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Old 05-18-2009, 04:27 AM   #1
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Using car/pickup engine/trans in heavy bus?(ie cad500/th400)

I'm trying to plan a bus conversion that I intend to live out of for an extended period of time (my handle should give you a clue) but I have a near-phobia over getting a $2500 bus that all the sudden has an $8000 transmission repair bill or a $12000 engine rebuild like some of the nightmares i've read about online. Because i'm concerned about becoming destitute or wiped out on an unforseen mechanical problem that I can't fix.

So i'm trying to find whether it's possible feasible or worthwhile to use more cheaply replaced components so that even in event of catastrophic failure (or shortened life) I can swap in another car engine/light truck transmission out of the junkyard for $500 using a standard light duty cherry picker and get back on the road or even put in a rebuilt and hopefully reliable engine for a fraction the cost of a rebuilt medium duty diesel and Allison.

I'm also hoping to solve the lack of power problem commonly experienced.

So what i'm thinking is an engine like the Cadillac 500, Oldsmobile 455, or of course just another big block Ford/Chevy/Dodge motor but not necessarily the truck duty motor. And a transmission like the TH400 which is very strong for light trucks, but obviously not made for something the size and weight of a schoolbus. I'm not expecting them to last 200,000 miles - what i'm wondering is whether anyone thinks they will last 30,000-50,000 miles reliably without breaking since the average load due to wind/weight will be much higher on the highway, or whether anyone else has considered conversions like this.


Asking on the "hot rod" boards nobody really seems to know, they dont deal with superheavy (by their ranking) vehicles.
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Old 05-18-2009, 10:33 AM   #2
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Re: Using car/pickup engine/trans in heavy bus?(ie cad500/th400)

Look at any common gas engine and a manual 4 or 5 speed transmission, a bus is just a different body on a medium duty truck chassis.
before the advent of the modern small diesel engines, most medium trucks used gas engines, even today a gas engine is an ecenomical way to power intercity, low mileage trucks, also we are seeing gas engines being used with alternative fuels in fleet vehicles.
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Old 05-18-2009, 12:37 PM   #3
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Re: Using car/pickup engine/trans in heavy bus?(ie cad500/th400)

why not just find a bus with a reliable diesel ie: cummins 5.9, dt series international, ford 7.8 litre with under 100K miles? Then you could travel the next 200K miles relatively worry free, and with double the fuel economy of a gasser.

the most recent bus i bought with 67K miles and a cummins 5.9 for $2K. I think that if you found a bus like that you'd be set for a long time.

a gasser would have much better performance than a diesel, but half or less the fuel economy. I don't know how easy it is to find good big block motors at the local junk yard. Seems that the big V8 cadillac motors, 455 rocket motors etc aren't that common anymore. Around here, most junk yards sent all their cars away to the metal recyclers when steel prices were sky high last summer, so most older auto's disappeared.
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Old 05-18-2009, 08:02 PM   #4
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Re: Using car/pickup engine/trans in heavy bus?(ie cad500/th400)

I know they used gas engines but the truck versions are usually built for the heavier loads just like a marine engines. (forged cranks, forged rods, etc.) Thats not always the case with passenger car/light truck stuff.

If I find one with a reliable diesel for $2k I definately would be set, i'm just afraid I may accidentally discover it's not really reliable and that the repair bill will exceed the cost of the whole bus. I'm more afraid of a single huge expense then a periodic smaller expense. But I might be going in the wrong direction too, I dont know so i'm just wondering out loud.

I know I still see entire older big block cars for like $600 - with a Cadillac 500 and such. Since i'm hoping Caddy drivers are easier on their cars, i'm hoping it would be a good swap.

Not as worried about fuel economy if I wont be driving it much. Plan to use it as a home much more than an RV. I mean yes I want fuel economy but i'm concerned the additional costs of diesel or the risk of a worst-case engine problem will outweigh it for the few times of year i'd be actually driving it. Actually i'm even more concerned about the cost of a transmission problem since those Allisons aren't cheap but TH400's are like $400 in the junkyard.
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Old 05-18-2009, 11:20 PM   #5
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Re: Using car/pickup engine/trans in heavy bus?(ie cad500/th400)

Ask Vanguy67 about his experience buying a bit of a lemon... or read his thread about his poor "Carpy".

He'll tell you that it is worth the money to have the engine oil and transmission oil analyzed by a lab. The report will tell you a LOT about the engine/tranny and then you'll know whether it is worthwhile to have a mechanic look over it before you buy it.

My take on the engine/transmission swap from a gasser is that it is likely a lot more trouble than it is worth. Frankly, if you want a gasser bus, buy one that is already a gasser.


Converting a diesel to a gasser seems like a backwards step to me. Seriously. But then, I'm a big fan of diesel grunt.

