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Old 03-15-2017, 08:58 PM   #1
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Why 2 engines

Ok, I know why i have 2 engines on the bus. One is for the Driving of the bus and the other appears to power the AC on this 1988 Chevy Thomas School Bus with a 366 v-8 and a driver side under the bus mounted inline 4 cylinder. But why and are they that good for AC anymore? I would like to know if anyone knows anything about servicing this engine and/OR is there away to convert this to an onboard Generator to power the buses electrical needs. Desperately seeking advise. Do i rip out every thing or keep the engine? Thanks peeps.

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Old 03-15-2017, 09:17 PM   #2
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Year: 1991
Coachwork: Carpenter
Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
I would keep it!!.. you now have A/C for when you are parked.. thats usually the Biggest user of electricity when boondocking there is...

slap a 200 amp alternator or 2 on it ( if it doesnt already have one), an inverter or 2 and now you have 110 volt AC power from it.. ill bet that engine can easilt run your air-conditioning and at least 1000-1500 watts of power.. I doubt you'll need more than that?

I know others will tell you to rip it out and put up solar or some other fancy stuff.. and get rid of the A/C.. (this crowd seems anti A/C).. but id keep it, modify it and use it, its already there.. you dont have to buy or retrofit anything to use it..
its something i could only wish I had in my bus..
-Christopher
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Old 03-15-2017, 10:06 PM   #3
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Year: 1991
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I would definitely keep it. Do like Cadillac kid said.
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Old 03-15-2017, 10:18 PM   #4
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I don't know anything about that particular secondary engine, but it sounds like a great find. As long as it works or can be repaired, you can probably hook up an alternator to it and generate power. You might want to look at some of the old designs made by people who created brackets to attach alternators to lawn mower engines and other such miscellaneous sources. Folks in the self-sufficiency business have been rigging generators out of anything that can produce rotational force for decades, so there's definitely a way to do it - it just might take a little inventiveness to machine or source the parts you need.
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Old 03-15-2017, 10:24 PM   #5
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Year: 1990
Coachwork: Crown, integral. (With 2kW of tiltable solar)
Chassis: Crown Supercoach II (rear engine)
Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
Rated Cap: 37,400 lbs GVWR
And from a committed solar proponent, I also say keep it! Do as Christopher says, put a big 12VDC alternator on it, and also a 120 VAC alternator, then you've got the same as a modern truck APU but for a fraction of the price. GM 4104 buses in the 1950s used a small gasoline engine for their A/C, so you're in good company. Later on if you want to add solar (and why not?), you've now got your back-up Plan B for when the sun's not shining.

Another option for a gasoline engine, especially one that may not be used much, is to convert it to propane. Assuming you'll have propane on board anyway for cooking and heating, you'll have a fuel that never goes stale and gums up the carburetor, like can happen to infrequently-used gasoline engines.

John
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Old 03-15-2017, 10:33 PM   #6
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Quote:
Originally Posted by Iceni John View Post
And later on if you want to add solar (why not?), you've now got your back-up Plan B for when the sun's not shining.
Precisely. A small motor coupled to a hefty DC alternator makes a great source for charging a battery bank if your sun intake has been low. It's more efficient for that purpose than charging from a typical generator. It's similar in concept to the more costly "inverter generators" that are sold in that it creates DC as its primary output and only produces AC by way of an inverter stage.
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Old 03-16-2017, 12:18 AM   #7
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Year: 1990
Coachwork: Crown, integral. (With 2kW of tiltable solar)
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Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
Rated Cap: 37,400 lbs GVWR
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Precisely. A small motor coupled to a hefty DC alternator makes a great source for charging a battery bank if your sun intake has been low. It's more efficient for that purpose than charging from a typical generator. It's similar in concept to the more costly "inverter generators" that are sold in that it creates DC as its primary output and only produces AC by way of an inverter stage.
In theory maybe, but in practice you'll still want to charge them through a proper 3-stage (Bulk, Absorb, Float) temperature-compensated charger set to exactly the voltages and times your specific batteries need for a correct charge. Just pumping 12 volts into them is like using an old-fashioned unregulated 'charger' or converter - they can easily boil batteries dry, or not charge them enough. Technology has progressed far since those days, and batteries will benefit from modern charging protocols.

John
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Old 03-16-2017, 01:02 AM   #8
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Most coach A/C systems take 10-40 HP to operate. The range covers the different sized systems.

It takes a lot of HP to turn compressors and alternators that are working harder to support the added strain of condenser and evaporators fans. Many buses have an additional alternator that kicks on when the clutch for the A/C compressor kicks on. The additional alternator is dedicated to running just the electrics for the A/C system (which makes troubleshooting a problem if the clutch doesn't kick on).

In your case, while the GM big block 366 gas V-8 is a healthy performer, in a full size bus it has to work really hard just to move the bus down the road or to climb a hill. If you added the additional work to run a coach A/C system the bus would be relegated to slow lane whenever it was running.

Using a pony motor to power the A/C system is a very elegant solution to having A/C and still being able to run highway speeds.

Others have pointed out ways in which to utilize the pony motor for other purposes than just for the coach A/C.
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Old 03-16-2017, 02:08 AM   #9
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Originally Posted by Iceni John View Post
In theory maybe, but in practice you'll still want to charge them through a proper 3-stage (Bulk, Absorb, Float) temperature-compensated charger
No one is advocating just pumping the alternator output into batteries directly. That's a great way to boil them dry and ruin them.

