Governor precision; how good should it be in a small engine

[daveNZ]

My Lombardini has a terrible shake at rpm below 950. (Fine at 700 or above 950). Max rpm for the gear shift is 1000 (twindisc transmission). If I set the idle to 950 or even 1000, when I shift in to gear the revs drop about 150, so just into the shaking range. So either I constantly reduce throttle, change gear, increase throttle to avoid the shake, (tedious when manoeuvring)or I set the idle higher than the 1000rpm (over 1000 sounds/feels too high, and of course is not a smooth gear shift).

Question: should the governor keep the rpm more constant? It drops approx.150rpm
I'm sure some engines will be better than others.
Thanks.



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[aluijten]

I've had experience with three mechanical controlled Volvos. None of them dropped RPM noticably when put in gear (no throttle). So I'm inclided to say 150 RPM at Idle speed is quite high.

[shakey doug]

Class 1 variable speed governors as used on marine propulsion engines 8% to 10%.


Class 2 governors as used on Generator sets 3%, so as to keep frequency in check.

[daveNZ]

Thanks for those, great to have some specs. to go by also. I'll need to check the rpm with a tachometer (mine was stolen!) to be sure of the true decrease if rpm, but it does sound like my governor is a bit sloppy. It looks like as much as 200rpm decrease at the engine panel, and it varies a little depending on ?? maybe previous gear shifting or throttle changes, but I said 150 so as not exaggerate.

Next question: is a governor something I should have a go at? or are they tricky or not serviceable?




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[shakey doug]

I am not familiar with what type of fuel pump or governor your motor has, your problem could be one of many issues from worn fly weight pivot pins to a weak balance spring. My advice would be to have a diesel pump shop run it up on a Hartridge machine. Before going to this trouble be sure the fuel delivery side of the pump including the timing & v/v clearances are within specs

[undercutter]

Originally Posted by shakey doug

I am not familiar with what type of fuel pump or governor your motor has, your problem could be one of many issues from worn fly weight pivot pins to a weak balance spring. My advice would be to have a diesel pump shop run it up on a Hartridge machine. Before going to this trouble be sure the fuel delivery side of the pump including the timing & v/v clearances are within specs

Wonder what model of engine? Our Kohler Genset has a Lombardini engine which of course is now owned by Kohler. These engines have cam driven pump/injectors (1 for each cylinder) which are very sensitive to timing adjustment as well as potential damage from debris or water contamination. The timing of each injector needs to be set separately. Ask me how I know. Basic mechanical governor which is probably not your problem. There is no externally mounted Injector pump. Yours could be different but assume they would use the same technology on all their engines????

Do you notice any changes in the exhaust? White or black smoke? Any changes in the sound of the engine? Injector knock? Does the engine seem to have the same top end speed and power? The harmonics of the engine could be a clue here as well.

1000 RPM seems high for a marine gearbox. Our engine idle speed is 600rpm.

[a64pilot]

OK,
I'm going to be argumentative as I don't think governors work like is being described.
I think the governor comes into play to check excessive RPM, it doesn't normally add fuel to maintain RPM or trucks wouldn't have to press the fuel pedal to pull a hill or farm tractors add fuel via the lever when they dropped a plow, but they do.

A generator is different in that the governor is set to maintain an RPM, but the fuel lever is advanced past this set point, allowing the governor to control RPM.

When I put my transmission in gear at idle there is no discernible RPM drop as there is essentially no load, but let my big alternator kick in, and there is an RPM drop.

If I had my engine idling at 1000 RPM, then I bet there would be a drop in RPM as now I would have significant load.
I think your going to have to live with the shake and advance throttle to get out of it, as turning your idle RPM up is going to be bad on the transmission.

[stone beach]

a64pilot
a governor (tries to) maintain a set engine speed, 3 factors at play, load, engine speed & fuel injected, this will explain the relationship.

https://www.youtube.com/watch?v=kfQPJ3WRfWo

most older small boat engines have a simple mechanical governor, not hydraulic as in the film, but the working is the same without the hydraulic servo part.
modern ones typically use electronics, working is completely different but function is identical.
with a mechanical governor there will always be an offset between the set speed and the maintained speed, however in the op case the offset (150 rpm) is larger than i would expect.
In most cases it is low idle speed that is used for gear change, don't know why you are not doing this?
i am not familiar with your engine, but i will assume it is a mechanical governor to try & explain further.....if the engine is stalling when you try to engage gear at low idle then the governor isn't doing what it should.
first thing is to find the "bumper spring" adjustment. idle speed setting is typically a combination of this and the control arm lower limit screw.
let me know if you need more explanation

[stone beach]

posted a response twice now....not sure why it is not there????
must be a post governor !!!

[four winds]

A64pilot, I think we have the same 3gm30f engines.

If you take a look at the governor and IP sections in the service manual, and read the explanation of operation of each you will find it interesting. Note the discussion of the governor's connection to the IP via the fuel rack.

