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J&T 692 ddec problem?

Discussion in 'Technical Discussion' started by snowkid, Jan 13, 2017.

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  1. snowkid

    snowkid New Member

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    Egg harbor 52 convertible with twin J&T 692 DDEC engines, 625 HP. Problem with starboard engine running fine up to 1825 rpm's, and then engine makes a slamming noise coming from just before turbo. The boost pressure runs 22 on this engine and the other running smooth at 11. Can not come up with any mechanic that has run into this problem? Motor runs out well below this rpm, temp, oil pressure and such register fine. Had injectors checked with electronic tool, and test within tolerances. Need suggestions and help?
  2. Pascal

    Pascal Senior Member

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    What happens besides the slamming noise? Loose power? Shut down? Smokes?

    I m not sure how it would relate to your symptoms but what about the emergency air shut down if you have them
  3. snowkid

    snowkid New Member

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    do not loose power and with the engine room door shut, can't hear or feel anything on the bridge. Sitting in the salon sounds like engine coming through the floor. Haven't checked the emergency shut off, and it does have them.
  4. rcrapps

    rcrapps Senior Member

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    Where are you measuring boost? In the air box (below the blower) of before the blower.
    I think Pascal is on the first thing you need to check, the shut down flapper.

    You should not see 21 psi of boost till the upper (way) rpms.
  5. snowkid

    snowkid New Member

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    talked back with my mechanic, and he was going to try and send the information you are asking about. The question are above me. I have told all I know, which isn't much, but want to get it running again.
  6. rcrapps

    rcrapps Senior Member

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    You have a mechanic? Heavy DDC tech? AND were going to help him?
    Please deposit cash in the slot at the front of your computer. If all of it does not fit, we take Pat-Pal.
  7. Capt J

    Capt J Senior Member

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    Yeah it sounds to me like the shutdown flap. The only other thing I can think of is the bypass valve.
  8. rcrapps

    rcrapps Senior Member

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    Bypass on a 92?
    Interesting. I'll have to study deeper. Always open to learn something new.
  9. Capt J

    Capt J Senior Member

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    Don't quote me on this as it's been about 4 years since I managed the last DDEC 6v92 yacht. I know the DDECs have smaller turbo cartridges to build boost earlier because they had trouble getting up into higher rpm's without them. I think the DDECs had bypass blowers and they have bypass valves, now I'd think the valves would open right around where the OP is having issues. If this is stuck shut, it might cause a problem like that OP is having. This is nothing but a guess and I'm just thinking out of the box.
  10. Bamboo

    Bamboo Senior Member

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    92's have two different versions of superchargers (aka "blowers")- those with a bypass and those without. The bypass version allows the turbo charged air to not have to completely pass thru the supercharger, while the non bypass version there is no such "bypass". A non bypass version has more low end power than a bypass version. The bypass version has more upper end power. When my 92's were rebuilt a few years apart Western Branch installed bypass blowers on the port and I noticed no difference (it had non bypass). When the second one was rebuilt I could tell the difference in the low end power- and I had noticeably more unburned fuel (smoke) at low end when I wanted to move fast. We- myself and Western branch- looked at quite a few items as to why this was until I asked about the blowers and this difference between the blowers. They then sent two techs up from VA to NY in a van and changed out all four blowers (I had 16v-92's so that's two blowers per engine) to the non bypass versions which were there prior. The low end smoke disappeared and I once again had the low end power but I lost a bit on the top end. I do not believe the blowers have anything to do with this issue the OP is having. My versions were non DDEC but I don't think there is a difference.
  11. rcrapps

    rcrapps Senior Member

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    Interesting again. I'm still trying to do my EOW and just poured another Friday night special. Two replies ring in my e-mail.
    Not had a chance to look any of this up yet but a quick question before I get back to work; How/where do you bypass the blower on a V block?
    Maybe I'm assuming TAs also and just can not picture in my (Friday night mind) the plumbing.

    I remember on straight 6-71 TIBs, the bypass went into the side covers.
  12. Capt J

    Capt J Senior Member

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    I've also had a motor once that the valve springs got weak and over a certain RPM the valves all floated and the rockers made one heck of a noise...... this was a gas motor though, but just a thought.
  13. snowkid

    snowkid New Member

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    there is a box with 2 piston in it just after the single wet turbo. The noise seems to be generating there at 1850 rpm's. I have replaced the springs and checked to make sure the pistons were not stuck, or broken ring. This all checks out? Sounds like the pistons are slamming in that box.
  14. snowkid

    snowkid New Member

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  15. snowkid

    snowkid New Member

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    We found the problem, fins on the exhaust side of the wet turbo were disintegrated. This resulted in high air box pressure, which finally caused one of sealing O-rings around piston sleeve to split and water seeped by into oil pan. Didn't think turbo was problem only 150 hours since replaced? The side of turbo with air sept attached was tight.
  16. rcrapps

    rcrapps Senior Member

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    Hang on Air compressor?
    The valve system makes a racket when the pressure it maxed out.
    Send a picture of the component or area.
  17. snowkid

    snowkid New Member

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    Motor is jacked up in the boat and sleeves and pistons have been removed. Having cylinder heads reworked, waiting on cylinder kits to arrive. The 0-ring on the number 2 cylinder on the outboard side was one leaking, evident when removed. Looks like it was cut when rebuilt at 900 hours.

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