Tachometer Replacement

Does anyone know how to select the correct tachometer to replace an older Motorola.* The engine is a newer American Diesel 139 HP.* I don't know off hand about the alternator.* Does the replacement tach have to match the*one that is working?* Can you get a Motorola or are they not in business?*

Yes, VDO have one which slots straight in. I had my Motorola one up on the flybridge die and that's what we used. Still using the old Motorola one downstairs, so they must be compatible, tho I notice they read a smidgeon different, but you work that out easily enough and allow for it.

Yes, VDO should have one.* The variables are the rpm range, electronic or not, and alternator voltage.* VDO has some of the world's worst service, so take a Valium before trying to communicate with them.

I bought a pair of VDO when I repowered and the engines I put in only came with one pair. the Volvo price was twice the VDO price. Then I learned, you still get what you pay for. The VDO were erratic, impossible to calibrate, so they went back and I got the Volvo units. The literature on the VDO said they would work with the Volvo engines, but that wasn't my experience with them.

VDO, have had to return up to 4 oil pressure units to get a working one.

Ok, well that's bad luck, but I have one VDO tachometer and 2 oil pressure gauges and they are working fine after 7 yrs, for what it's worth.

I have used Faria and VDO. Faria was on a 200 hp Johnson, VDO on my 160 hp Perkins 6-354T. Been happy with both.

Rob
37'Sedan

I replaced my fly bridge guages with the "Heavy Duty" series of SW guages. The tach is designed to get it's signal from the alternator and has adjustments for setting the calibration. Was easy to do and makes for a nice looking setu up.
Here's a link to Lauderdale Speedometer where you can get them.

Bill

http://www.lspeedo.com/

Thanks guys.....I will look into the SW gauges at the Lauderdale Speedomter site. Sounds like the VDO may not be the one to get. The marina I have my boat at wants $250.00 for a Teleflex unit. Seems a bit too high.

Put a new VDO one in a couple of months ago. After calibrating with a phototach, I'm very happy with it as it's nicely damped compared with the old Isspro.

VDO supplied a mounting ring so that I could fit a slightly smaller unit in the same hole. I needed the smaller one as that was the only one available with the range that I wanted (0 to 3,000 rpm in 100 increments with 1500 top centre).

There was a bit of math involved in checking the number of pulses from the alternator per revolution and the belt ratio - but it all worked out OK.



-- Edited by Bendit on Tuesday 8th of June 2010 07:52:48 PM

For folks replacing a SW with the smaller VDO, a single strand 10ga black wire will work as a spacer , and is almost invisiable when done .

Done it for folks many times , but on my own boat the SW is replaced with a SW.

When measuring the pulley diameters, is it the overall outter diameter or the diameter less the depth of the belt? I measured my crank pulley at 7 3/4" but the belt could take*1/2" out of that. The alternator pulley is 3 1/2" overall but the belt could take maybe 3/8" out of that also. What measurements did you guys use?

-- Edited by reefdrifter on Sunday 13th of June 2010 06:54:56 PM

Just use the overall diameter.
The depth of the belt doesn't really matter since you will have to calibrate the new tach anyway.

Thanks to all that replied. I ended up getting a VDO Tach from Lauderdale Speedometer. The guys over there said the SW guages are not as good as the VDO and they had lots of SW returns. It took a little fussen to calibrate the VDO although was pretty easy. My initial calculations with the pulley diameters didn't seem to work so I called Lauderdale Speedometer for some help. They came up with a different pulley ratio so I tried that and it seems to be working now. My lower tach is an old Motorola and is very steady and seems accurate. The new upper VDO seems to read pretty close to the lower unit but backing down from say 1600 RPM to idle it fluctuates a little. I probably won't see exact readings but the will be close and I will have something to go by now rather than a dead tach.