Annoying vibration.

[Mick and Maggie]

Our boat has a most annoying vibration just at at tickover speed. I have checked the engine mountings and all are in good condition. The vibration seems to have a drum effect on the engine bay sides. Even a small increase in engine speed and the vibration goes away. If I go down into the engine compartment I can deaden the vibration created by putting a small amount of side pressure on the engine. I know that I could just up the engine speed by a few rpm to cure the problem. But! Is it usual on a diesel engine ion a narrow-boat to have something like a rubber mounted engine stay to the top of the engine to cut down on the side to side movement?

 

Mick

[WotEver]

Sounds like your tickover speed is just at the resonant frequency of something - raising it or lowering it slightly ahould make it go away.

 

Tony

[Dovetail]

I to have similar problem with the engine on low revs and slow speed runs smooth up the revs to what I consider a good cruising speed vibrates all over the place up the revs again now going to fast and requires lots of concentration and no day dreaming but no vibration and smooth engine.

[Redeye]

I to have similar problem with the engine on low revs and slow speed runs smooth up the revs to what I consider a good cruising speed vibrates all over the place up the revs again now going to fast and requires lots of concentration and no day dreaming but no vibration and smooth engine.

 

On my last boat the engine developed a habit of hammering like mad at low speeds when in gear. At the time the only answer was to increase the idling speed which cured the problem. I subsequently changed the drive plate (plate that connects the flywheel to the gearbox) and used a decent quality centraflex coupling. This instantly solved the problem.

 

Might be worth checking.

 

Cheers

 

redeye

[Bobbybass]

I get this problem especially after I have repacked or tightened the stern packing.

I have a new prop shaft and it is all dead in line.

It gradually goes away as the stern packing loosens..but when I start to get small leaks and tighten..it starts again.

 

Bob

[Tony Brooks]

I get this problem especially after I have repacked or tightened the stern packing.

I have a new prop shaft and it is all dead in line.

It gradually goes away as the stern packing loosens..but when I start to get small leaks and tighten..it starts again.

 

Bob

 

 

That sounds like the flexible coupling (if there is one and the engine is flexibly mounted) is incapable of allowing sufficient radial misalignment as the engine moves on its mounts. Hence my preference for the Aquadrive type or LONG Centaflex.

 

If the engine is solidly mounted I would suspect a bent shaft and I know new shafting can be supplied bent.

[journeyperson]

My engine developed an annoying vibration which first appeared just as I exited the Anderton Lift onto the Weaver. I couldn't increase or decrease revs without going through this rough rev range. At first I thought it must be something that just hadn't manifested itself on canals but eventually, after finding it was still there when I was back on the canals, I traced it to a loose engine mounting which just needed tightening to solve the problem.

[bottle]

Perhaps Tony (Brooks) could confirm or otherwise.

 

If an engine mounting is found to be loose, the bottom nut is tightened up, not the top nut down.

[journeyperson]

<!--quoteo(post=575530:date=Aug 23 2010, 06:29 PM:name=bottle)--><div class='quotetop'>QUOTE (bottle @ Aug 23 2010, 06:29 PM) <a href="index.php?act=findpost&pid=575530"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->Perhaps Tony (Brooks) could confirm or otherwise.

 

If an engine mounting is found to be loose, the bottom nut is tightened up, not the top nut down.<!--QuoteEnd--></div><!--QuoteEEnd-->

 

I'll have to check next time I'm at the boat but I'm fairly sure I tightened the right one.

Edited August 24, 2010 by journeyperson

[Tony Brooks]

Perhaps Tony (Brooks) could confirm or otherwise.

 

If an engine mounting is found to be loose, the bottom nut is tightened up, not the top nut down.

 

 

What you should do is to realign the engine to the shaft, but few do.

 

Given than many mounts have self locking nuts on top and plain nuts underneath then your statement is probably true, but if both are ordinary nuts it could be either have come loose/

 

Often, however its the small screws holding the mount to the bed that come loose and cause vibrations.