Yanmar 1GM Riddles (in CD 25D)

[Larry DeMers]

After all the responses, my bit will be to simply repeat..FUEL. If you are running ok at idle,, then you have clean fuel, clean air and compression. So as you increase power demands, more fuel gets delivered as needed, giving the requested power. At these high rpm points, the fuel would be the first thing to check. If the fuel has emulsified water in it, that is you put in your Bio-Bor and Iso Alcohol to emulsify the water droplets so they can pass thru the engine safely, that itself may be the problem. The pump is providing a measured dose of fuel at each stroke. If a part of the fuel is watered down, it plainly does not burn, and the engine will be minus the power the bad fuel should have provided you.
There are more esoteric causes of lower power at top end too. Valve timing is a large effect, which if recently adjusted, may be the cause..or in fact running at these rpms may have readjusted the valves for you, making top end performance less than before (at these rpms, you are pounding the living hell out of the valve seats, and so at some point the valve springs will begin to float, that is the valve will bot be forced to close entirely, allowing some combustion gasses to escape out the back end, and form your black transom syndrome).

WHAT IS THE TOP RPM OF THIS ENGINE SUPPOSED TO BE? The engines rpm governor should keep you from exceeding it.

My vote is watered down fuel, but the symptoms fit a number of increasingly expensive scenarios. Let us know what it turns out to be please!

Cheers and best of luck,

Larry DeMers
s/v DeLaMer
Cape Dory 30 Sailing Lake Superior

I know that we have been down this road before, but please indulge me. I am confused.

When I first got my 25D about 9 yrs ago, the Yanmar 1GM turned about 3100-3200 prm under load, and moved the boat at what seemed to be hull speed. (My knot meter showed just over 6 knots, which is a little optimistic, but that jived with the reading I got when I was sailing fast, in good wind, on a beam reach. I still get that reading while SAILING fast.)

Gradually it got to the point where I was getting only 2700-2800 rpm, and the boat moved a full knot slower through the water. It also came to deposit more and more black grundge on the transom. I dove under and looked at the prop; it is not fouled.

I have just spent about a thousand bucks chasing this problem, with two different mechanics. The injector was sent out and serviced, the lift pump was serviced, the valves have been adjusted, the air filter checked, the fuel filters replaced, and the second mechanic did an "engine wash," in which he injected some concoction through a syringe into the air intake while it was running. I have also tried additives in the fuel. Net result (hardly any): I am only up to 2900 rpm, and still get lots of grundge on the transom. And the boat goes no faster through the water. Despite optimistic predictions before the work, both mechanics, AFTER the work, decided that the propeller needs work!

From what I can gather, the engine should turn about 3400 under load, and 3600 in neutral. I do actually get MORE than 3600 in neutral. I will probably get the prop re-worked at the end of the season, but unless I want to incur signifigant extra expense (launching/hauling), I will not be able to test the results until next season. Is this a bad idea?

What I don't get is that, IF IT IS the prop, then why did the problem establish itself only gradually? The prop has not changed. (And why did Cape Dory put the wrong prop on the boat?) AND, if I get the prop "detuned" so that the engine turns higher revs under load, isn't there a chance that the boat will then actually go SLOWER? (Since the prop will have less "bite?") The theory is that if the engine cannot turn the recommended revs, then it burns fuel inefficiently, hence the black soot coming out of the exhaust. The first mechanic said he thought that the boat was going hull speed at about 2500 rpm, and anything beyond that was laboring the engine. I don't buy that; the boat used to go a full knot quicker through the water, at the same recorded (by the knot meter) speed as sailing fast. Now it won't.

Any input would be MOST appreciated. And not just from 25D owners. My guess is that a lot of you folks out there know at least as much about this as these two mechanics. Both mechanics, btw, work for Yanmar dealers.

demers@sgi.com

[Lou Ostendorff]

