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History 671 detroit diesel questions

Discussion in 'The Hokey Ass Message Board' started by uglydog56, Apr 20, 2011.

  1. uglydog56
    Joined: Apr 8, 2008
    Posts: 331


    I'm looking at an old Crown bus to convert into an RV. It has a 6-71 detroit in it, and a 5spd trans, 2spd axle. All I know about these detroits is one of the neighbors had one on a well and you could hear it 10 miles away at night. From the internet I believe it has 195hp or so, a little less than the usual because it is a "pancake motor" to fit under the bus. Are these reliable, and can you turn them up at all? I'd like to pull a car trailer behind this thing and be able to pull a grade on the interstate in line with the semi's and not hold things up too bad. Maybe 250-300hp?

    Thanks, Rick
  2. badshifter
    Joined: Apr 28, 2006
    Posts: 3,400


    Yikes, 2 stroke diesel. Hope you saved up fuel money! You can turbo/supercharge them like they did on the later engines. They pump good black smoke and are leakers! That's my limited 2 cents.
  3. willymakeit
    Joined: Apr 13, 2009
    Posts: 1,326


    Put a later Cummins or something else in it. 3-5 mpg is not fun.
  4. budd
    Joined: Oct 31, 2006
    Posts: 3,478


    the HP on a diesel means very little, it's the torque your interested in, should have around 600fbs, your bus will pull a trailer and might not even notice the difference, i love the sound myself

  5. aaggie
    Joined: Nov 21, 2009
    Posts: 2,531


    You need to repower with something a little newer. The 71 series GM diesels were all two stroke and had blowers as the forced induction. Mechanical fuel injectors and a centrifugal govenors. The fuel mileage would make a Suaudi Prince smile.
  6. gas pumper
    Joined: Aug 13, 2007
    Posts: 2,957

    gas pumper

    I love 6-71's:D

    Later ones have 4 valve heads, early have 2. Not really much difference.
    In an 18,000 lb bus, they can give 9-10 mpg. Don't know what yours weighs. They like clean fuel, #2 Diesel is fine, house heating oil is not liked. They leak when caveman mechanics take them apart and don't clean gasket surfaces nice.

    Turbo engines have much lower compression, stay away from them.

    N-60 injectors work great. More power use N-70, any bigger and you will get a lot of black smoke and no more power, just smoke.

    They need a LOT of clean air with no restriction for the intake. Sometimes a larger filter element and can is needed.

    2100 RPM is where they like to be. They have a real flat torque curve, and will pull good off idle all the way up to the governor rpm. Downshifting is important on hills to keep the rpm up, this takes advantage of the flat torque curve by multiplying the torque with the gears.

    Run a muffler and all you hear is the good Diesel noise instead of the exhaust.

    Firing timing is done at the injector by setting the injector height. Old ones were set at 1.460. later smog engines were set at a higher dimention and will run crappy and smoke more but be PC. Lowering the injector setting to 1.450 will improve power and efficency.

    Some engines have retarded cam timing for pollution. Some have advanced cam timing for more power. Standard cam timing is best.

    Hopefully your engine is all mechanical, no electronics.

    Keep water and oil in it and it will run forever.


    Anything with a 6-71 blower on it can't be bad, right?
  7. 6narow
    Joined: Jun 1, 2008
    Posts: 525


    A little late to the party, but my dad was pretty adept at DDA's and I once worked at a DDA dealership.
    There was a version of the two-strokes that was called "Silver".
    It was basically a package deal but the motors were fairly strong.
    I think a Silver 6-71 was rated at about 250hp (normal is 238).
    I remember dad coming home with the litrature, when the Silver's were introduced.
    That engine should be governed at about 2100 rpm right now.
    That's about as fast as you want to turn a 71 and maintain reliability.

  8. the detroit makes lots of noise, i have put 2 mufflers on them and the noise will still come off the engine
  9. Black Primer
    Joined: Oct 1, 2007
    Posts: 966

    Black Primer

    I think the silver series was a v6. The 238 6-71 was inline. You gotta "keep um on the pipe" like riding a dirtbike. If the rpm's are lugged down enough, they will actually run backwards, sucking air through the stack and exhausting through the air cleaner.

