#1
IP: 96.244.151.23
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Marine tach?
I stumbled upon an old Stewart Warner tach, p/n 997DS7.
I'm unsure if it's a diesel tach. It has three taps: Gnd, Ign and "S". I think Ign is the + side and "S" goes to a tap on the alternator, so maybe a diesel tach. Does the stock alternator have a signal tap for a tach? |
#2
IP: 98.125.195.46
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A picture would help. I suspect it's a diesel tach, too, with a "S" sensor wire. I suspect you meant the coil or distributor wire, the alternator shouldn't come into play. Did you get the sensor with the tach? The tach should have some switches, that set it it for a specific amount of teeth, which are set to specific instructions.
The main difference between a gas tach, and a diesel tach is in the counter interface, and the counter itself. The counter interface for a gas tach will have a high voltage signal conditioning to handle the spikes coming from the coil. Once past the interface, the counter counts the pulses and divides by time. The number of pulses for a 4-stroke gas engine is 4 per revolution, but the sensor for a diesel tach is a pulse on every full revolution. Note what happens when a gas tach is hooked to a diesel. [YOUTUBE]HPc16hU690M[/YOUTUBE] [YOUTUBE]EvwN1LK8AVY[/YOUTUBE] Last edited by Boomer; 09-25-2015 at 07:35 AM. |
#3
IP: 24.152.132.65
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Actually alternator driven tachometers are quite common on diesels and the input terminal is identified 'S'. Here are pictures of my Datcon tach.
__________________
Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others |
#4
IP: 98.125.195.46
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I edited that phrase out, knowing that would come up. But put it back in after your post. Yes quite right on diesel engines, however the alternator shouldn't come into play on a gas engine, unless one wants to go that route.
Quote:
Last edited by Boomer; 09-23-2015 at 06:23 PM. |
#5
IP: 24.152.132.65
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Does on mine. An alternator driven tach works equally well on diesel and gas engines, exact same input. Said another way, there's nothing prohibiting an alternator driven tach form working on a gas engine. Ajax needs to find out exactly what input his tachometer is designed for.
Alternator taps are not standard equipment but a good alternator shop can install one in minutes. Be advised, after installation an alt driven tach must be calibrated. Harbor Freight Tools to the rescue again.
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Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others |
#6
IP: 98.125.195.46
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It would be easier to buy a gas engine tack....but Ajax can have at it if he wants. I know he likes recycling old parts and equipment, after helping him mount a recycled bulkhead compass.
Last edited by Boomer; 09-23-2015 at 06:22 PM. |
#7
IP: 24.152.132.65
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It would be easier to buy a Moyer rebuilt engine with all the bells and whistles too. My Datcon was under $30 on ebay. That it was alt driven didn't give me the slightest concern. In fact, remembering a recent thread where a coil style tach shorted, killed the engine and created a challenging troubleshooting episode, maybe there's merit to the alt style. Here's the Datcon in the latest panel iteration.
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Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others |
The Following User Says Thank You to ndutton For This Useful Post: | ||
Administrator (09-23-2015) |
#8
IP: 98.125.195.46
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There you go then, not only easier, but less expensive as well. BTW...nice upgrade!
Last edited by Boomer; 09-23-2015 at 06:40 PM. |
#9
IP: 24.152.132.65
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Thank you. Joe turned me on to the gauges from Chief Aircraft. I really liked the big needle sweeps. What you see fits into the MMI large panel recess.
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Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others |
#10
IP: 98.125.195.46
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I like the big needle sweeps as well.
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#11
IP: 134.223.230.154
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This gauge is pretty old and Google isn't coming up with any information on it whatsoever, so the odds of figuring out what kind of input it wants, is pretty slim.
I guess I'm just going to buy a new, ignition-driven tach and be normal like everyone else. |
#12
IP: 137.200.0.109
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I got a "deal" on a VDO tach from FleaBay. It was an odd metric hole size, so I had to spend $20 on a special hole saw. Then I went nuts tracking down a manual and getting it calibrated. I would have been better off with the right tach in the first place. YMMV
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