Reply
 
Thread Tools Display Modes
 
Old 04-04-2015, 08:32 PM   #1
Guru
 
JDCAVE's Avatar
 
City: Lions Bay, BC
Country: Canada
Vessel Name: Phoenix Hunter
Vessel Model: Kadey Krogen 42 (1985)
Join Date: Apr 2011
Posts: 1,605
Tachometer adjustment

When I set up my alternator with a double pulley and twin belts last spring, I think it put my alternator off by about 150 rpm: I seem to get the same cruising speed of 7.5 kts at 1650 rpm that I achieved at 1800 the previous summer. I presume I can check with a photo tach, but I'm having trouble finding one I can borrow. Is there an adjustment screw on the gauge in the Pilothouse?

I noted someone in an earlier thread had installed a Tinytach. Is this another option for checking engine rpm?

http://www.tinytach.com/pdf/diesel_instructions.pdf

Jim
Sent from my iPad using Trawler Forum
__________________
Advertisement

JDCAVE is offline   Reply With Quote
Old 04-04-2015, 10:07 PM   #2
TF Site Team
 
FlyWright's Avatar
 
City: California Delta and SF Bay
Country: Sacramento, CA, USA (boat in Vallejo)
Vessel Name: FlyWright
Vessel Model: Marshall Californian 34 LRC
Join Date: Apr 2008
Posts: 10,178
Jim, when I changed my alternator, my tach reading changed 200 RPM even though I used the same pulley. It must have been due to the stator count on the alternator. The stator setting on the back of the tach was correct. I found an inexpensive photo tach for under $30 like this.

Buy Digital Laser Tachometer with Pouch (2.5~99999.9RPM Range / 0.1RPM Resolution)

I used it to verify the tach's accuracy and found it to be within 40 RPM at cruise power of 1800. So it turns out my old alternator was giving me an inaccurate reading of 2000 RPM at cruise and now it's accurate. Knowing this made it worth the $30.

I'd send you mine to borrow but it'll cost more than $30 to send it there and back.
__________________

__________________
Al

Custom Google Trawler Forum Search
FlyWright is offline   Reply With Quote
Old 04-04-2015, 10:16 PM   #3
Guru
 
mbevins's Avatar
 
City: Windsor
Country: Canada
Vessel Name: Keeper IV
Vessel Model: 44 Viking ACMY
Join Date: Nov 2013
Posts: 1,305
Quote:
Originally Posted by FlyWright View Post
Jim, when I changed my alternator, my tach reading changed 200 RPM even though I used the same pulley. It must have been due to the stator count on the alternator. The stator setting on the back of the tach was correct. I found an inexpensive photo tach for under $30 like this.

Buy Digital Laser Tachometer with Pouch (2.5~99999.9RPM Range / 0.1RPM Resolution)

I used it to verify the tach's accuracy and found it to be within 40 RPM at cruise power of 1800. So it turns out my old alternator was giving me an inaccurate reading of 2000 RPM at cruise and now it's accurate. Knowing this made it worth the $30.

I'd send you mine to borrow but it'll cost more than $30 to send it there and back.
In case it is easier....I bought the same tach on Amazon and i think it was a couple of bucks less.
__________________
"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

mbevins is offline   Reply With Quote
Old 04-05-2015, 08:12 AM   #4
Guru
 
ranger42c's Avatar
 
City: Maryland
Country: USA
Vessel Model: 42' Sportfish
Join Date: Aug 2013
Posts: 3,158
Our Faria tachs had course and fine adjustment screws... but then it also turned out the tachs were only semi-accurate at the "set" RPMs. We set them at 2000, so we were off at idle and off at WOT.


I've since changed to Aetna digital tachs; the setting is simply the number of teeth on the flywheel. Accurate throughout the full range of RPMs.


