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12v71 Detroit Diesel Govenro Shim Spec

Discussion in 'Engines' started by CaptOz, May 20, 2016.

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  1. CaptOz

    CaptOz Member

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    Hi Everyone,

    I finally got around to getting my both DD's rebuilt. They were originally 930Hp versions using the 9A31 injectors (From a 12v92) however I decided to return them to original spec of 870Hp using the 9215's.

    I went on the first Sea Trial and everything looks good except that WOT is only 2000 rpm and only buring 38 GPH on the flowscans. The throttle at the helm reaches that RPM about 70% of the travel range. Down on the engine the Governor is top'd out at that setting does not have more travel.

    Both Engines are at the same RPM and fuel consumption. Speed is 23.5 knots and the boat has a clean bottom but needs paint and is also very light at the moment.

    My Mechanic says that I might have to cut the Props but I also think the this engine needs to see more fuel.

    What is the Governor Shim spec for a 12v71TI with 9215 injectors, 870hp. The spec show 48gph at WOT and im no where near that.

    Current props are 29 x 33 no cup.

    Thanks in advance,
    Ozzy
  2. CaptOz

    CaptOz Member

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    My theory is that the Governor was restricted a little to prevent the large old injectors from dumping too much fuel and perhaps now with the smaller injectors, it needs to be opened back up.

    So can some one tell me what the Governor Shim Spec is for this motor setup?
  3. Capt Ralph

    Capt Ralph Senior Member

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    What is your max NO-LOAD rpm? I think you should see 2300 rpm there. This is the governor test and requires a result before we can comment on it.

    First guess without the above data; If I read your comments correctly, and if the rack & timing was set correctly, loosing 60 HP may have cost you some top end rpm. Without spinning up to the correct rpm, you will not make hp and not consume the the correct fuel / hp.
  4. CaptOz

    CaptOz Member

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    2650 is the Max RPM no load.
  5. Capt Ralph

    Capt Ralph Senior Member

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    Your over set. You do not have a governor problem.

    My theory is that the Governor was restricted a little to prevent the large old injectors from dumping too much fuel
    That's why there is a throttle delay system in some engines. Not a governor function.

    I assume you made rpm before your injector change. I am guessing also you had some plan in tuning down your engine.
    Now you have to tune down your props.
  6. CaptOz

    CaptOz Member

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    Before rebuild and injector reduction the old setup was maxing out at 2250 on a good day before engines lost the rest of their power.

    The 9215's where the largest injectors ever put into a stock 12v71TI. Thats what I have returned to. The company that marinized these engine back in 1986 decide to drop in the 9A31's from the 1080hp 12v92TA's. Those injectors bumped up HP to 930 from the stock 870. Hence I'm having 6.5% drop in HP if my engines before rebuild where at full power which is totally not the case. Props were are set at 29 x 33 which is what the calculator comes up with for 900hp engines. (Not sure if calculator does Crankshaft HP or Prop HP). Do I have to cut the pitch? Sure. but an inch maybe 2. Thats only 6 % at most, however I'm 300 rpms short at WOT which is 13% of the total max.

    And just to add insult to injury boat is super light as it is going through a major refit. Missing are: 1 generator, all the salon furniture, all the gear and crap stored aboard. Back fuel tank is empty (600 Gal) , water tank is empty (250 Gal), So let just say she is not her usual self.

    Plus, there is no black smoke at the current full throttle rpm of 2000. It almost seems and feel like a fast cruise speed.
  7. Capt Ralph

    Capt Ralph Senior Member

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    If the engines were removed and rebuilt, can anybody comment on the cam timing? On some of the taller horse power tunes, advanced cams with larger injectors were used.
    I would have to do some high dives into my library to find my notes on this. Hopefully your mechanic has this info quickly available.

    As a do-it-yourselfer; There is one or two things to check; ensure the shutdown lever is free and at full fuel position when running.
    Maybe pull the right valve cover, ensure the throttle delay (if equipped) allows the control tubes to swing full fuel. W/WO throttle delay, ensure the control tubes and injectors really do swing full fuel.

    Your trying to visualize a linear line in using your percentage figures. Horse power, torque, propeller loads & fuel consumption are on curves.
    AND, when it comes to propellers, It's still all theory, practice and more guessing (SWAG).

    What ship do you have and what reduction? 3 or 4 (more?) blade wheels?
  8. Capt Ralph

    Capt Ralph Senior Member

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    I just remembered a bug that bit a friend of ours,,, Double check the tachs.
    Really.
  9. Capt J

    Capt J Senior Member

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    What boat are these engines in, what gear reduction? If the boat came with the 12v71's TI's, I would see what props the factory used and go from there. I'm guessing you have Johnson and Towers.

