12.7 Detroit rebuild questions

Discussion in 'Western Star Forum' started by Eric Strongbear, May 1, 2022.

  1. Eric Strongbear

    Eric Strongbear Light Load Member

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    Is it possible to rebuild a 12.7 with rotating assembly parts from a 14 liter Detroit? The truck I'm in right now is a rental and it's finally put me off all emissions ######## with the bad EGR cooler that's putting me at risk of limp mode should the DPF get plugged up enough, and this has reminded me of my desire to build a 14 liter without emissions and won't get me ####ed by the feds at first glance. So is this possible? Would I just need a good crank and an in-frame kit for a 14 liter? Or would I need everything else from a head for a 14 liter to the oil pump? What turbo and injectors would I need for 700 horse? The truck I'm eyeing is a 13 speed, would it be worth my time, the extra size, and weight to go to an 18 while the engine is down given I do refrigerated and dry van work? Thanks in advance
     
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  3. Eric Strongbear

    Eric Strongbear Light Load Member

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    Last question for now. Is it worth the time and effort to swap to air disc brakes all the way around on the truck at the same time?
     
  4. Dave_in_AZ

    Dave_in_AZ Road Train Member

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    I don't know about the engine, but the stopping power of disks compared to drums is unbelievable.

    I also know you can get suspension parts cheap cheap like the birdy goes at the salvage yards that will work just fine.
     
  5. Eric Strongbear

    Eric Strongbear Light Load Member

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    My thought as for the engine is because it's a wet sleeve design it should be possible because I don't see why Detroit would have used different blocks or different dimensions for the 11.1, 12.7, and 14.0 because of cost and other issues. If I mess with the suspension I'm going to get a shop to do so because while I trust that I can do it with cars and pickups I'd rather not risk it with a semi because of the magnitude of the consequences, and that'd probably be the new Hendrickson fab'd steer axle and air ride combo. As for disc brakes, I figure if I'm gonna be doing all this I may as well go with new components and so I'd do the Bendix setup
     
  6. Dave_in_AZ

    Dave_in_AZ Road Train Member

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    My disks are awesome. They're a snap to change the pads and just a few hundred bucks.

    If let them wear into the rotors, you'll be into it for thousands.
     
  7. AModelCat

    AModelCat Road Train Member

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    There's a couple threads on here about that. From what I remember a 14L crank won't fit a 12.7L block. Counterweights or something don't clear.

    @benjamin260_6 knows these engines in and out.
     
  8. Eric Strongbear

    Eric Strongbear Light Load Member

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    That's a bummer. Is there any noticeable longevity sacrifice at the higher horsepower range? Eg, would a million mile engine be reduced to 3/4 of a million? Is there any difference in Jake's between regular duty and heavy haul duty variants like there is with the 3406B Cat?
     
  9. benjamin260_6

    benjamin260_6 Medium Load Member

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    There are a few wide block 12.7s out there that are the same as the 14L but most won't allow the crank to turn once the rods are installed. To make a ddec 4 14L, I've found it's easier to build a ddec 5 with a 4 head and ecm. You have to get an adapter made for the cam but that's no big deal.
     
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