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Discussion Starter #1
My first post- most assuredly not the last!

I have a 1977 Volvo Penta MD6b in my new-to-me 30' Santana (W.D.Schock) she takes a LOT of cranking to fire up when cold. Once she has been started she runs perfectly. If she is restarted within a few hours she starts up easily. But if she sits a few days, its back to 10 minutes or so of cranking (during which she fires intermittently and displays burnt exhaust smoke). This was completely disclosed by the previous owner, no issues there, I knew what I was getting into. Getting her home took two 6-7 hour runs during which the engine ran fine (once started)

I have been told if she runs fine once started, that the injectors are nominally OK. I believe this person as they are a mechanic and could have sold me new injectors if he wanted to, but he didn't. He is an honest guy.

I also had diesel in the oil, so this led me to believe that the lift pump had a bad diaphragm which caused the fuel in the oil and the hard starting.

I have replaced the lift pump and the fuel filter, and the pump did indeed have a very small tear in the diaphragm. Buttoned all up, no leaks bled everything and- it’s better but still hard to start - as in I have to crank for a while. So the fuel in the oil is probably fixed, but the fuel system must be leaking pressure somewhere over time.

I am going to do two things- First, create this post , to solicit ideas and second , I am going to crack the injector nuts and use the hand pump to try to bleed everything up to the injectors BEFORE I start cranking- and see if this helps.

Questions:

I have read in my searches that there is a cold start system fitted to the engine - as there are no glow plugs it must do something with the fuel. It is supposedly activated by shutting off the fuel when you stop the engine, which sets the cold start system for the next start, No mention of this is made in the service manual. I am dying to know how this works and how I can determine if mine is functioning correctly.

Second, where should the throttle be when the engine is being started? I typically have it at idle but I have read about people using 1/2 or even full.


Thanks in advance!
 

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Once known as Hartley18
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I'm not all that familiar with the MD6A, but if the engine starts and runs fine once warmed up, then it sounds to me like it could be a compression issue rather than a fuel supply one. If you've bled everything already, I wouldn't be doing it again.

I'm sure someone will come back with the cold-start system details. In the interim, try starting at full throttle instead of idle. Here's a link to the Workshop Manual if you don't have it already:

http://www.bluemoment.com/manuals/Volvo_MD6A_MD7A_Workshop.pdf
 

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Discussion Starter #3
Low compression is a likely candidate given the age. I need to eliminate any fuel delivery problems too. I will bleed her again. Thanks for the suggestions.
 

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Does it start when you give it some throttle when you crank? That makes a huge difference on my MD7A (5 seconds vs. minutes- though admittedly mine may have its own issues)

My throttle/gear shift lever has a pull knob to disengage the gearshift from the throttle so you can give it ~1/4 throttle in neutral for starting- it's limited to this amount by the knob blocking the throttle when pulled out. Does yours have a similar system?
 

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I've a MD7a and that engine starts very easily. Even after being laid up all winter.
 

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I would really suggest not cranking for more then 20 seconds at a time. A diesel can actually build compression after you stop cranking. Really. So I would crank for 20 secs wait a few secs and crank again. the cost of rebuilding or buying a new starter is not an interesting thought!!

I would agree it is a possible compression problem. I had a similar problem with a very old tractor. I used Lucas engine oil conditioner. The problem was cleared up.

If you have a glow plug that is not working, it is an easy replacement once you locate its location. I might suggest downloading a parts book so you can see how each piece fits together and it will give you and idea of how to change your glow plug or wire, which ever system is in your engine.

Hope this helps
Rochelle
 

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Discussion Starter #7
I did kill the solenoid- but installed a new one. (volvo used the same solenoid on 1977 cars as well as the Md6b engine) I found a fitting that is not visible except with a mirror. It is the line from the low pressure pump to the high pressure pump- at the high pressure pump, the fitting was slightly loose. I was able to give it 1/8 turn pretty easy , once i got the wrench on it with the help of the mirror. The engine then started up relatively quickly ( but still had air in the lines, so it took some cranking) once it started it ran much better, idle was smoother and she revved up nicer. She restarted instantly . I have left it sit for 4 days and will see if she starts up more easily after sitting. Wish me luck !:)
 

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Discussion Starter #8
Does it start when you give it some throttle when you crank? That makes a huge difference on my MD7A (5 seconds vs. minutes- though admittedly mine may have its own issues)

My throttle/gear shift lever has a pull knob to disengage the gearshift from the throttle so you can give it ~1/4 throttle in neutral for starting- it's limited to this amount by the knob blocking the throttle when pulled out. Does yours have a similar system?
Thanks ! Yes i have the same system- I am using about 1/2 throttle.
 

