Vibration at low revs

[Rigger]

Whats the likely cause of increased vibration at low revs,coupled with occasional not engaging gear initially but then engaging with a clunk. Once revs have built up she runs as sweet as ever but tends to vibrate at lower revs espeicially when pushing against a load (stationary boat,tidal stream etc) Engine is Yanmar 3GM30 with 3 bladed prop. Cutlass bearing seemed OK when inspected earlier in year,and no obvious problem with flexible coupling or engine mounts. Any ideas much appreciated.

 

[ShipsWoofy]

yanmar mounts are notoriously soft.

But, my experience of a 3gm30 is that it is a wonderfully balanced and smooth engine. Could it be that you have pranged the prop and put it out of balance. Most prop people will be able to quickly repair a bent prop.

Other options are the engine has come out of alignment, have you checked it? Do you use a flexible coupling.

I can not work out if you are getting high vibration in neutral or only in gear.

Have you felt the mounts ( the solid main engine mounts glassed to the hull), are they still solid. Try holding them during the excessive vibration check they are not moving.

Have you tried engaging gear manually, i.e. take the cable off the gear lever and push it into gear, on the yanmar box this should be finger light to do.

I am trying to avoid bent prop shaft, but ...

Just thoughts!

 

[oldsaltoz]

Sounds like engine mounts causing the vibration, have you looked at them when the engine is under load and vibrating?

The gear selection may be another problem altogether, check the adjustment.

Andsavagoodweekend......

 

[Pye_End]

Have you checked the gear cable to make sure it is still true, and engaging the gears correctly? If it has become out then may go into neutral ok, but can not wuite make forward if incorrect.

 

[Rigger]

Vibration only happens when engaging forward gear , smooth in neutral and when going astern.

 

[marcusgillies]

Engine out of line?
is it an angled box?