Hi Folks. I'm looking at purchasing a planning type 39' launch with 2x of these engines. These ones however are only doing 3050 or so rpm flat out (about 14knts). They're supposed to rev to about 3600 which is where they make their max power (165hp or there abouts). Boat is shaft drive. Other examples of this model achieve around 20 plus knts presumably up around 3600 revs. Other than being fitted with the wrong props is there anything else that I should look into? Engines seem responsive and don't seem to smoke much at all on cold start. Could it be governed to protect the engines? Any input would be greatly appreciated.
Volvo TAMD40B won't rev past 3000 - props or worse?
- Thread starter Jeff390
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STB
Guru
It could be a ton of things.
-- The control cables could be adjusted such that they don't fully open the throttle.
-- The stops in the controls could be set to prevent fully exercising the throttle cable
-- The governor could be limiting, perhaps intentionally, or perhaps mis-set
-- They could be different models than you expect.
-- They could have been modified to produce less output, e.g. w.r.t. turbo and injector pump/injector tuning.
If there isn't significant grey or black smoke, my first guess wouldn't be props, transmision, or loading.
My first test would be, and I know many would gulp at this, to see if it reaches no-load WOT RPMS in neutral at the slip when adjusting the throttle directly at the engine.
If it caps out at about the same place, and is running smoothly, then governor is a good guess. If it starts to surge crazy before it gets there, then there might be something interfering with the test, like fuel, or a real problem.
My next test would be, with the engine off, while the control cable is disconnected at the engine, to note the position for full throttle. Then, I'd reconnect the throttle cable and advance the throttle fully via the control.
If the throttle doesn't go as far when exercised via the controls vs when exercised without them -- that tells you something about the controls is miscalibrated.
If it'll make no-load WOT RPM, it isn't the governor. If the controls fully advance the throttle it isn't the controls. If it isn't making dark smoke, dramatic overloading is unlikely. Diagnosis goes to less common thing from there.
Ultimately, it could still be overloading, even without a ton of smoke.
But, it could also be weird stuff, like injector pumps calibrated to the wrong curve, etc. Or, maybe even a real problem. It would take a lot more focused information to sort it from there, I think.
-- The control cables could be adjusted such that they don't fully open the throttle.
-- The stops in the controls could be set to prevent fully exercising the throttle cable
-- The governor could be limiting, perhaps intentionally, or perhaps mis-set
-- They could be different models than you expect.
-- They could have been modified to produce less output, e.g. w.r.t. turbo and injector pump/injector tuning.
If there isn't significant grey or black smoke, my first guess wouldn't be props, transmision, or loading.
My first test would be, and I know many would gulp at this, to see if it reaches no-load WOT RPMS in neutral at the slip when adjusting the throttle directly at the engine.
If it caps out at about the same place, and is running smoothly, then governor is a good guess. If it starts to surge crazy before it gets there, then there might be something interfering with the test, like fuel, or a real problem.
My next test would be, with the engine off, while the control cable is disconnected at the engine, to note the position for full throttle. Then, I'd reconnect the throttle cable and advance the throttle fully via the control.
If the throttle doesn't go as far when exercised via the controls vs when exercised without them -- that tells you something about the controls is miscalibrated.
If it'll make no-load WOT RPM, it isn't the governor. If the controls fully advance the throttle it isn't the controls. If it isn't making dark smoke, dramatic overloading is unlikely. Diagnosis goes to less common thing from there.
Ultimately, it could still be overloading, even without a ton of smoke.
But, it could also be weird stuff, like injector pumps calibrated to the wrong curve, etc. Or, maybe even a real problem. It would take a lot more focused information to sort it from there, I think.
STB
Guru
Oh. That's step 0!
Thanks STB. I appreciate the detailed response and the wisdom shared.
My first thought beyond props was whether the throttle cables were adjusted short (by accident or design). Also saw a graph showing different injector curve settings and wondered if it could be that. There were rumours around the marina that the rebuild that supposedly happened a few years ago was more of a patch up than a proper engine reconditioning which is why I'm a bit suspicious. As it's only been offered to me for sale I can't really try revving the engines in neutral. Was hoping to avoid the cost of a full engine inspection/survey because if it's something that can't easily be fixed (eg wrong engines or other major mechanical) I would not go ahead. Perfect in nearly every other way just don't want one so speed limited.
My first thought beyond props was whether the throttle cables were adjusted short (by accident or design). Also saw a graph showing different injector curve settings and wondered if it could be that. There were rumours around the marina that the rebuild that supposedly happened a few years ago was more of a patch up than a proper engine reconditioning which is why I'm a bit suspicious. As it's only been offered to me for sale I can't really try revving the engines in neutral. Was hoping to avoid the cost of a full engine inspection/survey because if it's something that can't easily be fixed (eg wrong engines or other major mechanical) I would not go ahead. Perfect in nearly every other way just don't want one so speed limited.
STB
Guru
Why can't you try revving the engines in neutral? I'm assuming the seller is also curious what is up, no? They not interested in playing?
When engines have problems, they usually don't just cleanly and smoothly not male rpm. They surge. They smoke. They make bad noises. They do something.
So, in my thinking, something isneither set or configured this way, perhaps intentionally for benign reasons, perhaps intentionally tonprevent the engine from getting to the rom range where it misbehaves, or perhaps unintentionally.
Without more info, there's just no way to know. I don't think. :-(
When engines have problems, they usually don't just cleanly and smoothly not male rpm. They surge. They smoke. They make bad noises. They do something.
So, in my thinking, something isneither set or configured this way, perhaps intentionally for benign reasons, perhaps intentionally tonprevent the engine from getting to the rom range where it misbehaves, or perhaps unintentionally.
Without more info, there's just no way to know. I don't think. :-(
No one has mentioned a dirty bottom or even dirty props. Those are the number one cause of low revs. Admittedly the loss of 500-600 rpm is a lot and probably won’t be corrected with a clean bottom and prop. But I would sure check that first.
David
David
STB
Guru
I did, but also suspected a difference on rpms this big should grey up the smoke noticeably vs run clean but low revs if the cause is any type of overloading, including the bottom being dirty, prop pitch, etc.
Agree? Disagree?
The owner says that the bottom and props are clean. So check wot rpm’s in neutral and go from there.
FWIW I had a Yanmar on a sailboat that would only rev to 3,100 rpm’s. Cleaned the bottom and it shot up to 3,600. So it is possible.
David
FWIW I had a Yanmar on a sailboat that would only rev to 3,100 rpm’s. Cleaned the bottom and it shot up to 3,600. So it is possible.
David
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