Happiness is...
 

On Sun, 25 Nov 2007 21:37:55 -0500, "Roger Long"
wrote:

My 2QM20 has a thermostat. It is also a very cool running engine. I have
heard several places that they are among the coolest running diesels in
common use and mine seems quite happy running that way. I have also heard,
but not substantiated, that this engine runs just as well, or better, with
the thermostat removed. I don't recommend it or plan to do it though.

The 2QM20 has a precombustion chamber which I don't think is common in small
diesels. This might account for different operating characteristics. It
might also account for their reputation for lasting a long time with poor to
non-existent maintenance. With a precombustion chamber, a clogged injector
maybe isn't consentrating the combustion into hot spots on the piston head.
I'm speculating a bit and would like to know more however.

Yanmar's factory parts books lists two thermostats and two overheat
sensors for the small engines. One for salt water cooling and a higher
temp one for freshwater.

Also all the small Yanmar engines and I assume the larger engines use
pre-combustion chambers as do Caterpillars and many other engines. The
idea of the pre-combustion chamber is that the fire starts there and a
gout of burning fuel is injected into the combustion chamber rather
then simply spraying a jet of fuel into the combustion chamber. I
believe it is intended to provide better flame propagation and
improved combustion.

I would hesitate to recommend that anyone remove the thermostat unless
the engines is equipped with a temp. gauge as in some cases removing
the thermostat actually increases cylinder head temperatures.

It seems contrary to logic but on some engines - there was a Ford V-8
I remember - that actually run hotter without the thermostat as the
thermostat in addition to controlling temperature acted as a orifice
and restricted the speed of coolant flow through the block and head.


Bruce-in-Bangkok
(Note:remove underscores
from address for reply)

Happiness is...
 

On Sun, 25 Nov 2007 20:10:04 -0500, Wayne.B
wrote:

On Sun, 25 Nov 2007 07:20:49 -0500, "Roger Long"
wrote:

Engines that are idled a lot simply get overhauled a bit sooner. If you
don't have good reasons to idle, why throw away your engine time which =
money?

That's the way I understand it also. Instead of getting maybe 5,000
hours between overhauls, you end up with 3 or 4,000 instead. With a
turbo it can be a lot worse than that.

I have some hard numbers for single vs low speed twins on my own boat,
based on a relatively small number of data points. Running both
engines slowly to achieve about 1.0 x SQRT(LWL), the best fuel economy
I've been able to achieve is 1.4 NMPG.

Running single engine with the other one freewheeling I have been able
to get 1.7 NMPG.

The boat has sight guages on the tanks so that I can measure fuel burn
to within 5 gallons accuracy. The boat is a heavily loaded,
semi-displacement GB49 with total weight in the of range 60 to 70,000
lbs. The engines are 2 stroke DD 6-71s, naturally aspirated, rated at
280 hp each. They will hit their rated max of 2400 RPM at WOT.
Props are 4 bladed 30 x 25, reduction gears are 2.5 to 1.

With both engines the boat will reach 1.0SQRT(LWL) at 1200 RPM,
burning about 5 gph total (about 85 actual hp). Single engine at 1500
RPM, same speed, burns about 4 GPH (68 actual hp) .

Since it seems reasonable to assume that the overhead of running a
large engine slowly is greater than a small engine, it is entirely
possible that a different outcome would be obtained with smaller
engines running closer to their rated power output.


Interesting. Have you tried other fractions of "hull speed" to see if
the same ratio of one engine fuel consumption to twin engine
consumption remains the same?

As an aside all 6-71's weren't rated at the same power and one of the
differences was the injector s. They came with different colored tags
as I remember. If you are interested in improving fuel economy (and
losing horse power) talk to an experienced Detroit diesel mechanic
about changing injectors. It might give you a bit better economy, if
you are interested.


Bruce-in-Bangkok
(Note:remove underscores
from address for reply)

Happiness is...
 

On Sun, 25 Nov 2007 20:10:41 -0500, Red wrote:

On Sat, 24 Nov 2007 23:49:00 -0500, Wayne.B
wrote:


On Sat, 24 Nov 2007 22:12:41 -0600, Brian Whatcott
wrote:


Diesels don't have this problem, and so are less wasteful at low
revs.


That's true but they have maintenance issues if run at low speed/low
load for extended periods of time.

Bruce said:
Yes there "seems" to be that but mention of "it is bad to run the
engine at low poser" seems confined to the boating world. I've worked
many construction jobs where diesel engines were started in the
morning and shut down at the end of the day. During smoke breaks or
lunch they just sat there and idled. Cranes are a perfect example,
that spend most of their life at very low power settings.

Generator sets - I've never seen a gen set operating manual that said
"run this engine at high power settings".

Not that I'm advocating idling your diesel for days and days but I do
wonder about the people who worry about letting the engine idle. I've
seen people that would hardly let the poor old thing cool down before
stop-cocking it, "because it is bad to let the engine run at low
load".

