How To Fix A Boat Tachometer 115hp Evinrude Outboard
posted 05-xx-2002 09:49 PM ET (U.s.) 
The TACHOMETER guess needs iii things to work:
1. Source of pulses from engine sender;
2. Wiring connecting sender to gauge;
3. Gauge.
It is unlikely, given your apparent unfamiliarity with the circuit, that y'all will be able to make repairs to the estimate portion, nor would about.
These leaves two areas to inspect: the sender unit and the wiring.
If you are familiar with unproblematic electronics and possess some simple test instruments, you tin can appraise the sender unit. Measure out the voltage and frequency of the pulses it produces. A railroad train of pulses which are clamped between ground and battery postive should be seen. The frequency of the pulses should be an integer multiple of the crankcase speed, typical iv to 8 times, depending on the arrangement of magnets and pickups.
If you have even a slight notion of electrical circuits you lot can check the wiring between sender and estimate for continuity or shunts.
If you require greater elaboration of whatever of these procedures please propose and I volition attempt to provide it.
posted 05-21-2002 09:23 AM ET (United states of america) Final twelvemonth I was diagnosing some tachometer problems on my boat. I hauled a 120 VAC powered Tektronics 100MHz, dual trace, triggered sweep oscilloscope out to the boat. Using it to check the signals coming from the engines to the tachometers, I could apace see the trouble.
Where I work, nosotros take oscilloscopes similar that lying around unused (because in these days of high speed digital video nosotros need much facier 'scopes to run across what the heck is actually happening). As I was making these observations on the tach pulses, the idea came to mind that this might have been the start time in the history of outboard engine diagosis and repair that anyone used a Tektronics oscilloscope to fix a tach!
Typically, on traditional 2-stroke engines, the tach pulses are derived from the battery charging circuit and are but the raw, pulsating DC coming off the curlicue winding, alee of the rectifier.
The rectifier does non make the pulses. In the typical configuration the rectifier is wired so that it provides the ground reference for the roll and also clamps the pulse amplitude at battery positive voltage.
When the rectifier fails, there are many possible failure modes. If it opens to ground, information technology may disable the tach. If information technology shorts the coil, it may diable the tach (and burn upwards the coil).
I had a bad rectifier on my old 1976 Merc 50-HP, but information technology had failed in such a fashion that the tachometer kept working just fine. The excursion that resulted was not doing any battery charging, but it made dainty tach pulses.
The other component of the tach sender excursion is a coil, usually located nether the flywheel. This is often called a stator, because it is stationary. Permanent magnets glued to the flywheel rotate above the scroll and induce current flow in the ringlet when they pass over it.
The stator is subject to harm in several ways. Usually too much heat causes them harm. Since they are at the top of the engine and under the flywheel, they are in i of the hottest areas of the engine and not well ventilated. Heat from current flowing in them also builds up. If you are chronically in need of maximum charging electric current because of depression battery voltage and high electrical load, the consequence over time can be to overheat the stator coil.
Connecting the battery to the engine with the polarity reversed is another fashion to practically instantaneously damage the engine charging circuit. You volition probable destroy the rectifier and peradventure the stator scroll if you have done this. It seems quite a common fault.
If you lot tin disconnect the stator coil leads from the rectifier, yous can measure the resistance of the stator coil and check it for shorts to ground (if it is floating electrically, as they usually are).
You tin also disconnect the rectifier and measure it, although on occassion a rectifier volition measure out as "good" but will fail in the existent excursion. The failure may only occur with elevated temperature, for example.
The good news is that an OEM rectifier costs $35 (Mercury) or ($65 Yamaha---simply of course those never fail, eh?). You tin supervene upon it in 5-minutes with unproblematic tools.
The bad new is that a bad stator coil is more expensive, and much harder to supersede. On some engines, the "stator" is office of a larger assembly that contains other coils. Sometimes these can be expensive. A friend with a MARINER engine (a Merc-Yamah hybrid) had to pay over $300 for a stator coil assembly. I have new stators on both my Yamaha engines and the coils only toll $90, in part because there are iii unlike assemblies for coils under the stator and I only needed 1 of them. (And the one I needed was the cheapest, likewise!)
Even getting the part, there is still much work ahead to replace the stator. You accept to remove the flywheel. From my feel with a trivial 70-HP Yamaha, it is impossible to remove the flywheel without the proper tools and an air-driven touch driver.
One time the flywheel is off, replacing the coil should be straightforward. When you put the engine dorsum together you may need to retime the ignition pulses. That is probably more truthful if your stator whorl assembly was an all-in-ane unit of measurement which besides had the ignition timing pulse coils in information technology.
Based on my experience, I would let a shop handle the flywheel removal, unless you happen to have the right tools lying around.
To sum upward: TACH doesn't work volition probably be:
--Bad wiring; a $5 prepare.
--Bad gauge; a $75 fix.
--Bad rectifier; a $35 - $65 fix.
--Bad stator; a $xc - $300 parts plus $75 - $150 labor fix.
--jimh
posted 05-21-2002 10:19 AM ET (United states) I approximate when you looked at the pulses with the scope you lot were only checking to run into if they were there, and not that they were the right period. Would make sense that whatsoever pulses at all would at least give some kind of tach reading.
I was going to use a Techtronic telescopic on mine last year when I had a problem (we have them at work too). I was as well caught up not really knowing what the waveform "should" look like instead of just seeing what was there. Wished I'd have tried information technology every bit it would have been interesting.
Practiced job Jim!
posted 08-13-2005 08:47 AM ET (US) The pulse output per revolution depends on the number of magnets in the flywheel and the number of poles in the curl winding over which the flywheel passes. Historically it was typical that there be a single winding and a unmarried phase rectifier, but newer engines (such equally the Evinrude E-TEC) may have multiple windings and utilise a polyphase rectifier.
Aftermarket tachometer gauges usually have adjustments for calibrating them to work with different engines what may develop tachometer pulses at different integer multiples of the crankshaft speed. An OEM tachometer may not have such an adjustment.
I take frequently read that OMC engines work best with OMC tachometers, but the precise reason for this is unremarkably not mentioned, nor practice I know why this preference is often repeated. Information technology may exist there is something about the tachometer signal from an OMC engine which is slightly different. For example, they could clamp the voltage to a lower level which might affect the reading on some gauges not expecting that.
posted 08-27-2005 11:07 PM ET (US) Since one of the main manufacturers of marine instrumentation puts plenty of their noesis on the web, I consulted them.
Tach settings for the shade tree mechanic: http://www.tflx.com/obtachtrad.html
The real fun is seeing the O-telescopic sweep in the bright sunlight... (why exercise you guys borrow these from piece of work? my father keeps ane in a closet at the house).
How To Fix A Boat Tachometer 115hp Evinrude Outboard,
Source: https://continuouswave.com/ubb/Forum3/HTML/002072.html
Posted by: wilsonceshounce72.blogspot.com
0 Response to "How To Fix A Boat Tachometer 115hp Evinrude Outboard"
Post a Comment