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Old 04-16-2016, 05:13 PM   #21
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Location: Lehi, Utah
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Year: 1985
Chassis: Crown Supercoach
Engine: Cummins 855 (300 HP)
Rated Cap: 92 Passenger
Howdy! I bought its sister bus, the '85 tandem. It had a 300hp Cummings 855 in it, so my experience won't help you much, but it started right up after we installed new batteries in it.

It needs some brake and suspension work, but the engine runs great.
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Old 04-16-2016, 06:09 PM   #22
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Nice buy. Many of us were watching that group of buses.
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Old 04-17-2016, 08:41 AM   #23
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Quote:
Originally Posted by Kipin View Post
I never knew a diesel engine could or would do that. Is that with all diesel engines or just the older ones and what causes that to happen?
Any diesel engine CAN run away... in a gasoline engine you cointrolled the air getting into the engine for throttling it.. in a diesel engine you are controlling the FUEL getting into the engine..

a runaway occurs if something else other than the diesel fuel becomes the Fuel for the engine.. ..

on an old diesel engine where the rings are in bad shape its entirely possible to suck enough oil into the cylinders on an intake stroke that it could conceivably burn and make power causing the engine to run away..

the only way to stop it is to cut off the air to the engine.. cover the intake with somehting HEAVY.. or a CO2 fire extuingisher has been used..

I dont klnow much about 2 stroke diesels (the 671) and why they tend to have a higher chance of running away.. (im sure someone can explain why)..

I saw it happen to an old tractor one time but was easily stopped because the owner kept a piece of heavy plywood handy just for the occasion and stopped it before damage was done..

-Christopher
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Old 04-17-2016, 01:38 PM   #24
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Join Date: Jan 2015
Location: Oakland, Ca
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Chassis: Crown Supercoach
Engine: Detroit Diesel 6-71 Mid-ship
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Early Progress

Hey Everyone! Time for an update!



Seats coming out:



I used a 1/2" and 9/16" socket on a swivel and an impact driver, no problems. I checked out a sawzall and angle grinder from the library, but didn't need them. What, your library doesn't let you check out dangerous cutting tools? Sometimes I love this town.



I pulled about 2/3 of the seats out so I could get to the engine access hatch. Would of done them all, but I need to move stuff around to make space to "process" all these super heavy things and get them to the scrapper.



Darn gum chewing kids *shakes fist*

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Old 04-17-2016, 02:00 PM   #25
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Here's the side of the engine, aka the top of the engine in my configuration through the hole in the floor. Big-!@# starter, and the rectangle with the two shafts is the blower. That universal joint is the shift linkage.

I spent the better part of an afternoon just poking around and familiarising myself with the layout of the DD 6-71. For the record and future searchers, the turbocharged version, like the one I have here, does not have the emergency air shutoff on the intake manifold, as the internet hive mind tells me the NA versions do. But between the good suggestions from this forum about keeping a CO2 extinguisher on hand, familiarizing myself with the throttle/fuel mechanism, and some amount of reckless abandon and uncontrollable amount of just wanting to f-ing do it, I fired her up yesterday!

She caught almost right away! I have to crank my pickup longer on cold mornings! 2 fresh batteries, a tank of 10 YEAR OLD diesel. What a racket! I shot some video that I'll upload at some point, but here's where I'm at:

She starts. She airs up. She blows huge grey clouds of smoke. There is a pronounced knock that sounds like one cylinder misfiring somehow.

The plan for next week:

  • Start her on clean diesel with a bunch of that miracle engine/injector cleaner stuff. Anyone have suggestions?
  • Since that's unlikely to actually do anything, dive on into the engine. Start at the top, pull the valve cover and injectors.
  • Test the injectors, maybe try to service them, maybe replace them.
  • If nothing obvious wrong with the injectors, use the injector hole to do a compression and leak down. Actually, I'll probably do this anyway
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Old 04-17-2016, 02:28 PM   #26
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@Robin Thanks for the CO2 Extinguisher tip!

