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Old 22-09-2016, 19:14   #1
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Md7a fresh water conversion heat exchanger sizeing help

Hello every one, got a "few"questions.. I googled so much my heads spinning I'm dealing with a 1977 Volvo penta md7a. As of now it the typical raw water cooled. So far I bought a piggyback pump to add on (10-241143-1 & 10-35157-1) f35b. I'm converting it to fresh water cooled. they used to make conversion kits and I think Volvo even sold some fresh water cooled. however I think the exchangers are sized for use with a pto pump off the fly wheel jabsco (possibly 5281 or 3760) and some electric pump kits as well. I tried to track down the flow rates of both pumps to no avail,and even if I knew them I wouldn't know how to size the exchangers accordingly ( I don't even know how the exchangers are sized other then length width and number of tubes, I was thinking more in terms of cooling capacity) I was wondering if any one has a motor with the piggy back pump and if so what size exchanger they use? Or if any one knew the cooling requirements I could specify if I ordered one?I guess an exchanger with a relief cap and over flow hose would simplify things and save space? I also had a few other questions ; if I go with the copper nickel does the heat conductivity difference affect the siz I'll need? More the likely I'll be mounting the exchanger off the bulkhead ( I can't seem to find the motor mount brackets) does the horizontal or vertical xchanger have an advantage over the other? When I do mount it I assume I'll want it level with the top of the motor?. Does any one have a piggyback pump set up? I'm new to marine diesels, but the correct exchangers for the md7a seem so small I wouldn't think they would xfer enough heat to cool the motor, the again I'm new to this. Another thing there's a popular bidding site that has Chinese exchangers listed claiming they're copper nickel etc. for much less then the manufacturers....tempting..any how sorry for the 100 & 1 questions any insight would be appreciated.
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Old 22-09-2016, 19:20   #2
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Re: Md7a fresh water conversion heat exchanger sizeing help

P.s I'm currently sailing the Chesapeake with intentions of sailing to the tropics , I'm hopping to have an exchanger sized to accomadate all regions, since i never know where I'll end up.
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Old 24-09-2016, 17:48   #3
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Re: Md7a fresh water conversion heat exchanger sizeing help

Check out Sen-dure Marine.... They made a FWC kit for the MD 7A engine and it still shows up on their web site Model K 2158, I think.

DougR
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Old 24-09-2016, 18:31   #4
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Re: Md7a fresh water conversion heat exchanger sizeing help

Thanks I'll check it out I've contacted sen dure they Just know it's for the md7a but I think that for a pto water pump.. Think it'll make a difference?
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Old 24-09-2016, 18:45   #5
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Re: Md7a fresh water conversion heat exchanger sizeing help

Hi.

We have one. I think it is a Martec unit. It is not big at all. When I change the coolant it is maybe 2 liters of it. It is driven by a bosch coolant pump.

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Old 24-09-2016, 19:03   #6
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Re: Md7a fresh water conversion heat exchanger sizeing help

Is that bosch pump driven by a belt or is that an electric?
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Old 24-09-2016, 19:09   #7
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Re: Md7a fresh water conversion heat exchanger sizeing help

Attached you will find a pdf with our unit on MD7A.

The picture in the linked article (link below) shows the pump to be a Bosch PCA is the fresh water pump USD 100 or thereabouts. You can use any other pump. I have a Johnson spare.

Intercooler pump flow testing results - Lingenfelter Performance Engineering Forum


Bosch flow is 19 liters per minute (@ no pressure).

Martec volume says ca. 3 liters.

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Old 24-09-2016, 19:10   #8
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Re: Md7a fresh water conversion heat exchanger sizeing help

Electric.

Where do you put an extra mechanical pump on an MD7? I cannot see any extra power uptake.

b.
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Old 24-09-2016, 19:23   #9
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Re: Md7a fresh water conversion heat exchanger sizeing help

It looks like there's a pto pulley installed over where the hand crank would go ( I have the diagram on my other computer in my email in jpg).it's a sen-dure kit as well. By the way any one tried hand cranking theirs? I'm guessing since my piggy back pump is basically just a double sea water pump it'll have the same flow rate or psi as the raw water pump does. I'll have to check into it more... Unless any one knows the psi for it off the top of their head.
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Old 24-09-2016, 19:41   #10
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Re: Md7a fresh water conversion heat exchanger sizeing help

But how is it driven? Is there a twin grove on your flywheel or do you place a twin pulley on the alt?

Off to bed now (I am on the EU side of the pond). I will check the box tomorrow again.

Should you need any images or whatever just ask.

Our kit (Martec/Bosch) came with the boat 15 years ago and was not new back then either. It is still strong except the exchanger tends to corrode somewhat in the area just next to the anode.

If you can build something similar you will be happy with the conversion.

Cheers,
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Old 24-09-2016, 19:47   #11
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Re: Md7a fresh water conversion heat exchanger sizeing help

My double pump has a shaft that fits into the shaft on the existing pump.( Where the key way is for the impeller) this shaft then turns the new shaft and impeller.
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Old 25-09-2016, 06:28   #12
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Re: Md7a fresh water conversion heat exchanger sizeing help

If you remove the cover from the existing pump the new pump has a shaft that fits into the key way where the impeller is and bolts on where the old cover is. So the old pumps shaft turns the new shaft thus creating the " piggy back " pump.
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Old 25-09-2016, 08:00   #13
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Re: Md7a fresh water conversion heat exchanger sizeing help

Quote:
Originally Posted by Eastward ho 24 View Post
If you remove the cover from the existing pump the new pump has a shaft that fits into the key way where the impeller is and bolts on where the old cover is. So the old pumps shaft turns the new shaft thus creating the " piggy back " pump.
OK. I see. I have imagined such pumps to exist. Making me think if one could fit under our exhaust elbow.

I will check them out. Thanks for the info!

Let us know how you converted yours. I am sure readers further down the road will appreciate.

b.
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Old 25-09-2016, 11:07   #14
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Re: Md7a fresh water conversion heat exchanger sizeing help

I searched forever finding the double pocket pump found it on eBay. Might be the only one on the planet left. Good thing about it is it's female not. My raw water pump has them goofy slip in squared off o rings with a retaining clip that goes over the cover. I took it to a machine shop to see if they'd tap it but it's also tapered so there's not enough meat to tap it. Was looking into brazeing bronze nipples to it but the taper kinda leaves a big gap to fill so I'm a little Leary of that. I think I'm just going to cut the tube before the 90s where it comes from the tranny and where it goes into the motor,leaveing a kinda nipple but I'm still gonna have them goofy or rings..any one have better ideas on a more bulletproof way to tap into the pump? I also think I may need to get a tstat that opens hotter but im still in the preliminary thought stage of that.. Do you know what tstat can't with your kit? Yes Ill do a little build along w pics hopefully some one will find handy.
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Old 25-09-2016, 12:46   #15
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Re: Md7a fresh water conversion heat exchanger sizeing help

Our thermostat is the regular unit.

Johnson pump outlet tube is cut and a hose is clamped on. This hose runs then to the exchanger. On the other side of the pump is the original tube from the transmission.

The tube from the exhaust block has also been replaced with a hose - this one too goes to the exchanger, it hot fresh water to be cooled in the exchanger. Never too hot to touch but too hot to hold once hot.

All hoses look plain fuel grade hoses. Black rubber and some mesh in between the layers.

I do not think there was any machining done here - just some tubes cut and replaced with hoses.

It all seems to work fine. The engine never overheated once. Not even in the hottest tropics (sea water 30 degs cent.)

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