    My boss used to say "slam your fingers in the door every morning when you get in, and drive it like your mad at it". Basically they converted diesel fuel to noise. Wouldn't be my first diesel choice for sure.
  10. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    from BC

    I thought the silver was a 8v-71 with a turbo blowing into the roots? mid seventies deal?
  11. bandit14569
    Joined: Jul 18, 2011
    Posts: 69


    The old detroits were "fuel converters". they converted fuel into noise. Then came the "silver 92" series which were better. And in the 90's the merged with john deere I believe to the technoligy of today. 4 stoke for the higher torque and hp in whats known as the "series 60". Willymakeit was right on, try and score a newer cummins.
  12. Black Primer
    Joined: Oct 1, 2007
    Posts: 966

    Black Primer

    The guy I drove dump truck for in the 70's had 6-71s and the 8v-71. The 318 had the power steering driven direct off the blower. Not fun trying to manuver around jobsites at low rpm.

    If I remember, the silvers were 6v-92 and 8v92, early 1980's
  13. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    from BC

  14. 6narow
    Joined: Jun 1, 2008
    Posts: 525


    The Silvers came as inline and V's.
    IIRC, they were limited to 71 and 92 series.
    Series 60 was the replacement for the two-strokes.
    Came on in the late 80's.
    11L and 12L originally.
    I think only the 11L exists now, as it is the "old" engine these days.

  15. curly 54
    Joined: Jan 17, 2012
    Posts: 8

    curly 54
    from Australia

    they are a good motor. keep the rpm's up to them to get them most out of them. you can fiddle with the governor and get 3000rpm out of them but i wouldn't suggest that for your bus. i have a little to do with them im putting a 471 in my truck.
  16. Lytles Garage
    Joined: May 6, 2011
    Posts: 621

    Lytles Garage

    Inline 6-71 one of the best sounding motors ever,sat beside one of them for many hours in an old Jimmy pug nose haulin corn. they don't like hills,punch yourself in the face several times while driving one so you stay pissed off and you will get along fine with that old sonofabitch!!! I have an Cummins ISX now, don't think I would want to go back to driving some of the trucks I've had in the last 40 years!! but I miss the sound of that old inline Jimmy! THANKS Chris
  17. BootleggerJim
    Joined: Dec 14, 2007
    Posts: 202

    from SC

    Poor man's diesel.....Great motors.....leak oil like no tomorrow, slobber oil. You can turn that motor any way you want....
  18. mammyjammer
    Joined: May 23, 2009
    Posts: 505

    from Area 51

    Used to drive a 6-V71 powered truck and I would dump a gallon of Delo in it every morning....and THEN check the oil and top it off.
  19. alanwoodieman
    Joined: Jun 14, 2011
    Posts: 63


    ran various 71 series engines on our minesweeper, 4-6-12-16, some turbo's some not, but they always ran best when at the limit of the governor's. When I got out of the service the GMC truck dealership had a factory 12-V 71T in a demonstrator road tractor with an automatic trans, the factory man told us to floor the engine to the governor stop and let the trans shift until we reached running speed, 12V ran 2450rpm.
  20. I knew of a fellow in Rapid City, SD who bought a Crown bus. He flew to CA and drove it home. I think he takes it to Bonneville yearly. One thing he did was put a 10-speed behind it and said it helped tremendously.
  21. budd
    Joined: Oct 31, 2006
    Posts: 3,478


    in 1972 my dad bought his first diesel tractor trailer rig, an IH with an 318, 8V71, and a 13 speed OD, we flew up to Ontario from Nova Scotia and drove it home from the factory, i think dad drove most of the way with his head out the window, i was 13 at the time and when we got the truck home it was my turn to drive on the logging roads my dad hauled on, my dad would get all excited and yell at me, SLOW THIS DAM THING DOWN A LITTLE, the next GM was a 435 silver 8V92 in an Astro cabover, i think that was one of the best trucks he has ever owned, the next GM was the last, the silver tip grizzly 475, by that time i was 19 and had my class 1 and he and i drove that together alot, one of the last trips was down to NY with a load of christmas trees, we would go down through Maine on route 1, or the Haynesville woods, i remember my dad getting all excited and yelling at me, SLOW THIS THING DOWN OR YOUR GOING TO BUST THE STAKES OFF IT, i'm 53 yesterday and dads 75, he's still trucking and i havent been behind the wheel in ten years, once in awhile i here a Gimmy running down the road and get the feeling i want to drive one again, if it wasent for the EPA they would still be on the road. GM 71 engines will go down in history as the hot rod motor of trucking.

    speed shifting a GM
    Last edited: Dec 8, 2012
  22. Roger Walling
    Joined: Sep 26, 2010
    Posts: 1,149

    Roger Walling

    Don't waste your money doing a conversion yourself.