Hello Dean and Others;
I've been following this thread with interest since I'm also a 25D owner, and have a 1GM10, which is 'close' to the 1GM model. Not being a diesel expert, but having some limited experience with engines in general and my own diesel in particular, and having read a considerable amount about them, here is my take on your problem...first, the other posters have given you a wealth of info. and leads to try and I must say that I agree with them all. I do, however, think that after reading your description of the problem, there are two distinct possibilities. First, as Larry and others stated, 90% of a diesel engine's problems can be traced to fuel. Either it's good, or it's bad. If bad, performance suffers or it won't run at all. Part of the problem with our Cape Dories is that few of the smaller models came with reliable or easily readable fuel gauges, making frequent fill ups a matter of 'peace of mind'. This, unfortunately, leaves you with unused fuel at the end of the year, to which you add more fuel, to top off and prevent the dreaded 'condensation'...over the years, your tank gets full of crud, and maybe some water because of this. You said performance suffered steadily over a 9 year period; that sounds like it could be the culprit...the best solution is 'fuel polishing' or tank cleaning...BTW don't bother to change filters until after this is done. The second most probable senario, assuming prop. and bottom are OK, is that your little Yanmar is wearing out...you didn't state how many engine hours it had, but I'd guess several thousand if it's the original mill...diesels are different from gas engines in several respects, but the most obvious are finer tolerances and high compression. If either of these features have been compromised, the power rendered from even clean fuel would be modest at best...since you didn't elaborate on your maintenance intervals or habits, it appears to be a possiblility. If compression is good and tolerances are within range, you should get all the power necessary with almost no smoke. The smoke (black) is from incomplete combustion. I'm not discounting some of the other observations either, because they may be contributing to the overall problem. If you check the archives and look at boats for sale, you'll find that other 1GM owners repowered after 16-20 or so years. Rebuilding is not a popular option because the GM series has a sleeveless cylinder and the warranty is short. Repowering is expensive, but a viable choice if you want to keep the boat...Funny, how we sailors, soon after the proud purchase of our 'sailing machine', initially concerned only with our movement on the wind, must eventually give 'homage' to the steel beast found below...good luck with your project!
Lou Ostendorff
CD25D Karma
Berthed in Havelock, NC



louosten@ipass.net

[Michael Abramson]

Abe,
If after trying all the suggestions here, you are still a knot slower
than you used to go, than you and Marilyn may want to consider dieting.
Love,
Michael

I have had no overheating at all. And I have had no indication that the shaft or stuffing box needs adjusting. No excess dripping; no lack of dripping. No excess vibration. In fact, the engine sounds and "feels" pretty good. Just slowish under load, and putting out this grundge which seems more carbon-ish than oil-ish.

mabramson@cox.net

[Dean Abramson]

Larry,

The manual says:
"Continuous rating:" 6.5 hp @ 3400 rpm,
"1-Hr. rating:" 7.5 hp @ 3600 rpm.

My mechanic seems to translate that to mean 3600 in neutral, 3400 under load, max. It's a one-cylinder engine, raw-water cooled.

Back when I used to be able to get 3200 rpm under load, I used to routinely run it at about 2800, and that seemed to move the boat close to hull speed. Now I only get 2800-2900 under load, and if I back it off to 2500, I only go about 4.5 knots.

One thing I am confused about is that the mechanics say I need the smaller prop so that the engine can turn 3400 under load. But in the next breath, they say I should not run it at full revs. What gives? Is it that if the engine were ABLE to do 3400, then it would be happier at 2550 (75%) then the same engine/boat only capable of 2800, but run at 2100 (75%)? (Not to mention faster.) I should also add that I have had lots of folks tell me that one should ALWAYS run a diesel at full revs whenever possible, but I have never really bought into that, mainly because it just goes against my instincts.

I find it interesting that this time around, hardly anyone on this forum seems to buy into the too-big-prop theory. I thought that in an earlier thread (not mine), that had several supporters. FYI: mine is a two-blade prop, and I think it is the original prop. I do not know the specs of the prop.

One reader wrote in about growth on the boat's bottom. I am starting to lean in that direction. It has been WARM this season, and my guess is that the bottom is pretty shaggy. Could this lose me a full knot? And keep the engine from being able to rev higher just because of increased resistance on the hull? I repeat, the engine will rev to 3700 in neutral, and I dove down to confirm that the prop is NOT fouled. I only use one coat of bottom paint, Petit Unipoxy Plus. I definitely plan to be there when they haul the boat this time, so I can check it out.

Another question: if my compression was low, would I still get the 3700 rpm in neutral?

THANKS to everyone out there. Cape Dory folks are the best!

Dean

The formula for max hull speed is actually Sqrt of LWL (19.5 for the 25D)x1.34. This will give a top end of 5.92 kts I believe.
1.34 for the constant has been around for awhile now, and cruising boats seem to fall in the 1.25-1.34 range for that constant.

I think the first thing I need to know is what the spec is for that engine as far as max rpm. Cruising speed should be about 75% of that rpm for best mileage and life of the engine.

Larry DeMers
s/v DeLaMer
Cape Dory 30

Dean

At what RPM do you run the engine? I have run mine ar or above 3000 only once or twice and only then to see if it would do that. I typically run about 2800 and that gives me 5.5ish (by GPS) knots if the hull is fairly clean....I compute hull speed at 5.3 ish (Sqrt of 19.5x1.2ish)????? Should we expect more than that?????

Fair Winds
Bill

I know that we have been down this road before, but please indulge me. I am confused.

