The tach on my Yamaha 2QM20 started dropping back intermittently about 100
RPM. A couple days later, I noticed that this was accompanied by the
briefest flash of the "Charging" light on my minimalist engine panel. The
engine is absolutely smooth so I'm certain there is no actual change in RPM
or cylinder misfire.

Although infrequent, these events have increased slightly and happen most
often shortly after startup. In the past couple of days, there have been a
few large drops of about 500 RPM, equally quick, with brighter flashes of
the charging light. These are about the quickest flicks that the needle of
the instrument can make. After startup last night on the way to the
fireworks, the tach did it several times in succession with the needle going
wildly back and forth and the charging light much brighter, flickering in
sync with the needle movement.

I've checked all wiring connections and tried wiggling the wiring harnesses
to see if I could create the problem. No result. I adjusted the alternator
belt after the first few occurances. Batteries 14 V and engine starts
briskly.

The tach on this engine is the kind that has a sensor that reads the
starting ring gear teeth going by.
Is it time to pull the alternator and have it checked out or are there other
places to look before I disable my boat for the several days that will take?

The alternator is a 35 amp Hitachi, pretty long in the tooth. I have a 55
Amp Hitachi with the wrong kind of internal regulator that I've been
thinking of having modified for an external regulator, perhaps one of the
Balmar three stage units. The engine has plenty of power for the boat so
the extra charging load shouldn'g be an issue with batteries that don't get
drawn down much. Maybe this would be a good time to get that done.

--
Roger Long

Roger Long wrote:
The tach on my Yamaha 2QM20 started dropping back intermittently
about 100 RPM. A couple days later, I noticed that this was
accompanied by the briefest flash of the "Charging" light on my
minimalist engine panel. The engine is absolutely smooth so I'm
certain there is no actual change in RPM or cylinder misfire.

Although infrequent, these events have increased slightly and happen
most often shortly after startup. In the past couple of days, there
have been a few large drops of about 500 RPM, equally quick, with
brighter flashes of the charging light. These are about the quickest
flicks that the needle of the instrument can make. After startup
last night on the way to the fireworks, the tach did it several times
in succession with the needle going wildly back and forth and the
charging light much brighter, flickering in sync with the needle
movement.

I've checked all wiring connections and tried wiggling the wiring
harnesses to see if I could create the problem. No result. I
adjusted the alternator belt after the first few occurances.
Batteries 14 V and engine starts briskly.

The tach on this engine is the kind that has a sensor that reads the
starting ring gear teeth going by.
Is it time to pull the alternator and have it checked out or are
there other places to look before I disable my boat for the several
days that will take?

The alternator is a 35 amp Hitachi, pretty long in the tooth. I have
a 55 Amp Hitachi with the wrong kind of internal regulator that I've
been thinking of having modified for an external regulator, perhaps
one of the Balmar three stage units. The engine has plenty of power
for the boat so the extra charging load shouldn'g be an issue with
batteries that don't get drawn down much. Maybe this would be a good
time to get that done.

The drop in revs you mention would seem to be indicative of the alternator
"kicking in", causing the load on the engine to increase, hence the drop in
revs. If your batteries are "full", this would happen intermittently as the
battery voltage fell.

Probably nothing to worry about, unless someone more familiar with this
electrical set-up contradicts my prognosis!

Dennis.

There is no drop in actual RPM. Any drop that brief and sudden would be
detectable in the sound of the engine, especially on soft mounts with all
that rotating inertia. I've listened carefully when this is happening and
there is *absolutely* nothing detectable in the engine sound or feeling
through my feet.

This is also a change in behavior. It didn't do it the last two seasons or
early this year.

--
Roger Long

This sort of problem can simply be that the slip ring brushes are wearing
out.

It is usually an easy matter to replace them, in many cases you do not have
to remove the alternator.

Could even be that they just need cleaning.

Alec


"Roger Long" wrote in message
...
The tach on my Yamaha 2QM20 started dropping back intermittently about 100
RPM. A couple days later, I noticed that this was accompanied by the
briefest flash of the "Charging" light on my minimalist engine panel. The
engine is absolutely smooth so I'm certain there is no actual change in
RPM or cylinder misfire.

Although infrequent, these events have increased slightly and happen most
often shortly after startup. In the past couple of days, there have been
a few large drops of about 500 RPM, equally quick, with brighter flashes
of the charging light. These are about the quickest flicks that the needle
of the instrument can make. After startup last night on the way to the
fireworks, the tach did it several times in succession with the needle
going wildly back and forth and the charging light much brighter,
flickering in sync with the needle movement.

I've checked all wiring connections and tried wiggling the wiring
harnesses to see if I could create the problem. No result. I adjusted
the alternator belt after the first few occurances. Batteries 14 V and
engine starts briskly.

The tach on this engine is the kind that has a sensor that reads the
starting ring gear teeth going by.
Is it time to pull the alternator and have it checked out or are there
other places to look before I disable my boat for the several days that
will take?

The alternator is a 35 amp Hitachi, pretty long in the tooth. I have a 55
Amp Hitachi with the wrong kind of internal regulator that I've been
thinking of having modified for an external regulator, perhaps one of the
Balmar three stage units. The engine has plenty of power for the boat so
the extra charging load shouldn'g be an issue with batteries that don't
get drawn down much. Maybe this would be a good time to get that done.

--
Roger Long

* Roger Long wrote, On 7/5/2007 9:31 AM:
There is no drop in actual RPM. Any drop that brief and sudden would be
detectable in the sound of the engine, especially on soft mounts with
all that rotating inertia. I've listened carefully when this is
happening and there is *absolutely* nothing detectable in the engine
sound or feeling through my feet.

