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Detroit 671

Discussion in 'Engines' started by Gerdie, Aug 14, 2015.

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  1. ArielM

    ArielM Senior Member

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    checking the air box covers will get you an idea, but the only way to really be sure the condition of the rings is by doing a compression test. If you are burning oil it might also be leaking from the valve. compression test will help isolate which cylinder is low on compression. From there you can do a leak down test on that cylinder (Piston at tdc). if the valves are leaking you will hear the air leaking into the exhaust.
  2. Capt J

    Capt J Senior Member

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    You might also be able to tell if you have a dead cylinder just by running the motor with the valve cover off. Usually the injector won't actuate on that cylinder if the cylinder has really low compression. Air boxes are pretty quick to check though and that's where I'd start first. Actually I'd start with a detroit diesel mechanic first, even if I had to call the dealer in, rather than pissing in the wind.
  3. ArielM

    ArielM Senior Member

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    capt j is correct, usually as a cylinder loses compression that injector wont fire as strong as the rest of the cylinders. Place a screw driver on the injector and you can feel the vibration of the combustion through the driver. But again low compression could be a result of leaking valves.

    Get a good detroit mechanic who specializes in 2 cycles. I think thats the best advice...
  4. K1W1

    K1W1 Senior Member

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    The actuation of the injector on one of these old girls is absolutely independent of whether there is a hole in the piston and no compression or not. It is a fully mechanical action driven by the camshaft. a cam follower, pushrod and rocker arm.

    It is the atomisation of the fuel that will be affected not the action of the injector.
  5. Gerdie

    Gerdie Member

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    Thank you for all of the great information. I have called a diesel mechanic to take a look at it. Hopefully he can give some good insight without selling the farm.
  6. Capt J

    Capt J Senior Member

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    You can tell pretty easily with the valve cover off if a cylinder has low compression from the fuel injector on a Detroit both in noise and feel with Ariel's screwdriver method. They don't actuate nearly as hard as an injector on a good cylinder.
  7. P46-Curaçao

    P46-Curaçao Senior Member

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    Contact Bill Adams, the best Detroit mechanic I know in the area badiver2 at aol.com, tell him you got his email address from Eric from Curacao...
  8. K1W1

    K1W1 Senior Member

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    That is not what I was getting at - you as a self proclaimed expert who offers advice of varying quality should really be able to understand the difference between actuation and atomisation when saying one of them is at fault.
  9. Capt J

    Capt J Senior Member

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    They should still atomize the fuel the same as the fuel pressure in the injector and line is the same regardless of compression, that comes from the injector pump. They don't actuate as hard because there isn't much compression against them actuating. Whatever the case may be, it doesn't matter how the fuel is atomized in the cylinder if it has 90lbs of compression, and with the valve cover off it's distinctively noticable by sound.
  10. K1W1

    K1W1 Senior Member

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    You still don't get it do you. You have previously stated that the injector actuation is somehow connected to the compression. This is not the case as I have tried to pint out several times but you either haven't read what I wrote or your comprehension skills are about as good as your mechanical ones.

    Also as you no doubt don't know the DD 6.71 uses a pressure timed injector there is no HP fuel pump apart from the injector itself and the pressure is raised by yes you guessed it the actuation of the plunger which then leads to atomisation of the fuel.
  11. Capt J

    Capt J Senior Member

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    Yeah, call the local Detroit Diesel dealer and have them come out and diagnose it.
  12. Capt J

    Capt J Senior Member

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    You are correct, and I miswrote and was incorrect. However, that is neither here nor there in regards to the OP's problem. If a cylinder has low compression you can tell 90+ % of the time in how the injector actuates (whatever vibration or noise it makes when actuating, there is a very distinct difference in the sound of an injector on a very low cylinder or one with good compression on a D.D.) if you have the valve cover off.
  13. Capt Ralph

    Capt Ralph Senior Member

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    Any updates on the original post?
    ,rc
  14. Gerdie

    Gerdie Member

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    Finally found a mechanic in the area and he rebuilt the blower. Took it for a spin this last week and there is still blue smoke. The mechanic said there would probably be some from the sludge blowing out. Lot of smoke at first then kind of subsided. Still smoke at a certain Rpm and same rpm when slowing back down. No loss of power or rpms.

    Mechanic's next test is after running the boat test the heat of the cylinders to see if one of them is not firing.
  15. Bamboo

    Bamboo Senior Member

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    I've found dead cylinders by wearing over the ear "headphones" hearing protection and using the "screw driver stethoscope". (blade to the engine and handle to the outside of your ear protection.) No need to remove anything, just have the engine running at idle and listen to each cylinder. When most sound nearly identical and one is not like the other one(s) you know there's an issue in that cylinder. Yes it's crude, but it's simple, easy, quick and decidedly helpful.
  16. Gerdie

    Gerdie Member

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    Thanks you for the info. I will give it a try. Have you ever heard of a heat gun or if it works? Also where do you hold the screwdriver on? Is it against the inspection caps or directly on the block. We are realatively new to this and trying to learn as much as we can.
  17. K1W1

    K1W1 Senior Member

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    Another worthwhile thing to do on DD's is to remove the air box covers and turn the engine( make sure the fuel is in stop pozzie before rotating on at all times unless a start is the desired result as tey start very easy) look at the ring packs and liners as the pistons go up and down. Scratches and scoring can be a sign of fuel dilution and lube breakdown which will lead to ring scuffing and oil consumption as well as reduced compression.
  18. rgsuspsa

    rgsuspsa Member

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    An easy and reliable method to locate a cylinder that is not running, or is running at substantially less power output than the others is to utilize a
    Infra Red temperature gun equipped with a LASER POINTER. Point the laser at the non water cooled portion of the exhaust manifold runner, as close as possible to the intersection of the exhaust manifold runner and the exhaust manifold flange of each cylinder's exhaust manifold runner, preferably in the middle of the width of the exhaust manifold runner. Measure the temperature in the same location on the exhaust runner of each cylinder. There will be some difference in temperature between cylinders, but a grossly low temperature on one or more cylinders as compared to the other cylinders indicates a poorly running cylinder, or a cylinder that is not running at all. This is a particularly easy test to perform at idle RPM, both in neutral at the dock, as well as when underway at idle speed.
  19. Capt J

    Capt J Senior Member

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    Rons method is both the easiest and most accurate way to tell without digging into the motor.
  20. Capt Ralph

    Capt Ralph Senior Member

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    Ron has it. Our IR gun gets a workout when the engine starts up cold and I keep scanning the exhaust as the temps come up.
    Put your ear muffs on and scan the exhaust under a light load also.

    From my old school before IF guns were so popular, I would use kids crayons; heavy scratch the cold exhaust runners. Start it up and watch for the wax to melt at different rates. A weak or dead lung will be the last to melt.