Cummins Marine Diesel Repower Specialists › Forums › Cummins Marine Engines › 2011 Cabo 40 WOT rpm

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  • November 28, 2022 at 7:16 pm #139319

    James Roach
    Participant
    Vessel Name: Callie May II
    Engines: Cummins qsc 600
    Location: St Mary’s GA
    Country: US

    Hello  I have a 2011 Cabo 40 that just underwent full service including a top end rebuild on the stbd QSC600 and two new turbos.  We have sea trialed the boat 3 times and we are constantly getting just under 3000 rpm at WOT. Fuel burn and load look pretty good etc. wondering if these 600hp 8.3s with Zeus pods should be turning up over 3000. Attached are the screen shots of WOT today.   

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  • December 18, 2022 at 11:01 pm #140006

    James Roach
    Participant
    Vessel Name: Callie May II
    Engines: Cummins qsc 600
    Location: St Mary’s GA
    Country: US

    Here are some decent pictures of the breather system on these QSC 600 motors. 

    December 18, 2022 at 9:15 am #139998

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    I really do not have the “ring” experience to comment.

    Oil coming out the breather tube? 

    Maybe some good pics of your crankcase breather system–no close-ups–need to see it all

    December 17, 2022 at 8:15 am #139982

    James Roach
    Participant
    Vessel Name: Callie May II
    Engines: Cummins qsc 600
    Location: St Mary’s GA
    Country: US

    Thank you for that info. I will probably contact Cummins this week regarding the Zeus drives/props etc.  What are your thoughts on the rings lining up and the oil coming out of the breather tube?  

    December 16, 2022 at 8:58 am #139945

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    You are lucky your aftercoolers were serviceable–Many times they will not even come apart.   

    When running on the edge of  absolute test cell data / maximum power ( you are), many things can affect RPM– Water temp,  water salinity, a tad of bottom growth, a few more lbs here or there, and windage are the most common ones.

    If you were propped to see the governor at 3070-ish from years back then you would not  see this type of RPM  change.   Read what Cummins says  a few times —-Not me. 

    December 16, 2022 at 8:25 am #139939

    James Roach
    Participant
    Vessel Name: Callie May II
    Engines: Cummins qsc 600
    Location: St Mary’s GA
    Country: US

    Tony 

    the soot was pretty much black residue on the turbo and we were told this was turbo blowby and couldn’t be corrected by servicing so we had both turbos rebuilt so they were fresh for us. <br /><br />

    yes on the aftercoolers. I have hundreds of pictures of the service by Donnelly Yachts. Attached are a few. The thing  stumping me is that we were turning up fine after the service by Donnelly’s but now we are a few rpm short. With stainless props could they “wear”. I don’t think we have even 100 hours on the boat since the 2000 hour service and only sea trial hours after the port top end. 

    December 16, 2022 at 7:33 am #139938

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    Not sure what “blowing soot” into the engine room explains?   That explanation from a mechanic would be  100% unacceptable in my book

    Have  the aftercoolers on the engine ever been off ,  on the bench  in pieces, and then serviced per my protocols?  Aftercooler servicing should never  be based on engines hours, only on Marine Age and whether your boat sits in salt or fresh what when at the dock… If not, get a mechanic that understands a SWAC , very high performance,   DIESEL ENGINE  that uses a “mixed metal” aftercooler ( like most engines of this design today) .

     

    How many years have these engines been in service since new? 10+?

     

    IMO, you need to pitch d0wn about 1.5″ to  get another  100++ RPM

    December 15, 2022 at 6:54 pm #139927

    wexblast
    Participant

    Tony

    Thanks for the reply.  My reply I just wrote got blocked for some reason but here goes-

     

    Few months ago we found that we were getting oil coming out of the starboard breather.  Started small but got bigger on a trip Charleston to Savannah.  We also had pressure in the crankcase.  Upon tear down the mechanic observed rings that were perfectly lined up but no indication of wear etc.  This might explain why our numbers were all good but we had oil passing by.  Not sure how this could happen.  Anyways,  hours were just shy of 1900.  Turbos were rebuilt a year ago along with a full 2000hour service.  We had one turbo that was blowing soot past into the engine room and we were told they were not serviceable.  They were also on back order so we just had both rebuilt to start fresh.  Only after this service have we realized the RPM not getting to 3000.  We had an issue with getting the bottom cleaned regularly and well enough so Im wondering if this has to do with 1 year old propspeed or maybe some imbedded growth that hasnt been cleaned well enough.  

     

    Last run was 2970 rpm 98% load 100% throttle 35.2 knots.

    Thanks in advance!

     

    Jim

    December 15, 2022 at 5:22 pm #139920

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    They need to make an accurate 3050-3065 RPM and make it EASY with the vessel loaded for bear..

     

    Curious:

    How may hours to the “top end” and why the 2 x turbos?

    Was a  “why” the engine  needed this type of work ever explained? I can’t imagine the engine actually “wore out”..

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