tach calibration

[BillG]

I attempted to calibrate my tach last week with little success.  I have an 87, #446 and the tach has no dip switches.  It does have a small hole that is marked as "cal" but when I inserted a small slot screwdriver and a phillips, there was nada. 
There doesn't appear to be any screw to adjust and I was wondering if maybe there had been some adjusting stem that had been broken off by a previous owner.  Any enlightment would be appreciated.

[Ron Hill]

Bill : I don't know if you have a Teleflex tach or not.  I'd call the manufacturer of the instrument for their instructions.  All of the 1987 C34s that I've seen have a Teleflex Tach with dip switches. 
I suspect that a PO put in a differant Tach.  A thought

[Roland Gendreau]

Same topic but different problem.

Over the past winter I replaced my stock alternator with a Balmar 90 amp alternator. So I knew the tach would need to be recalibrated.

I also adjusted the valves for the first time since I purchased the boat.  The engine now idles much more smoothly and at a higher rpm than before.

So I need to know how to measure the engine speed so I can readjust the idle; then I need to recalibrate the tach.

I had read about using a 120v fluorescent light to measure engine speed but now I can not locate the posting.

Can anyone point me to how to measure the idle speed so I can adjust it to specs?

Thanks

Roland
Gratitude #1183

[prh77]

You can buy optical tachs on the internet for about $25. Then you just stick the supplied tape on the crank pulley and check your tach at all RPMs. Mine was about 300 low.

[Ken Juul]

 I too had problems seeing the tape.  As I played with the rpms I noticed that the pulley mounting bolts were doing the wagon wheel dance.  Played with the rpm, got them to stop moving.  Assuming that was 1200 I looked at the tach.  Read 1450.  Adjusted down to 1200.  Ran engine up until the bolts stopped the dance again.  Tach read 2550.  Again adjusted down to get 2400.  Did this a couple times to fine tune.

Original article was posted in by the C36 Assoc.   http://www.catalina36.org/articles/reference/dieselAndPropellerTutorial.htm

Its also be in the Tech Notes, August 99 "Engine speed"

[Steve Sayian]

I adjusted my tach last year with an optical meter.  Initially I got readings all over the place until I figured out that I had to paint the crank pully flat black before putting the reflective tape on.  Once I painted it, the readings became very stable.  Adjustment was easy after that.

[Tom Soko]

Ken,
Our website has moved since you saved that link to the C36 article.  The new link is at:
http://www.c36ia.com/old_site/articles/reference/dieselAndPropellerTutorial.htm
Hope this helps.

[Ron Hill]

Guys : I put that "Tip" about using a 110v AC fluorescent light in the C34 Mainsheet tech notes about 12 years ago. 
That was before a laser tach became so inexpensive.  You now can purchase a much more accurate one for under $35 so purchase one or use the fluorescent light.  After all you do own a "Yacht"!! 

[BillG]

I know that if I looked hard enough I would find an answer.  Early C-34 apparently had a different type of Teleflex tach on them that
are calibrated by first using a selector switch to rough in the RPM and then a second screw to fine tune the RPM.
The following are the instructions for calibration per the Teleflex instruction manual.

If the number of alternator poles is not known, measure the actual RPM with a Master Tachometer. Rotate the 
selector switch to the letter that puts the tachometer closest to the actual RPM. Final Calibration adjustment   
requires the use of a Master Tachometer. Connect the Master Tachometer and start the engine. At about 
1500-2000 RPM, use a jeweller's screwdriver to carefully adjust the potentiometer in the "CAL" hole (about 10 
o'clock on the rear of the tachometer), bringing the tachometer into agreement with the Master Tach. Only a 
minimal amount of turning is required. Overtorquing of adjustment will damage gauge mechanism. Turning   
clockwise increases tach reading, counter clockwise reduces reading. If the tachometer cannot be brought into 
calibration, the black Range Selector Switch is probably on the wrong setting.

[SeaFever]

Just a quick comment about Steve's comment in the thread above:

"Initially I got readings all over the place until I figured out that I had to paint the crank pulley flat black before putting the reflective tape on.  Once I painted it, the readings became very stable."

After reading the post about the photo tachometer (also called laser tachometer) I got one from my favorite too store, Harbor Freight Tools (http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=66632), and was able to check my tach's calibration. I too got the first reading all over the place as Steve has indicated. I inferred that that was because the beam was getting reflected by the shiny (painted) surface of the pulley and was messing up the reading. Rather than paint my pulley black I used some ordinary black electrical tape and taped it around the pulley except for the place where I had applied the reflective tape. That did the trick. I got a rock steady reading after that and removing the tape was a breeze as against needing the repaint the pulley.

Just thought I would pass that on. I will also try to past a picture below.

Note: Although the tape surface appears to shine in the photo, as it reflected the flash of the camera, it did not affect the photo tach.

Mahendra