    You are going to have to cut the pitch by buying new props, how much is the question. There's no getting around that. You should have had 29x32's with the old engines. 29x29's with the new setup would be a good start, I'm guessing you're looking at 29x28's ideally, but then the boat needs to be at normal weight before I'd even bother with borrowing props and trying them,but I don't think your existing props can be re=pitched more than 3". Generally cutting 1" of pitch equals 50 rpms. The problem with Detroits is it's a tough call because they're dependant on RPMs to make more power AND send more fuel, the governor will not send more fuel without more rpms, and 38 gph at 2000 is right on the money from experience. I would try to find a loaner set if you can. Give Frank and Jimmy's prop shop in Fort Lauderdale a call, they have a lot of loaner sets you can try. Also get a photo tach to get an accurate reading of rpm at the harmonic balancer.
  10. Capt Ralph

    Capt Ralph Senior Member

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    I was almost thinking Covingtons, J&T would my next guess.

    Wish full thought for the OP, maybe he still has an old spare set.
  11. CaptOz

    CaptOz Member

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    Ship? I think you mean tranny. ZF BW 195's reduction is 1.54 or close to that.

    Engines were rebuilt in place. I agree the curve on the chart are not linear. However at WOT engine is doing 38 GPH (870HP 12V71TI with 9215 Injectors) and only 2000 RPM on 3 bladed 29x33's . Yes I have to cut pitch by 1 at most 2 inches, but boat is extremely light!
  12. CaptOz

    CaptOz Member

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    Thanks Capt. J. Good feedback.

    Boat is a 1986 54' Bertram with original 12v71TI's marinized by BK Power in Miami. 930hp using the 12v92TA 9A31 Injectors which we know we know produce 1080HP for that motor.

    I have run Prop Calculation and yes I have to reduce my pitch a little. I have original 3 bladed props 29 x 33 and new calc says 29 x 31.5.

    The prop calculation says I should be doing 28 knots at 2300. Currently doing 24 knots at 2000. Im thinking It should at least get to 26 knots at 2300.

    I will call F&N on Monday to see if I can get a loaner Prop.
  13. Capt J

    Capt J Senior Member

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    You're going to need to cut pitch by a lot more than that. You were over propped by an inch of pitch with the previous injectors and should have been spinning 29x32's.

    Once you add all of the heavy gear that is not on the boat. Which by my best guess is at least 3,000 lbs plus 6000lbs of fuel and water load, you're going to lose another 100 rpms. Not to mention you'd be a lot better off if they turn more RPMs than not enough. When the dust finally clears you're going to be spinning 29x28's or 29x29's. Call Frank and Jimmy's, give them your current specs and where you are on weight and hp loss and they'll calculate it for you. They're very good at that.
  14. Capt Ralph

    Capt Ralph Senior Member

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    Would you still have the old injectors?
    You did not comment why you changed the injectors; Lots of discovered problems during rebuild?
  15. Capt J

    Capt J Senior Member

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    Probably because they just threw way too much fuel in there and slowly washed liners. 140 LPH injectors on a 12v92 are a bit too much and tend to run very dirty trolling, on a 12v71 I can only imagine how rich they run on the troll and dilute the oil.
  16. Robertoman

    Robertoman Member

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    What do you have for throttle controls?
  17. CaptOz

    CaptOz Member

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    F&J does not lend out props.. I guess you have to be a Family member or something.
  18. CaptOz

    CaptOz Member

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    I agree to cutting props some, but down to 29 x 29 might be too much. Im only dropping HP by 6.5% so I expect to get 26-27knots at 2300(WOT) and 22-23 at 1900(cruise). 29 x 31 is what boatdiesel.com prop calc comes up with.
  19. CaptOz

    CaptOz Member

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    No old injectors where traded in to remove core charge.

    Rebuild was caused by Startboard engine ingesting sea water on the right bank. Water leak was fixed immediately however Intercooler was clogged and ran quite a bit of time like this forcing the already tired Port engine to work even harder.

    Upon disassembly Port engine has, broken Fuel/Air Modulator, a couple of broken piston heads, broken rings, bad injectors, etc. Starboard had blowers locked up, turbos locked up, slight crack on one head not machineable.

    In the end boat would not plane. Hence full rebuild.
  20. CaptOz

    CaptOz Member

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    Another piece of information that I left off for this first sea-trial is that the Mechanics disconnected the Air/Fuel modulator on both Engines so that we were guaranteed max fuel out of the hole. This was done because boat would not plane on previous sea-trial attempt. It was noted that all four racor bowls were full of algae from the boat sitting for 1 years with out planning. They were removed and cleaned obviously.

    So at 2000 RPM's we were seeing 10 PSI on both engines. Is that the normal? Seems a little low for me. Does the modulator being disconnected affect the PSI?