Engine Vibrating Violently when Shifting to Neutral

[Heikki]

Now, after two more days and 80 more miles, I know a bit more about the problem:

- it does not appear when the engine is cold. It does not matter how I shift, fast or slow to neutral or to gear. No vibration or shaking, no matter what the revs are
- being misled by the previous observation, I did not check the damper plate, but took the almost 80 miles through eight locks and Russian waters to Baltic Sea - and the problem sure came back when the engine was driven hot
- the ending works perfectly and runs evenly when in use, but it sure shakes like crazy when I shift to neutral
- sometimes the vibration goes off after few seconds by itself, sometimes shifting back and forth helps, sometimes nothing helps and it just stays on until I stop the engine or put more revs on the engine
- if I have managed to get the vibration off engine still running, it will shake a few time when the I put a gear on, but it stops shaking when the revs increase
- if the engine is turned off and turned on again after a few minutes, it idles just nicely

The verdict? This sure beats me.

I really appreciate the help from all of you - without knowing all I have learned from you I would still sit in the same port I was a few days ago. After all, we have made some progress and my wife and kids are happy. Tomorrow, I have just 25 miles to a dock of authorized Volvo Penta service center, so I hope that is where my problems (and money) will disappear…

[sailingaway221]

Engine alignment should be within about 1 / 15000 so you are not going to eyeball that. The engine mounts could just be getting old and need replacing, but as the rubber compresses it changes the alignment. Get someone to measure your alignment.... if it is off... go replace all the engine mounts and have someone align it again.

I am pretty suspicious of blaming something in the engine.... about the only things that could change usually would be hitting something or tangling the prop.... a loose blade maybe, the engine mounts and then the alignment... Id start there first and work up the list before removing anything off the engine... Just a little change in alignment can create a lot of vibration... did you foul the prop lately?

[Alberto]

I would check the idle-speed adjuster. When cold your engine runs faster until it warms up (which could take several minutes), same when in gear. It seems to me that at idle your engine is running at very low RPM.

[sailingaway221]

Air lock in the fuel system.... maybe some water?

[shakey doug]

G'day,
Do you have a PTO fitted ?

[DeepFrz]

I second what Alberto says about the idle adjustment. I suspect it has something to do with the governor/hp fuel pump.

[boatman61]

Originally Posted by pillum

I'm with Boatman on this, I'd be looking at engine imbalanced operation as the load comes off. Could be worthwhile to have it tuned even if just to eliminate it as an issue. Remember the old engineering adage about process of elimination.

“Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”

Cheers Pillum... I was starting to feel really stupid going for the most obvious and simple fault...
At least now I have company....

[Boracay]

As it only happens when you shift gear have you checked the gear shift mechanism?

I'd suggest going over it feeling for free play. There should be virtually none.

Particularly have a look at where the cable connects to the gearbox. The mounting hardware should be quite solid and the cable should throw the gear shift lever on the gearbox over its full throw.

If time is not pressing it may be worth disconnecting the cable from the lever and moving the the lever back and forward to see what the full throw is. Then reconnect and check that the cable is moving the lever over its full distance.

Gently moving the lever in and out and listening for any sound may also yield clues.

You'll need to get someone in the cockpit to help you with this so do be careful not to get fingers or anything else caught up.

While doing this it may be possible to feel (by moving the inner part of the disconnected cable back and forward) if there is any free play in the cockpit control unit.

Control cables do need replacement from time to time.

My best guess is that the hydraulic or cone (or whatever) clutch in your gearbox has worn unevenly and is not disengaging smoothly (They should be self adjusting). If this is the case and if you can adjust the linkage for maximum throw there is just a chance it may correct itself...

[cwyckham]

Originally Posted by sailingaway221

Engine alignment should be within about 1 / 15000 so you are not going to eyeball that. The engine mounts could just be getting old and need replacing, but as the rubber compresses it changes the alignment. Get someone to measure your alignment.... if it is off... go replace all the engine mounts and have someone align it again.

I am pretty suspicious of blaming something in the engine.... about the only things that could change usually would be hitting something or tangling the prop.... a loose blade maybe, the engine mounts and then the alignment... Id start there first and work up the list before removing anything off the engine... Just a little change in alignment can create a lot of vibration... did you foul the prop lately?

Alignment can't be eyeballed, but it's pretty easy to check. Undo the coupling and slip some feeler gauges in on each side of the coupling. With the coupling hard up against the transmission (zero gap on one side), the max gap you should get is one thousandth of the diameter of the coupling. So for a 10 cm coupling, you should get 0.1 mm gap at the most. Very easy to check with feeler gauges.

[DeepFrz]

Heikki, was there ever a resolution to this problem?