-Chris
__________________
South River, Chesapeake Bay
ranger42c is offline   Reply With Quote
Old 04-05-2015, 08:48 AM   #5
Veteran Member
 
City: Salt Lake City, UT
Vessel Name: Kia Orana
Vessel Model: Bayliner 4788
Join Date: Jul 2011
Posts: 35
When you replaced your Faria tachs did you have to run new wires for the aetnas?
woodsea is offline   Reply With Quote
Old 04-06-2015, 07:00 AM   #6
Guru
 
ranger42c's Avatar
 
City: Maryland
Country: USA
Vessel Model: 42' Sportfish
Join Date: Aug 2013
Posts: 3,158
Quote:
Originally Posted by woodsea View Post
When you replaced your Faria tachs did you have to run new wires for the aetnas?

No, just used the existing power, ground, and signal wires. Very simple swap, and in fact I worried more about the cut-out sizes than anything else. (Turned out to be a non-issue.)

The Faria gauge also had an extra wire for dash lighting, but the Aetna tach has backlighting built in, so that extra wire became unnecessary.

-Chris
__________________
South River, Chesapeake Bay
ranger42c is offline   Reply With Quote
Old 04-06-2015, 08:33 AM   #7
Guru
 
High Wire's Avatar
 
City: Cape May, NJ and Englewood, FL
Country: USA
Vessel Name: Irish Lady
Join Date: Dec 2007
Posts: 1,600
I found my alternator driven electrical tach is 10 percent fast across the whole scale using a $30 photo tach. IE 1800 rpm reading is 1620 actual, which is my normal cruising speed of 6.7 knots. I'm just not ready to fool around trying to adjust a pair of 30 year old tachs.
__________________
Archie
1984 Monk 36 Hull #46
Englewood, FL and Cape May, NJ
High Wire is offline   Reply With Quote
Old 04-10-2015, 07:24 AM   #8
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,524
Alt driven tachs are always off. No way for them not to be.

IF accurate RPM is required ask the engine builder how to hook up a tach sender , and purchase a tach that can read the sender.

After adjustment , this gives most accurate readings .
FF is offline   Reply With Quote
Old 04-10-2015, 07:49 AM   #9
Guru
 
jleonard's Avatar
 
Join Date: Jun 2008
Posts: 2,739
I check my tachs every season and adjust them if necessary. I had to adjust them both last season when I changed to a Balmar alternator.
It's really not that hard to do. I set the engine to somewhere around 1800 rpm then adjust until I get within about 25-50 rpm. That's close enough.
Then I check them at idle speed and they stay within that 25-50 rpm range.
My experience is that once they are set they hold pretty well.
__________________
Jay Leonard
Attitude Adjustment
40 Albin
Mystic,Ct. /New Port Richey,Fl
jleonard is offline   Reply With Quote
Old 04-10-2015, 08:45 AM   #10
TF Site Team
 
Larry M's Avatar
 
City: JAX, FL
Country: USA
Vessel Name: Hobo
Vessel Model: Krogen 42-120
Join Date: Nov 2008
Posts: 5,734
Quote:
Originally Posted by jleonard View Post
I check my tachs every season and adjust them if necessary. I had to adjust them both last season when I changed to a Balmar alternator.
It's really not that hard to do. I set the engine to somewhere around 1800 rpm then adjust until I get within about 25-50 rpm. That's close enough.
Then I check them at idle speed and they stay within that 25-50 rpm range.
My experience is that once they are set they hold pretty well.
Same here. Our adjustment is on the back. I checked our $11 tach against a $50 tach and it was right on. If the idle speed is off, the tach's mechanical zero or needle rest could be off and that does take some disassembly to set the needle stop. Not hard but just a heads up.

