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Old 10-23-2008, 08:52 PM   #41
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RE: Lehman Idle Speed

Hmmm..

If there is a throttle plate, the mechanical interconnection between that and the fuel control isn't an unreasonably complex mechanism.* Light aircraft fuel injection systems use that very system.* Of course, most light aircraft engine systems are 40 to 50 year old designs, but don't get me started...

There are a couple of possibilities that I can think of.* The air cutoff would be one possibility.* The other (this is purely a WAG) is that they might want to decrease the air charge a bit at near-idle settings to improve idle smoothness.* At idle, you don't need much air to still have a very oxygen-rich burn.* But having enough momentum to get that piston pushed up against a 17-or-so-to-1 compression ratio can be a problem at low idle speeds.* Either you need a massive flywheel, or I suppose decreasing the air charge might help (so long as it stays sufficient to generate enough heat to light off the fuel when it's injected).

MD-47 is really the model number?* I can't find any references to that on boatdiesel.com.* What are its features (# of cylinders, HP, turbocharged, ??)?* About when was it manufactured?** (Inquiring minds want to know!!)
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Old 10-23-2008, 09:37 PM   #42
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RE: Lehman Idle Speed

Cris - yes that is the correct model number and no you will find very little in the way of references to it. It was part of a series of marine engines that Volvo produced through the 50's and 60's and a whole lot of them found their way into commercial fishing boats up here.
There were 4 engines in the series, the MD-47 being the smallest followed by the MD-67, MD-96 and the TMD-96. They are all natural asp. except for the TMD-96 which was turbo boosted.
The MD-47 produces 91 HP / 2500 RPM and is a 287 cu/in displacement and the T96 was 175 HP.
Parts are very hard to impossible to locate in North America however I have been lucky to locate some parts such as gaskets and valves in Switzerland as the 47 is very similar to a fixed power plant engine they also made and which is still used in large machinery and generator plants.
In our 36 foot ex fish boat I get a cruising speed of 6.8 knots with a burn rate of 1.25 GPH so she is well worth trying to keep.
I did a "head job" on it about 500 Hrs ago and at that time it was sitting at just over 8500 Hrs since it was totally re-built in 1980. The liners were in great shape as were the valves so all I did was de-carboned the heads and put her back together again. A nice feature is that there are 2 access plates on the port side of the engine which allow you to access that crankshaft and actually service the bearings if required. An oil test revealed very little in the way of metal particles so I have left that area alone with the exception of "swabbing" out the oil pan. She starts within half a dozen revolutions cold or hot and smokes very little when cold so how can I convince the Admiral that we need a new engine
Hope this answers the inquiring mind but if not I have the manual and can quote lots of data.
John Tones
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Old 10-23-2008, 10:03 PM   #43
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RE: Lehman Idle Speed

Hmmm... no flashes of insight, except that I'd guess we're talking about a 4 cylinder engine, so perhaps the idle smoothing in some applications.

I'll put out*a query on boatdiesel and see if I get any bites.
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Old 10-23-2008, 11:16 PM   #44
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RE: Lehman Idle Speed

Chris - sorry, I forgot that one fact, its a 6 cylinder engine as is the whole series. Like I say my engine only has the injector control for engine speed but seeing the air control in the manual is what has me intrigued.
I was just looking very closely at the pictures in the manual (even with a magnifying glass) and it seems as though Volvo used ONLY the air control for throttle control on the earliest engines in the series. I also have a manual for a later version of the MD-47 and it shows the injector control as I have but the early manual shows only the air and there is no sign of any control on the injector pump ???? To make matters more confusing the early manual, in the section on the injector pump, shows the throttle control, but not in the opening photos of the series. Maybe the very early engines used the air control but later versions did not and only the injector section of the manual was changed. Again, who knows ??
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Old 10-24-2008, 01:21 PM   #45
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RE: Lehman Idle Speed

"Great information but now I have a curve for you."

Is the injection* pump a Bosch M60 by any chance? In the early '60s several diesel manufacturers used a pneumatic governor control that took its signal from the inlet manifold. The throttle plate was the speed control, when the plate was partially closed the vacuum created would reduce the amount of fuel injected, when the plate was open the vacuum was reduced and more fuel was injected.

These things would only work on an engine that worked with a linear relationship to load and speed such as a fixed pitch propeller or a forklift truck.*
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Old 10-24-2008, 03:36 PM   #46
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RE: Lehman Idle Speed

Rick - by gosh I think you have solved it. The "Throttle Body" has a pipe fitting coming out of it on the engine side of the butterfly valve and a tube running somewhere around the rear of the engine however the pictures do not show things in enough detail to see if it connects to the injector pump. The pump is listed as being a CAV and like I said the pictures show no sign of a "control" arm such as the Bosh pump that I have.
Your explanation makes a lot of sense and fills in the gaps left open in the manual so I think we now have answered my question and I will go away happy !!
Great bunch on this list - thanks much

John
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Old 10-24-2008, 08:40 PM   #47
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RE: Lehman Idle Speed

Tip of the hat to you, Rick.

Great call.
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