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Old 02-06-2018, 11:38 AM   #1
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GM 4107 Engine

I am going to be looking at this Coach here soon and the owner sent me pictures of the engine as I requested. Trying to figure out why an Alternator on the front. Owner of the coach belonged to her dad that has since passed. The owners couldn't give me a reason other then charging the batteries. Should I be looking for a problem somewhere? I am a Newbie so trying to figure out what to look for when I get there.Click image for larger version

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Old 02-06-2018, 02:19 PM   #2
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The old 8V71s could have drives on the front and rear timing gear covers for running things like an alternator or compressor. You can see the air compressor on the opposite end. The cam shafts were just below the head.

That's probably where a good size alternator would go, but that looks like a small frame 90 amp Delco.

While looking at that engine, keep in mind that its a V8 engine that they lean over on its side, making one bank of cylinders level with the ground and the other standing up. Its not a big deal but that's what they did it to fit them big, 2 stroke, Detroit Diesel engines in.
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Old 02-06-2018, 02:34 PM   #3
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Thanks Twinboat . It looks like a small alternator. But I guess I don't have to worry about it. The owners just emailed me telling me the coach was sold. I wished I could have looked at it first tho. There might have been a reason that they were selling at a low price too. So onward I go.
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Old 02-06-2018, 03:46 PM   #4
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They were probably selling it cheap because the drive train is pre-historic.

Most of today's mechanics would be scratching there head, looking at that.

Good luck shopping.
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Old 02-21-2018, 08:39 PM   #5
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Agree with twinboat. Not only is that engine ancient but it has a very bad habit of puking oil on the ground at startup. Not good....then there is the situation where oil usage is measured in gallons not quarts. Stay away from Detroit 8v-71s.
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Old 02-21-2018, 08:43 PM   #6
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Those busses are “city busses “. Meaning they have no basement for storage and equipment. Plus the chassis is geared for city driving. 65mph, not!
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Old 02-21-2018, 09:21 PM   #7
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GM 4107 Engine

The 4107 I thought /think was a 60s intercity bus had a fairly large luggage basement and were meant for highway use. The ones I think I’ve seen had a cool scenicruzer style roof window and slightly elevated passenger floor behind the driver. But I don’t know the numbers on these buses 4106 4107 etc Nice but you need the right mechanic. The 8v engine is a different animal
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Old 02-28-2018, 01:26 PM   #8
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sorry stretch, but a 4107 is not a city bus with no storage. It is just a shorter version of a 4905 inter-city coach.
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Old 02-28-2018, 03:33 PM   #9
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That little alternator is pretty sad. That is just enough alternator to power a single 12V battery to get that bus's instruments working and not much else.
There is no way it would keep the entire bus charged and running.

It's been over 35 years since I last worked on a GM bus but IIRC the alternator, actually generator on the ones I worked on, was PTO or belt driven off the back side of the engine. The generator was about the size of a 5 gallon bucket.

The 8v-71 DD, and its predecessor the 6-71, were a workhorse for GM for many years and with routine maintenance it would last 300000 to 500000 miles and it also helped to keep the dust down on gravel and dirt roads due to it's auto-road oiling feature.
I put on 250,000 miles on an 8v-71T among others, and rebuilt a few, so I have some background to make a valid comment instead of passing on anecdotal information.

If the rest of the bus is in good shape and the price isn't high, you could consider it. If the rest of it is as cobbled up as that little alternator, I would back off and find the next one.

Good luck,
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Old 03-01-2018, 06:32 AM   #10
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I would venture that the small alternator was added for the purpose of charging a separate battery. I know my 4905 bus had the original 24 volt electrical system that ran the over the road a/c, starter and other various systems, so, when I switched the headlights over to 12 volt, I also hooked up a smaller alternator and 12 volt battery to run the lights. Not all that unusual on older coaches.
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Old 06-17-2018, 03:45 PM   #11
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I actually worked on 4107s years ago. They were 12 volt and had a gear drive, oil cooled alternator.
I would guess either the original alternator parts are no longer available or the cost of rebuilding was prohibitive.
I have the maintenance manual for 4107s up in the attic.
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Old 07-08-2018, 02:57 PM   #12
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Quote:
Originally Posted by Stretch View Post
Those busses are “city busses “. Meaning they have no basement for storage and equipment. Plus the chassis is geared for city driving. 65mph, not!
Sorry Ross, all wrong. I had the 4905 which is the 40 ft version of the 4107. With 4 speed, would hit 83 mph and had over 400 cf of bay storage.
Great highway coach.https://en.wikipedia.org/wiki/GM_Buffalo_bus
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Old 07-09-2018, 06:40 AM   #13
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jcussen, you're spot on I had a 4905A #592 with the grumpy 4 speed, that I converted and it would hit the mid 80's anytime I wanted. (on the flat of course)
Kind of wish now that I had kept it.
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Old 07-09-2018, 08:12 AM   #14
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Me too, had about a million miles on it, have worn out several sticks and staples since then.
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