I have an 8KW Westerbeke diesel generator (about 12 years old) which
has an odd vibration issue at times. This happens most often under
moderate to heavy load and lasts for 15 to 20 seconds at a time. The
vibration is so violent that the guages are impossible to read and it
shakes the entire boat. Vital signs like temperature and oil pressure
look normal, there is no exhaust smoke, and other than the vibration
episodes, it starts and runs very well. There is ample raw water flow
and the electrical specs for voltage and frequency check out OK.
I hate to replace it if there is a simple fix.

Anyone have an idea what the problem could be?

On Friday 03 September 2004 3:48 am in rec.boats.building Wayne.B wrote:

I have an 8KW Westerbeke diesel generator (about 12 years old) which
has an odd vibration issue at times. This happens most often under
moderate to heavy load and lasts for 15 to 20 seconds at a time. The
vibration is so violent that the guages are impossible to read and it
shakes the entire boat. Vital signs like temperature and oil pressure
look normal, there is no exhaust smoke, and other than the vibration
episodes, it starts and runs very well. There is ample raw water flow
and the electrical specs for voltage and frequency check out OK.
I hate to replace it if there is a simple fix.

Anyone have an idea what the problem could be?

This is typical of an intermittent overload.

I would suspect a faulty electric motor starting somewhere
pulling a very heavy starting current. Try disconnecting
fridges, aircons, bilge pumps, etc and see if the problem
goes away. Anything with an electric motor which starts
and stops automatically.
It is probably a good idea to check all of the fuses to
see if someone has "fixed" a problem by replacing a fuse
with a larger rating or even a piece of wire/nail.

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My real address is crn (at) netunix (dot) com
WARNING all messages containing attachments or html will be silently
deleted. Send only plain text.

Wayne,
My guess is that it is not electrical. I think your flex plate drive is
either loose or worn out. The alternator has bearings only on the outboard
end. The engine rear main bearing acts as the other armature bearing. This
mechanical connection is usually done through a flex plate which is bolted
to the engine flywheel and a splined hub drives the armature or rotor. To
check this, the alternator must be removed from the engine.
Steve

"Wayne.B" wrote in message
...
I have an 8KW Westerbeke diesel generator (about 12 years old) which
has an odd vibration issue at times. This happens most often under
moderate to heavy load and lasts for 15 to 20 seconds at a time. The
vibration is so violent that the guages are impossible to read and it
shakes the entire boat. Vital signs like temperature and oil pressure
look normal, there is no exhaust smoke, and other than the vibration
episodes, it starts and runs very well. There is ample raw water flow
and the electrical specs for voltage and frequency check out OK.
I hate to replace it if there is a simple fix.

Anyone have an idea what the problem could be?

On Sun, 5 Sep 2004 09:49:03 +0200, "Steve Lusardi"
wrote:
My guess is that it is not electrical. I think your flex plate drive is
either loose or worn out. The alternator has bearings only on the outboard
end. The engine rear main bearing acts as the other armature bearing. This
mechanical connection is usually done through a flex plate which is bolted
to the engine flywheel and a splined hub drives the armature or rotor. To
check this, the alternator must be removed from the engine.

===============================================

Thanks, your assessment of not being electrical jibes with my
observations. What would explain the intermittent nature of the
vibration given a more or less constant electrical load? Is the flex
plate a coupling with a rubber hub?

I would think that it is just simply a resonance factor.
Ever heard one of those old Cummins 160's?
Let them idle & they are as quiet & smooth as a church mouse. Increase the
revs very slowly & you'll find that at 1400, 1600, 1800 & 2000 revs they
just about shake out of the chasis. (truck)
Most diesels do it to a certain extent. Next time it does it, try adjusting
your governer up or down a few revs & see how it goes.
My guess is that under that certain load, it hits the "rattle" speed.
Maybe if you can tweak it a weeny bit, it might not come down to that rattle
speed under load?
BruceM


"Wayne.B" wrote in message
...
On Sun, 5 Sep 2004 09:49:03 +0200, "Steve Lusardi"
wrote:
My guess is that it is not electrical. I think your flex plate drive is
either loose or worn out. The alternator has bearings only on the
outboard
end. The engine rear main bearing acts as the other armature bearing.
This
mechanical connection is usually done through a flex plate which is
bolted
to the engine flywheel and a splined hub drives the armature or rotor. To
check this, the alternator must be removed from the engine.