Here's a tutorial that Dave on fryedaze did that shows the disassembly of a VDO tach.

http://www.odometergears.com/documen..._To_Repair.pdf
Attached Thumbnails
Click image for larger version

Name:	023.jpg
Views:	86
Size:	94.5 KB
ID:	39069   Click image for larger version

Name:	022.jpg
Views:	83
Size:	76.1 KB
ID:	39070   Click image for larger version

Name:	024.jpg
Views:	78
Size:	90.5 KB
ID:	39071  
Larry M is offline   Reply With Quote
Old 04-10-2015, 10:08 AM   #11
Senior Member
 
Doug's Avatar
 
City: Victoria, BC
Country: Canada
Vessel Name: Timeless
Vessel Model: CHB 34
Join Date: Aug 2009
Posts: 102
Tach/sender for Lehman 120

Quote:
Originally Posted by FF View Post
Alt driven tachs are always off. No way for them not to be.

IF accurate RPM is required ask the engine builder how to hook up a tach sender , and purchase a tach that can read the sender.

After adjustment , this gives most accurate readings .
We have always had issues with the alternator driven tach on our Lehman. Once the batteries are charged the tach pulses as the regulator turns on and off.
Any recommendations for a tach/sender combination for this engine?
Doug is offline   Reply With Quote
Old 04-10-2015, 12:15 PM   #12
TF Site Team
 
FlyWright's Avatar
 
City: California Delta and SF Bay
Country: Sacramento, CA, USA (boat in Vallejo)
Vessel Name: FlyWright
Vessel Model: Marshall Californian 34 LRC
Join Date: Apr 2008
Posts: 10,178
Same on my Perkins, Doug. When I increase the electrical load on the batt, the increased alternator output stabilizes the tach. If it's the start bank, I close (switch on) the combiner to share the charges and loads.
__________________
Al

Custom Google Trawler Forum Search
FlyWright is offline   Reply With Quote
Old 04-10-2015, 03:57 PM   #13
Guru
 
JDCAVE's Avatar
 
City: Lions Bay, BC
Country: Canada
Vessel Name: Phoenix Hunter
Vessel Model: Kadey Krogen 42 (1985)
Join Date: Apr 2011
Posts: 1,605
I was at Brighouse electric with my winch the other day. They work on starter motors, alternators etc, and they put the double pulley on my alternator last spring. I raised this issue with them and they confirmed what has been mentioned here...that alternator tachs are unreliable and there are too many variables that affect the accuracy. I will probably give them a quick calibration if I can and get a more reliable instrument. That "Tiny Tach shoukd like one option.

Also, it seems to me that engine hours might be affected too. I noticed that sometimes my hour meter indicates more hours at the end of my trip than my recorded hours in my logbook, and the engine isn't sitting around idling more than 15 minutes or so bed or we get underway.


Jim
Sent from my iPad using Trawler Forum
JDCAVE is offline   Reply With Quote
Old 04-11-2015, 01:03 PM   #14
Guru
 
JDCAVE's Avatar
 
City: Lions Bay, BC
Country: Canada
Vessel Name: Phoenix Hunter
Vessel Model: Kadey Krogen 42 (1985)
Join Date: Apr 2011
Posts: 1,605
I found a digital laser tach on Amazon.ca, for $44 Cdn, including express shipping. More than what it would cost in the US, but I got it nonetheless. I wasn't able to find one at Canadian Tire or Lordco. Princess auto had one advertised for $60, but none in stock.

http://www.amazon.ca/dp/B000I5LDVC/r...088100_TE_item


Jim
Sent from my iPad using Trawler Forum
JDCAVE is offline   Reply With Quote
Old 04-11-2015, 04:02 PM   #15
Guru
 
JDCAVE's Avatar
 
City: Lions Bay, BC
Country: Canada
Vessel Name: Phoenix Hunter
Vessel Model: Kadey Krogen 42 (1985)
Join Date: Apr 2011
Posts: 1,605
Tachometer adjustment

Ok. The tachometer is a Motorola model. I dropped a panel down and the back of the tach looks like page 2 of this doc., and I've located the calibration screw, so should be able to figure it out. I'm going to adjust the calibration so it is accurate for 1800 rpm, and then measure rpms at each 200 increment on the dial to WOT.

