Mechanical N14 Parts Help

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Hopeaholic, Dec 3, 2020.

  1. Hopeaholic

    Hopeaholic Bobtail Member

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    Hoping to get some help from some old school folks that might have cummins pt pump reference manuals and part numbers from the early 1990's.

    I've recently installed a mechanical N14 STC into a 1991 Pete 379 but the motor is only 330 HP and governed at 1700 RPM. It's a ranch use truck so don't use it a ton but when I do, it's loaded heavy (hay, cattle, gravel) and we have lots of hills so trying to up the performance and RPM's to around 430HP and 2,100 which was the highest Cummins went with the mechanical N14.

    I put the bigger injectors in it but now need some parts for the PT pump. I'm trying to get it from CPL 1532 to CPL 1878 and to do so I need the corresponding button part number (aka idle spring plunger) and corresponding high speed governor spring part number. Cummins technical support has been a no go as they can't break the PT pump down into the individual parts within their system (they want me to buy the entire pump which is cost-prohibitive).

    Any thoughts would be appreciated.
     
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  3. pup

    pup Light Load Member

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    A mechanical N14 is a great engine. Any of the low rpm engines really wake up simply by changing the high speed spring. No need to chase cpl #s as those 2 cpls are very different. Don't worry about the button. The fuel pressure will build with the increased rpm's. If you could find a core pt pump you could rob the spring & shims from that & experiment a bit. Trial & error to find the right rpm's, I'd think any local injection shop may be able to help you with a spring.
     
  4. pup

    pup Light Load Member

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    If you bought a 2100 rpm pump from Cummins for that engine it would still be a dog. It may drive a little better from the increased rpm's but the pressure would still be set to spec.
     
  5. Hopeaholic

    Hopeaholic Bobtail Member

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    Based on research and conversations with an old school pump builder, I'm thinking that going from a 27 button down to a 15 (with the bigger injectors I already installed) would make a decent difference in the drivability similar to the old big cam 400's. I've heard the Mechanical N14 referred to affectionately as the BC 5. I guess time will tell...
     
  6. pup

    pup Light Load Member

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    The rpms really help a ton. The button swap likely wouldn't be needed. We'd turn up the 1800 formula big cam engines with only adding rpm's & it was amazing the performance difference. A good idea to measure the fuel pressure before any adjustments. A road test is best for that but you could also pump up the afc chamber & do a snap test. That will also prove the diaphram isn't ruptured & a player in your low power.
    We still work on some of the mechanical n14s. By the time they came out the stc system was really working well & the engine was very sturdy
     
  7. OLDSKOOLERnWV

    OLDSKOOLERnWV Captain Redbeard

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    I could be wrong, but I’m thinking the timing is different between the 330 & 430....? I’ll have to look at my book when I get back.

    When you say bigger injectors, are you saying for a bigger horse engine, or they are custom built bigger...?
     
  8. OLDSKOOLERnWV

    OLDSKOOLERnWV Captain Redbeard

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    Yes the diaphragm....... ^^^^


    A bad diaphragm will make the engine weak as cat piss as the old saying goes......
     
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  9. pup

    pup Light Load Member

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    The 330 hp times at .154 the 430 hp times at .172. other than that & the injectors it looks like they are the same. That timing change would involve a change in the camshaft key
     
    OLDSKOOLERnWV Thanks this.
  10. Hopeaholic

    Hopeaholic Bobtail Member

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    On the n14, Cummins switched to STC which I think stands for step timing control (rather than prior mechanical valve timing) where oil pressure advanced the injection at the injector itself, rather than at the cam follower, I don't think I'd need to change camshaft key but clearly still learning here. Thx.
     
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