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I have a Newport 30 with the MD7 Engine, which is essentially the same as you have. first, check to see that you don't have any air in the line...mine was hard to start and I had a small air leak in the fuel line...replaced it and now no issues. The engine is historically a cold beast...I put mine to full throttle and it usually catches within 8-10 seconds...if it doesn't , then let it rest for about 30 seconds and do it again. As soon as it catches, pull the throttle back to about 1000 RPM and let it sit for a couple of minutes, then take off. Mine runs best between 1800 and 2200 RPM and tops out at about 2600 RPM.
Good Luck
Ed Simpson
Newport 30 II #854
 

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Just an update- a new starter spins the motor 2X faster and it started immediately- however after sitting 2 weeks I was not able to get it started again ( however with starting fluid it started immediately again) It still must have an air leak . I also see a lot of unburned diesel out the exhaust.
 

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..... I also see a lot of unburned diesel out the exhaust.
Scott, that says to me that you don't have a fuel delivery issue and it's more likely to be either (a) low compression or (a) fouled injectors.

I'd suggest getting the local marine service place to check the compression.
 

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I have an MD7A. I get the best cold engine starting results with the throttle wide open. Once it starts, bring the idle back to slow idle. Don't want to run a cold engine wide open. Before I discovered this starting technique, the engine would take forever to finally start. I'm pretty sure the manual recommends a wide open throttle at start. Try it next time.
 

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Discussion Starter #14
Classic 30 - I think you are right , I would not have unburned fuel if no fuel was getting to the cylinders. I would not be surprised if it was low compression after 37 years. That also may be why the new starter that spun so much faster got her started right away too,

is it possible to throw the decompression lever while cranking with the electric starter ? maybe I could get her spinning faster and then flip the lever and she might start more easily.

Another thing I suppose I could check would be the valve clearances. They likely have never been checked or adjusted.

I was told by a mechanic ( whose opinion I trust ) that removing the injectors to is to be avoided at all costs as they likely have not been moved in decades and will likely not go back in without replacing the sleeves they are in , which must be done with the cylinder head on the bench. I know I can turn the engine over fairly easily by hand using the flywheel , but the flywheel is pretty large diameter. That could also be a symptom of valveses not adjusted to close all the way ?
 

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Hmm... I'm a tad surprised to hear removing the injectors is such a big deal, but if the engine runs ok (doesn't blow copious amounts of smoke) once it IS running, then that is probably not the first place to go.

Checking valve clearances should be relatively easy and would be worth doing given the age of the engine and the symptoms you have.

..and, yes, start with the throttle wide open and be ready to throttle back when it fires.
 

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Discussion Starter #16
Yes , that is what the mechanic felt- if it ran ok once started ( and it does ) then the injectors must be functioning properly. However that means I do not have compression information.

I can check the valves , to ensure they are closed when they should be - and I am going to try to figure out how to check the injector timing. I can't find the flywheel mark referenced in the service manual. and I still have not learned how the cold start system is supposed to work , because she starts up immediately when warm also.

She starts immediately on starting fluid- I think if the fuel lines had bled down while sitting it would take more work to get her running. So it seems there is fuel immediately.
 

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Yes , that is what the mechanic felt- if it ran ok once started ( and it does ) then the injectors must be functioning properly. However that means I do not have compression information.

I can check the valves , to ensure they are closed when they should be - and I am going to try to figure out how to check the injector timing. I can't find the flywheel mark referenced in the service manual. and I still have not learned how the cold start system is supposed to work , because she starts up immediately when warm also.

She starts immediately on starting fluid- I think if the fuel lines had bled down while sitting it would take more work to get her running. So it seems there is fuel immediately.
If your engine has pre-combustion chambers I have read ether can do heap big damage. I used it once, just a small whiff, on my VW diesel in 15 below Fahrenheit weather & it worked. I used to use it all the time on my Detroit 3-71 diesel, which was direct injected with no glow plugs, & it worked fine, starting in just a few turns.


Starting fluid - Wikipedia, the free encyclopedia

Paul T
 

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Scott...be careful when using starting fluid with the MD6 or 7 engine with only compression start...you can do damage to the engine if you use it too much as the ether "explodes" in the cylinders at a much higher pressure than the fuel. I have found that mine starts pretty well if I push the throttle to full and once it catches, back it down to idle...and mine is just a year younger than yours...I usually end up cranking for about 15 to 20 seconds, then back off for about 10 seconds...then on the second crank it usually starts up within 5 or 10 seconds...This engine is a cold hearted beast, but will run forever if you treat it right.
Ed
 

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According to my engine manual the cold start set on my volvo 2003t is pull out the engine stop and push back in. This actuates a cam in the governor and kind of acts like a choke. Then set throttle to full, in neutral, and turn over. Be ready to idle back. The engine starts immediately. Until I read this technique my motor was very hard starting.
Jim
 

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Wow, you guts are making me feel VERY lucky. My MD7a always starts very easily. It was out of the boat under a tarp all winter. I pumped up the lift pump. Threw the decompression lever and cranked her for 3 or 4 20 second sputs. Then closed the compression lever and did the same thing. On the third go she fired up. Ran rough and died a couple of times as the air worked through.

Once, last summer, I had a devil of a time getting her going. No idea why other than I must have run out of fuel as I docked. Yeah, it was THAT close. Other than that she will crank up almost immediately, even after a 10 month lay up.

I've never had to run the throttle up much at all.

Guess I'm a lucky guy.
 
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