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Thread: Any info on the 6-71 Detroit?

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    Default Any info on the 6-71 Detroit?


    I'm looking at a toterhome that a guy has for sale. The chassis is a 72 with an 86 cab on it. He told me that the engine is a naturally aspirated 6-71 six cylinder Detroit diesel. From my research so far, the 6-71 is a two stroke engine and likes to make its power with high rpm's. Because they're two stroke, do they need any special treatment with the fuel or not? I've also been led to believe that they have a supercharger if they don't have a turbo (not completely sure on that one though). I've also seen that Detroits (not just the 6-71) are notorious for leaking oil.

    That's pretty much all that I've dug up on my own. I was wondering if there's any more details about the 6-71 that I should look into? The current owner doesn't know exactly how many miles are on the truck because the odometer has been broken ever since he bought it. He says it has no leaks aside from a small power steering leak. He also told me that it can't go over 70 mph with the 9 speed in it but it will pull anything.

    Here's a picture of the truck that I'm referring to.


    Any help is greatly appreciated.

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    The One Blue Thing ameristar1's Avatar
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    The 6-71 is probably one of the most reliable Detroit Diesels, sort of a staple engine that has been around forever. There's a bus site that talks about the care and driving of a 2 stroke Detroit, and the first rule is is that you drive the thing like you stole it. Don't lug this engine, put her to the floor and rev her out. All Detroits have a Roots blower that scavenges the cylinders (it won't run without it) and turbos have been added for extra power. Do not use a multi viscosity oil in these things, only straight 30W or 40W, elsewise you are going to scuff the liners. If Delo 100 is available, that's what you use. There are a couple of members that work on these things for a living and can probably tell you more than I can. But aside of being noisy, they're good engines.
    You don't need to premix the fuel or anything like that (you're thinking gasser).
    If you need to get more power out of it, you can easily add larger injectors and turn the rpm up on them.

    Your engine is rated at 238hp and 650 ft/lbs of torque. Max on road rating is 290hp and 810 ft/lbs with a turbo and aftercooler (factory rating)

    Before you drive it, the cardinal rule is to smash your hand in the door and take it out on the motor. Don't ever be nice to it except for maintenance.
    Last edited by ameristar1; 10-13-2009 at 08:33 PM.

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    Quote Originally Posted by ameristar1 View Post

    Before you drive it, the cardinal rule is to smash your hand in the door and take it out on the motor.
    That's funny, I thought that was the rule for shifting the old 4 speeds they stuck on them in the old busses.

    My bro in law ( who is a Diesel mechanic by trade ) says of the old 2 strokers that "if it aint leaking, it aint running". I've got an 8v71, dads got a 6-71. Bothgreat engines. Like was stated earlier, no multi vis oil. Straight weight only.

    Some good reading to be found here.


    http://www.axlealliance.com/pdf/voca...quirements.pdf

    Read the section regarding the 2-Strokes.
    Smaug --> 1986 Ford F-250 4x4
    6.9L,Banks Turbo,Stacks
    Hexus---> 1985 M-B 300D
    Friggenbroken--->1985 VW Golf 1.6IDI 5Speed 46MPG - under the knife
    FarfromFast--->1990 wolfsburg Jetta 1.6IDI 5speed
    Brick----> 1986 Jeep Comanche (MJ) (needs a diesel!)
    Nameless-->1965 GM 4106,8V71 2stroke Diesel,4-speed trans. 15mpg!

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    The One Blue Thing ameristar1's Avatar
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    Quote Originally Posted by RustyRecycledT View Post
    That's funny, I thought that was the rule for shifting the old 4 speeds they stuck on them in the old busses.

    My bro in law ( who is a Diesel mechanic by trade ) says of the old 2 strokers that "if it aint leaking, it aint running". I've got an 8v71, dads got a 6-71. Bothgreat engines. Like was stated earlier, no multi vis oil. Straight weight only.

    Some good reading to be found here.


    http://www.axlealliance.com/pdf/voca...quirements.pdf

    Read the section regarding the 2-Strokes.
    Rusty, I still can't get over the fact that your bus knocks out 15 mpg at 22k#. I need to stick your motor in a straight truck and make some money with it.

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    Thanks for the info so far. Hopefully I can get some more information out of the guy tomorrow while he's at his shop.

