Some general Diesel questions..

[Savantster]

Hey guys.. some questions for you expierenced types

How many miles before you'd expect to "need" a rebuild on a 6v92TA?
And what's the "most miles" you'd consider on an engine/trans when
buying a bus (with intent on mimimal repair costs, if possible).

What's the cost in/out frame for rebuilds? Is it something someone
could do on their own with a kit? (i.e. cylinder liners, injectors, etc)

What's the guesstimated top speed with 4.56 gears and a ZF5-HP 590
speed tranny? Are you typically limited by the govenor? or mechanical
limits? (considering I've heard of "chip changes" in the DDEC II comps
to get higher speeds, or that you were limited by chips, anyway).

What makes a motor a right hand rotation versus a left hand? I mean,
when do you use this or that? .. is it dependant on the transmission
you will have hooked in?

If an engine has "california smog controls" on it (if there is such a
beast, as such), what's involved in getting those off (if you don't
live in Cali), and how much extra HP would that gain you? And, more to
the point, how much better MPG?

Well, that about does it for now..

TIA!

[RJ]

Savantster -

If you're looking at a bus with 4:56 gears, you must be looking at a transit, most likely an RTS.

2100 rpm (max recommended by Detroit) will get you 65 mph with 12.00R x 22.5 tires, maybe 67 with 11Rx24.5s.

Turn it 2300 > 2400 at your own risk. . .

Fuel mileage will be in the 5 - 6 mpg range, depending on your right foot.

250 - 300K miles is about normal MTBO for a transit 6V92TA.  Double that for a highway coach.  Why?  Think of the type of use.

Complete rebuilt?  Much easier to buy a Reliablt exchange unit from Detroit for about $12K - which is roughly the equivalent you'd pay a shop to do the same work, w/o the warranty.

Yes, you can do the work yourself, but Detroits are not VWs, Chevys or Fords, there are several critical assembly points and adjustments that take a lot of experience to do correctly.  Not to mention it's a LOT bigger!

Original V-drive design by GMC required LH engines.  Both manual and V-730 automatics are set up for these.  (Exception is the VR-730, that's a RH version.)

Later-model transit manufacturers who used the V-drive layout started experitmenting with Voith and ZF gearboxes, which are RH rotating designs, thus some V-drive coaches have RH engines in them.

Fuel mileage and HP will be virtually the same between a CA engine and a Federal one, if it's a DDEC.  The major difference is that there is a more pronounced throttle-delay when starting from a dead stop - computer refuses to let engine come up to full fuel until the turbo produces enough boost - keeps the black smoke from choking the tree-huggers.

Since you mentioned that the coach has a ZF gearbox, you need to know that the electronic ZF needs to "talk" to the DDEC computer in order to operate properly.  Thus, you will not be able to remove the CA smog controls - Detroit won't do it on a DDEC motor, just like they won't up the HP to 350, the max recommended as the best compromise between HP and longevity.

If you want to run 70+ mph, you'll need a set of 4:10 gears (rare & $$$$$$$$) or seriously reconsider what shell you're looking at.  Most highway models will run 70+ w/o breaking a sweat, something a transit is hard-pressed to do.  Not that it cannot be done, there are several transit owners that post to this and other bus boards that have made that model work for them.

BEFORE you plunk down your hard-earned pesos for a shell, you need to seriously think thru and answer the following question:

"What do I want to DO with my bus"

Boondock on backwoods fire trails?  (Best shell - a dog-nosed skoolie)

Campground to campground with full hookups?

Long highway runs while on trips?

Work the fair circuit selling knick-knacks out of the baggage bins?

On-line Internet business?

Full-time?

Once you thoroughly think about your intended usage, the type of shell to buy becomes more obvious.

Then the questions REALLY begin. . .        

Clear as mud?

