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Engine survey, 6-71's TI in good condition.

Discussion in 'Technical Discussion' started by dennismc, Feb 6, 2019.

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  1. dennismc

    dennismc Senior Member

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    OK, next step the mechanic want to run at wot for 10 minutes to check all temps , engine power output and any other issues that may come during that event. airbox inspection indicates approx 40% wear , no scoring all rings good.
    I was a bit taken back as I was under the impression that in pleasure craft with recreational use that a max of 2-3 minutes was the acceptable time for that run up. High idle was fine, ran up and held at 2200 with no issuesm may need a rack adjustment after load test.
    any comments appreciated.
  2. Capt J

    Capt J Senior Member

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    Usually we do WOT for 5 minutes...….but if all is well they should go 10 minutes without issues. You should be a lot higher than 2200 rpms though WOT I think 6-71's are WOT of 2600 or 2800 rpms, I forget.
  3. Capt Ralph

    Capt Ralph Senior Member

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    Yes, High idle should be around 2600 for TIs.
    WOT in gear should be 2350. 10 minutes is a bit more than our trials but it will do it.
    I'm confused with; may need a rack adjustment after load test. Who said this and why?
    It's a simple and reliable rack once set up correctly. Operating at any speed will not alter any settings.

    I recall your running 12v71s now? It's the same engine setup.
  4. Pascal

    Pascal Senior Member

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    I m pretty sure 6-71s are 2300 rpm motors so 2200 is a BIG a red flag depending.

    10 minutes on the pins is a bit long. 3 to 4 minutes is what most surveyors do. It s not unusual for temps to creep at max rpm.
  5. Bill106

    Bill106 Senior Member

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    Way back in the day many of the older guys who worked at Covington (once the local Detroit dealer) used to do startups on the dyno after full rebuilds by a full power under load run of 15 minutes or so after they came up to temps. Not all of them made it and I saw some pretty spectacular block ventilations but those that did almost always went on to long lives. If they're propped right and are hitting the governor at WOT there shouldn't be a problem but if one pops up it was likely going to happen soon anyway.
  6. dennismc

    dennismc Senior Member

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    Helping a friend on purchase of these 6-71's, the high idle was close to 2200 I noticed on the guys tack was a look before going down to 600 low idle so I may be mistaken , all to be reconfirmed after we have done sea trial and load test , one turbo was not fully free turning and would bind ever so slightly, mech. would not accept responsibility for any sea trial WOT issues after finding that. so turbo in the dr's office getting overhauled. we have no confirmed background on previous readings of rpm's under load , hopefully next week we do that, we ran up my 12-71's after rebuild to 2100 pinned as we had downsized the injectors a few years earlier, if memory is correct about 5 mins was the timing on those runups. after shut down we discovered a stuck injector, luckily in the no fuel position, fixed that and re test all good.
  7. Capt J

    Capt J Senior Member

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    You're 2100 rpms on your 12v71's is too low and you need to cut the props if you want them to live a happy long life. I ran a set of 8v71 TI's with downsized injectors and they ran great, crystal clean, but you must cut the props to match the reduced HP and still achieve WOT rpms
  8. dennismc

    dennismc Senior Member

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    Good point, Tks.

    Probably easiest way is to go back to N70 injectors, the 65's where put in many yrs ago as a recommendation from a DD mechanic, no suggestions to recut props or otherwise, am now in contact with dealer for explanation of lower wot rpm and not advising of potential issues..at that time I was a true diesel novice, still am in actuality. again, thanks for the great feedback.
    Last edited: Feb 7, 2019
  9. Capt Ralph

    Capt Ralph Senior Member

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    IMO; All 71s should at least have N60s, I prefer N90s on 4 valve heads (TIs or Ns).
    If you want to run cheap, pull that throttle back.
  10. Capt J

    Capt J Senior Member

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    Yeah, I've never heard of 60's on a 8v71 TI, the ones I ran went from 110's to 90's when they did the overhaul.

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