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6V92's TAB lack of RPM

Discussion in 'Engines' started by Robertoman, Aug 30, 2015.

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  1. Robertoman

    Robertoman Member

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    I recently bought a Californian 42' flybridge with low hour 6V92 engines @ 550hp. Engines rebuilt at 1500 hours and rebuilt again at 3000 hours. Second rebuild because of glazed cylinder walls, from what I have been able to deduce.
    Last rebuild appears to be a quality rebuild by a knowledgeable Detroit guy in 2007/2008. Engines have about 400 hours now. Start right up no smoke. The last cooling service was about 5 years ago. Other recent service is not documented.
    At the time of sea trial the engines ran up to about roughly 2150 rpm+- under load. These engines are rated at 2350. Light fuel, light water, little personal effects, in other words pretty light.
    Fast forward about 2 months. Added weight, 400 gallons fuel and 200 gallons of water, in other words HEAVY.
    I have changed oil, Delo 100 40w. Changed fuel filters, added vacuum gauges to RACOR filters, cleaned air sep main filters, but not vacuum breaker, replaced fuel priming pump (the one that looks like a 1 lb. coffee can)that didn't work and had no check valves inside, other pump works ok. The Racor filters were 2 micron and the spares were 2 micron as well so because of the black stringy stuff that showed in the view bowl I put 2 micron filters back to keep things clean and am keeping an eye on the restriction gauges, currently 5lbs port and 7lbs starboard, I will put 10 micron filters in next time until I am sure of the fuel condition.
    No load, engines turn 2500 +-.
    Yesterday, fishing trip return, engines would only turn about 1850 rpms.
    After a couple hours watching the grey smoke we cooled down the engines and shut them off and went diving.
    The bottom looked. as my professional diver buddy said "looked like a dock". The bottom was cleaned good 16 days ago, and my regular diver says the bottom growth, is just out of control.

    My question is, do I have an engine problem, prop problem, growth problem or ?
    All opinions welcomed.
  2. Capt Ralph

    Capt Ralph Senior Member

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    Our diver has to clean some boats around here twice monthly also. Heck of a year so far.

    400 hours in 7 years could of been a hint.

    Find what prop dimensions your are suppose to have and make sure you have it. Some people out there still like to go slow with over pitched wheels.

    Who told you to run 2mic filters? Your starving your mains rite there. Your secondary filters are 5 mic and your not doing anything positive. Lets start here first. Don't ad any snake oil to the fuel yet, lets dissect some elements. Get some fresh 30mic primary and fresh secondary filters installed and go for a ride with a clean bottom. Report on what you find in the filters.

    I'm afraid your already pulling to mach vacuum at the filter.
    after the secondary; 5 max @ wot.

    ,rc
    Last edited: Aug 30, 2015
  3. Capt J

    Capt J Senior Member

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    Too hard to say, but your bottom shouldn't look like a dock if it was cleaned 16 days earlier. Maybe after 4-6 weeks it'll have good growth. But you guys have cold water so the growth should be a lot slower than south florida. I'd say to find a better diver. You need to run it with a clean bottom and see what it turns. Then if the motors are in good repair, you need to cut some pitch from the props to get you to 2350 rpms. What condition are the secondary fuel filters in?
  4. rgsuspsa

    rgsuspsa Member

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    The general rule of thumb for primary (Racor) fuel filter change requirement is when the vacuum is twelve Inches of Mercury (12 In.-Hg.), which is nominally 6 PSI vacuum. As rcrapps said, put some 30 micron filters in, and get the bottom, props and struts REALLY clean. Then take the boat and run it for maximum engine RPM test. If you do not get at least 2,350 RPM, preferably 2,400, then further investigation is called for. Please post your results and then a plan of action can be defined.
  5. Robertoman

    Robertoman Member

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    Thanks guys,
    30 microns and a clean bottom it is.
    Thanks so much and I will report back soon.
    Rob
    Last edited: Sep 1, 2015
  6. Capt Ralph

    Capt Ralph Senior Member

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    psi vacuum, is what I meant to type, just got carried aweigh. Thx Rgsuspsa

    Lets really look at the exhaust. Get a few eyes on it and give us the color when cold, cruising and when trying to make wot.
    Can use vacuum readings all during trials also. Is there a pressure gauge after the secondary (fuel out from pump)?
  7. Capt Ralph