When I first got my 25D about 9 yrs ago, the Yanmar 1GM turned about 3100-3200 prm under load, and moved the boat at what seemed to be hull speed. (My knot meter showed just over 6 knots, which is a little optimistic, but that jived with the reading I got when I was sailing fast, in good wind, on a beam reach. I still get that reading while SAILING fast.)

Gradually it got to the point where I was getting only 2700-2800 rpm, and the boat moved a full knot slower through the water. It also came to deposit more and more black grundge on the transom. I dove under and looked at the prop; it is not fouled.

I have just spent about a thousand bucks chasing this problem, with two different mechanics. The injector was sent out and serviced, the lift pump was serviced, the valves have been adjusted, the air filter checked, the fuel filters replaced, and the second mechanic did an "engine wash," in which he injected some concoction through a syringe into the air intake while it was running. I have also tried additives in the fuel. Net result (hardly any): I am only up to 2900 rpm, and still get lots of grundge on the transom. And the boat goes no faster through the water. Despite optimistic predictions before the work, both mechanics, AFTER the work, decided that the propeller needs work!

From what I can gather, the engine should turn about 3400 under load, and 3600 in neutral. I do actually get MORE than 3600 in neutral. I will probably get the prop re-worked at the end of the season, but unless I want to incur signifigant extra expense (launching/hauling), I will not be able to test the results until next season. Is this a bad idea?

What I don't get is that, IF IT IS the prop, then why did the problem establish itself only gradually? The prop has not changed. (And why did Cape Dory put the wrong prop on the boat?) AND, if I get the prop "detuned" so that the engine turns higher revs under load, isn't there a chance that the boat will then actually go SLOWER? (Since the prop will have less "bite?") The theory is that if the engine cannot turn the recommended revs, then it burns fuel inefficiently, hence the black soot coming out of the exhaust. The first mechanic said he thought that the boat was going hull speed at about 2500 rpm, and anything beyond that was laboring the engine. I don't buy that; the boat used to go a full knot quicker through the water, at the same recorded (by the knot meter) speed as sailing fast. Now it won't.

Any input would be MOST appreciated. And not just from 25D owners. My guess is that a lot of you folks out there know at least as much about this as these two mechanics. Both mechanics, btw, work for Yanmar dealers.

dabramson@mainephoto.com

[Dean Abramson]

Or I could just follow that Time-Honored Nautical Tradition: buy a bigger boat. (With room enough to give a smart-aleck brother his own cabin. With plenty of room left for food.)

Abe,
If after trying all the suggestions here, you are still a knot slower
than you used to go, than you and Marilyn may want to consider dieting.
Love,
Michael

I have had no overheating at all. And I have had no indication that the shaft or stuffing box needs adjusting. No excess dripping; no lack of dripping. No excess vibration. In fact, the engine sounds and "feels" pretty good. Just slowish under load, and putting out this grundge which seems more carbon-ish than oil-ish.

dabramson@mainephoto.com

[Mike L.]

Interesting thread, I've learned a thing or two from this knowledgeable group about my engine. One thing to consider is that it's quite normal to accumulate a lot of stuff in 9 years We just remove most of the accumulation from within to give our boat a thorough cleaning. Easily several hundred pounds worth of stuff not including the optional equipment permanently attached, bottom paint, etc.



mikit@pioneer-net.com

[Larry DeMers]

Dean,

If the bottom is growing a 'lawn', you will certainly lose 1 or more kts. That I would look into as THE reason. To your other questions:

The manual says:
"Continuous rating:" 6.5 hp @ 3400 rpm,
"1-Hr. rating:" 7.5 hp @ 3600 rpm.

Wow! My Volvo has a top end of 2600 rpm. That is hummin'. In a one lung machine, I would not run it that fast, but I have no experience witht he Yanmar engines..they may be able to take high revs like that. I know my Honda cars and cycles have all been high rpm machines, and they work very well. But it sure does seem too high.

My mechanic seems to translate that to mean 3600 in neutral, 3400 under load, max. It's a one-cylinder engine, raw-water cooled.

I would think that is correct. However, at 3600 in neutral, I would never try it. Occasional bursts of full power under load are fine for cleaning out carbon etc., and checking on the max performance of the engine, but usually you should stay below 75% power in my book.

Back when I used to be able to get 3200 rpm under load, I used to routinely run it at about 2800, and that seemed to move the boat close to hull speed. Now I only get 2800-2900 under load, and if I back it off to 2500, I only go about 4.5 knots.

There seems to be additional resistance to the boats gaining speed. Your dirty bottom scenario sounds better all the time heh..;^)

One thing I am confused about is that the mechanics say I need the smaller prop so that the engine can turn 3400 under load. But in the next breath, they say I should not run it at full revs. What gives? Is it that if the engine were ABLE to do 3400, then it would be happier at 2550 (75%) then the same engine/boat only capable of 2800, but run at 2100 (75%)? (Not to mention faster.) I should also add that I have had lots of folks tell me that one should ALWAYS run a diesel at full revs whenever possible, but I have never really bought into that, mainly because it just goes against my instincts.

