I am trying to sort out why my motor is not reaching its stated maximum rpms. I have a Yanmar 4JH3BE with a plate showing 3650 rpm's. I have never been able to get past 3400. It is not a propeller issue because I have just gone through two adjustments of a feathering prop which should have shown different speeds. It didn't. In fact, my old 2-blade fixed also got 3400. I'm thinking it might be a linkage issue. Or, it might be something else set to prevent the motor from reaching its higher figure. If it is something like this, can you guys tell me how to troubleshoot and then adjust what needs to be adjusted? Or, am I being too anal and obsessing over something that is not a big deal? Best, John Richard s/v Jack's Place
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What RPM do you get in neutral?
If you can get 3650 in neutral and only 3400 in gear than you are slightly over propped. Not a big deal...you will only be running at around 3000 most of the time anyway.
If you can get 3650 in neutral and only 3400 in gear than you are slightly over propped. Not a big deal...you will only be running at around 3000 most of the time anyway.
Probably the govenor!
John: If you cannot get over 3600 in netural it may be the governor (basically a rev limiter). You may want to get a Yanmar mechanic out to look at it.
John: If you cannot get over 3600 in netural it may be the governor (basically a rev limiter). You may want to get a Yanmar mechanic out to look at it.
Another Possibility
I have the same engine and, out of curiosity, I put a proper calibrated mechanical tacho on the crankshaft pulley. My Yanmar tacho reads about 5% low. This means, when the engine is rotating at 3600 rpm the tacho is reading 3420. Yours might not be the same, though I would wager that it is. Can you get your hands on a proper instrument and check it that way?
I have the same engine and, out of curiosity, I put a proper calibrated mechanical tacho on the crankshaft pulley. My Yanmar tacho reads about 5% low. This means, when the engine is rotating at 3600 rpm the tacho is reading 3420. Yours might not be the same, though I would wager that it is. Can you get your hands on a proper instrument and check it that way?
rpm check
John, if you think it is a linkage issue diconnect the linkage and see what the tach reads. I tend to agree with the yanmar tachs read slow (they are known for this)If all else fails a good mechanic should have a electric (12v) rpm gun type gauge that he can test yours against.
John, if you think it is a linkage issue diconnect the linkage and see what the tach reads. I tend to agree with the yanmar tachs read slow (they are known for this)If all else fails a good mechanic should have a electric (12v) rpm gun type gauge that he can test yours against.
RPM update
Gentlemen, et al: I was able to do a neutral test this morning and the engine reached 3500 rpm's. It's rated at 3650. To recap: The boat reached 3400 rpms with the OEM fixed 2-blade, Max Prop set at 22 (13.6") degrees and Max Prop set at 20 degrees (12.4"). So, does this mean, a), the tachometer is probably not reading correctly; b) there might be a governing widget on the motor that is preventing the higher rpm; c) I'm making a big deal over nothing, or my favorite; d) the boat is screwing (pun intended) with me? Oh...one other unrelated issue. We took the boat out yesterday in conditions that reached 22 knots apparent with breaking 6' average seas. We went out and back with the wind about 60 degrees off. The seas were contentious so I had to be mindful of the breaking crests on our beam. We only were able to reach 8.05 knots. It was quite a ride! JP felt very stable and exibited no propeller oriented vibration whatsoever. Back to you, John Richard s/v Jack's Place John Richard
Gentlemen, et al: I was able to do a neutral test this morning and the engine reached 3500 rpm's. It's rated at 3650. To recap: The boat reached 3400 rpms with the OEM fixed 2-blade, Max Prop set at 22 (13.6") degrees and Max Prop set at 20 degrees (12.4"). So, does this mean, a), the tachometer is probably not reading correctly; b) there might be a governing widget on the motor that is preventing the higher rpm; c) I'm making a big deal over nothing, or my favorite; d) the boat is screwing (pun intended) with me? Oh...one other unrelated issue. We took the boat out yesterday in conditions that reached 22 knots apparent with breaking 6' average seas. We went out and back with the wind about 60 degrees off. The seas were contentious so I had to be mindful of the breaking crests on our beam. We only were able to reach 8.05 knots. It was quite a ride! JP felt very stable and exibited no propeller oriented vibration whatsoever. Back to you, John Richard s/v Jack's Place John Richard
What's The Instrument Called...
that measures the actual RPM's off the engine. I have had the same problem as John. This past fall I had the engine looked at and the mechanic used one of those things and told me my RPM's was right where it was supposed to be. He said I could either get a new tachometer or live with it since it had no ill effect on the engine. I'm living with it for now. One big difference is that my tach was 1000 RPM's off. So I'd like to be able to check it once in awhile. Can someone tell me the name of the tool. Thanks, Joe Mullee
that measures the actual RPM's off the engine. I have had the same problem as John. This past fall I had the engine looked at and the mechanic used one of those things and told me my RPM's was right where it was supposed to be. He said I could either get a new tachometer or live with it since it had no ill effect on the engine. I'm living with it for now. One big difference is that my tach was 1000 RPM's off. So I'd like to be able to check it once in awhile. Can someone tell me the name of the tool. Thanks, Joe Mullee
Instrument Name?
Joe, I have two TACHOMETERS one is very old made by Hasler Telegraph Works. It has a 2 1/2" dial and an internal clockwork mechanism. One applies the rubber cone on the Tacho's shaft to the rotating crankshaft pulley end and presses the tacho start button. Then the pointer rotates whilst the internal clock ticks. After a few seconds the clock stops and the reading on the dial is RPM. All very quaint but very accurate. The second tacho is an all electric job where the shaft drives a small generator and the dial reads RPM instantly. Made in England by Smiths Industries. Both come with several cups and cones and wheels to contact the rotating parts. There are modern units also which flash a light onto the rotating part and one adjusts the speed of flash until the rotating part appears stationary. These can cause accidents when people put their hands into machinery rotating at high speed but which looks still and they sometimes lead one to believe the speed is double or half the actual. All cost quite a few bucks and are best borrowed!
Joe, I have two TACHOMETERS one is very old made by Hasler Telegraph Works. It has a 2 1/2" dial and an internal clockwork mechanism. One applies the rubber cone on the Tacho's shaft to the rotating crankshaft pulley end and presses the tacho start button. Then the pointer rotates whilst the internal clock ticks. After a few seconds the clock stops and the reading on the dial is RPM. All very quaint but very accurate. The second tacho is an all electric job where the shaft drives a small generator and the dial reads RPM instantly. Made in England by Smiths Industries. Both come with several cups and cones and wheels to contact the rotating parts. There are modern units also which flash a light onto the rotating part and one adjusts the speed of flash until the rotating part appears stationary. These can cause accidents when people put their hands into machinery rotating at high speed but which looks still and they sometimes lead one to believe the speed is double or half the actual. All cost quite a few bucks and are best borrowed!
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