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    yeah we had twin 6-71s in our boat and they were great except for that oil thing. Each one burned a quart of oil for about 3 hours of run time. The only problem we ever had was when we were in rough water and some junk plugged up the fuel filters causing one of the engines to go down. Thats not really detroits fault though. Ours ran a little dirty too, we had to wash the transom after each trip
    -Jimbob-

    1991 F-250 Custom, 7.3 with factory turbo, ZF42, regular cab, 4x4 (all 4 wheels turning now - Posi front, LS rear), 10-1/4 4.10LS, Baby Moose, Hydroboost, Napa coolant filter, Reading utility bed, meyer E-47 snow plow, ladder rack, Cobra CB radio, Push button ignition- no keys required. 9 Stewart-Warner gauges.
    New front end!!! Add a leaf, bilstein shocks, bushings, bearings and Posi installed. Who said D50s are junk? Now its good for another 300k

    Rebuilt engine as of 8/12. All work except machining done by me. Bored .030 over. Flycut pistons with 202 cam.

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    I noticed that no one mentioned to avoid idling as much as possible, keep it against the governor and it will run forever! I have a few old DD in my stable and they are dependable engines if properly cared for.

    Rustys bus is another thread in itself! :lol: I have never seen a 568cu in engine get 15mpg
    in anything!
    Trying to figure out where to put the 12v Cummins.....

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    The One Blue Thing ameristar1's Avatar
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    Quote Originally Posted by Captain Morgan View Post
    I noticed that no one mentioned to avoid idling as much as possible, keep it against the governor and it will run forever! I have a few old DD in my stable and they are dependable engines if properly cared for.

    Rustys bus is another thread in itself! :lol: I have never seen a 568cu in engine get 15mpg
    in anything!
    By the way, did you get that 6.2 turbo going yet?

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    I am gonna head over to the shop here in a bit, I am waiting on a used downpipe to finish it up. I have to plumb the turbo oil and put on the phony GM "quick connect" heater hose fitting at the water crossover. I kinda wanna hear it run! :lol:
    Trying to figure out where to put the 12v Cummins.....

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    The One Blue Thing ameristar1's Avatar
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    Quote Originally Posted by Captain Morgan View Post
    I am gonna head over to the shop here in a bit, I am waiting on a used downpipe to finish it up. I have to plumb the turbo oil and put on the phony GM "quick connect" heater hose fitting at the water crossover. I kinda wanna hear it run! :lol:
    I've got a feeling you may not want to give it back.

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    See my thread in the GM 6.5L section!
    Trying to figure out where to put the 12v Cummins.....

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    rampage, if you are interested, I have all of the Detroit manuals on cd. v71, 149, 92 etc.
    Alot of the info won't apply to your particular engine, but alot can be used.
    Pm me if your interested.

    I work with 16v149 and 4-71's daily. Either myself or my co-worker Geonc can give you some tips if you're in a bind.
    '76 F100, 390FE, c6
    '63.5 Galaxie fastback, 429cj, c6

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    Quote Originally Posted by Captain Morgan View Post
    Rustys bus is another thread in itself! :lol: I have never seen a 568cu in engine get 15mpg
    in anything!
    If parking were not an issue, I would drive IT to work on days I need to haul someting in rather than the Ford. IT gets better mileage than the F-250 does!

    Parking lot at work isn't big enough to turn around. something like a 42ft turning radius.
    Smaug --> 1986 Ford F-250 4x4
    6.9L,Banks Turbo,Stacks
    Hexus---> 1985 M-B 300D
    Friggenbroken--->1985 VW Golf 1.6IDI 5Speed 46MPG - under the knife
    FarfromFast--->1990 wolfsburg Jetta 1.6IDI 5speed
    Brick----> 1986 Jeep Comanche (MJ) (needs a diesel!)
    Nameless-->1965 GM 4106,8V71 2stroke Diesel,4-speed trans. 15mpg!

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    Quote Originally Posted by DeepRoots View Post
    rampage, if you are interested, I have all of the Detroit manuals on cd. v71, 149, 92 etc.
    Alot of the info won't apply to your particular engine, but alot can be used.
    Pm me if your interested.

    I work with 16v149 and 4-71's daily. Either myself or my co-worker Geonc can give you some tips if you're in a bind.
    Thank you, first I have to get the thing and in order to do that, he needs to send me some more pics and answer his phone so I can make a decision. For some reason he hasn't answered since yesterday.

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    The One Blue Thing ameristar1's Avatar
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    Quote Originally Posted by RustyRecycledT View Post
    If parking were not an issue, I would drive IT to work on days I need to haul someting in rather than the Ford. IT gets better mileage than the F-250 does!

    Parking lot at work isn't big enough to turn around. something like a 42ft turning radius.
    You need to tell the story about the bus as far as what was done to the motor. I remember you saying that it was rebuilt not too long ago. Who did it and who does the tuning? Any special mods?

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