MC-9 / 8V71 Woes

[JohnEd]

Clifford,

You are just so much info.  Really!  FOG?  I can guess what that means but could you do that for the 4 months it would sit over the winter?  How long would the down time have to be to warrant a FOG job  and I am not being funny.   What is the process to UN FOG or DE FOG?   Now that was a sorta joke but not really.

This leads me to a really painful observation.  I let the RV sit for w "few" years and only gave the engine its annual ....run till sorta warm.  I took the front bearings of to check the grease cause Da  Book said to and I found "RUST" on the upper surface of the bearing and inside the hub.  RUST!  Cleaned the hub and put BOAT wheel bearing grease in there.  Recently I read on my Black Powder board that petroleum base products don't actually like metals.  Testing various "gun lubes and such" the metallurgist, nice guy by the way, hammered common nails flat and dipped them and then stood them up in a controlled 80% humidity.  You can intuit a lot but there were some serious surprises for me.  Bees Wax did poorly, and all the pet base stuff gave up and let the nails rust.  He had some mixtures that did well but you would never put Caster bean oil in your crank case and some of the other stuff was also not suitable but it was great for guns and such.  Lanolin was a winner so I guess we have solved the mystery of "why don't sheep rust?".  He did this test on all sorts of concoctions but one was conspicuous in its absence.  SYNTHETICS!  Recently I read that Syn has an affinity for metal and using it to lube isn't just avoiding wear but making absolutely sure you don't start DRY no matter how long it sits.   So: syn is a must because....It is slipperier and gives better MPG, runs cooler in engine, lasts longer between changes AND FINALLY....gives you an extra 300K miles between overhauls (150 to 450K miles).  Well, GOSH, any one of those would be a good reason to switch over all by itself.   Seriously....is that true?

Thanks,

Clifford,

John

[cody]

At some point before I croak I want to build the ultimate conversion,w ith all the goodies, I have no idea what that is yet but I'll figure it out lol.

[luvrbus]

JohnEd, they make a fogging oil used a lot in the marine world has been for years I don't fog mine but I do follow most DD instructions if the bus is going to set for 90 days.
In all fairness to you and engine milage the 2 stroke will live as long as any engine in a bus.
I do not know why but engines in buses have short lives compared to over the highway truck and you would think it would be the oppsite.
People at Stewart and Stevenson have told me 400,000 miles is the average life of a 60s in a bus.
Speaking with folks at Cashman Cat they say 300 to 400,000 for the C-12 or C-13 in a bus the people at ABC say 200 to 300,000 for Cummins in the Vanhools and I believe the guys, at ABC every time I stop to visit a friend at the Dallas yard they always have 2 or more in the shop with engine failure same at Stewart and Stevenson in Houston they always have a yard full of buses with bad engines.
Forgot to mention when in Phoenix last week the Volvo dealer where another busnut works they had 3 H-45 with the D-13 very low mileage with blown engines I laughed and told him looks none of the engines with 13 as model number are working out
Now that will keep you busy trying to figure that out LOL have a happy New Year John and good luck

[JohnEd]

Now that will keep you busy trying to figure that out

Well Clifford, facts be known, I have been kept a whole lot bussier by a heck of a lot less.  Mostly that involved women, though.

Back at ya,

john

[bobofthenorth]

We used to leave a whole yard full of diesel engines sit for at least 6 months and most of them for 10 months (only ever used them for 2 months in the spring).  Just because we did it doesn't make it right but we sure never even thought about fogging them down and there's a whole industry that we were just a tiny part of who does it that way.  I routinely fog my boat engine down but its a gasser and its always in a wet environment.  I run it hard for 3 months, change the oil, fog it down and let it sit for the other 9.  But it never crossed my mind to do that to the bus.

[Ed Hackenbruch]

Lin, i just saw an older Prevost for sale here in Yuma. Did not look at it yet so do not know the price or year.  I see you are in Joshua Tree Ca.  Do you know Jim Craig?