Here is where I part company with the mechanics. The prop is probably fine. If you were able to get the prop to give you hull speed at 2800 rpm previously, then it should be possible to do so now, if the factors that slow a boat down were the same. Something has changed on you. Ths pitch of the prop is as you guessed, better with it sized for the maximum rpm. At lower rpms, it will then be the right pitch to give you best performance. Forget that advice about *always* running a diesel at full rpms. That is hogwash on boats..maybe a forklift or bobcat, but NOT a boat. Your instincts are correct on this.

I find it interesting that this time around, hardly anyone on this forum seems to buy into the too-big-prop theory. I thought that in an earlier thread (not mine), that had several supporters. FYI: mine is a two-blade prop, and I think it is the original prop. I do not know the specs of the prop.

Reason I doubt that the prop is the culprit is that you had good performance at one time with this prop. So it should be available again, all things being equal.

One reader wrote in about growth on the boat's bottom. I am starting to lean in that direction. It has been WARM this season, and my guess is that the bottom is pretty shaggy. Could this lose me a full knot? And keep the engine from being able to rev higher just because of increased resistance on the hull? I repeat, the engine will rev to 3700 in neutral, and I dove down to confirm that the prop is NOT fouled. I only use one coat of bottom paint, Petit Unipoxy Plus. I definitely plan to be there when they haul the boat this time, so I can check it out.

This is the one that I would lean on hard. It makes sense, and seems logical to boot. It certainly would cause the trouble you have.
But the fact that you can reach 3700 R's without load means less than you think. If there were a fuel quality problem or cetane problem for instance, you would be able to coaxe 3700 R's out without load, but under load, it would choke at that rpm I bet. The power is not there with the fuel, so the resistance of the load would prevent getting that high an rpm out.

Another question: if my compression was low, would I still get the 3700 rpm in neutral?

I expect so, as there is little resistance in neutral. The compression factor will come into play under load. The max HP the engine can put out is determined by the compression and other specs.
If you are concerned here, do a "wet" compression check..or have it done. It will tell a lot about the engine's condition.

THANKS to everyone out there. Cape Dory folks are the best!

Of Course! Look at what we sail! heh..

Best of luck,

Larry DeMers
s/v DeLaMer
Cape Dory 30 Lake Superior..where the Canadian Geese are already heading south..sigh

Dean

The formula for max hull speed is actually Sqrt of LWL (19.5 for the 25D)x1.34. This will give a top end of 5.92 kts I believe.
1.34 for the constant has been around for awhile now, and cruising boats seem to fall in the 1.25-1.34 range for that constant.

I think the first thing I need to know is what the spec is for that engine as far as max rpm. Cruising speed should be about 75% of that rpm for best mileage and life of the engine.

Larry DeMers
s/v DeLaMer
Cape Dory 30

Dean

At what RPM do you run the engine? I have run mine ar or above 3000 only once or twice and only then to see if it would do that. I typically run about 2800 and that gives me 5.5ish (by GPS) knots if the hull is fairly clean....I compute hull speed at 5.3 ish (Sqrt of 19.5x1.2ish)????? Should we expect more than that?????

Fair Winds
Bill

demers@sgi.com

[John M Freeman]

Dean,
Having not been on the post in a few days, and then only briefly for selfish reasons (posting my own bragging message), I am just now looking at your question. Your mechanics are decidedly wrong, and most all of the postings I have read in here are (probably) right. (this is kind of like being an arm chair quarter back, a bit hard to diagnose the true problem correctly from email or over the phone, even though you have put alot of info in your posting, just not the same as watching and listening to the engine)If you have never cleaned your tanks, and the prop is the original, and the overhead (valve lash adjustment) was done correctly, then your problem is crappy fuel. Not only does the diesel accumulate water in the form of condensation and water found in the fuel bought at the marina, it loses the cetane level over the years, much the same way that gasoline turns to varnish when unused. The condition of your hull will contribute to the reduced speed and some rpm loss, as will the condition of your wheel, but not the power loss that you have indicated. Get rid of your old fuel, get the tank cleaned, clean your fuel/water separator, and I would just about bet that your problems will be 90% solved, the other 10% being the bottom growth and stuff on your wheel. By the way, I don't work at a Yanmar dealership, but working on Diesels is what I do, and sideline with the marine business. Give me a yell if you have any other questions, or if this doesn't solve your problems. At that point I may have to leave the remote and the armchair and do a little bit more diagnosing.



capn_jack68@yahoo.com