    Capt Ralph Senior Member

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    Any propeller specs from original and what you have now?
  8. Robertoman

    Robertoman Member

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    The props were stamped 28 but didn't see the pitch because of fouling. There was some prop work but I can't find specs right now. will research more.
    One other thing, Dual floscans, Starboard indicates much more fuel burn than Port. EX: Port 5 gph- Star 7.5 gph pretty even thru rpm range.
    Diver works tomorrow, repeats the growth is crazy, never seen anything like, it the water is 78*
    Rob
    Last edited: Sep 1, 2015
  9. Capt J

    Capt J Senior Member

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    Find a new diver, or get in the water after he's done and check it yourself.
  10. dsharp

    dsharp Senior Member

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    When's the last time the bottom was painted? It doesn't take but a few barnacles and growth to kill engine rpms.
  11. Capt Ralph

    Capt Ralph Senior Member

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    Lets not count on the Flow Scan exact numbers as yet but keep a log. Notable changes in these numbers may be more helpful.
    Changing away from the 2 mic will make a difference in the readings.
  12. Robertoman

    Robertoman Member

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    First I would like to thank everyone who has responded to my post.
    After talking to my diver today he convinced me that even though now is not the best time to do bottom paint, it really needs bottom paint! It is clean for now but it will be overgrown in the next 10 days or so. I have a couple of things coming up but as soon as possible it is into the boatyard for bottom maintainence.
    Now, as long as it is clean for the time being, I will change the Racors fron 2 micron to 30 micron, and give it a trial this weekend and see how she runs.
    In answer to Capt J, about the condition of the secondary filter condition, I changed both of them when I changed toe Racors', should I change them again? About 10 hours since installing the Frams with 2 micron Racors ahead of them, about 140 gallons of fuel burned.
    Ralph, no installed pressure gauge after the pump.
    Ron, and all I will keep you all informed as we go along.
    We will get this thing running right sooner or later.
  13. Capt Ralph

    Capt Ralph Senior Member

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    Were always excited to hear about results. Please keep us up on any improvement and activity.
    We all learn a lil more as the results and feedback get posted and updated.

    We manage a '88, 48', Californian with 671TIBs. What a fun boat that can zip rite along.
    She is heading to the Keys in 2 weeks.

    ,Ralph
  14. Capt J

    Capt J Senior Member

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    I delivered one with screaming demons....6v53's.....it cruised at a whopping 13.5 knots. It was a VERY long trip from Fort Lauderdale to Lake Pontratran, LA with Dewey Gumbo and his momma.
  15. Robertoman

    Robertoman Member

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    Quick update on 6V92 Detriots, low rpms.
    Per Info from you guys.
    I pulled out the 2 micron Racor filters, the starboard filter was 3/4 discolored from ?, wasn't water as there was no water in sight bowl, and black fine strands of something, floating in filter fuel which I drained out to get the sediment out of the bowl, sediment in sightglass appeared to be, sand, dirt, debris of unknown origin.
    Black algae like organisms globbed on the outside of the filter element, a real witches brew.
    Cleaned out the mess and installed 2 new 30 micron elements.
    I talked to my diver and showed him my appreciation for doing an extreme cleaning.
    The engines sounded way happier, both settled into an even idle,(starboard had been idling at 670+-, port at 605+-) both now idle smoothly at 605 rpm.
    No more grey smoke and without a lot of trim tab tuning both were turning about 2290 rpm.
    Next step is to paint the bottom, and keep running the old fuel out and keep an eye on the filters.
    Those are some good ol engines, I don't care what anyone says.

    Thanks, all for all of your time working thru this.
    Now, the watermaker needs some TLC.
  16. Capt J

    Capt J Senior Member

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    If you've got that mess, clean the racors out completely. Buy new gasket sets for them. The bowl comes down with 4 3/8" (headed) bolts, unscrew the turbine and the ball and gasket come out and entirely clean the turbine out housing etc.....
  17. Robertoman

    Robertoman Member

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  18. Robertoman

    Robertoman Member

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    Will do, Thanks
  19. Capt Ralph

    Capt Ralph Senior Member

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    did you notice a change in the vacuum gauges?
  20. Robertoman

    Robertoman Member

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    image.jpg image.jpg Here is a photo of a dirty filter.