    You can buy a converted coach for 15-20% of what it would cost you to do it yourself.

    Thre are a ton of them on the market now. At 50 cents a mile, save your money for fuel and oil!

    ( Don't ask me how I know {and mine is a fresh rebuilt})

    Ps, don't buy a city bus, they are not made for the highway.
    Last edited: Dec 8, 2012
  23. I just sold a 6V92 silver detroit powerunit it pulled 350 hp. Torbocharged and supercharged. The inline 6V71 arent that bad. the need to be at least 1800 rpm when pulliing. I always adjusted the govenor to 2450.max and tried to drive about 2000 rpm. I liked them with a 13 speed. the old 10 speeds didnt have the low gear the 13,s or 9 speeds have. That five speed and two speed should be good. the early terex (euclid) earth movers had 6 -71,s we drove them flat on the floor all day long I never seen one that blew up. Hot rod the pee outa that engine and you will be ok. There are spit tubes at each end of the air box. they would let oily discharge escape from the airbox. that was a lot of the so called oil leakage. put a hose & catch can on them and the engine wont be so greasy. Dont stop those tubes up. If the get clogged the engine can start sucking oil from the air box and oil pan and run away. there should be a emergency kill on the air inlet that sometimes will choke down a runaway engine. OldWolf
  24. captmullette
    Joined: Oct 15, 2009
    Posts: 1,929


    would love to see pics of the bus....have always wanted one...
  25. duncan
    Joined: Aug 23, 2006
    Posts: 1,162


    The 6/71 holds a special place in my heart. A good one almost has a soul and they'll work their guts out for you if treated right. Lots of clean air with oversize intake piping. Set the governor at 2250 and shift when they fall off 1800 and they'll sing all day long and run forever. I used to get 8 mpg with a 12 yd. rock box Kenworth dump, so 10-12 should be attainable in a bus.
  26. dan c
    Joined: Jan 30, 2012
    Posts: 2,359

    dan c

    i drove a lot of ready-mix trucks with 6-71s and what everyone is saying is right: they're noisy, thirsty and underpowered. and the reverse rotation thing reminded me that they will start running in reverse if you stall them. it was funny when a newbie did that and would be freaking out because his truck would "only go backwards!"
  27. Old School Crown
    Joined: Feb 15, 2013
    Posts: 1

    Old School Crown

    Here you go. I bought it last July

    Attached Files:

  28. lht
    Joined: Jan 18, 2013
    Posts: 243


    yea real oil sloppers but if you run the rack right those things will crakle
  29. #19
    Joined: Dec 27, 2007
    Posts: 9


    Yea they'll crackle allright with strights on em. 671 & 318 were ok in there day but as u all know they were flat land motors had both of em would not give a nickle for one today.the last one i bought new was a 350 thats a turbo charged 318 with 70 injectors it was the biggest pice of sh%# i ever owned,throw that 671 at some boat owner & get a good 4 stroke not a 60 series either CAT are CUMMINS & u can cruise in peace. Been there done that for 50 years & i bough a t shirt too.
  30. BigPerm365
    Joined: Jan 8, 2012
    Posts: 47


    Believe these folks. Bleedin' loud no power grenades. A good late model Cummins 6B / CT or ISM will never let you down, or cause you to lay on your back in the dirt, w/ crap dropping in yer eyes. Find a wrecked Dodge p/u...get all the electronics, & go.

    All...repeat...ALL DDA V-71/92 Silver /Green/ Purple, or any other colors are lipstick on a pig.

    Been sellin' parts since '71. Series 60 is electronic...big$$'s but great motors. You don't need that much H.P. / weight. This is can do much better.

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