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Old 11-10-2014, 08:49   #1
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Badly overheated Volvo MD6A....now no compression??

Hi all...I'm new here. Long story with important questions follows:

I recently bought a 1975 Santana 30 with I believe the original engine. Prior owner had her for 30 years and had the engine professionally rebuilt but I'm not sure exactly how many years or hours ago. Its not been used much at all the past few years, but I need to deliver the boat in the next couple of weeks for winter storage and that will include transiting the East River in NYC...so a healthy motor is required.

I'm not familiar with marine diesels (yet) so each use I've verified cooling water flow as shown by the PO. No functional gauges - tach, oil pressure and temp are all inoperable. Two engine uses ago I didn't see flow so I inspected the impeller and it looked good. Opened sea clock and water flowed well. Reassembled and observed water coming out with exhaust as PO advised was normal. As we were returning to mooring under power I noticed white smoke/steam building out exhaust...then motor rpm slowed by itself. I put it in neutral and the rpm came back up. Since we were close to the mooring and in a tight spot, I put it back in gear to get to the mooring. Engine slowed, then stalled and won't restart.

So far I have removed the thermostat (rusted mess), exhaust manifold (fairly plugged with iron oxide bits and carbon) and the head (looks like it's a bit warped on the non - cam side and has been weeping seawater down the block for awhile). Piston tops, valves and cylinders look great. No funny or bad noises. No water in oil and doesn't seem to be oil in the water.

Before pulling the head I could fairly easily turn the flywheel through many revolutions by hand regardless of the decompression lever position. This scared me into pulling the head but there's nothing obviously wrong so far...???? Maybe its something unrelated/coincidental that's keeping it from restarting? I have about 1/3 tank of fuel.

Money and time are serious hurdles at the moment (but I know I'm not the only one in that boat :-D)

Thoughts????

Thanks in advance,

-Keith

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Old 11-10-2014, 08:56   #2
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Re: Badly overheated Volvo MD6A....now no compression??

One thought, compression test. Two things make a diesel go. Fuel and compression.
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Old 11-10-2014, 09:29   #3
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Re: Badly overheated Volvo MD6A....now no compression??

I'll grab a compression tester and hook it up after cleaning/reassembly. I imagine I want to crank several revs with the starter to build pressure before measuring leakdown... (?)

With a small 2 - cylinder engine though should I be able to rotate the flywheel by hand regardless of the position of the decompression lever?

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Old 11-10-2014, 09:49   #4
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Re: Badly overheated Volvo MD6A....now no compression??

Where was the water leaking from, the head gasket? You might need to just replace the head gasket. Mine cost $120. Someone recommended using a sheet of copper cut to size but that seemed more difficult than $120.

I am in the same process with my md7a. Replaced the head gasket and it starts, but still fine tuning.


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Old 11-10-2014, 10:00   #5
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Re: Badly overheated Volvo MD6A....now no compression??

It looks like it's been leaking on the exhaust side; the whole motor was nicely painted but under the heat exchanger there's rust own the side of the block and it looks like some mild corrosion on the block and head mating surfaces. I will need to keep an eye on that area for leakage once I get it running again. In the interest of time I may try to reuse the head gasket I have after coating with copper anti-sieze compound - some old timers say that can work...then I could get new gaskets over the winter.

Can you turn your flywheel by hand without moving the decompression lever?
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Old 11-10-2014, 12:15   #6
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Re: Badly overheated Volvo MD6A....now no compression??

I have the M D 6 A in a 29 cascade I left her sitting for 2 years came back and no compression either my mechanic removed the valve cover filled the valves with seaform and kerosene and we are going from there I will keep you posted with my progress Sur la Mer feel free to text me we can compare notes 949-877-6667

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Old 11-10-2014, 12:42   #7
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Re: Badly overheated Volvo MD6A....now no compression??

That's raw water cooled right? it would be real nice to know if the engine really overheated or you have another problem. The whole block could be filled up with corrosion if RWC'd.
If the overheat didn't happen and it's been sitting a long time it could very well be a fuel issue.
If the rings are shot, you cant tell by looking at the top of the pistons. How much ridge is there near the top of the cylinder wall?
I've been told you cant test compression on a diesel with a hand held gauge. It need to be screwed into the injector hole to get a good test. (by hand pops off before the max pressure is read)
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Old 11-10-2014, 12:54   #8
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Re: Badly overheated Volvo MD6A....now no compression??

With compression you can turn the flywheel but it gets difficult when each cylinder is on the compression stroke. You will notice a significant difference between having the decompression lever engaged and not. With my new head gasket I notice a difference.

Jeff


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Old 11-10-2014, 13:12   #9
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Re: Badly overheated Volvo MD6A....now no compression??

Jeff beat me to it. MD7A, 13 hp vs your 10. I can hand crank by grabbing the flywheel. It will move slowly. Operate the decompression lever and it will spin right through.
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Old 11-10-2014, 13:42   #10
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Re: Badly overheated Volvo MD6A....now no compression??

me thinks tear down.inspect/clean/descale and at least new ring set.Must have at least temp gauge to run otherwise pissing $ away.
Think it through-what is your goal?
I could NEVER feel good about sailing without secure knowledge of motor backup!
Get the parts/repair manual.and do it yourself if $ is in short supply.
Overtime you'll come to know your vessel and its abilities-Plus you'll garner confidence few "mechanics" could ever give.

An engine without temp gauge is a lump of iron all to soon.



All the Best.
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Old 11-10-2014, 13:49   #11
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Re: Badly overheated Volvo MD6A....now no compression??

and be sure to determine if the block is too clogged up to use before you buy a bunch of parts etc! it may be fine... but just sayin'....
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Old 11-10-2014, 13:54   #12
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Re: Badly overheated Volvo MD6A....now no compression??

PM with your email me if you want the user manual and shop manual. I have them both in PDF.

I just installed a new engine control panel for my MD7A. About $500 but I also needed to get a set point alarm to get an over temp alarm. So, call it $600 total.

See this thread.

Replacement Control Panel [Sitemap] - Cruisers & Sailing Forums
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Old 11-10-2014, 21:54   #13
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Re: Badly overheated Volvo MD6A....now no compression??

Before you put it all back together, you might want to take the head to any good automotive machine shop and have them check it for warping, and most can check for valve leakage , without it costing an arm and a leg. Did you look closely at the cylinder walls for scoring, which would be an indication that you really overheated it, and seized it up when it quit. Also, before you put it back on you might want to go to a gun shop (no comments here please) and buy some barrel cleaning brushes that you can chuck into a drill and get a reasonable amount of corrosion out of the cooling passages. _____Just some thoughts. _____Grant.
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Old 12-10-2014, 10:08   #14
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Re: Badly overheated Volvo MD6A....now no compression??

Just a tip about the head gasket, after removing my yanmar YSM8 cylinder head for a valve grind, just coated head gasket both sides with a thin layer of Loctite 515 master gasket & put it back on after cleaning & degreasing the mating faces. Havent been running it for that long but seems to be working fine. Wasnt leaking before this. On the tube it claims its good for 100 psi but I work in engineering & have used it in much higher pressure applications than that and am pretty sure it will work . It's very pleasing to bypass the ripoff parts prices not to mention faster & easier.
Hope that helps
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Old 12-10-2014, 10:46   #15
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Re: Badly overheated Volvo MD6A....now no compression??

When you put it back together, dont run it without the thermostat. On a previous Volvo thread there was an explanation of why the cooling water flow bypasses the engine without the thermostat in place. It is different than most motors. Another 2 cents worth. ____Grant.
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