Vetus diesel shakes at idle

[Bill O]

Originally Posted by Ryban

The alternator is certainly not the original, but I also don't know when it was last replaced. I'll check to see if there is a tach head anywhere with an adjustment screw.

If the tach is off the relay stud on the back of the alternator, there most likely will not be an adjustment screw. Probably doesn't need to be that precise as long as you know you have a slight offset to adjust the idle and the top end to not over rev. the motor.

Again I'll ask, is the rough idle something new or is this a new to you engine and trying to fix it?

[deblen]

The tach runs off the W terminal of alternator.
Perhaps a replacement alternator uses a different diameter pulley?


Another possibility is poor valve adjustment or a leaky valve.


https://search.canbarchives.ca/downl...collection.pdf

[sveinung]

Make sure all 4 cylinders are firing. If you're missing one it'll run rougher and vibrate more. You can open the compression release per cylinder and see if one doesn't affect the operation, that's probably the bad egg.

[sailorladd]

If you have reset your idling adjustment to where she runs smoothly at 1000 rpms, you have solved the problem.....I am presuming at 850 rpms you had disengaged the gearbox....you might try that at under load, as the manufacturers may have intended, (idling the engine under load which is a common and recommended practice), and if she is still vibrating badly, adjust the revs to where she is not vibrating, that can be pretty detrimental to engine and mounts etc....(this information comes from a diesel engine manual)...

[Goodxcharly]

I would try some fuel additive, Stanadyne is what I use and run the engine for longer hours. Motor sailing trips of at least 6 hours a day at a working rpm.
I went through the same thing with my last boat. Catalina270 with a Perkins 20. I replaced the motor mounts with the next grade up in stiffness and it helped some but still had a shake. Then over time I noticed the shake was getting better and I contributed it to running the engine for longer periods of time ,3-12 hours a day for my longer trips up north.
So Fouled injectors ,carbon,we’re probably the culprit.
I should also mention too that the exhaust elbow was shot, scaled up on the inside with a 3/4” passage for the exhaust, can’t breath,which would be another factor for carbon build up.



Anyway, good luck!

[col50]

Is the exhaust smoking when the idle is rough?
That would mean one or more cylinders are not firing when the engine is cold.
How many running hours since the valves were adjusted?

[Rob H]

I am a retired diesel tech. Watched your videos. With that RPM it is hard to tell whether it is shaking or possibly (Hunting) pulsing. Is the engine cold when it does this? Does it stop when hot? In any case, it does not look severe at that RPM. Would like to see it a lower idle. Also in gear at idle. Many diesels sometimes hunt when close to idle throttle especially when cold if out of calibration. If it is hunting many injection pumps have a buffer screw to level out the idle. Actually just had to adjust one on a friends Volvo 4cyl. turbo model.



Rob H.

[Icarus]

Originally Posted by Ryban

To answer the above, those videos were taken without any load on the shaft. Before I go playing with anything else, I did manage to get a direct RPM measurement.

Update:
I decided to start with what was easy and check the RPM with several different "strobe light" RPM apps you can download that just flash your phone's flash LED at a specified rate. It will have to do until I get my hands on a tach gun.

Using these tools, I've found that my RPM gauge is reading 300-400 RPM high. For example, in the 1400RPM video above, the crankshaft seems to be turning at closer to 1050-1100RPM. At the 1100 RPM on the gauge, about 910 RPM was measured.

I guess the next question to address is why is the gauge reading high.

Get a proper laser RPM gun..

[Perna]

Rubber engine mounts can get stiffer as they get older which means that the resonant speeds, shaking that is, move up into the engine idle range or higher.

They are laid out so that the resonant speeds and shaking are below idle. That is why car engines shake when they are shut off.

So I'd add a vote to checking the condition the engine mounts and trying to make sure they are not harder than when new.

[col50]

Ryban, I don't mean to annoy you, but I will ask again; is the exhaust smoking when the idle is rough?
If so, there is a high probability that one or more of the injectors is not spraying properly.
There is very little fuel flow at low load and the injectors have more of a tendency to dribble.

[BBill]

My first guess is motor mount but check your exhaust to make sure its clear...strange but this happened on a cruisers Grampion 34 in Nassau. Volvo diesel started vibrating at idle but didn't show a problem at cruising speed. It gradually got worse and would die at idle with big vibrations. Nobody could find the problem until another cruiser (me) reached back and fully opened the gate valve on the exhaust at the transom. It had vibrated slowly closing. He voyaged all the way from Canada before this happened. Lesson learned and easy to check off the list.

[Ryban]

That's a good idea -- I'll check the exhaust.

Wanted to provide a quick update though. I learned that the instrument panel for the engine was actually a replacement from the original, and not designed for the exact model of engine. I was able to turn a screw on the back of the tachometer to match the measrurement I was getting off the engine, and now it idles smoothly at the correct indicated RPM. I'm not sure if the previous owner just never calibrated the tach when he installed the new panel, or if it somehow slowly drifted out of calibration.