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Old 07-06-2013, 21:20   #1
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MD7a Newbe

Hi All
Great forum you have here. I have read many and learned plenty before now making my very first post. I have a Volvo Penta MD7a with a starting problem in a 30 footer I just purchased.
Firstly the engine did overheat and was about to stop prior to me pulling the engine STOP. Through info found here I checked and replaced the impella which was slipping on the spindle. Now the engine spins up like it wants to start but won't run?? Maybe a head gasget?? How can I be sure before pulling it down?
There is no discolouration in the sump oil but a creamy colour on the underside of the oil filler cap. What damage have I caused by allowing the engine to get so hot. Any advice will be greatly appreciated. Cheers
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Old 09-06-2013, 08:18   #2
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I have two of the engines in a catamaran and have rebuilt them from the ground up. They now run as perfect as any 30 year old engine can.
Had a similar problem with one of them. Repeated or extreme overheating caused the ring faces to melt against the much harder cylinder wall this caused the rings to stick in the grooves resulting in lost compression. Relatively simple to fix, though it was a knuckle buster to do with engine in place.
Parts can be difficult to find and they are expensive. But it was cheaper than a repower in my case, with me providing the labor. Marine Parts Express and Dick Vosbury at Vosbury marine were lifesavers in this regard.
Before you tear into the engine, though, make sure you have fuel at the injectors. Twice now I have had an injector pump just stop working. Same symptoms as you describe. Had them rebuilt by Bob Bergin at Bergin Diesel in Laurel, MS. $800-1000 each. Cheap when you consider the pump is obsolete and unavailable!
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Old 09-06-2013, 08:56   #3
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Re: MD7a Newbe

Same opinion here - start with making sure injectors get the fuel, then only check other things.

Great engines well worth repair, as long as parts available.

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Old 09-06-2013, 19:47   #4
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Re: MD7a Newbe

You don't say how hot the engine got but many alarms are set quite low, (85 C and above). However it is unlikely that an overheating incident that was terminated manually would have caused a major issue on the engine.
I suggest you concentrate on the fuel supply to the injectors, even using a temporary supply source and bypassing the filter if necessary to ensure clean new fuel at the injectors with no air leakage to the system.
If the engine is spinning up on the starter well you should be able to get it running provided fuel integrity is good.
Don't start pulling the mechanics apart until you have had it running even if it runs rough you will learn more from the operating engine. Then you can make more informed decisions on the next move.
Most issues such as you describe are fuel related by a large margin.
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Old 09-06-2013, 20:01   #5
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Re: MD7a Newbe

Thanks all for your advice. I have cracked open the fuel lines at the injectors (one at a time) and pumped fuel. The manual says to do this until no air bubbles are seen. I am unsure how much fuel I should let flow but as I only let a tiny bit go I think I will repeat and see if I can get a solid flow.
Would you consider it normal to have a small amount of discoloured oil on the filler cap? Perhaps there is some condensation or is that just wishful thinking?
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Old 09-06-2013, 20:12   #6
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Regarding milky color on bottom of the filler cap. I have found this to be normal in my area. Meaning south Mississippi. With high humidity. It is less prevalent in the winter than spring and early summer.
I would not focus on this if the dipstick has no indications of water intrusion.
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Old 10-06-2013, 01:08   #7
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That is what I wanted to here!!
Regarding how hot she got, well I was single handed and delivering the boat from where I purchased her to my mooring. As it happened it was a nil wind day so I was motoring. I never heard the alarm and had just moved from the helm to the bow and was doing a bit of Captan Jack Sparrow when I noticed the engine tone change, sounding laboured. I rushed below and killed it but thought I had a fire as the cabin was full of smoke. So my attention was focused on finding that, I didn't think to look at the gauge.
Turned out there was no fire but the exhaust water trap had a hole melted in it and the smoke was exhaust fumes! So pretty hot I expect, it sounded as though it was about to stall.
Thanks again for your advice with this. I'm new to diesel engines and a pretty ordinary mechanic to boot but very keen to learn all i can about this motor.
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Old 10-06-2013, 05:52   #8
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Here is a good place to start -

http://www.bluemoment.com/manuals/Vo...A_Workshop.pdf
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Old 10-06-2013, 19:41   #9
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Re: MD7a Newbe