This is also a change in behavior. It didn't do it the last two seasons
or early this year.

Are you sure then that your tach is reading the flywheel? My Yanmar
does that and the tach is pretty steady, even when there are serious
charging "events" going on. Yesterday my belt was getting cooked so
it slipped badly - the Amps were all over the place but the rpm was
still rock steady. Its possible someone replaced the tack with an
alternator sensing type, which of course can lead to all sorts of
curiosities.

"Roger Long" wrote in message
...
The tach on my Yamaha 2QM20 started dropping back intermittently about 100
RPM. A couple days later, I noticed that this was accompanied by the
briefest flash of the "Charging" light on my minimalist engine panel. The
engine is absolutely smooth so I'm certain there is no actual change in
RPM or cylinder misfire.

Although infrequent, these events have increased slightly and happen most
often shortly after startup. In the past couple of days, there have been
a few large drops of about 500 RPM, equally quick, with brighter flashes
of the charging light. These are about the quickest flicks that the needle
of the instrument can make. After startup last night on the way to the
fireworks, the tach did it several times in succession with the needle
going wildly back and forth and the charging light much brighter,
flickering in sync with the needle movement.

I've checked all wiring connections and tried wiggling the wiring
harnesses to see if I could create the problem. No result. I adjusted
the alternator belt after the first few occurances. Batteries 14 V and
engine starts briskly.

The tach on this engine is the kind that has a sensor that reads the
starting ring gear teeth going by.
Is it time to pull the alternator and have it checked out or are there
other places to look before I disable my boat for the several days that
will take?

The alternator is a 35 amp Hitachi, pretty long in the tooth. I have a 55
Amp Hitachi with the wrong kind of internal regulator that I've been
thinking of having modified for an external regulator, perhaps one of the
Balmar three stage units. The engine has plenty of power for the boat so
the extra charging load shouldn'g be an issue with batteries that don't
get drawn down much. Maybe this would be a good time to get that done.

--
Roger Long

I would suggest connecting a good quality digital voltmeter to your
alternator output and ground. See if the voltage drops when the tack rpm
drops. If that is the case I would suspect the regulator rather than the
alternator but I guess it could be either one. You didn't say what type
alternator you have. Is this the original Hitachi internal regulator?
By the way, I have an 80 amp Yanmar/Hitachi alternator rebuilt and modified
to use a simple external regulator. Never used since rebuild. The
regulator allows you to increase the alternator output voltage to compensate
for isolator diodes, long wire runs and other voltage robbing factors.
Yours for $200 plus shipping from 98281.

Gordon Wedman wrote:


I would suggest connecting a good quality digital voltmeter to your
alternator output and ground. See if the voltage drops when the tack rpm
drops. If that is the case I would suspect the regulator rather than the
alternator but I guess it could be either one. You didn't say what type
alternator you have. Is this the original Hitachi internal regulator?
By the way, I have an 80 amp Yanmar/Hitachi alternator rebuilt and modified
to use a simple external regulator. Never used since rebuild. The
regulator allows you to increase the alternator output voltage to compensate
for isolator diodes, long wire runs and other voltage robbing factors.
Yours for $200 plus shipping from 98281.



Sampling rate problem.

Try a good quality ANALOG meter...

"Roger Long" wrote in
:

The alternator is a 35 amp Hitachi, pretty long in the tooth. I have
a 55 Amp Hitachi with the wrong kind of internal regulator that I've
been thinking of having modified for an external regulator, perhaps
one of the Balmar three stage units. The engine has plenty of power
for the boat so the extra charging load shouldn'g be an issue with
batteries that don't get drawn down much. Maybe this would be a good
time to get that done.

--


The internal regulators on most alternators are also the "hot" brush to
the slip rings controlling the field. Not sure about Hitachi, but many
alternators have this regulator held in with a couple of screws for easy
replacement and you get to see how much brush is left by pulling it out.

As you say it's really old, that's my guess if you're absolutely sure the
cables to it are clean, the connections tight and all the wires at those
connectors are not broken off by all the VIBRATION of the beast.
Sometimes the smaller wires switching the regulator on and off get broken
inside their insulation from the constant flexing.....and some BOATER
getting too damned neat with his tywraps...grrr...

It isn't rocket science to pull the alternator out and take it to an auto
electric shop for a refresh. Just don't let the yachties on the dock
know where you took it. If they ask, tell them you took it to the most
expensive "marine electric" shop in town. They'll all feel better...(c;

Larry
--
While in Mexico, I didn't have to press 1 for Spanish.
While in Iran, I never had to press 1 for Farsi, either!
It just isn't fair.

"Larry" wrote in message
...
--
While in Mexico, I didn't have to press 1 for Spanish.
While in Iran, I never had to press 1 for Farsi, either!
It just isn't fair.


Perhaps not fair, but we're more hospitable. ;-)

"KLC Lewis" wrote in news:GY6dnVCUg-
:


"Larry" wrote in message
...
--
While in Mexico, I didn't have to press 1 for Spanish.
While in Iran, I never had to press 1 for Farsi, either!
It just isn't fair.


Perhaps not fair, but we're more hospitable. ;-)

Simply not true.....in either country.
Iranians don't hate Americans. Iranians hate our Israeli-run government.


Larry
--
While in Mexico, I didn't have to press 1 for Spanish.
While in Iran, I didn't have to press 1 for Farsi, either.
It just isn't fair.