amount of "poles" for 1990 90hp engine? for tach setup

stackz

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I bought ss competition gauges two years ago for my boat. its got a 1990 M90 90hp 2stroke mercury engine on it. I'm sorting out some problems with a couple of the gauges and one of them being that the tach reads too high at idle. Apparently the company is still selling gauges but the contact emails are down so they arent getting my questions.

I'll post up pics tomorrow at work and scan up the schematics I have from back in the day when I got them from their tech line...they are sorta dirty and faded but I'm pretty sure you can still make them out.

I just wanted to get this out tonight in case anyone had a remote clue to what I'm talking about before tomorrow.
 

j_martin

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Re: amount of "poles" for 1990 90hp engine? for tach setup

should be 6 cycles or 12 poles.
 

stackz

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Re: amount of "poles" for 1990 90hp engine? for tach setup

just trying to understand, is that because its a 3-cyl 2-stroke? so you'd have two cycles per cylinder = 6 cycles and then you just double that?

so if it were a 2-cylinder it would be 8 poles....4-cylinder it would be 16 poles??

anyway, I found my old documentation last night including a listing for engines. I also found an email I apparently printed long ago where the seller stated my engine was either a type II or type III, the tach diagram says type II is for 6cylinder/3pulse and type III is for 8cylinder/4pulse.

I have no clue lol.

pics (if you cant see them fullsize just right click and copy/paste the pic link to the address bar for fullsize)
tach.jpg

tach2.jpg
 

j_martin

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Re: amount of "poles" for 1990 90hp engine? for tach setup

What you fail to understand is that the tachometer is driven off the alternator, which is totally unrelated to the number of cylinders. Count the poles on the stator, and set it to that. You'll find it to be 12.
 

stackz

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Re: amount of "poles" for 1990 90hp engine? for tach setup

ah ok, gotcha. I'm still confused though on the tach diagram posted above as to whether its a type II or type III to get the correct tach reading as it doesnt cross reference 12 anywhere?

I guess I could just keep flipping the dip switches until I get the correct reading at idle maybe?
 

j_martin

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Re: amount of "poles" for 1990 90hp engine? for tach setup

Where does it wire into the engine or dashboard harness? Is it a standard alternator driven tach, or are they getting a coil pulse to drive it? The standard dashboard harness goes to the alternator, either at a rectifier connection, or a wire off a regulator that gives the same signal.
 

stackz

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Re: amount of "poles" for 1990 90hp engine? for tach setup

well there is no dashboard harness. I pulled all that out and rewired the boat from scratch as it had all deteriorated. only thing I kept was the controls w/wiring to the dash/engine and the battery positive/negative from the engine. I'm still trying to figure out if I have a commander or commander 2000 control setup (posted a question in another thread) as they seem to wire up slightly different.

I've basically just been tracing the 5 wires at the dashboard side as they have different colors than the ones shown for both control types in my service manual for some reason.

so basically just looked in the service manual at all of the charging system diagrams (there were about 10 or so) each and every single one of them had a grey wire coming off the rectifier that said "to Tachometer". I checked mine, sure enough it was a grey wire. Even though both control setups said it was the black wire that was the tach feed while the grey was the emergency stop feed. I hooked up the tach feed at the gauge to the grey wire on the 5-wire harness leading to the old dash and it works but reads high at idle (like 1800rpm). Dont think I ever got around to playing with the dip switches originally as the schematic I posted above says you cant damage the tach by having it set wrong or hooked up wrong.

on the gauge I have it wired to the (s, blue wire) terminal for "from ignition coil". the (w, green) terminal for "from alternator" is left empty.

did I wire it to the wrong signal lead?

and thats about where I am.
 

j_martin

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Re: amount of "poles" for 1990 90hp engine? for tach setup

I'm having a hard time following your story, but the gray lead off a voltage regulator (either on in a dual reg 40 amp setup) is the tachometer feed. On a rectifier either stator terminal will do.

It feeds a distorted AC signal with 6 cycles per revolution, or 12 polarity changes (poles)

Normally on a switchbox motor you don't feed from the ignition because any one ignition pulse will occur only once per revolution, or about 10 per second at idle. That makes the needle jumpy, or you'd have to damp the tachometer to the point of uselessness.

hope it helps
John
 

stackz

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Re: amount of "poles" for 1990 90hp engine? for tach setup

dont worry, I'm having a hell of a time trying to explain it lol. here's the link to my other thread with pictures. the second to the last is the 5-wire plug from the control box with the front portion of the plug in my hand simply going up under the dash and terminating with what you see in the last pic there.

http://forums.iboats.com/showthread.php?t=487574

here's pics from my service manual I just scanned in (knew it would be a good idea to bring it to work). I'm also going to take several more pics and write down the color codes per pin on each connector so I can try to pinpoint what control setup I have to try to get all this resolved once and for all.

but anyway...(only reason there's two of each is because I dont know which setup of either I have yet...I will try to figure that out this afternoon at home)
you can see in both charging diagrams, the grey wire is labeled for tach. I did a ohm test on the grey wire under the dash and at the terminal block and used it as a result...I have no idea why the two control diagrams have the black wire as the tach lead...