@serpant Thanks for sharing the reckless abandon. I knew coming into this that a $500 bus would be a self-taught class in the inner workings of the 2-stroke diesel and not a drive it off the lot kinda deal. My style is always to take it apart and see how it works anyway, so might as well start with something that needs work. If you can't open it, you don't own it, as they say, and I'd rather learn it inside and out in my workshop then on the side of the highway some night!

@opus and @tango (and for future searchers) the way the intake and air filter is set up, it'd be hard to smother the air intake without cutting something permanently. Very good point about not using a rag or your hand on a turbocharged diesel!

@crazycal They were listed as having cummins 220's, but I can assure you that I've been wrenching on a Detroit! Also, they were listed as "ran when parked" but the huge maintenance log I have indicates that this one was having engine problems when they mothballed it. Learn from this, future bus shoppers, gov deals dot com doesn't have the most reliable descriptions! On the other hand, the contact person was extremely friendly and helpful, and I got a 38Klbs bus for $550, so, as with all things, trust but verify!

@cowlitzcoach Great Info! The build plate says it's model A-426TAC-275/80 and the tires are 11 R 24.5. On the block, I cleared the crap off the id stamp plate and can read the serial number, but the model number is behind a coolant hose so I can't read the last four digits... you know, the important, relevant ones... But the ones I can read tell me it's a 6-71 for vehicle applications! Ha! Defiantly not electronically controlled, and has a bunch of pneumatic actuators/solenoids on the coolant and throttle systems.

@takoisam Hey! Glad you're here! Cool Bus!
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Old 04-17-2016, 02:29 PM   #27
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I hate to tell you this at this point, but when they say "must be towed", you only have to tow it off the lot. Granted you can get in trouble fixing something on the side of the road, but I've bought stuff and fixed it just outside the gate of the auction. If you had your batteries and filters with you, you could have stopped anywhere once you left the property pickup area. That seems like an awfully high tow bill.
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Old 04-17-2016, 02:37 PM   #28
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Yeah, it was more then quoted. A bummer. But also, had no plates and had to go about an hour and a half up the highway. What are yah gonna do?
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Old 04-17-2016, 05:48 PM   #29
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It's so cool this seems to be working out for you. I've wanted one of those since I was a kid in grade school (older Crown obviously).

You're misunderstanding the invisibility of a big yellow bus. Most people don't look twice, and they don't cut you off on the highway like with a normal POV.

This time I was legal, but I had tinted windows and there's no way to see the temporary sticker in the back window. I drove around for the next two weeks and never got stopped. I know I've got to paint before I go interstate, but I like the more respectful way drivers act toward yellow buses.
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Old 04-24-2016, 07:44 PM   #30
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engine work

Started getting into the engine...

Oooo, look, I have Jake Brakes! Bonus!



I wasn't expecting them! There's a covered knock-out on the dash panel for the exhaust brake switch. My working theory is that the school district disabled them because of noise complaints. I don't know much about them. Anyone?



Here's a cylinder with the injector pulled. The first one took me a couple hours to figure out. After that it was more like 20 min per. This is a 2-stroke diesel, so all 4 of those valves are exhaust. The intake is down at the bottom of the cylinder. Three rocker arms, the middle is for the injector, the two outside ones for the exhaust valves. The injector sits in that copper sleeve; the sleeve is water cooled. The jakes sit on top of this and push down on the exhaust valves, changing the exhaust timing in a way I don't fully understand, increasing compression on downshifts and making that loud noise that you hear from decelerating trucks. The yellow wire nuts are on the fuel line flare nuts just to keep things clean.



And there they all are. 6x 7G70 injectors. I don't know much about the "G" series injectors, I think they might be california CARB specific? Anyone know? The injectors are all mis-matched, some with rebuilt stamps, some not, with what i think are date codes all over the place, from 78 to 89.

Next up: Compression and leak down tests! Then, deciding whether to diy a injector pop tester, or bring them to a shop... probably would be a good idea to try to make friends with someone with more DD experience...
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