[RJ]

I would like some clarification on this lugging thing.  My 8v71/Spicer combo when running 2000 rpm in 1st, meshes perfectly to about 1100 rpm in 2nd.  Hence, it would seem that one must run at lower rpm when building speed.  I don't remember exactly now, but the rpm differential becomes narrower as you climb the gears.  2000 rpm in 3rd is just over 1400 rpm in 4th.  So I guess the point is that one should not try to cruise or climb below 1600rpm in a 2 stroke.  Am I missing something here?

Lin -

First, the gear ratios in the MCI Spicer are slightly different than the Spicers in the GMCs, as is the rear axle ratio, but the powertrain engineer's results are pretty close to the same for each.

In stock "bus" trim, the 8V71 was set up for 275 hp @ 2100 rpm and 770 ftlbs of torque @ 1200 rpm.  Standard cam timing, N60 injectors.  GM Spicer transmission 4th ratio 1:1, bevel gear ratio 0.808, rear axle ratio 4.125:1 (overall = 3.333:1)  In the case of the 4106, 4107 and 4108 models, they were set up for 60 mph @ 1650 rpm using tires that turn 495 revs per mile.

Somewhere I have a HP/Torque graph for this set up, not sure if it's electronic or hard copy buried in a binder.  Anyway, IIRC, the torque builds rather quickly, peaking at 1200, then staying fairly flat until about 1800, where it begins to fall off, but gets "passed" (if you will) by the HP curve, which peaks at 2100.

So, the old adage applies:  Torque gets you going, HP gets you top speed.

Now, to translate that into real world language, yes, you start at the lower end of the rpm/torque range as you're building speed, and at the upper end of the rpm/torque/hp curve to maintain road speed.

Wish I could find that graph, but IIRC, there's a "sweet spot" around 1700 -1800 or so where the torque curve and the HP curve meet/cross.  This is the point where the engine just hums along happily all day long, running on the flat or pulling a grade.

Have you noticed, by chance, that the simple four-speed in our coaches really is well suited for our (relatively) light-weight vehicle, based on it's original design criteria (revenue service)?  First gets you going.  Second is used for those city blocks and residential neighborhoods where the speed limit is 30 or under.  Third is perfect for the suburban four lane routes with 40 - 45 mph speed limits, and finally, fourth gets you comfortable on the interstate.  And that "tall" reverse?  Hey, 99.9% of the time, it was used for backing out of a flat stall at the local bus depot, not trying to wiggle into an uphill campsite at Oh Dark Thirty.

A final thought on lugging.  With the two-stroke Detroit, the general consensus is that if you're pulling a grade and you see black smoke out the exhaust, back out of the throttle.  If you can still maintain your road speed, you're ok.  But if you back off the throttle to clear the smoke, and your road speed starts falling off, then it's time to downshift.  You want to keep the engine in that "sweet spot" on a partial throttle, where if you step on it, you'll get some acceleration, but it will still pull w/o having it floored & smoking black.

(The problem with the non-electronic Allisons, btw, is that when driven w/o manual control by the driver while pulling a grade, they will often downshift too late, bringing the engine so low on the torque curve that it cannot recover, and another downshift becomes a necessity.  And at that point, should it not downshift again, guaranteed you're going to have an overheated engine.  I believe the DDEC/ATEC combination is smarter, perhaps Buswarrior can elaborate more on this.)

Clear as mud?

FWIW & HTH. . .

[Lin]

RJ,

Thanks for the explanation.  

Ed,

No, I do not know Jim Craig.  Is he here in this area?  What is his name on the board?  Thanks, I would love to meet a compatriot here.  We could encourage each other's foolishness.  By the way, I was in Yuma last week (busless).  Is that your home?

[Ed Hackenbruch]

Lin,  Jim is on the MCI board as jtmonza.  He has a 5A, a Flx, and several ultravans.  Really nice guy, and yes, he is in your area.  We have a 5A that we fulltime in.  For the last 5 winters we have called the Foothills home. Summers, i work up in the Seattle area usually, although this year i was on the east side of the mountains near Ellensburg, and will probably be there again this summer too.

