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Author Topic:   Re-using 28-year-old Gauges When Updating to Modern Engine
87montauk posted 04-01-2015 08:03 PM ET (US)   Profile for 87montauk   Send Email to 87montauk  
I'm doing a re-power this month, and I am getting quotes from a number of shops. Some have told me I can't use the old gauges from my 1987 Yamaha 90 [with a new Yamaha F70 outboard engine]. Some say I can. Does anybody know the real deal? Thanks
tedious posted 04-02-2015 08:19 AM ET (US)     Profile for tedious  Send Email to tedious     
I'd be quite surprised if your analog gauges are not usable with a new F70. The newer, larger motors are only available with digital controls, and that may be confusing the shops you have talked to.

I would recommend getting in touch with Andy from Shipyard Island Marine ( - he helped me install my F70, including using a trick that the Yamaha rigging guide did not mention, but which saved me a few bucks. If you're planning to install the motor yourself, you might even ask Andy for a quote - he was able to beat my local prices by a good margin.

The F70 does output a complete suite of digital information, and you can tie that into a NMEA2000 network or just use the Yamaha CommandLink bus, which is what I did. With the right cables, you can connect to your GPS display head and get the full set of information, while also keeping the analog gauges you like. I'm an info junkie, so I like being able to see detailed data - temperature, water pressure, fuel flow, etc.


jimh posted 04-02-2015 08:44 AM ET (US)     Profile for jimh  Send Email to jimh     
I suspect that a 1987 Yamaha 90-HP outboard engine was probably a two-stroke-power-cycle engine. A new Yamaha F70 is a four-stroke-power-cycle engine. That might cause a problem for re-use of the tachometer.

You do not mention what other gauges you plan to re-use. Many gauges show parameters that are not dependent at all on the engine design. For example, a Voltmeter measures electrical voltage. It has no idea what model year outboard engine or what type of outboard engine is associated with that voltage. Similarly, a water pressure gauge that operates by direct attachment with a hose to a water line would care little about the engine. It only measures water pressure.

It is impossible for anyone to give you "the real deal" until you give more information about the 28-year-old gauges you desire to re-use.

jimh posted 04-02-2015 12:43 PM ET (US)     Profile for jimh  Send Email to jimh     
A duplicate of this thread begun in another forum has been deleted.
87montauk posted 04-02-2015 08:52 PM ET (US)     Profile for 87montauk  Send Email to 87montauk     
Sorry for not being more specific. What I have now are the tachometer and trim gauges. The tachmeter has a low oil warning light, which one shop said they could convert so that it's a low oil pressure light. And, yes the old motor was the two-cycle 90 and I'm concerned the tachometer won't work with the four-cycle engine.

I just really like the classic look of the YAMAHA analog tachometer. I wouldn't mind pulling the trim gauge and putting a multifunction gauge in its place; the trim hasn't been working right anyways for a while. So, the primary concern is will the tach work? Secondarily, will the trim work? I will definitely be getting an hour meter of some sort.

jimh posted 04-03-2015 08:51 AM ET (US)     Profile for jimh  Send Email to jimh     
Here is "the real deal" on using an old tachometer and old trim gauge with a new engine:

A tachometer is really a frequency gauge, that measures the frequency of pulses from the engine. Whether your 28-year-old tachometer will work with the new engine is hard to say; it will depend on how the tachometer signal is created in the new engine. The frequency of the pulses, their polarity, and their voltage would have to be compatible in the new and old engines. I'd defer to an experienced Yamaha technician and rigger for a decision. Or, insert an oscilloscope on the tachometer signal line and measure the voltage, frequency, and nature of the waveform from both engines to compare them. If they are the same, then the old tachometer should work on both.

A trim gauge is usually a voltmeter in a bridge circuit. Part of the bridge circuit is in the gauge itself, and on the engine there is a variable resistor that is wired into that bridge circuit. If the same value of trim sender resistor is used on both old and new engines, then the old trim gauge should still work.

There might be changes in the wiring harness and in the connectors used for the particular circuits needed. This might also hinder use of the gauges. Many time older rigging methods used individual conductors with ring terminals to wire to gauges. Modern rigging methods tend to use multi-pin connectors to connect to the gauges.

You will need to determine if the gauges are compatible or not. If they are compatible, then determine if the connectors and harnesses are compatible. If they are, there should be no problems in using the gauges.

If the gauges are compatible but the connectors are not, you could modify the connectors and wiring harnesses. But I wouldn't expect a dealer's technician to be allowed to modify any part of a new engine being installed. Any modification would probably be considered as breeching the warranty conditions. You'd be best to leave the new engine and its rigging harness unmodified, and, if anything must be changed, create your own inter-connection to the old gauges from the new rigging.

Let us know what you find out about both the gauges and the rigging. If they're not compatible and wired identically, you'll be looking at a project to maintain your esthetic preference for the appearance of the older gauges.

msirof2001 posted 04-03-2015 09:51 AM ET (US)     Profile for msirof2001  Send Email to msirof2001     
When I repowered my 1995 Outrage 21, Yamaha had a power-matched deal, where, if I [re-did] the current rigging, the whole thing from key to propeller had a one-year warranty. As for your specific question, West Coast Marine Service in Costa Mesa is Yamaha Five-Star-Gold and very knowledgeable. He may not be in your area.
tedious posted 04-03-2015 12:30 PM ET (US)     Profile for tedious  Send Email to tedious     
Yamaha still sells analog gauges today. If you do a search on "Yamaha outboard rigging guide" you can get more information on them, including setting them to match different outboards. Now that you have clarified that these are Yamaha gauges, it would be even more of a surprise to me if they wouldn't be able to plug right into the F70. Your situation is a common one, and Yamaha wouldn't want to open the door to customers considering a different brand by requiring them to buy a new tach with their new Yamaha.

I may have the F70 specific rigging info at home - I will check tonight if I get a chance.

For hour meter, I went with the Yamaha square digital tach, which can be switched to show hours, water pressure, water temp, or system voltage reading, or a graphical combination. It also has the trolling speed control - not that I have ever used it.


87montauk posted 04-03-2015 06:25 PM ET (US)     Profile for 87montauk  Send Email to 87montauk     
Thanks for the feedback. After further discussion with a couple of shops, the old two-cycle tachmetre could probably be made to work but it would be a bit of a custom job and still iffy.
It looks like I will go the way of purchasing new yamaha analog proseries tach which includes low oil pressure and temp alerts.

[Changed to new topic. Please start a new thread for the new topic. If you need advice on propeller selection, start the thread in PERFORMANCE.--jimh]

DVollrath posted 04-03-2015 07:33 PM ET (US)     Profile for DVollrath  Send Email to DVollrath     
With regards to your gauges, as others have pointed out the NMEA2000 link you can get from engine to your chartplotter is very nice. I do have a Yamaha digital multifunction gauge, but I rarely use it. The chartplotter linked to the engine gives all of the information I commonly use, at an angle convenient to my standing or sitting boating position.


jimh posted 04-04-2015 07:29 AM ET (US)     Profile for jimh  Send Email to jimh     
[Moved to Small Boat Electrical.]
jimh posted 04-04-2015 07:40 AM ET (US)     Profile for jimh  Send Email to jimh     
Here is a direct hyperlink to the Yamaha Outboard Rigging Guide:

The above literature is a very comprehensive summary of Yamaha gauges, their wiring, their connectors, and their application to specific engines.

Perhaps it contains information on your 28-year-old Yamaha gauges which could be useful in rigging them with a modern engine.

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