Worst case, you have $2,000 tied up in your bus plus all your conversion work and the engine or transmission craps out. $8,000 for a transmission repair? 12,000 for an engine repair? Heck, just buy another $2,000 bus and pay a mechanic $1,000 to swap the good part into your bus. Then sell the other good part for $$$ and get the chassis hauled off for scrap (more $$$)

These busses were designed rather modularly. Assuming you don't have major frame or body damage, pretty much everything else can be fixed, and much of that can easily come from a cheap donor bus.

good luck,
jim
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Old 05-19-2009, 12:48 AM   #6
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Re: Using car/pickup engine/trans in heavy bus?(ie cad500/th400)

Well I wasnt suggesting converting a diesel to gas unless it's some abnormally old bus or some expensive to fix engine, just taking an existing say gas 366 with an Allison (a slow combination) perhaps with high miles, and dropping in the Caddy 500 and TH400 to up the power substantially and if it's lower miles potentially increase the reliability. I wont be rebuilding an Allison for pennies thats for sure... the big block chevies can be rebuilt for a decent price, it's mostly the transmission i'm concerned about. Dont want to be stranded halfway to burning man and needing a 100 mile tow.

Of course I suppose a manual transmission with a new clutch would make the "your transmission instantly dies" fear I have of automatics alot less likely, hmm. It just scared me reading about a guy who bought an MCI bus for $8000, and then had the Cat 3208 cost thousands in repairs on the way home and then the Allison transmission went out once he got home and needed total replacement for even more. I don't want financial time bombs and on a long cross country trip I might rather try to do an eng/trans swap over trying to find a new skoolie on short notice and not really having a chance to properly check it over especially with what it will take to convert it there.

I'll take to heart the oil analysis idea though, what specifically would I want to have tested or what would it tell me? I dont know anything about it.
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Old 05-19-2009, 02:04 AM   #7
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Re: Using car/pickup engine/trans in heavy bus?(ie cad500/th400)

oil analysis is most beneficial if you have a running history so you can see changes in component wear and impending failure, the process involves taking a sample of oil and having a lab run it thru the mass spectrograph and then identifing and counting the different materials in the oil, a new engine will show high metal and silica content which is normal for the breakin process, then the metal and silica counts should go way down and stay down after the second or third oil change, after that an increase in content indicates wear, depending on the type of metal and content of different compounds the wear items can be diagnosed and repair/rebuild can be done before catastrophic failure. the lab will want to know what oil is in the engine, how many miles/hours on the oil and engine and what fuel and coolant is used as well as any addatives. some fleets of large equipment sample fluids on a regular basis and use the sample results to identify when to change fluids and perform maintainence.

test the engine,trans and rear axle, at the purchase point you mostly want to look for high metals, coolant, and "snake oil" addatives that could be hiding bigger problems. coolant in the oil is always a sign of something not good, high metals means either high wear or a lack of maintaince, fresh oil and addatives are an indication of a cheap fix to "get it out the door". a coolant sample is ood to see if their is any sign of oil and to make sure that the addative package is good.

If your really concerned about trans failue, go with a manual trans and have a competent mechanic inspect the clutch, if it's less than 50% schedule a replacement at your convenience and price point, if the ringgear shows wear replace it with the clutch, "parts are cheap, the labor is expensive".

If you go diesel the inline 6 cylinders are easiest to work on,the ih 6's have replaceable liners while the 5.9 cummins and 3126 cat do not have replaceable liners
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Old 05-19-2009, 10:58 PM   #8
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Re: Using car/pickup engine/trans in heavy bus?(ie cad500/th400)

I've found several "deals" but they always have a manual transmission. I can only drive an automatic. The last one was an '85 Chevy w/ gas motor that's already converted except holding tanks. $1,500. I think this would be worth getting and swap TH400 for the manual if it would hold up.
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Old 05-20-2009, 09:52 AM   #9
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Re: Using car/pickup engine/trans in heavy bus?(ie cad500/th400)

Quote:
Originally Posted by keithsmadscience
I've found several "deals" but they always have a manual transmission. I can only drive an automatic. The last one was an '85 Chevy w/ gas motor that's already converted except holding tanks. $1,500. I think this would be worth getting and swap TH400 for the manual if it would hold up.
Have someone teach you to drive a manual transmission vehicle, it's a coordination thing . can't is an attitude, the truth is their was a time when you couldnt crawl or walk and someone helped you learn and then you practised and probably learned to run, ride a bike, drive a car, talk, read etc. you can learn the basics on a riding lawnmower or in a rental vehicle.

Back to the original post, their were lots of old MDT's with 6 cylinder gas engines and small gas v-8's built, usually with manual transmissions, lots of 1 ton pickups came with passenger type automatics, as a matteer of fact, I have a 92 dodge dually pick-up with a cummins 5.9 with a 727 torqueflite trans. that I use on a regular basis to pull a 24' gooseneck trailer with 1 or 2 jeeps on, 165,000 miles on fluid changes and a large external trans cooler. It's not a rocket but it pulls down the road @ 60/65 mph loaded. the only engine mods are a low flow aircleaner and a custom 4'' header all the way to the rear bumper
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Old 05-21-2009, 02:34 AM   #10
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Re: Using car/pickup engine/trans in heavy bus?(ie cad500/th400)

My 30 foot bus has a 350 chevy engine in it! Came with a 327 origionally!Its still here!
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