[Geoff]

Savantster---

If you are interested in converting an RTS, please join the Yahoo RTS group where you will get *correct* and unbiased information:

http://web.archive.org/web/20041023002236/http://www.cris.com/~nolids/rtsmain.htm

--Geoff
'82 RTS AZ

[Savantster]

Already over there, Geoff. Yet, no one answered my questions for 2 days, so I thought I'd ask the general diesel questions around.. to get a feel for what I should be offering on some RTSs.

some have 70k - 100k on them, then others from 140k - 200k, then the bulk are at 350k+. I was just trying to see if it was worth even looking at the 350k+ guys. I'd guess I need to stay under 200k if I expect to drive it for a few (5+) years Though, I'll only be putting on 3k - 5k a year, I'd guess. Maybe 10k on a busy year, but we'll see.

[RJ]

Savantster -

The RTS is a great bus, built like a tank, primarily because GMC designed it that way initially.

Geoff's is absolutely georgous, he's very proud of it, and rightfully so.  I have a tremendous amount of respect for what he's done with it, as well as some of the other RTS owners that frequent the bus boards.

I do like to tease Geoff about owning the "Second Generation Sports Car of Buses" (the GMC 4106 being the first generation), but it's all in good fun, and not meant to be disrespectful in any way, shape or form.  Think of these as the difference between a 1961 Corvette and a 1982 model - both sports cars, just natural evolution of the model.  (Geoff - Am I right - your RTS is an '82?)

If I was going to convert a transit, the RTS would be my first and only choice, hands down.

It's not that transit's don't make a good conversion, they do, but with this caveat:  They require more work to obtain the basement storage for house systems, their low top speeds must be dealt with, and the interior wheelwells create more of a challenge for your interior design.  Those are really the only major negatives to them, which I feel the newbie needs to know and understand.  OTOH, you generally do not have to raise the roof, because they've been designed for standees from the beginning.

Again, think about what you want to do with your coach, before you make a shell choice.  That's not a biased statement at all - it's been the mantra for everyone involved in the bus conversion process for years. . .

HTH. . .

[TomC]

There are a whole host of transits you can use.  First make sure they are high floor (usually single level inside) so you have room underneath for tanks and such.  Personally I considered an RTS, but after going inside and seeing the severe slant of the walls (which gives the bus its great looks!) I ended up with an AMGeneral that has almost straight walls, 6'10" headroom, the roof has a shallow slope so headroom is still good at the wall (for inside the bathroom), and has 22" high under floor to the bottom of the body skirt.  Some of the cousins to the AMGeneral are the Flyer D800 & D900; the GM Classic; MCI Classic.  The last version of the MCI Classic was made in a T drive with a Series 50.  Santa Monica, Ca. bus lines has some of these, but don't know when they are letting them loose.  Others to consider, Gillig-which has straight sides and T drive; Orion; older GM transits.  While the V730 only has three speeds, you can get 4.11 gears for it that with 11R-24.5 rubber will give you a 1800rpm cruise at 65mph.  But only would suggest that with a turbo engine since a non turbo engine might get you stuck on a steep hill with its' lower torque rating.  I currently have 4.56 (which is an improvement over the 5.57 [58mph top speed] it had when I first bought the bus) that gives me 2100rpm at 65mph and a top speed of 70mph.  While the V drive engine is the easiest to work on (it is slanted outward to make the top end easy to get to-and the rear end of the engine is on the right.  Only the starter is a bit of a challenge) I would suggest a T drive.  I wish I could have gotton one of the MCI Classics that Santa Monica bus lines is using with the Series 50 and 6 speed Allison World transmission.  My next bus is going to be an MCI 102C3, that is a whole bunch easier to convert than the transit.  Good Luck, TomC

[Savantster]

Russ.. Really, more what I was looking for was direct info on the questions. I've already decided it's an RTS

The only questions remaining are:

How do I go about upping the HP on this motor. Can I adjust the computer either with programming or with a chip? Are bigger injectors an option on the DDEC motors? I didn't think they were. What kind of cost are we talking about to get a Cali-smog motor bumpbed up a few HPs (20 or 30 would be fine, I'd think).

