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Old 05-14-2009
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DIY top end job - am I crazy? Or is this possible?

I sailed my old but new to me boat home this weekend, a Cape Dory 28, and it seems as though the engine top end is going to need some serious work.

On this trip, we overheated three times, and killed the engine within 30 seconds once, and more like 10 seconds the other two times. Repairs were performed twice – impeller replacement the first time and a hose from the water-cooled exhaust the second. On the third overheat, we just let the engine cool for an hour, and felt this was caused by having sails up for 15 minutes with the engine idling in neutral, and the boat going on her ear. Our thinking was that air had got taken into the cooling system while heeling, and this had caused the problem. Of course, this thinking may be entirely flawed.

Then, after motoring happily and a nice cool engine temperature for an hour or so, the engine started making a vastly different sound – I suppose one could describe it as a rattle from the valve area. The engine was killed within seconds, allowed to cool for an hour, then restarted. It immediately made a much louder version of the first sound. The engine was killed instantly, hasn't been restarted since.

This is a Volvo Penta MD2B, by the way, which was sounding absolutely fabulous until the rattling started.

We didn’t try the engine again, and sailed 120 miles down the Hudson and into our slip in Brooklyn. This was interesting, to say the least! Perhaps I’ll write a diary of my trip, but right now, I want an engine so I can go sailing.

My semi-knowledgeable companions on board thought I was going to need a top-end job.

Today, two days after we got back to Brooklyn, we looked under the valve cover and there seemed to be some oil, but not a lot. I take this to be because the engine hadn’t been run in 3 days and most of the oil had run off by now. The engine oil in the sump is full and clean.

Of course, here in the northeast, we’re getting started for the season, and all reputable diesel mechanics are way too busy to talk to the likes of me. So my question is, how smart or foolish is it for me to attempt this job myself. Obviously, there’s some machining to be done, and new parts to buy, and I expect to take the head to a good shop (perhaps an auto one?) for some of the work. But I am considering doing most of this myself, with the assistance of semi-knowledgeable friends.

My own mechanical skills are limited, but not without capability. I have worked on a lot of motorcycles, for example. But never a diesel marine engine. One friend who wants to work on this with me is considerably more knowledgeable, but this would be a first for him, too.

Am I crazy to try? What good resources are there out there that could help me through this? I’m not even sure how to tell if my valves need work, or if the problem is something else. But the nasty noises did indeed seem to be coming from that part of the engine.

(Of course, if anyone reading this in the NYC area wants a gig, they are welcome to apply!)
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Old 05-14-2009
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Considering that marine diesels engines tend to be relatively uncomplicated beasties, aside from being a major PITA to get parts for.. I'd say go for it.
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Old 05-14-2009
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Queen, you'll have to forgive me b/c most of my experience lies in pushrod gas auto motors, but for the most part the engines are a lot a like. So if I say something that's way off base, just ignore it.

The oil would've drained back into the pan in two days. Heck, most of it would've drained back in just two hours. So you can't tell if you have an oiling issue by checking that way. However, look for signs of overheating due to friction, blued steel on valve stem tips, excess wear on rocker hardware, etc.

Did the sound make a ticking noise, or did it sound like a deeper knocking noise. The ticking noise will sound like its coming from the head or valve cover, and that's a top end problem. Usually a lifter, pushrod, rocker arm, valve spring, or rocker stud. Worse case senerio in the top end would be wipping a lobe or damaging a valve (tip, stem, seat, etc).

The bottom end will sound like a jack hammer on the engine block if left for too long. If you threw a rod, there's no other sound like it. Bottom end stuff in a boat means yankin the engine, pulling the heads, and you might as well rebuild it if your that far already. Lets pray its top end.

Pull the valve covers again. Check to make sure all the studs, springs, pushrods and rockers are accounted for. Now double check your valve springs to make sure one isn't cracked on the back side way in the corner that's hard to get to. Wiggle the rocker arms, some will be a little loose, some will be tight, that's normal, if you can wiggle one off of the valve stem tip, then there's something wrong. Tripple check that assembley, spring, valve tip for wear, rocker arm for cracks, pushrod for straightness.

A compression test would also be helpfull, but I'd like to do a visual inspection first. If you're hanging a valve, it'll be obvious in the visual, compression tests take a little longer.

Not to insult your intelligence, honestly, but have your friend read this as well, if you or him don't fully understand all the terms and how to check these things, then I'd suggest finding someone who does know. Tell him you'll buy him 2 dinners at Outback to watch over your diagnoses and 2 more dinners to have him/her watch over your repair proceedure. Well worth the ~$120 in steak and beer.

DISCLAIMER: Yet again, take this with a grain of salt, as this advice applies to gasoline engines in cars and bikes.

Good luck to you, and enjoy learning more than you ever wanted to know about your boats darkest corners....

PS - If you do find something weird, barrow, buy, or rent a digital camera and take some pics to post up here. I'd really love to see them.
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If it were me...

It sounds like you have the skills needed to tackle such a job.

Although I don't think it's the exhaust mixing elbow, it might be wise to check anyway to see if it's clogged. When mine (mixing elbow and manifold water jacket on Yanmar) clogged by carbon buildup, the engine overheated at anything much over idle. However, there were no new noises which makes me think this isn't your problem.

From the very limited experience I've had... The most "high tech" part of a diesel is the fuel pumps and injectors. The rest should be simular to a gas engine.

Breaking out my crystal ball... I see the purchase of a repair manual in your future (unless you already have one).

To answer your question... You don't sound like you're nuts. I don't think I have as much mechanical knowledge/experience as you do; and I wouldn't be afraid of pulling the top end off and checking for excessive wear, or even pulling the engine and doing a rebuild.

I hope it turns out to be something easy.

Skipper, J/36 "Zero Tolerance"
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Old 05-14-2009
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In my lifetime of fixing stuff

When it goes bang bang in a nasty sounding way it generaly sends metal bits through out the motor

SO if you open it up a bit and see anything that got eaten you will need to take it apart and REALLY clean things up it its going to live


IMHP you need to ID what you have first and look into if you can get parts and a manual before you waste much time becasue you would be supprised what you can FUBAR buy taking something apart without a manual
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Just a word of warning - Volvo parts are VERY expensive. It would be worth getting a diesel mechanic to look at the engine to diagnose things before you proceed. Good luck.
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Old 05-14-2009
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Don't do it

Old Volvo parts are extremely expensive and assuming yours is raw water cooled, rebuilding an old MD2B is throwing away money. It won't last many more years. Get a new engine, perhaps a Beta, I did and I couldn't be happier. I bet you can get a new engine for the price of fixing your old one. Check the Betas out at betamarine.net.
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Rule #1
The last thing you mucked with is the first to mess up.

The engine over heated
You messed with the pump
engine ran fine for an hour
engine started making noise
go back and check you work on the pump first
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Old 05-14-2009
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Quote:
Originally Posted by timebandit View Post
Rule #1
The last thing you mucked with is the first to mess up.

The engine over heated
You messed with the pump
engine ran fine for an hour
engine started making noise
go back and check you work on the pump first
I'll second that.
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As the engine warms up valve clearance will tighten up a cold engine will make more noise. When you restarted was it the same kind of noise just louder? A long screwdriver held in different places can help track down the area topend or bottom.If you end up taking the head turn upsidedown valveheads up fill combustion chambers with oil than blow compressed air in intake/exhaust ports a little bubbles are ok you are looking for somthing inconsistent my most likely exhaust side.Overheating is hard on valve springs have them check if you find burnt/leaking valves.
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