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Old 30-07-2015, 21:57   #1
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Need help understanding MD7A fuel lines

I searched the forums for good detailed pics about this and found nothing. Thanks for the help in advance.

What I am really looking for is a little advice and a few pictures of good MD7A fuel line setups.

Here are some pics of my morass.

The two l-o-n-g fuel lines from the left and right side of the engine both go up to the fuel tank to a T connector (that attaches to the tank).

I realize that the left line is for leftover un-burned fuel, but why this type of setup? Two lines like this seem awfully long.

I have the owners and workshop manuals, but they are not specific on these points.

Suggestions besides "throw it away" would be welcomed.

Note, my to do list already includes: moving the battery negative, replacing the rusty fuel line, cleaning and testing the sensor, and painting the engine.
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Old 31-07-2015, 04:04   #2
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Re: Need help understanding MD7A fuel lines

Quote:
Originally Posted by esarratt View Post
I searched the forums for good detailed pics about this and found nothing. Thanks for the help in advance.

What I am really looking for is a little advice and a few pictures of good MD7A fuel line setups.

Here are some pics of my morass.

The two l-o-n-g fuel lines from the left and right side of the engine both go up to the fuel tank to a T connector (that attaches to the tank).

I realize that the left line is for leftover un-burned fuel, but why this type of setup? Two lines like this seem awfully long.

I have the owners and workshop manuals, but they are not specific on these points.

Suggestions besides "throw it away" would be welcomed.

Note, my to do list already includes: moving the battery negative, replacing the rusty fuel line, cleaning and testing the sensor, and painting the engine.
OK, I don't have a MD7A but fuel line setups are pretty basic on all small boat diesel engines.

Simply put, you need a fuel one from the tank to the lift pump on the engine (supply line) and a return line from the engine back to the fuel tank.

The supply line will originate at the tank, either from near the bottom or from a pick up point from the top of the tank. It is important that the line does not draw fuel from the very bottom of the tank. It is very usual to have primary filter in this line with Racor being the favourite but diehards (like me) still have a CAV filter. Position the primary filter somewhere you can have good access to it.

If the supply line is long, I prefer using SS tube, say 8 or 10 mm for your size engine (5/16" or 3/8") with flexible fuel line connecting the ends of the piping.

The return line usually goes back to the top of the tank but occasionally one sees other variants like having it go back into the top of the primary filter. Some like to have the return line one size smaller than the supply line for easy identification of the lines but I prefer having them the same size so one size of fuel line and hose fits both.

I don't have good photos but here is what I have. The engine is a Yanmar 2GM20 (2 cylinder, 18 Hp), the supply and returns line are about 10 feet each and I use 5/16" SS tube and flexible hose.

One shows the exit from the tank via the red handled stop cock near the bottom of the tank (but not the one in the tank sump) along with the return line going into the top of the tank. The other is the SS tube lines under the cockpit floor; the bottom one is the supply and the top is the return. The last shows the CAV primary filter near the engine. There is a flexible hose from the output of the filter directly to the lift pump on the engine. After that, it goes to the engine fuel filter and then into the injector pump.

If you meet the basics described above, your fuel lines with be OK
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Old 31-07-2015, 04:13   #3
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Re: Need help understanding MD7A fuel lines

After a repaint, it will something like this (but only green)
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Old 31-07-2015, 05:29   #4
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Re: Need help understanding MD7A fuel lines

Ahhhh. Perfect. That was what I needed to know. Thank you!
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Old 31-07-2015, 05:36   #5
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Re: Need help understanding MD7A fuel lines

Nevermind: Found a 10 micron on Fleabay with 35GPH.

Quote:
Originally Posted by Wotname View Post
It is very usual to have primary filter in this line with Racor being the favourite but diehards (like me) still have a CAV filter.
Where did you get your CAV filter HOUSING with the glass bowl? I am aware of Racors and the like, but I like the prices on the CAV filters.
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Old 31-07-2015, 06:36   #6
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Re: Need help understanding MD7A fuel lines

Please note, they are bludi messy to change the filter element. There are 3 small orings and 3 big orings. Not a simple spin off, spin on like Racor.

I like the glass bowl though, easy to see any water or crud starting.
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Old 31-07-2015, 06:47   #7
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Re: Need help understanding MD7A fuel lines

What you have looks to be something someone cobbled together to use a an outboard fuel tank? Actually pretty ingenious for a short time fix.
I would not want to tie my return fuel to the same line as my fuel feed as I believe it's not too uncommon for air sometimes to be in the return line, and by connecting it to the feed line, you may have issues with air in the fuel
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Old 31-07-2015, 08:41   #8
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Re: Need help understanding MD7A fuel lines

Some of the VolvoPenta engines of the same vintage as your MD7 were set up with the fuel return lines running back to the top of the fine filter, but the MD7 engine using the CAV or Bosch fuel pumps returned fuel back to the tank.
As A64pilot states, it is better to plumb your return fuel back to the tank to avoid the possibility of getting an air lock in the system. It might be worthwhile to look into installing a small permanent fuel tank instead of the outboard tank. Inasmuch as the engine has evidently been run for some time without a primary filter, you should clean the fuel screen which is located under the cone shaped cover on the lift pump.