Coming from an old hot rodder/gearhead background I'm still trying to wrap my head around this in prep for the day I have to work on these areas like everything else on the boat.

And consider this, motoring at say 1800rpm with the current and then turning around into the current. Sure the SOG drops some but the rpm stays the same, right? How does it do that without adding more fuel?

[daveNZ]

Originally Posted by undercutter

Wonder what model of engine? Our Kohler Genset has a Lombardini engine which of course is now owned by Kohler. These engines have cam driven pump/injectors (1 for each cylinder) which are very sensitive to timing adjustment as well as potential damage from debris or water contamination. The timing of each injector needs to be set separately. Ask me how I know. Basic mechanical governor which is probably not your problem. There is no externally mounted Injector pump. Yours could be different but assume they would use the same technology on all their engines????

Do you notice any changes in the exhaust? White or black smoke? Any changes in the sound of the engine? Injector knock? Does the engine seem to have the same top end speed and power? The harmonics of the engine could be a clue here as well.

1000 RPM seems high for a marine gearbox. Our engine idle speed is 600rpm.

Thanks for this. Engine is a 1404M 4 cyl, 1400 cc. 40 HP.
I agree that the governor probably only limits the max rpm. and the throttle controls fuel flow.
Yes I do have those unit injectors. Bosch cam driven pump and injector per cylinder. As the engine idles well at 650-700 but is rough at 800-950 and good at >= 1000 I suspect there is a fuel delivery/balance issue. I hear it is common with these engines! You can isolate one injector with a spanner to hold the pump off the cam. No one cylinder seems to be worse than others. The engine even ran better on 3 cylinders sometimes!
Can you explain the 2 (?) parts to tuning these injectors, or point me to a description. The service manual is a bit brief. The setup for fuel flow adjustment is time consuming so I might have to put up with it.
Cheers.

[a64pilot]

Originally Posted by four winds

A64pilot, I think we have the same 3gm30f engines.

If you take a look at the governor and IP sections in the service manual, and read the explanation of operation of each you will find it interesting. Note the discussion of the governor's connection to the IP via the fuel rack.

Coming from an old hot rodder/gearhead background I'm still trying to wrap my head around this in prep for the day I have to work on these areas like everything else on the boat.

And consider this, motoring at say 1800rpm with the current and then turning around into the current. Sure the SOG drops some but the rpm stays the same, right? How does it do that without adding more fuel?

RPM stays close to the same due to prop slip, it is the reason of course why a speed boat doesn't have to change gears.
Try this, set an RPM before the boat starts moving and don't touch the throttle, boat speed will increase of course, but engine speed will change very little, it will climb some, but not much I don't think.
A generator's governor is set to maintain X RPM and the throttle is advanced well past that, so that when you load the generator down, RPM remains constant.
Now you could of course have an engine where the throttle was wide open all the time and you controlled RPM via a controllable governor, such an engine would maintain RPM regardless of load of course, but I have never seen one.


I have an old 4JHE engine, but in the old mechanical injection engine world I don't think it much matters, common rail of course could easily be different, throttle could easily be an LVDT on the throttle lever itself and be purely electronic. My CC boat with a Mercury Verado outboard had what they called DTS, or digital throttle and shift, just wires going to the throttle lever, nothing mechanical at all.


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[shakey doug]

Google governor droop.

[a64pilot]

I didn't watch the whole film, but simply said, I believe we have overspeed governors, not control governors.
An overspeed governor can be used as a control governor, just you have one set operating RPM and to change that requires a governor adjustment, generator for example, if it's running, it's running at one set RPM.

I could be wrong though, but my engine RPM changes with alternator load.


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[four winds]

Originally Posted by a64pilot

RPM stays close to the same due to prop slip, it is the reason of course why a speed boat doesn't have to change gears.
Try this, set an RPM before the boat starts moving and don't touch the throttle, boat speed will increase of course, but engine speed will change very little, it will climb some, but not much I don't think.
A generator's governor is set to maintain X RPM and the throttle is advanced well past that, so that when you load the generator down, RPM remains constant.
Now you could of course have an engine where the throttle was wide open all the time and you controlled RPM via a controllable governor, such an engine would maintain RPM regardless of load of course, but I have never seen one.


I have an old 4JHE engine, but in the old mechanical injection engine world I don't think it much matters, common rail of course could easily be different, throttle could easily be an LVDT on the throttle lever itself and be purely electronic. My CC boat with a Mercury Verado outboard had what they called DTS, or digital throttle and shift, just wires going to the throttle lever, nothing mechanical at all.


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Well I thought we had the same engines.

Nor is it the same as the OP's. But it does have three individual pumps in a housing. On my Yanmar the governor limits max RPM, of course, but it also controls a fuel rack that rotates the pumps in the housing and fuel to the injectors. (pressure? volume?)

Here's a page from the manual with a operation description and schematic diagram.