http://www.westerbeke.com/mdtools/se...ins/sb_148.pdf

Jim
Sent from my iPad using Trawler Forum
JDCAVE is offline   Reply With Quote
Old 04-20-2015, 05:54 PM   #16
Guru
 
JDCAVE's Avatar
 
City: Lions Bay, BC
Country: Canada
Vessel Name: Phoenix Hunter
Vessel Model: Kadey Krogen 42 (1985)
Join Date: Apr 2011
Posts: 1,605
Tachometer adjustment

I got one of those Laser Tachometers from Amazon and it works like a hot damn! Here's the calibration curve and it's not linear (no surprise). It's probably some sort of a quadratic relationship. I shall have to see, but I will calibrate the tach at 1800 and resample at different readings.

Click image for larger version

Name:	ImageUploadedByTrawler Forum1429566862.162864.jpg
Views:	103
Size:	62.3 KB
ID:	39346

Jim
Sent from my iPad using Trawler Forum
JDCAVE is offline   Reply With Quote
Old 04-20-2015, 07:34 PM   #17
TF Site Team
 
FlyWright's Avatar
 
City: California Delta and SF Bay
Country: Sacramento, CA, USA (boat in Vallejo)
Vessel Name: FlyWright
Vessel Model: Marshall Californian 34 LRC
Join Date: Apr 2008
Posts: 10,178
I calculated the % error and they lie fairly close to each other...within about 2.7% margin of error. Here they are:

800 - 12.9%
1000 - 13.1%
1200 - 14.3%
1400 - 16.6%
1500 - 16.1%
1600 - 17.9%
1800 - 18.3%
2000 - 16.5%

Your total average error is 15.7%. Your average error at the 14-1800 RPM cruise range is 17.2%.
__________________
Al

Custom Google Trawler Forum Search
FlyWright is offline   Reply With Quote
Old 04-20-2015, 10:27 PM   #18
Guru
 
JDCAVE's Avatar
 
City: Lions Bay, BC
Country: Canada
Vessel Name: Phoenix Hunter
Vessel Model: Kadey Krogen 42 (1985)
Join Date: Apr 2011
Posts: 1,605
Yes, but the % deviation is increasing with RPM. I will calibrate the tach for 0 deviation at 1800 and check the deviations at low idle and at 2400. WOT was 2650 when the tach was accurate before I changed the alternator pulley and threw it off.


Jim
Sent from my iPad using Trawler Forum
JDCAVE is offline   Reply With Quote
Old 04-20-2015, 10:30 PM   #19
TF Site Team
 
FlyWright's Avatar
 
City: California Delta and SF Bay
Country: Sacramento, CA, USA (boat in Vallejo)
Vessel Name: FlyWright
Vessel Model: Marshall Californian 34 LRC
Join Date: Apr 2008
Posts: 10,178
Are you planning for a new pulley?
__________________
Al

Custom Google Trawler Forum Search
FlyWright is offline   Reply With Quote
Old 04-20-2015, 11:11 PM   #20
Guru
 
JDCAVE's Avatar
 
City: Lions Bay, BC
Country: Canada
Vessel Name: Phoenix Hunter
Vessel Model: Kadey Krogen 42 (1985)
Join Date: Apr 2011
Posts: 1,605
Tachometer adjustment

No, I already did that last year. I was advised by several people, (a mechanic, a shipwright and the alternator repair outfit I go to) to put a double belt on my alternator and that required installation of a double pulley. That put the calibration of the tachometer "out of wack" and I pretty much guesstimated the cruising RPM's last summer. I figured that that 1600 on the tach was actually 1800, and I was close based on the measurements I took today.

Approximating the engine RPMs from the alternator isn't ideal, I now realize.


Jim
Sent from my iPad using Trawler Forum
__________________

JDCAVE is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 07:54 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012