If you are interested, I can make a copy and send you the original installation manual for the MD7 which describes the systems necessary to properly install the engine. ( fuel, electrical, air, etc) Also, as you expressed an interest in the glass bowl CAV fuel filter, I would be happy to sell you a new one that has been sitting around in my garage for way too long.

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Old 31-07-2015, 09:14   #9
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Re: Need help understanding MD7A fuel lines

@Wotname #2

Luvverly :-) I like your bespoke wooden pipe clamps!

TrentePieds' setup was a mess when I took her over. Still is, tho' workable when closely monitored. She's in for a rework before next season following the guidelines you have so succinctly set out here.

Small addendum for the benefit of demure lurkers who might like/need to know: The "sump" Wotname mentions is a water trap to permit you to drain condensation from the tank before it rises to the level of the pick-up for the fuel feed.

In installations (such as mine) where you can't reach the bottom of the tank from below, the sump should be fitted with a pipe coming through the top of the tank to which you can attach a small suction pump like the ones that are common for draining oil from engines.

TrentePieds
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Old 31-07-2015, 09:55   #10
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Thumbs up Re: Need help understanding MD7A fuel lines

Wotname,
very nice installation....
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Old 31-07-2015, 10:14   #11
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Re: Need help understanding MD7A fuel lines

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Please note, they are bludi messy to change the filter element. There are 3 small orings and 3 big orings. Not a simple spin off, spin on like Racor.

I like the glass bowl though, easy to see any water or crud starting.
Yeah, I've heard (read) about them--the forums here are excellent.

I'm going to try it and see if I like it; the inexpensive price of filters (NAPA or Fram) is compelling. If I don't like it in a few seasons I'll chuck it and go with Racor.

It has a glass bowl.

My total cost was $59.95 after taxes and that number included shipping. The filters are $6, 10 micron and flow 35GPH--the engine burns 1/3GPH I've heard.
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Old 31-07-2015, 10:20   #12
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Re: Need help understanding MD7A fuel lines

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What you have looks to be something someone cobbled together to use a an outboard fuel tank? Actually pretty ingenious for a short time fix.
Ooohhh! That's it. He has an outboard tank with the boat.

I will remember his "system" for future reference AND re-install the original diesel after a good cleaning and pressure testing.

Quote:
Originally Posted by a64pilot View Post
I would not want to tie my return fuel to the same line as my fuel feed as I believe it's not too uncommon for air sometimes to be in the return line, and by connecting it to the feed line, you may have issues with air in the fuel
Good point, I was thinking "dirt" but air truly is the real problem here.
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Old 31-07-2015, 10:29   #13
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Re: Need help understanding MD7A fuel lines

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As A64pilot states, it is better to plumb your return fuel back to the tank to avoid the possibility of getting an air lock in the system. It might be worthwhile to look into installing a small permanent fuel tank instead of the outboard tank.
Yeah, there is an old and very dirty metal tank with the boat that will be showing up on the forums soon with my questions.

Quote:
Originally Posted by DougR View Post
Inasmuch as the engine has evidently been run for some time without a primary filter, you should clean the fuel screen which is located under the cone shaped cover on the lift pump.
Got it. The old Volvo workshop manual is sparse to say the least. I read that section a few times then it dawned on me that I needed to do that.

Quote:
Originally Posted by DougR View Post
If you are interested, I can make a copy and send you the original installation manual for the MD7 which describes the systems necessary to properly install the engine. ( fuel, electrical, air, etc)
I have the actual MD7A owners manual (with the blue engines on the cover) and the MD7A workshop manual (with the green wrench). If it something other than these two I am interested. Thanks.

Quote:
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Also, as you expressed an interest in the glass bowl CAV fuel filter, I would be happy to sell you a new one that has been sitting around in my garage for way too long.
DougR
Sorry Doug. I acted too quickly on Fleabay or I would have taken you up on the CAV.

Thank you for all your advice and the nice offer.
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Old 31-07-2015, 10:40   #14
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Re: Need help understanding MD7A fuel lines

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@Wotname #2

Luvverly :-) I like your bespoke wooden pipe clamps!
Huh? Is this a joke I am missing or is it something in one of the pics you're referencing?

Or are you referencing the clamps on the engine heater/fuel lines? All these will be replaced with proper stainless clamps that have no "grooves" on the next haulout.

Quote:
Originally Posted by TrentePieds View Post
Still is, tho' workable when closely monitored.
Yeah, I'm going to give her a try and see how many years she'll give me.
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Old 31-07-2015, 15:58   #15
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Re: Need help understanding MD7A fuel lines

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Huh? Is this a joke I am missing or is it something in one of the pics you're referencing?

.......
No inside joke, TP was referring to the wooden supports of the SS supply and return lines shown in the second photo.

Thanks TP, I though they were are nice touch when I made them early on in the 7 year refit.
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