[C320-list] Tach reads only 3000 rpm at full throttle

[Jim and Stacey]

I have a 3GM in my 2003 C320, Hull no. 937.   I have 300 hours on the
engine.   Full throttle has always yielded a tach reading of just over 3600.
Yesterday I noticed that with the throttle full forward, the tach reads only
3000 rpm.     What gives?   I don't have a keen enough ear to say whether
the engine sounds like it is actually at 3600 even though the tach says
3000.    Thoughts and suggestions appreciated.    

Jim Bredar, "Ranger", C320 No. 937, Oxford, Maryland



-----Original Message-----
From: c320-list-bounces at catalina320.com
[mailto:c320-list-bounces at catalina320.com] On Behalf Of brucestanley
Sent: Tuesday, August 28, 2007 5:42 PM
To: C320-List
Subject: Re: [C320-list] calibration of my Tach

Thanks Jeff
your explanation is appreciated.

BruceStanley

----- Original Message ----- 
From: "Jeffrey Hare" <Catalina at thehares.com>
To: "'C320-List'" <c320-list at catalina320.com>
Sent: Wednesday, August 29, 2007 12:24 AM
Subject: Re: [C320-list] calibration of my Tach


> The Yanmar 3GM series engines use a pickup on the flywheel to handle the
> Tach instead of the terminal on the alternator, so those with the 3GM 
> engine
> don't usually have any re-calibration necessary when changing alternators.
> Given that you probably have the 3YM engine, it appears that they aren't
> using the flywheel pickup anymore in favor of the Tachometer terminal on 
> the
> back of the Alternator like they do for the other non-yanmar engines on 
> the
> C320.
>
> -Jeff
>
> -----Original Message-----
> From: c320-list-bounces at catalina320.com
> [mailto:c320-list-bounces at catalina320.com] On Behalf Of brucestanley
> Sent: Tuesday, August 28, 2007 3:14 AM
> To: C320-List; oldman1030 at hotmail.com; sthompson at toad.net
> Subject: [C320-list] calibration of my Tach
>
> Hi All
> re: the calibration of my Tach after I switched from the Hitachi 60Amp
> to an older Hitachi 80Amp. The 80amp Alt produced far higher Tach 
> readings.
> This I solved by a terminal wiring alteration to the back of the Tach.
> This terminal was straight forward. I did this approx 14 mths ago.
> I am far from an electronics expert, but that is exactly what I did.
> I am a DIY advocate and love doing most of my own work on my Yacht.
> Parts I do not understand and parts I break. I still enjoy the journey.
>
> BruceStanley C320#1084
> Sydney Australia
>
> ----- Original Message ----- 
> From: "Chris Holt" <oldman1030 at hotmail.com>
> To: "C320-List" <c320-list at catalina320.com>
> Sent: Monday, August 27, 2007 9:48 PM
> Subject: Re: [C320-list] Club Racing the C320
>
>
>> That was what I had thought also.  I also did not experience any 
>> perceived
>
>> change of my tach readings after the installation.  I have a 1997 with a
>> 3GM motor.
>>
>> Bruce,  maybe you experienced this because of a different setup on the 
>> 3YM
>
>> engines.
>>
>> Chris
>>
>> ----- Original Message -----
>> From: "Scott Thompson" <sthompson at toad.net>
>> To: "C320-List" <c320-list at catalina320.com>
>> Sent: Sunday, August 26, 2007 7:09 PM
>> Subject: Re: [C320-list] Club Racing the C320
>>
>>>I don't know about the newer or older boats, but on my 1999 boat there is
>>>no need to recalibrate the tach when switching alternators.  That's
>>>because on the Yanmar 3GM series of engines, the tachometer reading comes
>>>from a sensor in the flywheel housing that counts the flywheel teeth as
>>>they rotate past.  In these engines tachometer calibration has nothing to
>>>do with the alternator.
>>>
>>> Scott
>>>
>>> brucestanley wrote:
>>>> Hi Stephen
>>>>
>>>> re Kiwi Prop and Engine Revs
>>>>
>>>> Fantastic Lady's 3YM30 cruises at 2100 to 2900 rpm.
>>>> Depending on tide/wind, this delivers 4+++ to 6+ knotts.
>>>> Occasionally I advance the Revs to 3000 and 3300rpm.
>>>> Sometimes to 3500++RPM for only a few minutes.
>>>> Revs are a bit of a lottery, in that one hopes the Catalina Tach is
>>>> calibrated accurately.
>>>> I am reasonably sure they are close to correct on Fantastic Lady.
>>>> Note: if you change your alternator you have to make a change at the
>>>> Tachometer.
>>>> I have an 80amp Hitach Alternator and have made this change.
>>>>
>>>> You must be able to Rev to 3600RPM (Yanmar's requirements).
>>>>
>>>> Hope this helps
>>>>
>>>> Bruce Stanley
>>>> C320  #1084 Fantastic Lady / Sydney Australia
>>>>
>>>> ----- Original Message ----- From: "Stephen Cox" <scox at timmin.com>
>>>> To: "'brucestanley'" <brucestanley at optusnet.com.au>
>>>> Sent: Thursday, August 23, 2007 1:30 PM
>>>> Subject: RE: [C320-list] Club Racing the C320
>>>>
>>>>
>>>>> Thanks Bruce.
>>>>>
>>>>> What revs can you get your motor up to with this prop?
>>>>>
>>>>> Stephen Cox
>>>>> Canberra
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: c320-list-bounces at catalina320.com
>>>>>> [mailto:c320-list-bounces at catalina320.com] On Behalf Of brucestanley
>>>>>> Sent: Thursday, 23 August 2007 8:20 AM
>>>>>> To: C320-List
>>>>>> Subject: Re: [C320-list] Club Racing the C320
>>>>>>
>>>>>> Stephen
>>>>>>
>>>>>> My Kiwi prop is 16.5"
>>>>>> and The factory has set the angle at 22 degrees.
>>>>>> This pitch setting of 22degrees is based on the engine you have.
>>>>>> Mine is the Yanmar 3YM30.
>>>>>>
>>>>>> Bruce Stanley
>>>>>> C320  #1084 Fantastic Lady / Sydney Australia
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
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