Vibration at idle rpm

[cmedsailor]

A mechanic has changed the engine mounts of my engine and has balanced (is it called like this?, or is it alignment?) the engine. Now at any rpm from 1000 to 3500 the engine is really "sweet" and quiet and does not vibrate at all. However at idle rpm (800) there is relatively a lot of vibration. Is it a matter of covering a few working hours and balancing again?
Thanks

 

[boggybrn]

How many cylinders has the engine got?

With a single cyclinder I doubt that there is much you can do to reduce vibration at very low RPM. My 1GM10 seems to jump all over the place at idle, but is relatively smooth with a few more rpm.

 

[cmedsailor]

3-cylinder. It's a Volvo Penta MD2030D.

 

[tri39]

I suspect there's nothing wrong. Slightly increase the idle speed if nec. I had to do it on a two cylinder Yanmar when I fitted a kiwi prop.

 

[cliffordpope]

I think flexible engine mounts have to be a compromise design to give optimum damping at chosen speeds. If you change the mounts the resonant frequency will probably be altered.

 

[Deleted member 36384]

I remember the Sigma 33 Engines (Volvo) "jumped" around a lot at low rpm and then was smooth at anything above idle.

Go round all the mounts and check that the bed mounting nuts and engine to mount nuts are tight.

My Perkins 4236 had an engine to mount nut loose; it jumped about at low rpm, was OKish at cruising rpms and then sheared off at the gear box flange .

The root cause was misalignment due to the loose nut - the point is my engine jumped about at idle and looked smooth at cruising rpm. The engine mounts were old then and I assumed that the vibration at higher rpm was just old mounts.

My advice is just check the nuts - especially as you have new mounts.

As a by the way I installed new mounts all round, original Perkins, and an Aquadrive unit - what a difference, so smooth.

 

[jason -and the arguenauts]

3-cylinder. It's a Volvo Penta MD2030D.

One thing that is vital and sometimes overlooked is to get the engine sat equally on all four mounts - its very easy to get three mounts bearing 95% of the load.

Undo the locknut on each mount, put a crowbar under the engine and lift first the fron t and then the back to ensure that it lifts off each mount simultaneously.

The other issue is that people have been know to replace just three of the four mounts cos the remaining one looked OK. Doesnt work - dont ask me how I know. Admittedly that was on a 2003 and havent yet done it on the current 2030.

A third issue is idle speed - is it below spec.

Alignment will only affect vibration when idling in gear. When idling out of gear it is irrelevant if you think about it.

My 2030 doesnt vibrate significantly at idle when warm.

 

[Bilgediver]

3-cylinder. It's a Volvo Penta MD2030D.

This is usually a smooth running engine.....Is it firing on all 3 cylinders.

 

[Heckler]

A mechanic has changed the engine mounts of my engine and has balanced (is it called like this?, or is it alignment?) the engine. Now at any rpm from 1000 to 3500 the engine is really "sweet" and quiet and does not vibrate at all. However at idle rpm (800) there is relatively a lot of vibration. Is it a matter of covering a few working hours and balancing again?
Thanks

my 2030 in my old boat used to move a bit on tick over but was ok in gear. My recent research has shown how to find proper engine mounts. VP uses Metalastic Cushyfloats, if i remember rightly they were smaller versions of the ones on my current MD22, with something that looks like a cowbell shielding the rubber. Check your old ones if you can and see what is stamped on them, particularly on what is stamped on the top of the base plate. see here for the parts http://www.marinepartseurope.com/en/volvo-penta-explodedview-7746410-21-2411B.aspx
they look as if they are different front and back.
Also

 

[Amulet]

One of my mounts has just failed. I am advised to replace symmetrically - both front in my case.

If my Farymann's vibration can be reduced to the point where it doesn't loosen the keelbolts I'll be satisfied.

 

[tri39]

If you're going to lift the engine I would replace all four.
I did after one failed and the Yanmar ran quieter and smoother, it even seemed to deliver more power!!

 

[macnorton]

3-cylinder. It's a Volvo Penta MD2030D.

Quite normal for this engine, if it bothers you fit a motorcycle steering damper to the head and a solid mount, it wont stop it but it will reduce it a bit..