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Old 30-08-2015, 15:11   #1
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Rebuild time for a 3GMF 20hp

I'm considering a 1984 Endeavor 33, that has been modified by owner for single handling and extended offshore with rolling main and genoa sails, solar, wind generator, etc and "seems" in pretty good condition for an '84. Obviously I'm getting a survey done, but I'm curious about life expectancy of Yanmars. I'm "told" the owner had the engine professionally maintained (hope to see records of this next weekend when I visit). Assuming it was well maintained what hours can I expect before rebuild; I'm thinking around 6-7K. If not well maintained, I suppose it's down to cylinder pressure, oil burn in exhaust, etc to indicate rebuild needs. The engine is reported to have 4k now.
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Old 30-08-2015, 16:19   #2
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Re: Rebuild time for a 3GMF 20hp

Age in my opinion does play into it, it may be that a small Diesel will go 10,000 hours if meticulously maintained, but maybe not if they are over 30 yrs old too.
I think your conclusions are correct, it really mostly boils down to condition. If it "looks" good as in no rust, clean, no leaks, fresh coolant etc., and starts very quickly and burns little to no oil, it may well have many thousands of hours left.
Note though, Yanmars seem to suffer a little from incomplete combustion, they seem to smoke a little, and it is fuel, not oil.


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Old 30-08-2015, 16:28   #3
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Re: Rebuild time for a 3GMF 20hp

Well at 1000 hours my engine had no measurable wear. That is rings, cylinder and bearing were withing new tolerance. Other then the $%^&* piston with broken lands.

It really depends on how much it is used. The gm series is a stout and simple little engine. If used regularly it should be quite easy to get 10k hours out of it. The problem is most engines sit for looong times between runs. This allows rust to form on cylinders with an open intake or exhaust valve. Also many sailboat engines are only used for the time getting in and out of slips. Short running is harder on engines

Generally 6k is what some say, but 10k would not be unheard of. Cost to rebuild for parts and machining would be <$1500 plus labor. I did mine for $1000, but I did not touch the head or injector pump.
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Old 30-08-2015, 17:27   #4
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Re: Rebuild time for a 3GMF 20hp

Get an oil analysis. That will tell you the state of the bearings, etc by what they find in the oil. Sailboat diesels die more from lack of use than over use.
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Old 30-08-2015, 18:37   #5
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Re: Rebuild time for a 3GMF 20hp

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Originally Posted by roverhi View Post
Get an oil analysis. That will tell you the state of the bearings, etc by what they find in the oil. Sailboat diesels die more from lack of use than over use.
The people who do oil analysis will the very first to tell you that the results they give you, are for the day you took the sample. Unless there is so much junk in your engine it's about to blow up, they can't really tell you much. They wouldn't even tell you it was about to blow up. They would just give you a bunch of numbers. Perhaps a comment that the number was high. The test service is meant to be a trend analysis not a one time thing. You could have a bigger number on something but it has been a steady and gradual increase so things are not unusual. You can't know that from a one time test.
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Old 31-08-2015, 08:59   #6
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Re: Rebuild time for a 3GMF 20hp

I think we would all like to be able to look inside our diesel engines and know how long they have left. But no such luck. Best to stick to the basics...does it start easily? No smoke? Does it burn any oil? Clean oil, clean fuel, and regular use will allow a diesel to last for a very long time. As seen on these pages, even new/newer engines can have significant/expensive issues.

I'm running an 18hp 1985 Volvo Penta 2002. Thats 30 years old. Unknown hours. Doesn't burn a drop of oil. No smoke. Starts on the first click, even after winter storage.

I wouldn't trust "professional maintenance". Thats some guy going through the steps and getting paid at the end of the day. Owner maintained is a guy who knows he never wants the engine to quit on him, especially at the worst possible moment. Thats the diesel "love" that keeps an engine going for 10,000 hours, IMHO.
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Old 31-08-2015, 09:54   #7
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Re: Rebuild time for a 3GMF 20hp

I agree - don't let "professionally maintained" give you a sense of security. You have NO way of knowing the history, and therefore the prognosis, for an engine you haven't maintained yourself. Presentation of a collection of repair bills as evidence for having "maintained the engine properly" should make you suspicious and cautious. If the engine HAD been MAINTAINED properly, repairs might not have been required.

A rather trivial example of "professional maintenance" being deficient is this: On my Vetus 3-10 (Mitsubishi K3D) when she was "new to me" I went to pull the GPs. Couldn't get a slim socket around #s 2 and 3 cos someone had misaligned the rocker cover so it interfered. Couldn't change GPs cos I didn't have a rocker cover gasket to hand!

In a sense it is trivial, but in another not. It bespeaks work by someone - I suspect a "professional" - who simply didn't bother to engage in the performance evaluation of one's own work that is essential in professionals. If such a "professional" has somewhere in the engine's history done work of a more critical nature, how could that have affected the engine's reliability and longevity?

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Old 31-08-2015, 10:18   #8
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Re: Rebuild time for a 3GMF 20hp

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Originally Posted by Guy View Post
The people who do oil analysis will the very first to tell you that the results they give you, are for the day you took the sample. Unless there is so much junk in your engine it's about to blow up, they can't really tell you much. They wouldn't even tell you it was about to blow up. They would just give you a bunch of numbers. Perhaps a comment that the number was high. The test service is meant to be a trend analysis not a one time thing. You could have a bigger number on something but it has been a steady and gradual increase so things are not unusual. You can't know that from a one time test.
Yep, I've been told after having the analysis that they have the most merit if you do them consistently and watch the trend.

My opinion on the Yanmar 3gm30 is that at 4000 hours you are getting pretty iffy. it's a light engine, intended to be run at high rpm. I've had two fail with less than about 2400 hours. Those engines didn't sit much either.

But it's just a roll of the dice, you could get one with no issues and it could go as long as many other brands. Just real hard to say. The piston issues I've seen seem to be 1990 to mid 90's engines.
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Old 01-09-2015, 11:04   #9
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Re: Rebuild time for a 3GMF 20hp

As always, thanks for everyone's input, the boat has been "idle" for about 10 months since the owner upgraded to a large cat and headed to Carib. In addition to the standard survey I may just pay a little more for a detailed engine survey as well. Other than the hours on the engine the Endeavor seems in pretty good shape.
thnx again
Mike
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Old 01-09-2015, 13:41   #10
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Re: Rebuild time for a 3GMF 20hp

I wouldn't, personally, spend money on a "engine survey". We KNOW our engines are going to "fail". We just don't know when.

My solution is to get/keep a spare. Sailboat scrapyards - there is one in Arlington WA, I know - can provide you with a rebuildable core for the same money you would spend on a survey. Have the basic engine rebuilt at your leisure and placed in storage till you need it. If you are shore based, an 25HP Yanmar on a skid doesn't take up much room.

When the time comes, all you have to do is "re&re" using those "hung on bits" from the "failed" (read "worn out") engine that are serviceable, replacing only those that are getting dodgy.

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Old 01-09-2015, 17:37   #11
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Re: Rebuild time for a 3GMF 20hp

Mhansen, Yanmar Diesel complete Engine parts Catalog includes Models 1GM, 2GM, 2GMF, 3GM, 3GMD, 3GMF, 3HM, and 3HMF. Catalog Contains 246 pages and all illustrations and part numbers including transmission Parts. Send $20 for shipping and handling and catalog is yours.
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