I guess my last question before I blow your mind with huge pics is this...since the grey wire comes off the terminal block (was accidently calling this the rectifier earlier oops) which comes right off the stator (the stator is technically the alternator right?) I should move the signal wire from blue wire to the green wire on the gauge (see bottom middle of the tach diagram posted in #1 in this thread)?

scan_Page_1.jpg

scan_Page_2.jpg

scan_Page_3.jpg

scan_Page_4.jpg
 

j_martin

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Re: amount of "poles" for 1990 90hp engine? for tach setup

I don't know what you've done before to the harness. Bottom line, the grey wire off'n a VR as shown, or either stator wire of a rectifier goes to the tach input that wants a 12 pole alternator signal.

hope it helps
John
 

Silvertip

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Re: amount of "poles" for 1990 90hp engine? for tach setup

I think the confusion arises over the fact that a 12 pole alternator produces 6 complete pulses. A complete pulse is a rather warped sine wave going positive from 0 through 90 degrees, then dropping for 90 degrees to 0, then going negative for 90 degrees and finally swinging back toward 0 again. Therefore the tach calibration dial should be set to 6P. As was mentioned, the number of cylinders on your two stroke engine has no bearing on the tach setting.
 

stackz

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Re: amount of "poles" for 1990 90hp engine? for tach setup

this is all well and good but does not address the original issue.

here's the schematic:
http://www.superhonda.com/photopost/data/519/tach.jpg

the right hand side box is for how to set the dipswitches on the gauge. there is no section for 6pulse or 12pole.

highest I see is 3pulse, yes the very last section says "6" but 6 what?

I'm at the point I just want to play with the dip switches until the stupid thing reads 800rpm at idle as thats the factory idle speed. I know its not right but I'm getting fed up trying to figure this crap out.
 

j_martin

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Re: amount of "poles" for 1990 90hp engine? for tach setup

this is all well and good but does not address the original issue.

here's the schematic:
http://www.superhonda.com/photopost/data/519/tach.jpg

the right hand side box is for how to set the dipswitches on the gauge. there is no section for 6pulse or 12pole.

highest I see is 3pulse, yes the very last section says "6" but 6 what?

I'm at the point I just want to play with the dip switches until the stupid thing reads 800rpm at idle as thats the factory idle speed. I know its not right but I'm getting fed up trying to figure this crap out.

That's about the only way you have out of this. It sounds like you have a "universal" tachometer and the factory that made it is gone along with it's support, so guessing is all you can do.

We've tried to give you what information we have. Most of it is in the nomenclature of the trade, meaning that if you had a merc, or livorsy, or any other current tachometer in your hand made for switchbox mercury engines, the terms would be the same as in the instruction book. Hope it helps some

I have observed over a fairly long life that poor communications often will doom a technical company, especially if they market to the public. That's what killed most of the microcomputer players. IBM, and Microsoft don't have a corner on genius, they have a corner on communications.
 

stackz

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Re: amount of "poles" for 1990 90hp engine? for tach setup

yeah, definitely next time I buy gauges I'm springing for faria or teleflex or something mainstream.

hell, I'm halfway to that decision point right now as it is...
 

Silvertip

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Re: amount of "poles" for 1990 90hp engine? for tach setup

Look at the the Type N row in the chart. It says the DIP switches are both set to ON for BOTH 5P and 6P engines. The absence of the P may be an oversight on their part but a bit of deductive reasoning goes a long way to problem solving -- especially since this is a universal tach and therefore suitable for both battery and magneto ignitions. The accuracy of the tach is going to be questionable since they use the same setting for both 5 and 6P stators. However, the degree of error (if any) can be checked with a shop tach.
 

stackz

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Re: amount of "poles" for 1990 90hp engine? for tach setup

well, I just went ahead and set it to type 4 and cranked it up. tach is reading right at 800rpm at idle now so I'm guessing its all good. seems to rev fine as well. at least the tach is now done. thanks guys!
 

Silvertip

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Re: amount of "poles" for 1990 90hp engine? for tach setup

No -- you are NOT good. As I pointed out, the Type N setting is what you need. Do the math. This engine has a 12P stator that produces 6P/rev. That is the equivalent of a 500 Hz signal which is what the chart calls for. Your tach is wrong and your idle RPM indicates that.
 

stackz

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Re: amount of "poles" for 1990 90hp engine? for tach setup

yeah, thats what I set it to. probably hard to read on the chart but the type N is actually type IV (4).
 
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