The Perkins I have in the sail boat has a continuous rating of 3,000
RPM and for years I ran it at 1500 - 1800. When I overhauled it I
could see no evidence of abnormal wear or carbon or any other evidence
that slow running harmed anything.

have the feeling that someone once said "it's not a good idea to
idle a diesel for a long time" and as the message passed from dockie
to dockie it became an urban legend and now everyone is worried about
idling the engine.

But what do I know?

Bruce-in-Bangkok

Bruce, I suspect that all this came about as there are different types
of diesels out there, and *some of them* surely cannot be safely idled
for long periods. I knew a few tow truck operators that drove ford
diesels that told me that if the engines were not equipped with
high-idle switches the engines consistently did not last that long (tow
trucks spend a lot of time at idle). On the other hand, guys that drove
some other brands of tow trucks said they didn't need the fast idle, the
engines lasted just fine. My Dodge/Cummins pickup truck owner's manual
says to avoid idle any longer than 3-5 minutes - kind of a bitch since I
spend half the day in traffic.
In boats we have some (mostly older now) slow-turning diesels that
can be run all year at low speeds without any harm. But I suspect that
most of the newer, lighter, fast turning diesels of recent vintage are
better off above idle.
One more thing... *most* people I've observed around here driving
their boats into the dockage area are idling anyway. By the time they
are docked the engine is already sufficiently cooled and needs no more
idling at the dock, yet they usually spend another five or ten minutes
wasting fuel.
Red


I suspect that you are correct. I recently set the governor on a
Gardner 6 cylinder that turned a roaring 1,000 at full throttle and
drove a 50 foot teak junk at 7 - 8 knots.

My personal thoughts about diesels is that if you idle them for days
and days it is not good. However some idling followed by running them
at rated speed is not harmful.

I may be wrong but I've been treating them that way for a lot of years
and they haven't complained yet =:-)
Bruce-in-Bangkok
(Note:remove underscores
from address for reply)

Happiness is...
 

On Sun, 25 Nov 2007 20:19:46 -0500, Red wrote:

Roger Long wrote:
The bigger the diesel, the more of a factor this is
which is why railroad engines are seldom shut down for maintenance.

Roger, I am under the impression that railroad diesels are run at pretty
high "idle". In fact when waiting for the various commuter trains to get
out of the way around here I get the impression of a pretty fast running
engine when they are stopped. They do not sound anywhere near idle. Is
this the case just when they are dropping off and picking up and/or is
there another time when they actually idle slower?
Red


I think that railway engines are basically generator prime movers and
run at a constant RPM all the time. At least that is the way a power
plant engine runs. It always runs at approximately rated RPM
and the governor makes small adjustments up or down to maintain the
proper frequency.


Bruce-in-Bangkok
(Note:remove underscores
from address for reply)

Happiness is...
 

On Mon, 26 Nov 2007 23:03:52 +0700, Bruce in Bangkok
wrote:

Interesting. Have you tried other fractions of "hull speed" to see if
the same ratio of one engine fuel consumption to twin engine
consumption remains the same?

I have tried 1.0SQRT(LWL) and 1.1 - as Beebe and others predict, 1.0
is more efficient. 1.0 is about as slow as I'm willing to go, and
then only over longer distances where I'm already committed to running
day and night.

As an aside all 6-71's weren't rated at the same power and one of the
differences was the injector s. They came with different colored tags
as I remember. If you are interested in improving fuel economy (and
losing horse power) talk to an experienced Detroit diesel mechanic
about changing injectors. It might give you a bit better economy, if
you are interested.

Yes, I've considered replacing the injectors and may do it at some
point.

Injector N55, Fuel Output Min.24 - Max.30
''''''' N60 "''''''''''''' 30 - '' 36
'''''''' N65 ''''''''''''''' 40 - '' 46
'''''''' N70 ''''''''''''''' 38 - '' 44
'''''''' N80 ''''''''''''''' 44 - " 50

I believe that I have the N80s at this point, so in theory I could go
all the way down to N55s. That would clearly reduce power and torque
but it's not obvious what the impact on economy would be. It could
also have an adverse impact on the present reduction gear ratio and
prop pitch.

Happiness is...
 

On Mon, 26 Nov 2007 19:36:09 -0500, Wayne.B
wrote:

On Mon, 26 Nov 2007 23:03:52 +0700, Bruce in Bangkok
wrote:

Interesting. Have you tried other fractions of "hull speed" to see if
the same ratio of one engine fuel consumption to twin engine
consumption remains the same?

I have tried 1.0SQRT(LWL) and 1.1 - as Beebe and others predict, 1.0
is more efficient. 1.0 is about as slow as I'm willing to go, and
then only over longer distances where I'm already committed to running
day and night.

