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Detroit 671 TIB 485 H.P. only 2000 rpm

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Detroit 671 TIB 485 H.P. only 2000 rpm

Old 01-31-2019, 12:14 PM
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Default Detroit 671 TIB 485 H.P. only 2000 rpm

Hi there, i'm .about to purchase a 38' egg harbor with Detroit diesel 671 TIB 485 H.P. BUT ONLY RUNNING AT 2000 RPM FULL THROTTLE,, original props checked and are fine bottom clean 1/2 tank fuel, engine's Do not smoke at all and sound great , question is is there an issue??? Mechanic survey guy says it's fine at 2000 rpm ,,but the tag on valve cover says engine should run loaded at 2500 RPM. Full throttle,,,,The engine's were supposedly rebuilt 160 hours ago. Please send any comments with experience of these engines, Thank You Very Much!!!!!
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Old 01-31-2019, 01:50 PM
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Easiest to start if you didn't already check is make sure that the throttle at the pump is not governed by a stop to set this as the maximum rpms and prevent if from being pushed any further. I haven't looked at a 671 recently, but on other engines this can be as simple as backing out a screw or undoing a couple of bolts and nuts to move a plate. Seeing you had a mechanic survey, I'm sure it's not that easy. What did the mechanic that did the survey say? Next would be fuel, filters, airflow, etc, but surprised no smoke if they were problems.
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Old 01-31-2019, 01:57 PM
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Was it running full rated RPM before the rebuild? If not, could be over-propped which led to the rebuild. Not achieving full RPM, with a diesel particularly, reduces service life significantly, and can also lead to major failure.
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Old 01-31-2019, 02:00 PM
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My Survey mechanic says theres no issue not to worry about max rpm so much,,,, Sounds very odd to me..I even got a hand held tach and put reflective tape on balancer, and shot the rpm's and all tachs were right on.. the broker and mechanic were aqaintances, which made me wonder,But i guess my quesion remains if anyone thinks 2000 rpm full throttle is an issue or not ,,And no smoke at all smooth as can be ,a very small amount at start up then clean as can be,,,
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Old 01-31-2019, 02:03 PM
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The paper work i saw on the boat showed the boat ran at 2450 at one point and the propps are correct size we pulled out of the water yesterday to check and get hull survey Can props get steeper pitch over timee?? the speed at 2000 rpm is 19 knots which is correct for that boat
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Old 01-31-2019, 02:06 PM
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Its hard to believe an originall prop that the boat ran 2400 at one time can go out up to 400 RPM with ??? zero damage
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Old 01-31-2019, 02:13 PM
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RED FLAGS ALL OVER THE PLACE!!!.. broker and mechanic are buddies?
Yes there is a problem with a 671 only turning up to 2000 rpm you should be at 2500 to 2525 RPMs . What was the no load RPM values? that should be 2600 +/- ( I would have to look it up).
The higher hp DDs are sensitive to cooling issue and over propping.
Get the receipts for the " re-build" find our EXACTLY what as done.
Find a different DD mechanic and bring them in to do a survey.
Don't be afraid to push back and walk away.

We have a pair of re-built DD 671TI ( 450 hp) in a 44 Ocean. Loaded they max out at 2500 +/- The mechanic thinks I should tweek the props. He would cringe at this especially since the egg is lighter than the 44.
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Old 01-31-2019, 02:17 PM
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No way I would hire a mechanic that had a relationship with the selling broker.

You need a 2nd opinion from a qualified independent mechanic.

There is a reason that the engines only go to 2k you need to know the reason. The answer is not "don't worry about it"
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Old 01-31-2019, 02:18 PM
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Very simple. Tell the owner ‘ when they hit 2525 call me” Not your problem yet don’t make it your’s.
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Old 01-31-2019, 02:24 PM
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Not saying they are buddys but they definatly new each other well the reciepts showed full rebuilds bearings sleeves pistons new head ect. but no smoke....
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Old 01-31-2019, 02:38 PM
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Detroits do NOT like running overloaded like that! 500+ rpm off the top is something to be concerned about. It might be just a govenor setting but, this really needs to be fixed before buying! Good luck.
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Old 01-31-2019, 02:48 PM
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Did mechanic check no load rpm? Should be 2650-2700.
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Old 01-31-2019, 02:51 PM
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Yes Each engine ran up to 2600 in neutral....
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Old 01-31-2019, 02:54 PM
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Might be worth finding a good, old school Detroit mechanic to review receipts. Might be possible the engines were detuned for some reason- seems unlikely in the higher HP configurations but you never know
Many years ago, I grew up watching a then old (at least to my niave and young eyes) gentleman "de-tune" 6-71's to make them run forever-
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Old 01-31-2019, 02:55 PM
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I had a Whiticar years ago with 671's and I do remember the boat bottom being clean made a big difference.
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Old 01-31-2019, 03:00 PM
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Yeah bottom is clean as can be, and reciepts only show maintenance and rebuilds,,the whole boat only has 1300 hours from brand new ,,Its a one owner boat ,The owner never used it,,,, it sat a lonoong time not being used,, was what i was told the reason for rebuilds in the first place
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Old 01-31-2019, 03:06 PM
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Also just got oil sample back and all are good
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Old 01-31-2019, 03:29 PM
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maybe its water logged and alot heaver then it was years ago, i had a similar problem on a boat and found out it was saturated, good luck please keep us posted, you got my attention !!!!
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Old 01-31-2019, 03:33 PM
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I own a pair of 671 ti’s, immediately remove this mechanic from the equation and start over. If he said turning max 2000rpm on the pins is ok you ARE (not might be) getting screwed.
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Old 01-31-2019, 03:38 PM
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had a similar problem with my 450hp detroits, turned out to be weak springs in govenor , Wot 2500-2515--no Load 2650-2700, this is the sellers problem, drove me crazy before I sold my Topaz.
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