all the support and suggestions.
    Now to clean her up and get her loaded for the big April in the Carolinas rally in So. Car. this coming  week!
Mike in GA
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Past President, Southeast Bus Nuts. Busin' for more than 14 years in a 1985 MC 96a3 with DD 8v92 and a 5 speed Allison c/r.
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« Reply #20 on: April 22, 2011, 06:45:29 PM »

 A friend in the aircraft industry once explained that industry's technical description of an engine rebuild. Every part is disassembled and measured and miked for wear. Parts are then kept or replaced based on their industry tolerences for being "as new". Maybe overkill for engines in our kind of service, but great peace of mind.
Mike in GA

  Actually, what you described would meet the tolerances for what the FAA calls an "overhaul". Within the terminology of "rebuild", parts can actually be near wear limits. Theoretically, if every part within the engine had a maximum wear limit of .003", a mechanic could build an engine with used parts that are all at the .003" limit, and call it a rebuilt. But it would be pretty loose and wouldnt last very long. Overhaul refers to an engine with parts that meet tolerances for new parts.

  There were a couple clowns down in TX that built some engines that way, gave em a nice coat of paint and sold em as complete overhauls. I think they are still holding down rooms at Leavenworth.

  I really would hate to pull my motor out and find nothing wrong with it. But I think I would really be raging if I didnt, and some stupid little thing fubared the engine 500 miles out.
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happycamperbrat
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« Reply #21 on: April 23, 2011, 02:02:37 AM »

Good going Mike!

I saw the 8v71s were bad and the 8v92s were better but I didnt see mention of the 6v92s....... I would imagine they would be like the 8s?
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The Little GTO is a 102" wide and 40' long 1983 GMC RTS II and my name is Teresa in case I forgot to sign my post
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