===============================================

Thanks, your assessment of not being electrical jibes with my
observations. What would explain the intermittent nature of the
vibration given a more or less constant electrical load? Is the flex
plate a coupling with a rubber hub?

The problem Is VERY LIKELY to be a combination of a worn drive plate
(between flywheel and generator drive shaft) and the resonance factor
mentioned here.


"BruceM" wrote in message
...
I would think that it is just simply a resonance factor.
Ever heard one of those old Cummins 160's?
Let them idle & they are as quiet & smooth as a church mouse. Increase the
revs very slowly & you'll find that at 1400, 1600, 1800 & 2000 revs they
just about shake out of the chasis. (truck)
Most diesels do it to a certain extent. Next time it does it, try
adjusting
your governer up or down a few revs & see how it goes.
My guess is that under that certain load, it hits the "rattle" speed.
Maybe if you can tweak it a weeny bit, it might not come down to that
rattle
speed under load?
BruceM


"Wayne.B" wrote in message
...
On Sun, 5 Sep 2004 09:49:03 +0200, "Steve Lusardi"
wrote:
My guess is that it is not electrical. I think your flex plate drive is
either loose or worn out. The alternator has bearings only on the
outboard
end. The engine rear main bearing acts as the other armature bearing.
This
mechanical connection is usually done through a flex plate which is
bolted
to the engine flywheel and a splined hub drives the armature or rotor.
To
check this, the alternator must be removed from the engine.

===============================================

Thanks, your assessment of not being electrical jibes with my
observations. What would explain the intermittent nature of the
vibration given a more or less constant electrical load? Is the flex
plate a coupling with a rubber hub?

On Mon, 6 Sep 2004 21:44:37 +0930, "BruceM"
wrote:
I would think that it is just simply a resonance factor.
Ever heard one of those old Cummins 160's?
Let them idle & they are as quiet & smooth as a church mouse. Increase the
revs very slowly & you'll find that at 1400, 1600, 1800 & 2000 revs they
just about shake out of the chasis. (truck)

=========================================

The vibration in this case is way beyond anything normal, and the
generator is designed to run at a steady 1800 RPM regardless of load.

On Mon, 6 Sep 2004 13:56:38 +0000 (UTC), "James"
wrote:
The problem Is VERY LIKELY to be a combination of a worn drive plate
(between flywheel and generator drive shaft) and the resonance factor
mentioned here.

============================

Thanks. Any idea how much work is involved in replacing the drive
plate?

Wayne,
There are many different types.Some are rubber some are spring dampened,
like clutch plates. Others are just a splined hub with spring steel wings
that bolt at a large bolt circle. It is easy to disconnect the generator
from the engine, if it no longer is in the boat. The difficulty in the boat
is limited to the ease of access. On a shop floor, 15 minutes has the engine
and generator separated.
Steve

"Wayne.B" wrote in message
...
On Sun, 5 Sep 2004 09:49:03 +0200, "Steve Lusardi"
wrote:
My guess is that it is not electrical. I think your flex plate drive is
either loose or worn out. The alternator has bearings only on the outboard
end. The engine rear main bearing acts as the other armature bearing. This
mechanical connection is usually done through a flex plate which is bolted
to the engine flywheel and a splined hub drives the armature or rotor. To
check this, the alternator must be removed from the engine.

===============================================

Thanks, your assessment of not being electrical jibes with my
observations. What would explain the intermittent nature of the
vibration given a more or less constant electrical load? Is the flex
plate a coupling with a rubber hub?

On Mon, 6 Sep 2004 21:00:43 +0200, "Steve Lusardi"
wrote:

On a shop floor, 15 minutes has the engine
and generator separated.

Thanks, mine is in a fairly accessible location.