Reply
 
Thread Tools Display Modes
 
Old 08-06-2014, 08:06 PM   #1
Member
 
Chrises Craft's Avatar
 
City: Port of Everett Marina
Country: Mill Creek, Washington
Vessel Name: Chris' Craft
Vessel Model: Mainship 350
Join Date: Feb 2012
Posts: 17
Tachometer Accuracy

I have a 97 Mainship 350 with twin Volvo Penta TAMD-41p-a Diesels. Both tachometers on the starboard side read about 400 rpm too low. Any ideas why this could be and how to correct? Thanks
__________________
Advertisement

Chrises Craft is offline   Reply With Quote
Old 08-06-2014, 08:52 PM   #2
Guru
 
Brooksie's Avatar
 
City: Cape Cod, MA
Country: USA
Vessel Name: Island Seeker
Vessel Model: Willard 36 Sedan
Join Date: Oct 2007
Posts: 954
Your tachs run off your alternators. Make sure your belt isn't slipping of worn out. Then adjust using the screw on the back of the tach. Get a digital tach at Harbor Freight and check them both.
__________________

Brooksie is offline   Reply With Quote
Old 08-06-2014, 11:47 PM   #3
Guru
 
LarryM's Avatar
 
City: League City, TX
Country: USA
Vessel Name: Pelago
Vessel Model: Wellcraft 3300 Coastal
Join Date: Aug 2011
Posts: 843
I guess the obvious first question is whether or not the starboard engine is actually running 400 rpm too low. You should check it with a handheld digital tachometer to know if there is actually a difference between the indicated and actual engine speed.

I'm pretty sure the Volvo TAMD41 diesels all use a tachometer sensor p/n 862251 which is located on the timing gear casing. Here is a parts breakdown for your reference. If so equipped, make sure the sensor wiring is clean and tight. You might also make sure the sensor is clean and well seated. As the gear teeth pass the coil in the sensor, a pulse is created that triggers a counting circuit in the tachometers.

If there is no sensor, but only a blank plug, then your tachometers are sensing the alternator speed, so wiring, loose belts etc. could be the cause. Like Brooksie said, these tachometers generally have an adjustment.

In either case, you should use a digital tachometer to determine your actual engine speeds.

Good luck

Larry
M/V Boomarang
LarryM is offline   Reply With Quote
Old 08-07-2014, 02:38 AM   #4
Guru
 
boatpoker's Avatar
 
City: Port Credit
Country: Ontario
Vessel Name: DIRT FREE
Vessel Model: Benford Fantail 38
Join Date: Sep 2012
Posts: 2,011
or switch the tachs and see what happens.
__________________
If you can live with the consequences, go for it - wg
Y'am what I y'am an' thats' all that y'am - Popeye
As God is my witness, I thought turkey's could fly. Mr.C
boatpoker is offline   Reply With Quote
Old 08-07-2014, 09:51 AM   #5
Guru
 
City: gulf coast
Country: pinellas
Join Date: Jun 2014
Posts: 2,199
yes use a photo tach to verify what is happening.

Do they read the same at idle??


you could briefly run both engines at wot in idle. If they match in rpms and the tachs reads the same then it is not the tach
bayview is offline   Reply With Quote
Old 08-07-2014, 12:17 PM   #6
Guru
 
ancora's Avatar
 
Join Date: Dec 2007
Posts: 3,490
While we are on the subject, a friend has a Camano with a TMD41, and installed an AETNA digital tachometer. He had to glue magnets on the harmonic balancer to get it to work(?). I have TMD40s and the AETNA tachs plugged right into the original wiring. Why the difference?
ancora is offline   Reply With Quote
Old 08-07-2014, 07:02 PM   #7
Guru
 
Capt.Bill11's Avatar
 
City: Sarasota/Ft. Lauderdale
Country: USA
Join Date: Apr 2014
Posts: 5,422
Cheap laser photo tach

Digital Photo Laser Tachometer Non Contact High Accuracy MPU LCD Display Handheld - Rakuten.com Shopping
Capt.Bill11 is offline   Reply With Quote
Old 08-07-2014, 07:21 PM   #8
Guru
 
READY2GO's Avatar
 
City: Marathon, Florida
Country: USA
Vessel Name: Walkabout
Vessel Model: 1989 Sea Ray 380 Aft Cabin
Join Date: Jan 2012
Posts: 521
I put the Tiny Tach on our boat and am very happy with in. It connects to one of your fuel injector lines.

Design Technology, Inc., Home of the Tiny-Tach - Diesel Tiny-Tach Tachometer
__________________
"Whenever you find yourself on the side of the majority, it is time to pause and reflect." Mark Twain

www.mikeandsharondunsworth.blogspot.com
READY2GO is offline   Reply With Quote
Old 08-07-2014, 07:53 PM   #9
Guru
 
LarryM's Avatar
 
City: League City, TX
Country: USA
Vessel Name: Pelago
Vessel Model: Wellcraft 3300 Coastal
Join Date: Aug 2011
Posts: 843
Quote:
Originally Posted by READY2GO View Post
I put the Tiny Tach on our boat and am very happy with in. It connects to one of your fuel injector lines.

Design Technology, Inc., Home of the Tiny-Tach - Diesel Tiny-Tach Tachometer
Now that is cool!
LarryM is offline   Reply With Quote
Old 08-08-2014, 12:49 AM   #10
Veteran Member
 
Astral Blue's Avatar
 
City: California Delta
Country: Sacramento, CA
Vessel Name: Astral Blue
Vessel Model: Bayliner Victoria 2750 Command Bridge
Join Date: Apr 2012
Posts: 71
Send a message via Yahoo to Astral Blue
Just curious... How were you able to confirm they are running 400 RPM's off? Were you able to use a laser tachometer or similar device to test it. Also, if the laser tachometer's strip is attached to a pulley, you will get the RPM readings of the pulley, not the engine.
__________________
Ed & Lindsey
California Delta

1977 Bayliner Victoria Astral Blue Repowered with Perkins 4.108 Diesel
Astral Blue is offline   Reply With Quote
Old 08-08-2014, 08:08 AM   #11
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 15,902
Quote:
Originally Posted by Astral Blue View Post
Just curious... How were you able to confirm they are running 400 RPM's off? Were you able to use a laser tachometer or similar device to test it. Also, if the laser tachometer's strip is attached to a pulley, you will get the RPM readings of the pulley, not the engine.
most will put it on the pulley on the crank end so it is the engine rpm.
__________________

psneeld is online now   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 06:03 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