[Lin]

Ed,

Someone mentioned to me that there is a guy with several buses a couple of miles for us.  That must be him.  Thanks

[Ed Hackenbruch]

Lin, i was only at his place once a couple of years ago to get a few parts and I can't remember what street he is on. He is on the uphill side of the hiway.  His place is on the left as you go up the street and is fenced so you really can't see what is out back if i remember right.

[buswarrior]

I suppose from this point in history looking back...

The Allisons, 740/730 etc and their controls were very simple, mostly/all mechanical, some/most/all having no decision making capacity. The revs reached a certain value, or with an ATEC, some consideration for throttle position, and it shifted, whether that was good for anyone or anything or not. And they all shifted differently.

Now, put into perspective that the alternative was a 4 or 5 speed stick shift.

All of them mated to an excellent, for its day, engine, which did not know enough to meter the fuel as the load increased, it just poured the coals on like its mechanical bits were designed to do, all the way to suicide, if allowed. Again, no decision making.

And let's stop kidding ourselves, drivers then were no different than drivers today. Get away with whatever you can, and skills were all over the map. Some with skills and pride, some that should have been put in jail. The only difference is we have more time watching from then to today to get jaded and more time to forget the details and romanticize the bits we liked.

In revenue service, nobody cares, just get the thing down the road. Did it go far enough between breakdowns that we are still profitable? And the profit in the transportation business was a lot fatter in those days, so more abuse could be afforded... perhaps a reason these things are more thought of today?

Anyhow... leaving a 740 to downshift on its own climbing a hill has a bad habit of producing a much harsher shift or bang, which is less than nice to the passengers. And as RJ noted, by waiting for a deeper RPM drop before shifting, the RPM in the next lower gear is already down from peak HP. Your terminal velocity going over the top may be slower.

The Allison did at least downshift, which made it impossible for a careless or unskilled driver to refuse to downshift and damage the engine with huge piston temps as it lugged down. In that regard alone, the Allison paid for itself. Even at every corner, making the turn on the roll and carelessly leaving it in the now too high a gear that was being used on the approach and forcing the engine to smoke its way out of sub idle rpm takes its toll.

I am always suspicious of readings on dashboard gauges, and put little stock in their info. In fleet service, a matched set of 10 coaches will show you different RPM and speeds and temps and pressures for any given condition. and, your automobile is the same, the gauges are all over the map, you just happen to own one example.

Who has the gear ratios for the Spicer 4 and 5 speed transmissions? With those, we can work out the relative readings you want to see on your gauges, if they are at least measuring consistently, if not accurately.  IIRC, the 5 speed would drop from someplace 2100 to 1500 on each shift, but that was long ago, before I paid proper attention to these things.

happy coaching!
buswarrior

[bryanhes]

BW,

Here are the gear ratios on a Spicer 4-speed Model 7145VK.

Angle Drive Gears- 0.808 to 1
1st- 4.28 to 1
2nd- 2.50 to 1
3rd- 1.50 to 1
4th- 1.00 to 1
Reverse- 3.56 to 1

This is out of my maintenance manual X-6814.

HTH,
Bryan

[JohnEd]

GREAT THREAD!

[Lin]

I must say that I disagree about the 4 speed Spicer being a good application to even old Greyhound Service-- not in mountain/hill country anyway.  I think of it as another initial cost compromise made at the expense of good design.  True, the high reverse was okay for getting out of bus stations, but really I doubt that they had any reason to need to back up at 15 mph.  For hills, they really should have had a granny gear for starting on grades.  Imagine being in stop-and-go traffic on the Grapevine due to an accident up the road.  What would be the MPC (miles per clutch).  I realize that the pros could handle these things a lot better than I, but the physics of getting started on a 6% to 8% grade with a 4.25 gear ratio is just not friendly.  Having once got stuck on a hill that my 8v71 just could not handle with that gear ratio, I am particularly paranoid about it happening again.  I see it as a 5 speed being about ideal with the extra gear being below the current 1st.  The other forward gears could be exactly the same.  Reverse could about match the new first.  Thanks