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Old 29-10-2018, 08:52   #1
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Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

We have a 1971 Pearson 33, and just replaced the original 22 hp Palmer engine in it with a "newish" 1983 Yanmar 3 GM (f). The Palmer ( when it worked) would push her along at 5.5- 6 kts. There is nothing else that is printable that I can say about the Palmer).


The Yanmar starts up beautifully and runs fine. Except that rpms top out at 2400, and top speed is 3.7 kts. Same 12" two- blade propeller, and both engines are 22 hp. From what I have read in other forums, one issue may be a carbon occluded mixing elbow- or perhaps the propeller.



If you are familiar with situation, I'd de welcome your thoughts and suggestions.
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Old 29-10-2018, 09:08   #2
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

The 3GM30F is 29hp if I'm not mistaken. I have the same engine.

The mixing elbow is the place to start looking. This engine had 2 different models of mixing elbows- one has a sharp inverted U-shape and the other is a gently sloping curved piece with the water hose on top. If you need a new one, you can get them in SS from the US at a price considerably lower than the Yanmar original. Google "Ben Cotton, mixing elbows". It's worth replacing the elbow, even if it's not clogged. Eventually they break down inside and water can get back into the engine. I think I paid USD 150 for a new one.
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Old 29-10-2018, 09:28   #3
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

Thank you- I sourced a stainless "sharp bend" mixing elbow( that's the one on our engine) for 175 and purchased it. Note- our engine is a 3gm , not a 3gm30. They only made the 3GM ( F) for about 3 years ( 1980-83), and its a lower horsepower output. In any case it looks like we have the original elbow on it.
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Old 29-10-2018, 09:32   #4
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

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Originally Posted by dborrus View Post
Thank you- I sourced a stainless "sharp bend" mixing elbow( that's the one on our engine) for 175 and purchased it. Note- our engine is a 3gm , not a 3gm30. They only made the 3GM ( F) for about 3 years ( 1980-83), and its a lower horsepower output. In any case it looks like we have the original elbow on it.
Thanks for the clarification. I didn't know there was a 22hp 3gm model.

The new elbow will probably fix your problems, especially if it's currently running on the original- which must be clogged up at this point!

Let us know how it turns out.
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Old 30-10-2018, 00:01   #5
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

Quote:
Originally Posted by dborrus View Post
We have a 1971 Pearson 33, and just replaced the original 22 hp Palmer engine in it with a "newish" 1983 Yanmar 3 GM (f). The Palmer ( when it worked) would push her along at 5.5- 6 kts. There is nothing else that is printable that I can say about the Palmer).


The Yanmar starts up beautifully and runs fine. Except that rpms top out at 2400, and top speed is 3.7 kts. Same 12" two- blade propeller, and both engines are 22 hp. From what I have read in other forums, one issue may be a carbon occluded mixing elbow- or perhaps the propeller.



If you are familiar with situation, I'd de welcome your thoughts and suggestions.
Do you know what the gearbox reduction ratio is on both motors? 12" prop sounds small. What is the pitch? A 3gm should push that faster even at 2400 rpm. I would check on the vicprop calculator whats recommended for your boat.
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Old 30-10-2018, 09:43   #6
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

It is true that there is an older and a newer version of the same engine. The main difference is the size of bores, with the smaller older version having the smaller bore. I have been in both and have done detailed comparisons. The two engines are identical in design and therefore most parts other than pistons and rings are interchangeable.
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Old 30-10-2018, 09:53   #7
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

With a clogged elbow you will see black soot coming out exhaust and also possibly low water.... will definite hurt rpm’s. But check reduction ratio..... trans push differently and if engine sounds good it may infact be that. However start simple.... mixing elbow sounds like it’s ready to be replaced based on age..

Good luck
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Old 30-10-2018, 10:39   #8
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

Rev the engine in neutral briefly to check its maximum RPM with no load - (you can't hurt it - it has a governed max.speed) If it rev's to spec'ed rpm (3400 or 3600 ? ) then nothing wrong with engine ! Compair new gear ratio to old ! Gather all boat and engine / trans specs - plug into prop calculator available free on VicProp website to find out what prop you should be using !
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Old 30-10-2018, 13:12   #9
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

We had a similar problem – well, it sounds like the same problem. It turned out to be the kill lever was stuck partially closed. It would rev fine in neutral, but no power underway.

In our case, it was the kill cable that had rust at one end and would not release the entire way.
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Old 30-10-2018, 13:56   #10
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

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Originally Posted by johnjuliano View Post
We had a similar problem – well, it sounds like the same problem. It turned out to be the kill lever was stuck partially closed. It would rev fine in neutral, but no power underway.

In our case, it was the kill cable that had rust at one end and would not release the entire way.
My first thought too; ours does just the samewhenever the engine's not been started for a few months.
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Old 30-10-2018, 16:58   #11
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

Since you are about to change the elbow - once you have removed it look back into the exhaust manifold. My Perkins had considerable buildup there caused by a leak in the elbow that allowed raw water into the manifold. The only repair in my case was to replace the manifold. Also check the flexible hose attached to the elbow for accumulated junk.
+1 on the SS elbows. Better made, cheaper, should last much longer than stock. I would have put one on a new engine if I only I had known...
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Old 30-10-2018, 19:23   #12
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

You don't mention if the max RPM are at idle, or under load. Max Hi Idle should be in the 3400+ range. If so, max underway, with a clean bottom, should be 90% of that. If rpm lower, too big a prop, if higher, too small.
Verify the shut off lever is against its stop, and that throttle has full range of travel. Also check fuel filters for restriction.
Do these basics before tearing things apart.
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Old 30-10-2018, 21:37   #13
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

^^ the rpm quoted by the OP was probably under load since he reports a speed of 3.7 kts .

Apart from that, I gotta concur with your thoughts!
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Old 31-10-2018, 09:24   #14
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

THe manual for the old Palmer said the ration was 2:1.
The plate on the Kanzaki transmission on the Yanmar looks like "2.61", which I think means a 2.61 : 1 . I will check with Vicprop Website.

Thank you!
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Old 31-10-2018, 09:44   #15
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Re: Yanmar 3 GM (F), low rpms , top speed of 3.7 kts

What rpm can you get in neutral? I t sounds like you guessed that the original prop would be fine for the new engine.
Another possibility is a cracked piston, which the 3GM30 are famous for. Not sure about the 3GM. Engine starts fine, but wont reach speed. But look at simple stuff first.
-Does it reach rpm in neutral? May need to reprop it.
-Levers and wire controls all good? Try operating the fuel lever at the engine instead of from the cockpit.
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