As an aside all 6-71's weren't rated at the same power and one of the
differences was the injector s. They came with different colored tags
as I remember. If you are interested in improving fuel economy (and
losing horse power) talk to an experienced Detroit diesel mechanic
about changing injectors. It might give you a bit better economy, if
you are interested.

Yes, I've considered replacing the injectors and may do it at some
point.

Injector N55, Fuel Output Min.24 - Max.30
''''''' N60 "''''''''''''' 30 - '' 36
'''''''' N65 ''''''''''''''' 40 - '' 46
'''''''' N70 ''''''''''''''' 38 - '' 44
'''''''' N80 ''''''''''''''' 44 - " 50

I believe that I have the N80s at this point, so in theory I could go
all the way down to N55s. That would clearly reduce power and torque
but it's not obvious what the impact on economy would be. It could
also have an adverse impact on the present reduction gear ratio and
prop pitch.


True, but this raises the question of whether you are actually
developing " X" amount of horsepower at "Y" RPM. I assumed from a
previous post that you were calculating H.P. from fuel consumption
figures which is really just a ballpark calculation.

Given that the 71 series are no longer made what are rebuilt injector
prices like? Or have they gone out of sight because a lot of people
would rather have the old all mechanical engines then the new
electronic models?


Bruce-in-Bangkok
(Note:remove underscores
from address for reply)

Happiness is...
 

On Tue, 27 Nov 2007 09:45:46 +0700, Bruce in Bangkok
wrote:

True, but this raises the question of whether you are actually
developing " X" amount of horsepower at "Y" RPM. I assumed from a
previous post that you were calculating H.P. from fuel consumption
figures which is really just a ballpark calculation.


Without some way of measuring torque, that is the best you can do. 17
hp per gph is a pretty good approximation.

Given that the 71 series are no longer made what are rebuilt injector
prices like? Or have they gone out of sight because a lot of people
would rather have the old all mechanical engines then the new
electronic models?

Newly manufactured parts are available from various sources including
DD dealers. I've heard reports of some difficulty getting new
cylinder kits but the DD service center that I used in North Carolina
had no problem.

Happiness is...
 

On Mon, 26 Nov 2007 23:52:29 -0500, Wayne.B
wrote:

On Tue, 27 Nov 2007 09:45:46 +0700, Bruce in Bangkok
wrote:

True, but this raises the question of whether you are actually
developing " X" amount of horsepower at "Y" RPM. I assumed from a
previous post that you were calculating H.P. from fuel consumption
figures which is really just a ballpark calculation.


Without some way of measuring torque, that is the best you can do. 17
hp per gph is a pretty good approximation.

No. I wasn't casting aspirations about calculating H.P. from fuel
consumption, other then meaning that it is an approximation. I was
more talking about your comment referring to propellers and gearboxes.

Given that the 71 series are no longer made what are rebuilt injector
prices like? Or have they gone out of sight because a lot of people
would rather have the old all mechanical engines then the new
electronic models?

Newly manufactured parts are available from various sources including
DD dealers. I've heard reports of some difficulty getting new
cylinder kits but the DD service center that I used in North Carolina
had no problem.

Given the umpteen million of those things that must have been
manufactured I assume that parts will be available for some time to
come. I worked on a pair of original Detroit Diesels installed in a
landing craft. They started on the first turn of the starter and ran
about 10 PSI of oil pressure most of the time. It didn;t seem to
bother them at all. Finally the owner did an overhaul on them and got
the oil pressure up to a more healthy figure but they didn't seem to
actually run any better.

As another aside I worked on some Russian truck cranes that had a
exact copy of the 6-71 engine in it. It had the old single spring
governor that used to run away and they parked them outside our
office. At idle the engines wold sit there surging and we used to make
bets on which one would run away and crater. None of them ever did
though. They were such an exact copy that GMC injectors were an exact
drop in fit.


Bruce-in-Bangkok
(Note:remove underscores
from address for reply)

Happiness is...
 

In article ,
Bruce in Bangkok wrote:

Given that the 71 series are no longer made what are rebuilt injector
prices like? Or have they gone out of sight because a lot of people
would rather have the old all mechanical engines then the new
electronic models?

71 Series Injectors are still being built in the After-Market Parts
Business, by a whole passel of OEM's. The same is true for MOST of
the Overhaul Parts for ALL of the DD 53, 71, and 92 Series engines.
About the only thing you can't get NEW, is the Block itself.

Bruce in alaska
--
add path before @

Happiness is...
 

"Bruce in Bangkok" wrote in message
...


I think that railway engines are basically generator prime
movers and
run at a constant RPM all the time. At least that is the
way a power
plant engine runs. It always runs at approximately rated
RPM
and the governor makes small adjustments up or down to
maintain the
proper frequency.


A train engine will increase RPM as the electric load goes
up.