mainshiptom
Well-Known Member
What to look for when at sea trial ?
Detroit Engine Model 6-71 TIBs
- Thread starter mainshiptom
- Start date
rustybarge
Well-Known Member
There are dozens of DD owners on this forum: http://www.trawlerforum.com/forums/#trawler-forum
I believe they go on for ever with 1hp/cu.inch: so 6x71= 426hp.
1800 revs is the Max continuous speed, afaik: expect 16hp gal instead of 18hp/gal for modern 4str diesels.
Divemaster1
Well-Known Member
Got 671 TIA's myself...
Yup ... 425's go forever, but the Johnson Towers (JT) B's were often taken up to 485 which is a bit on the high end if pushed out of comfort zone ...
At 485, the cooling system is key... and that they reach full WOT without running hot.... If overheat alarm goes at WOT with 485's, you are already looking at a rebuild ....
OK... that's the bad news... onto better...
If not pushed... let's say 1800 RPM (and reach the stated WOT Max @2300) , then they may last forever ... and if not a rebuild in situ can be relatively cheap ... as in less than £2K (if doing work yourself, as I have).... and if re-build is required at purchase knock off about £1800 - £2000 per cylinder off price (that is what dealer will charge you).
What to look our for??
Engines should be cold ... as in exhaust manifold = cold to touch (if not, they may have been pre-started to hide something...so check before keys are turned)
Once key is turned (during winter you and owner may elect to hold down stop and turn around for 3-5 sec) to circulate oil and heat up combustion chamber as these engines run on single grade SAE40 oil and you may not want ignition straight away, but start oil circulation before ignition and idle.
Engines should be "keen" to start, but require quite high Amp batteries (around 200AH for the 6-71's) and should ignite within seconds .... all six cylinders .... if slow starting and four/five/six comes in, then a re-build is suspected...
Once ignited a slight sheen of diesel will be in exhaust water (they give full fuel as startup) and therefore a bit grey smoke is expected... engines will hunt for a couple of seconds but should soon settle down to a smooth idle at between 450 - 600 RPM (600 is actually quite high) ... and you should be able of balancing a 50p on the governor ... engine may sound like 1000 RPM, but that is the two stroke at idle for you...
DD's were usually mated with Allison gearboxes, and if this is the case, you can expect one of the engines being counter-rotating ... yes the engine runs the other way, instead of the gearbox dong the work.... as such one engine may sound different when on starter motor and may be slower turning around and igniting than the other... (mine are port fast, starboard slow).
Look out for "spare oil" of SAE50 grade as this can be used to "hide" compression issues at startup ...
Gear shift should be smooth and virtually un-noticable .... and you will have a smooth acceleration without excessive smoke...Temperatures and oil pressure should be rock solid once heated up and WOT should only see a small temp rise from normal cruise, but after that rock solid...
When throttling back, oil pressure may drop alarmingly low, and pressure lights may flicker ... this is not un-common on DD's, but should settle a bit higher again after 30 - 60 seconds...
Key is;
1) Need to get WOT !!
2) Easy start
3) Temperature
4) Temperature
5) Temperature
6) Temperature
ooh ... I forgot to mention, they may weep a bit of the black stuff ... not un-common...
What vessel are these in ??
Engines exist in Upright and Low Profile (block at 45 degrees) ... and when looked after is good for serious hours (I know of 6-71's with more than 40K hours).... The straight six's are not as thirsty as the V config ones and much easier to tune...
Happy to chat if you need any info/help etc...
Yup ... 425's go forever, but the Johnson Towers (JT) B's were often taken up to 485 which is a bit on the high end if pushed out of comfort zone ...
At 485, the cooling system is key... and that they reach full WOT without running hot.... If overheat alarm goes at WOT with 485's, you are already looking at a rebuild ....
OK... that's the bad news... onto better...
If not pushed... let's say 1800 RPM (and reach the stated WOT Max @2300) , then they may last forever ... and if not a rebuild in situ can be relatively cheap ... as in less than £2K (if doing work yourself, as I have).... and if re-build is required at purchase knock off about £1800 - £2000 per cylinder off price (that is what dealer will charge you).
What to look our for??
Engines should be cold ... as in exhaust manifold = cold to touch (if not, they may have been pre-started to hide something...so check before keys are turned)
Once key is turned (during winter you and owner may elect to hold down stop and turn around for 3-5 sec) to circulate oil and heat up combustion chamber as these engines run on single grade SAE40 oil and you may not want ignition straight away, but start oil circulation before ignition and idle.
Engines should be "keen" to start, but require quite high Amp batteries (around 200AH for the 6-71's) and should ignite within seconds .... all six cylinders .... if slow starting and four/five/six comes in, then a re-build is suspected...
Once ignited a slight sheen of diesel will be in exhaust water (they give full fuel as startup) and therefore a bit grey smoke is expected... engines will hunt for a couple of seconds but should soon settle down to a smooth idle at between 450 - 600 RPM (600 is actually quite high) ... and you should be able of balancing a 50p on the governor ... engine may sound like 1000 RPM, but that is the two stroke at idle for you...
DD's were usually mated with Allison gearboxes, and if this is the case, you can expect one of the engines being counter-rotating ... yes the engine runs the other way, instead of the gearbox dong the work.... as such one engine may sound different when on starter motor and may be slower turning around and igniting than the other... (mine are port fast, starboard slow).
Look out for "spare oil" of SAE50 grade as this can be used to "hide" compression issues at startup ...
Gear shift should be smooth and virtually un-noticable .... and you will have a smooth acceleration without excessive smoke...Temperatures and oil pressure should be rock solid once heated up and WOT should only see a small temp rise from normal cruise, but after that rock solid...
When throttling back, oil pressure may drop alarmingly low, and pressure lights may flicker ... this is not un-common on DD's, but should settle a bit higher again after 30 - 60 seconds...
Key is;
1) Need to get WOT !!
2) Easy start
3) Temperature
4) Temperature
5) Temperature
6) Temperature
ooh ... I forgot to mention, they may weep a bit of the black stuff ... not un-common...
What vessel are these in ??
Engines exist in Upright and Low Profile (block at 45 degrees) ... and when looked after is good for serious hours (I know of 6-71's with more than 40K hours).... The straight six's are not as thirsty as the V config ones and much easier to tune...
Happy to chat if you need any info/help etc...
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mainshiptom
Well-Known Member
Whitelighter
Well-Known Member
Divemaster1
Well-Known Member
OK ... thanks ... if it is the one with stabilisers and 1450 hours on the engines, one can assume that the heavy SD hull is used mostly at low speed and thus not run too hard. If the 6-71 TIB's @485 are run hard, then she will have already had a re-build ... or being due one (which should be pretty obvious at start-up/running)... Also.... if Stabilisers were installed post commissioning, then propellers should have been changed as she would not reach full RPM with the added friction... which is something else to look out for ...
Valencia is nice this time of the year.... but I would ask some more Q's on service etc.., first and also ask if they have the serial numbers of the engines available.... If you call UK DD dealer, they will upon request send you the engine datasheet of the engine configuration as it left the factory based on this, which you can use to check if anyone have changed configuration between shipping date and today...
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