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post #1 of 15 Old 02-05-2011 Thread Starter
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Compression test

So I have an accepted offer on a Crealock 37 yawl. Scheduled to go down to the boat this weekend for seatrials and survey. I decide to have a compression test on the engine, a 2003 28 HP Volvo with 2800 hours on it, even though my Broker was trying to talk me out of it, and it comes back with one cylinder having low compression. The engine needs a complete rebuild.
I wonder why such a relatively new engine would be blown out. Could it be undersized? The Selling Broker is contacting the owner to see if he will pay to have the engine rebuilt, otherwise the deal would be off.
We are still planning on going to the boat to have the survey done and see what else might be wrong with the boat. I told my Broker that I would rather have seatrials after the engine overhaul, again he disagreed and said it is never done that way.
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post #2 of 15 Old 02-05-2011
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Mite not be anything more than a blown head gasket or badly seated valve.
How far did the stripdown go?
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post #3 of 15 Old 02-05-2011
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Quote:
Originally Posted by brokesailor View Post
So I have an accepted offer on a Crealock 37 yawl. I decide to have a compression test on the engine, a 2003 28 HP Volvo with 2800 hours on it, even though my Broker was trying to talk me out of it, .
Why would your broker discourage a compression test? The more thorough the survey the better. If this broker has been working for you I'd start looking for a new broker, he gave you very bad advice. JMHO.
What did the mechanic tell you about low compression? He examined the engine and should have given you some sort of feedback.

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post #4 of 15 Old 02-05-2011
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Brokesailor,
As I was signing off I recalled looking at a 34 PSC years ago that was kept on a mooring. An elderly gentleman owned the boat but rarely took her out.
He did tell me that he religiously started the engine several times a week and let the engine run. The engine billowed blue smoke as a result.This is one of thing that will lead to low compression. Running the diesel with no load on it will glaze the cylinder walls and cause low compression. It takes far less than 2800 hours for this to happen.
Diesels like to be run hard with a load, people often break their engines in thinking they should baby them. This will also cause glazing resulting in low compression.

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post #5 of 15 Old 02-05-2011
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A diesel engine on a boat lasts about 5000 hours. Maintenance though is not always done as it should be and with direct cooling, corrosion, scale deposits and low running engine temperatures will adversely affect engine life. Get an engine with a heat exchanger! If the engine has a lot of blow by, lots of gasses coming out of the crank case, for instance out the oil filler while running, then I would expect a bad cylinder caused by a faulty fuel injection pump or injector that put too much diesel into that one cylinder overheating it. If you ever have a diesel with black smoke, check for this although with water cooled exhaust, this may take the carbon particles out of the exhaust so you will not know. It could also be a broken piston ring, but unlikely. If it is a bad valve, then maybe just a valve job would take care of the problem. Since the engine has about half the hours that would normally require a rebuild, you could split the cost and come out of it with a rebuilt engine; however, most boats do not have nearly this amount of time on the engine so maybe just look at other boats. The parts for that engine are going to be VERY expensive. By the way, I agree the broker just wants to make any sale and get his money, so maybe you should look for someone else to help you.

Last edited by LakeSuperiorGeezer; 02-05-2011 at 02:41 PM.
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post #6 of 15 Old 02-05-2011
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What were the compression #'s? Wet, and dry? Please ask for them, I will tell you what it means.

Why, why, why?
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post #7 of 15 Old 02-05-2011
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A compression test on a diesel engine is of little value, unless its accompanied by a 'pressure leak-down test' .... putting high pressure air into the combustion chamber via the injector port and then ascertaining where the leakage is noted .... exhaust (valve), intake (valve) or crankcase (piston ring). If it were me Id first SOAK the rings with Marvel Mystery Oil or other penetrating oil, let soak a WEEK, spin the engine with the injectors OUT, then re-do the compression and add a 'leak down' ....

Most times, especially when sitting for long periods, a piston ring will 'stick' in the piston grooves ... and you get LOW 'compression test' values; Ditto the valve seals. The 'soak' frees up the crud, polishes any 'rust' in the ring grooves and 'unsticks' the rings.

If you dont know how to do a leak-down test get a mechanic who doesnt expect to do a 'rebuild' nor sell you a new engine. ;-)
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post #8 of 15 Old 02-05-2011
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If you have low compression on one cylinder, you don't need a rebuild, you need to find out why one cylinder is low. Rich is right, a leakdown test will tell the tale, but the end result is going to be a) a head gasket, in which case you need to pull the head, in which case you might as well do a valve job and do the valve seals, b) stretched valve or bad valve seals, in which case you need to pull the head and you're gonna have to replace the head gasket and you might as well do the rest of the valves and seals while it's apart, or c) bad rings on that cylinder, in which case you are gonna have to pull the head anyway.... you see where I am going with this? Having a mechanic do a leakdown test, after soaking the cylinders with MMO for a week, on a boat you don't own is throwing good money after bad.

If you like the boat, figure the cost of the worst case- reringing the offending cylinder, new valves, seals and gaskets. Hit the owner with the figure. if he bites, you're golden, because it likely isn't the worst case. If he doesn't, walk away.
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post #9 of 15 Old 02-05-2011 Thread Starter
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Thanks for the input. The test results were:325, 330 and 275 I assume psig.
The good news is the Boat owner is paying for a full engine overhaul, approximately $5K including pulling the engine out, overhaul and reinstall.
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post #10 of 15 Old 02-05-2011
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I will assume those are the dry numbers,... now what are the wet #'s? Then we can get into your analysis.

Why, why, why?
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