Lots of modern generators create DC and run it through an inverter to get AC, which you would then have to feed back through a charger to get DC for charging. My point was that you benefit by not taking that inverter loss if you have a way to just plug straight DC into your charger.
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Old 03-16-2017, 03:33 AM   #10
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Engine: 366 Big block Chevy! :) w/ Stick shift
John's right

Quote:
Originally Posted by Iceni John View Post
In theory maybe, but in practice you'll still want to charge them through a proper 3-stage (Bulk, Absorb, Float) temperature-compensated charger set to exactly the voltages and times your specific batteries need for a correct charge. Just pumping 12 volts into them is like using an old-fashioned unregulated 'charger' or converter - they can easily boil batteries dry, or not charge them enough. Technology has progressed far since those days, and batteries will benefit from modern charging protocols.

John
Ask me how i know! Charge controller accidentally got set to gel and boiled two trojan deep cycle batteries. They need to be charged correctly or will be easily ruined.

And very cool about the 4cyl generator, also this 366 bbc is a superb motor. Been used in dump trucks and medium duty rigs for quite awhile; simple and easy to work on.
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Old 03-16-2017, 04:17 AM   #11
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Engine: DT466, MT643
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My bus has a diesel Mitsubishi L3e that operated the R12 A/C, and very bulky ductwork inside the bus, with 12 extremely loud fans.

I was given a 25k Generac whole house generator with engine problems, so I pulled the generator head with hopes of eventually Franken-Morphing the Diesel engine to run the generator.

Until that time, I'll simply use window a/c units as I'm stationary 95% of the time. I can't justify sinking money into it yet, just for road A/C... But, storing the components is costing me zero dollars at this point. I'd rather sink the money into roof a/c units or mini-splits.
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Old 03-16-2017, 06:34 AM   #12
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Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
convert the R12 A/C to a replacement drop in or simply change the TxV and run it on R134A.. remount the evaporators and re-duct.. and then you have nice A/C when driving rather than sweating..

I agree that the coach units installed by factory often are ugly and in the way... but they can easily be moved or modified without issue as long as you duct them somewhere , have a condensate pan, and reconnect the lines and charge correctly.. its not a great idea to mount coach A/C units lower than the condensor though.. you'll trap all the oil and ruin the system..
-Christopher
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Old 03-16-2017, 09:20 AM   #13
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Originally Posted by cadillackid View Post
I would keep it!!.. you now have A/C for when you are parked.. thats usually the Biggest user of electricity when boondocking there is...

slap a 200 amp alternator or 2 on it ( if it doesnt already have one), an inverter or 2 and now you have 110 volt AC power from it.. ill bet that engine can easilt run your air-conditioning and at least 1000-1500 watts of power.. I doubt you'll need more than that?

I know others will tell you to rip it out and put up solar or some other fancy stuff.. and get rid of the A/C.. (this crowd seems anti A/C).. but id keep it, modify it and use it, its already there.. you dont have to buy or retrofit anything to use it..
its something i could only wish I had in my bus..
-Christopher
tHE Kid is totally correct.
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Old 03-16-2017, 11:21 AM   #14
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My bus has a second engine, its a 3 cylinder diesel generator plumbed into the bus fuel tank. the generator puts out 12kw and runs the roof top A/Cs and the rest of my electrical.

personally i think its a huge advantage to your build. but i have seen another bus owner in the same situation sell their generator to pay for part of their conversion.

it just depends on what your ultimate goal with the bus is. mine included a generator, some others do not.
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Old 03-16-2017, 03:30 PM   #15
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Talking Dang the FACES of Bus Mount Rushmore

Im so glad i have you guys to lean on. I have collected all the ballots and i Have voted on KEEPING the PONY motor. I truly appreciate the feedback all have given. Now to get the dang thing started and running. Looks like i will need to set points for it. At one time it appeared that the PONY motor could be started from the cock pit. I m going to need to chase down all the firing and see what signals what. Super pumped about this bus as its from the year i graduated highschool 1988.

I have lots of crazy plans, seats i pulled out last week, soon to get the floor ready.

In advice on adding a deck to the top of the bus,,,, with a spiral stair case leading up from the back of the bus on a deck?

Bus Life, im liking the learning.

Again thanks Buddies
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Old 03-21-2017, 09:04 PM   #16
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Year: 1991
Coachwork: Thomas
Chassis: Thomas
Engine: CAT
Rated Cap: 60 passenger?
1991 Thomas Diesel Pusher

I have the second motor for sale. I took it out of my project.. I would love to sell it.. I dont want it to go to waste.. Just sit there and ruin. Please let me know if you know of anyone interested.. Thanks
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Old 03-21-2017, 09:13 PM   #17
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Quote:
Originally Posted by DaddyRabbit View Post
I have the second motor for sale. I took it out of my project.. I would love to sell it.. I dont want it to go to waste.. Just sit there and ruin. Please let me know if you know of anyone interested.. Thanks
I am interested. Where are you located?
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Old 03-22-2017, 07:43 PM   #18
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2nd Engine

I am in NW GA.. Outside Chatt, TN
Send EMAIL.. I will contact you if you send number
Thanks Daddy Rabbit
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Old 03-22-2017, 10:52 PM   #19
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Originally Posted by DaddyRabbit View Post
I am in NW GA.. Outside Chatt, TN
Send EMAIL.. I will contact you if you send number
Thanks Daddy Rabbit
I don't have your email address. I did send a PM though. Hopefully that works.
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Old 07-31-2021, 08:47 AM   #20
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How did this project turn out!?!?! I have the exact same bus in great shape and want to use the VW to power the fridge, lights, fireplace, TV, etc.
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