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-   -   Low hours on Yanmar 2QM20 (http://www.sailnet.com/forums/gear-maintenance/30931-low-hours-yanmar-2qm20.html)

zaldog 03-31-2007 10:12 AM

Low hours on Yanmar 2QM20
 
I am starting a new thread here from the discussion on buying a new boat. One concern several of you had was very low hours regarding the Yanmar 2QM20, on a 1978 Bristo 29.9 . The Meter reads 656 and is believed true. Motor is the original as far as I understand.

My question is how can this be bad for the engine? Potential corrosion of the rings and heads? Just curious as I have never owned a boat with a diesel. And I know I would put at least 2 hours a week on this engine during the season here in Chicago, if i decide to buy the boat. Also anything I should known about this particular engine both good and bad? For istance is this an 18HP or 20HP the PO claims it is 20HP from what I can find it is 18HP?

camaraderie 03-31-2007 11:22 AM

Zaldog...low engine hours are not a bad thing in and of themselves if the engine has been well cared for. What you would be checking for in surveying a 30 year old engine with low hours is not much different than what you would do surveying any engine. On the plus side...there is little danger of normal wear and tear that you would see on an engine approaching rebuild time. Obviously all belts, hoses and other rubber parts (impeller, fuel lift pump) would need to be inspected for aging and cracking. The other danger with long spells beween start up is that the oil has settled and lost it's protective qualities in the cylinders during start up cycles...this could result in the scoring of cylinders and/or corrosion over time. Also oil that is not changed regularly can cause problems as it changes its' chemical composition. A good diesel mechanic should be used to check ANY engine during survey and will be able to spot if any of the above issues apply to the Bristol you are looking at. Hopefully, he will find that any issues are minor and you will have the benefit of an engine with many hours ahead of it before an overhaul is needed.
I wouldn't worry about the difference between 18 and 20HP and actually some technical sites give the rated horsepower as 22 so 20 is probably a good number! Solid workhorse engine that should do fine for you if it checks out initially well.
Modellguide Yanmar

Guesser 03-31-2007 11:25 AM

I don't think low hours is a bad thing, it's a good thing. But it just means that some maintenance items, (filters, plugs, injectors, gaskets, belts etc) that would normally be replaced from use, probably have not been. Meaning, you may want to have a mechanic give it a "tune up" and replace any parts that may have deteriorated and/or failed from lack of use. Personally I wouldn't be to concerned with the internal moving parts, (rings, bearings etc), as low hours on any moving part is certainly preferred over high. Unless it's being just sitting for years, then there might be rust inside, but if it was started regularly, it should be fine.. The Yanmar 2QM20 is 20hp, I'm pretty sure the 18hp came out a few years later (mid 1980's)

sailingdog 03-31-2007 09:31 PM

Low engine hours can be a bad thing, as many people schedule their maintenance around running hours, and if that was the case, and an engine has low hours, it may be neglected. Cam's touched on much of what I am talking about... so I won't repeat him.

sailingdog 03-31-2007 11:26 PM

Guesser-

Exactly why do you think Cam and I are yahoos...

Low engine hours can be a really bad thing... This engine is almost 30 years old... and if the 656 hours happened in the first 10 years, it may have been sitting, without much in the way of maintenance for almost 20 years.

While I don't think that is the case, as that is an extreme case for illustrative purposes...

Can you explain exactly how is an engine sitting for 20 years, in a marine environment, could be in any way possible at all good for the engine?

Just curious as to how you can possible answer this in a positive way...

Also, oil and coolant are both contaminated over time, and the ingredients in them that are designed to protect the engine from wear and corrosion are also subject to breakdown to age, oxidation, evaporation, etc... If the owner of the boat stuck to an engine-hour based schedule... then the engine could be a giant block of rust... with missing zincs and such... An engine that is used regularly is far more likely to receive regular maintenance, as it is probably checked far more often than an engine that just sits for years on end.

While I hope the engine is in good shape, and it may be... if it received proper and timely maintenance... but it may also be a total writeoff.

Guesser 03-31-2007 11:35 PM

I guess I'm confused. You're saying: Low hours = Bad? High hours = Good? Maybe in Bizarro world, but not the real world. I don't care what you say, I'll take a low hours, over high hours any day of the week. (oh, and sorry about the yahoo thing, I deleted it right after I posted it).

sailingdog 03-31-2007 11:52 PM

Quote:

Originally Posted by Guesser
I guess I'm confused. You're saying: Low hours = Bad? High hours = Good? Maybe in Bizarro world, but not the real world. I don't care what you say, I'll take a low hours, over high hours any day of the week. (oh, and sorry about the yahoo thing, I deleted it right after I posted it).

I never said that... I said that an engine with low hours that was not properly maintained could be very bad... and that an engine that was used regularly often received better maintenance, due to the regular use. I never said that low hours was always bad... but that you have to be careful of very low hours on an older engine, since that can often mean its maintenance was neglected.

From my previous post:

Quote:

Low engine hours can be a bad thing, as many people schedule their maintenance around running hours, and if that was the case, and an engine has low hours, it may be neglected
From Cam's previous post:

Quote:

The other danger with long spells beween start up is that the oil has settled and lost it's protective qualities in the cylinders during start up cycles...this could result in the scoring of cylinders and/or corrosion over time. Also oil that is not changed regularly can cause problems as it changes its' chemical composition.
BTW, an engine that is rarely used and rarely heats up to working temps can often get condensation in the cylinders, and that can lead to corrosion in the engine block that is really detrimental to the engine's health.

Guesser 04-01-2007 12:42 AM

I hear ya, but take my engine for example. I daysail once or twice a week, it takes 10 minutes to get out of the marina, then I hoist the sails, and then another 10 minutes to get back into the slip. So let's say I run the engine 30 minutes a week, times 52 weeks a year, that's only 26 hours a year, over 20 years it's like only 500 hours. How is this a problem? I also have 1954 Chevy truck that I hardly ever drive; it has 45k original miles. should I be worried that the engine is going to rust up sitting in driveway? Does the low mileage make it less valuable? I think not.

sailingdog 04-01-2007 01:02 AM

Well, if you only run it 10 minutes at a shot.. what happens is that the engine now gets a good deal of condensation in it... and then sits with the condensation on the walls of the cylinders... Think about that.. is that good for the engine block?

While low mileage or hours can be a good thing, it can also be destructive to the engine. Your example is a good one of a possibly destructive pattern.

If you were doing your maintenance based on engine hours, and changed your oil every 100 hours, does that mean you've only changed it five times over the 20 years you own the engine.

How would you feel about buying an engine that had only had its oil changed five times in 20 years?

What do you think the condition of the engine would be???


See my point... if you changed the oil every year, instead of every 100 hours, then the engine would probably be in much better shape, compared to an engine with the exact same use pattern but different maintenance schedule.

camaraderie 04-01-2007 01:30 AM

Guesser...I'll jump back in here for a moment. Additional thoughts beyond what has been covered above.
1. Too many hours is always a problem as things DO wear out. Fortunately with diesels..this is generally many thousands of hours of use before significant wear occurs.
2. If you are only using your diesel 10 minutes each way, you are probably not getting it up to the 180 degree operating temp it needs to keep itself "springtime fresh" internally. <g> Be sure to get it up to temp when you use it or you will surely pay the piper down the road.
3. A low hour 30 year old engine that has been run regularly up to temp and meticulously maintained would be almost as good as a brand new engine. And you will find one of those engines right after the tooth fairy puts a quarter under your pillow! <g> The best you can generally hope for is that their is only minor and fairly inexpensive benign neglect.
2.


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