When bleeding the fuel system letting go "a tiny bit" is not enough. You must bleed enough to be satisfied that you have pushed fuel through from any possible leak site. Say you have just changed the filter then you need to push through enough fuel to remove all air from the system at all the high points by bleeding them individually and then finally at the injector inlets.
Some engines bleed easier than others and will self bleed once started, others will not.
Any slight leakage on the fuel system will stop the engine when it is running or stop it from starting. Remember that leakage on the fuel system is caused by air leakage into the system on the suction side (which you may not be able to see) rather than visual leak indication on the pressure side. Therefore all hose joints, fuel pipes, o-rings and compression joints before the fuel pump are all vulnerable and likely leakage sites.
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Old 10-06-2013, 21:19   #10
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Thanks for the continued excellent advice. Now I know I didn't bleed enough, (or if bleeding was even necessary) but will get lots of rags and give it a good pump through.
I thought because of the overheat, fuel might have evaporated!, is that even possible?
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Old 10-06-2013, 21:30   #11
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Re: MD7a Newbe

Quote:
Originally Posted by MollyJo View Post
Thanks for the continued excellent advice. Now I know I didn't bleed enough, (or if bleeding was even necessary) but will get lots of rags and give it a good pump through.
I thought because of the overheat, fuel might have evaporated!, is that even possible?
Not likely, fuel is cool. Fact is, sometimes you need to heat it up to burn.
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Old 15-06-2013, 04:26   #12
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Ok, got down to the boat today and had a go at bleeding the fuel. Undid the closest to the pump fuel line at the injector and pumped the manual pump.
Nothing coming out. The pump itself didn't feel as though it had a very positive action. It seemed only to have resistance in the last 10% of the stroke.
Any suggestions? What should I do now? Service the pump? Could there be air in the line before the manual pump preventing its proper action?
There was fuel at the connection point into the injector so I guess fuel flows when cranking. Cheers for you thoughts
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Old 15-06-2013, 05:26   #13
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You need to crank the engine as you bleed the syatem
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Old 15-06-2013, 16:46   #14
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Re: MD7a Newbe

The procedure is generally this, read the manual for details:

- bleed the prefilter (if you have one),
- bleed the filter (with the manual pump),
- then bleed the h/p pump (cranking),
- then bleed the injectors (cranking),

The pump is bled while undoing three bolts in SPECIFIC order.

The injectors are bled in any order.

If your manual pump feels flabby, turn the engine and try again. But I would recommend taking the pump off and giving it a good clean/overhaul. If the spring or membrane are gone or dirty, that's where your problem may be at.

Normally, it takes two people (one on the engine, one at the key).

Normally, you need a charger with you as past the procedure the battery may be just strong enough to start the engine, but it starts much faster if the battery is fully up.

Have fun.

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Old 15-06-2013, 18:49   #15
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Re: MD7a Newbe

You're getting a lot of a good advice and this is the manual I just found. Same as above I believe.

http://www.bluemoment.com/manuals/Vo...A_Workshop.pdf

Sometimes getting a new can of clean diesel and running a pickup hose in it just before your lift pump (the one you pump by hand) is a good way to tell if your fuel line is compromised or not. Then pump that hand pump to see if it pumps to the high pressure injection pump with good solid spurts of clean fuel. If you get the fuel that far then you can get it from there to the injectors by spinning the flywheel by hand if you have a hand crank and compression release. You can bleed the injectors this way, again, if you have a hand crank and compression release. Otherwise you'll have to spin the engine via electric starter.
Your batter needs to be topped off to get the necessary rpms to get it to fire. If it is not topped off then you might be able to start it by releasing the compression, spinning with the starter then closing the compression release.
Good luck.
I think you are on the way to getting this thing to run again. If you do have a compression tester for diesels that would be the thing to test before diving into the cylinder and head gasket.
Don't take the injection pump off the engine. The hand pump, yes, the injection pump, no, unless you really know what you're doing and mark the timing and don't turn the engine after it is taken off even a little bit. Be careful of timing.
kind regards,
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