Since this is a RH spinning motor/trans V-drive.. What potential donor busses are out there for rear gears? I realize the 4.10s aren't all that common, but $2,000 for new gears isn't gonna happen any time soon (though, with gas prices climbing, the savings over a few years might be worth it.. have to do the math ). As I understand it, these RTSs run Rockwell rear axles, right? Which other V-Drives out there run those as well? And, since we're talking axles, does the donor have to be a V-drive? Can't I just take any "Rockwell gears" and stuff them in? (any being loosly used). Is there any place to get a full listing of "possible gearings" for these axles? A 3.8:1 rear would do pretty well with that ZF, 3.56 gets "tight" on a few spots (2->3, for example) and might not be all that great for towing (though, at 3.8 you don't normally fall below 1400 RPM during shifting). Oh... I found a nifty "axle/trans/rpm/tires/mph" calculator (on my screen at home, I can post the link for anyone that cares to see it..it's pretty cool.. can't find it on google again). Using 45" tires and 4.10 gears and .83 final drive at 2100 rpm puts me at like 82 mph.. not bad.. switch to a 3.8 rear axle and that goes to ~90mph. And speaking of Transmissions.. anyone seen a 6-speed ZF for a v-drive? or -any- OD type trans? That .65 final would be pretty nice too. What kind of money goes into trying to "re-gear" a trans? Is it feasable to spread the gears a little and drop 5th to an overdrive?

Anyone know where I can get detailed info or online manual for the RTS and/or the ZF trans? I've not been able to find anything so far. The ZF site doesn't have info on my trans (that site is a total pain to navigate), I'd like to double check the final drive (is it .83 or .8, for example) and each gear.

Oh.. and what's the tallest tire one can put under an RTS? And what's the standard for most transit lines? Most of my calcs have been using 40 and 42 inches, to try and be realistic. But, if you can stuff 45" under there, and can find them cheap enough.. woot!

[kyle4501]

The pinion & ging gears must match up perfectly for them to work, so no, you can't get gears from any ole rockwell rear end & use them. The Ring & Pinion gears are a matched set - to each other & for a specific type axle housing.

The T-drive rear axle has the pinion entering the axle at a 90 degree angle to the axle.

The V-drive rear axle has the pinion entering the axle at an angle around 60 degrees.

And another thing, the V-drives have different angles depending on the application. This is why the gear sets for V-drives are $$$ & hard to find in the highway ratios.


Good luck in your quest, the fun is just begining 

[Savantster]

bah.. very good point, Kyle.. I don't know why I didn't stop and think about the entrance angle (though, I've never seen how the vj-drive hits the axle). For some reason, I was thinking the pumpkin must be on an angle.. but it makes sense that they would just cut the gears at the proper angle.

So.. I recon I'm stuck looking for 4.10 gears from a very limited set of axles.. Is there a short list of busses to check? Anyone have a nice little database of "this fits here from that or these"?

[TomC]

12R-22.5 is the standard for most older buses.  They are 42.6" overall diameter, 486rpm, 7390lbs per tire single, and 6780lbs per tire dual.  I switched to 11R-24.5 16 ply Michelin XZE which are 43.5" overall diameter, 478 rpm, 7160lbs per tire single and 6610 per tire dual.   Even though I could run up to 120psi, since I have 10,500lb front axle and 20,500lb rear axle weight, I run 90psi in all tires for a much better ride.  One of the most important aspects to getting both the longest tire life and best ride quality is to run the tires at the manufacturers suggested tire pressure for the weight that is on each axle.  Running maximum tire pressure will wear out the tire in the middle, make the bus ride like a fork lift, and have reduced traction since all of the tire is not on the ground.  Good Luck, TomC

[pvcces]

Savantster, the 35 foot GM parlor coaches of the 60s mostly came with 4.125 axles, stock. With the .808 overdrive from the vee drive, the final ratio is 3.33. This meant that a 2100 rpm engine was good for right around 80 mph.

That combination gives some of the best fuel economies in the two stroke coaches.

For what it's worth.

Tom Caffrey
Suncatcher
Ketchikan, Alaska