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Old 18-08-2015, 13:08   #1
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engine driven refrigeration

Hi
I have a volvo d2-40 engine,
some volvo dealer told me that placing the refrigerator compressor off the engine can cause damage to the engine crankshaft.
What are your thoughts?
Thanks
Sgel
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Old 18-08-2015, 13:32   #2
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Re: engine driven refrigeration

Looks like you have a compressor already?
I'd say your dealer is nuts, unless you get stupid about belt tightening, it's not going to hurt anything, might even be a case of your compressor belt may be an opposite force to your alt belt, thereby lessening the force on the crank?
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Old 18-08-2015, 13:35   #3
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Re: engine driven refrigeration

Wait, your compressor is mounted to the boat hull?
OK, maybe if your engine rocks enough on it's mounts, then I guess maybe it could exert excessive force on the crank?
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Old 18-08-2015, 13:52   #4
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Re: engine driven refrigeration

A friend of mine had the compressor mounted on the hull alongside the engine. The compressor was on a big hinge, the weight of the compressor along with a tension spring is all that tensioned the belt.. the belt doesnt need to be that tight to run a compressor.... so don't over tighten it... and consider how yours is mounted... is it forgiving if the engine moves a bit?
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Old 19-08-2015, 03:44   #5
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Re: engine driven refrigeration

Thank you for your replies,
In the previous engine the compressor was attached to the engine and now after it was re-powered by the po, it attached to the hull.
I thought of adding some tension pulley but i am not sure it is necessary
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Old 19-08-2015, 06:31   #6
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Re: engine driven refrigeration

All engines have limitations on the amount of torque that can be taken from the front of the crankshaft. Exceeding the torque limits may cause damage to the front main bearing or even the crankshaft itself. If that torque is taken off by means of belts, then there may be restrictions on the amount of torque in particular directions, and there might be restrictions on the allowable distance that the pulley (s) may be located from the front of the block.

In the case of the D2-40 engine the max allowable torque is 21.7 Nm (16 Ft.Lb.) in the direction that your belt is pulling. This translates into about 9 hp allowed at 3000 RPM or 4.5 hp at 1500 RPM. This amount of power can be taken from one pulley (assuming the belt size can handle it) or split among several pulleys as long as the distance forward from the standard pulley doesn't exceed three pulleys or a combination of spacers and pulleys of the same thickness.

As mentioned earlier, the combination of a flexible mounted engine and a fixed belt driven load isn't a good thing. It might be that normal engine vibrations wouldn't cause problems, but motor sailing into a nasty chop could cause the engine to move around enough to place excessive loads on the crankshaft. Some sort of spring loaded belt tensioner might be a good idea.

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Old 19-08-2015, 07:17   #7
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Re: engine driven refrigeration

I love spring loaded idler pulley tensioners, never have to adjust anything, yet belt tension is always correct.
Of course Cheechako's idea accomplishes the same thing, and may be easier to implement
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Old 19-08-2015, 07:22   #8
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Re: engine driven refrigeration

I have an MD17D with a compressor on the port side and a power take off on the fly wheel. No problems aside from perhaps loss of HP which is not noticeable. This is an old photo... have had the engine drive refer since 1989.
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Old 19-08-2015, 10:14   #9
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Re: engine driven refrigeration

On my old liveaboard cutter back in the '80s, the refrigeration installer mounted the compressor so that it was attached to the hull instead of the engine because there didn't seem to be a way to mount it on the Volvo MD21B with the room available.

Big mistake.

Even though it was a very smooth-running engine, the rocking of the engine on its mounts ate up belts at an astonishing rate. Luckily, it didn't damage the crankshaft, though.

You might be able to get away with it with some sort of spring-loaded idler pulley, but I was never able to find a good solution on that boat.
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Old 19-08-2015, 10:36   #10
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Re: engine driven refrigeration

I also dont like the pump being mounted to the hull, but my question is "If you switched pulleys to the new flat belt type, would that allow less side pull on the crank? I believe the advantage of the flat belts is that you can run less tension on them. Am I correct, or way off base????" Grant.
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Old 20-08-2015, 02:19   #11
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Re: engine driven refrigeration

Hi All
Really great advice!
I checked with the compressor manual and it takes up to 2 hp, so we are good.
I like the idea with the tension spring, and it shouldn't be too complicated to implement. (thanks for the photo)
regarding the wear of the belt i can't change it to wider one without too much modification, but ill keep monitoring the belts and see how it goes.

Another option i thought about is to mount some kind of shaft with two pulleys on the engine side (like empty alternator) and then one belt will go to the crankshaft and another belt to the compressor, so in case of massive vibrations, this part will take all the vibrations without affecting the crankshaft (i think i will wait with this plan for now)

Thanks again for all the advice calculations photo and kindness
Sgel
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