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Author Topic:   Tach Reading Too High
Ray posted 07-02-2001 10:46 PM ET (US)   Profile for Ray   Send Email to Ray  
My OMC Tach on my 225 Johnson often but now always reads about 1000 RPM's too high.. Is this a sign of a rectifier going bad? Last year on my 175 Evin. the tach. would occasionally go to zero and a new rectifier was the answer. Can anybody help?
Ray
Peter posted 07-03-2001 08:31 AM ET (US)     Profile for Peter  Send Email to Peter     
Ray,

Several years ago I had the same problem on my 1987 150. The tach was either reading too high or would go to zero. The cause was a blown voltage regulator. I would suspect that your regulator is shot. My mechanic was actually surprised that my motor had the original regulator (about 12 years old at the time). He said that they typically last about 3 to 4 years.

Bigshot posted 07-03-2001 09:21 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
ususally they go to zero for a rectifier. Try a nother tach before you replace the rectifier.
Ray posted 07-08-2001 10:38 PM ET (US)     Profile for Ray  Send Email to Ray     
Peter,
If you happen to see this, or maybe someone else can help, I looked at a wiring diagram for my 225hp and it appears that the 150 and 175 had a separate voltage regulator but the 225 does not. It appears to be part of the power pack or some other component. Does anybody have a clue?
Ray
Whalerdan posted 07-16-2001 11:52 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
I thought older motors didn't have voltage regulators. I've got a problem where the tach reads zero and I don't think my battery is charging properly. I this the alternator, voltage regulator (if I have one), or the rectifier? Motor is 1985 evinrude 115.
Bigshot posted 07-16-2001 01:18 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Tach would stop working if rectifier, not that.
caddis posted 07-16-2001 07:10 PM ET (US)     Profile for caddis  Send Email to caddis     
My tach stopped working this weekend. Won't move- stuck on below zero. We checked all the connections, and they are fine. From what I am reading, do I assume that the rectifier is the problem? I have no idea what that is. Are they easy to replace?
Bigshot posted 07-17-2001 10:24 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
What yaer and hp and make. If OMC, it is a piece of cake. A little silver round dohickey on the starboard side of the engine. Connects with I believe 2 yellow and 1 red wire. Cost about $20.
caddis posted 07-17-2001 10:32 AM ET (US)     Profile for caddis  Send Email to caddis     
Bigshot:

Sorry, yes, it is a 1981 235 hp OMC. I know the part you are talking about because we had to tighten the screws that hold it last weekend. Still didn't work, though. Thanks!

Bigshot posted 07-17-2001 11:21 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Get a new one. If you run it without a battery or the terminals come a bit loose, it will fry that rectifier/regulator. Cheap and if not the problem, you will use it one day. I always do.
triblet posted 07-17-2001 11:28 AM ET (US)     Profile for triblet  Send Email to triblet     
Rectifiers are easy to check with an ohmmeter.
They conduct electricity in one direction
but not the the other, so they show low ohms
in one direction, reverse the probes, and
they will show very high ohms.

That OMC "rectifier" is really two rectifiers
in one box. The red lead is probably common.

Chuck

Whalerdan posted 07-17-2001 12:22 PM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
This is all good stuff. I have the same problem and really appreciate all the info.
Whalerdan posted 07-17-2001 12:58 PM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
Hey! I just called my dealer on this rectifier thing. It's $205 for OMC engines with tilt and trim. The little round Bighot talks about is for engines without tilt and trim and cost $45. At least thats what they said. I'm going to check it out when I get home.
Bigshot posted 07-17-2001 01:56 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
No no no! My motors had TNT and this thing is like $20 from Sierra. The one on the bigger engines like my 94 225 is like $200 or $150(water cooled). Most older engines and smaller ones run these cheap ones. His 235 does, my 86 115 did and my 90 70hp. They are all the same too because I bought one for my 70 and it was the tach, later put it on my 115.
Whalerdan posted 07-17-2001 02:04 PM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
Bigshot, do you have a phone number for Sierra, and maybe a part number. $205 bucks seem pretty steep. Mine should be the same as yours as my motor is 1985 115 Evinrude.
Bigshot posted 07-17-2001 02:15 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Sierra is an after market manufacturer and I believe you can get them at NAPA. Your 85 has it. When this goes bad your tach usually stops and so does any charging. Try Napa and let me know. read the description above. Takes like 5 mins to pull it off(3 wires and 2 screws)Remember where the wires went. The 2 yellow I believe go together and the red goes next to it, etc. but write it down and take the part to NAPA.
Peter posted 07-17-2001 03:23 PM ET (US)     Profile for Peter  Send Email to Peter     
Yes, tach dies and so does charging. I would think an '85 115 would be the same as an '87 150. Old cross-flow cousins.
Bigshot posted 07-17-2001 03:31 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Yup!
Whalerdan posted 07-17-2001 08:25 PM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
If I'm looking at my engine right (again 115 evinrude 1985) it looks like the rectifier is a 3x5x1 box that sits on the top/back of the engine. I think is is a 35amp water cooled unit. The manual I have is for 75-225 HP and cover about 30 years so it really doesn't have a good schematic. Does this sounds right to you? It doesn't sound like the silver round thing you describe.
Bigshot posted 07-17-2001 08:33 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Nope! Look for the round silver thingy on the starboard side of engine. It is about the size of a quarter or half dollar.
Whalerdan posted 07-19-2001 07:41 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
Here's the scoop. In 1985 they went from a 6 amp rectifier charging circuit to a 12 amp. This caused them to go from the simple rectifier to a rectifier regulator. This is (lucky me) what I have. 6 amp rectifier - $45, 12 amp rectifier regulator - $205. By the way OMC didn't make the 115 engine form 1986-89, they made 110s and 120s.
Whalerdan posted 07-19-2001 07:43 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
One more thing I have to pull the flywheel to change. Not that big a deal just another pain.
Bigshot posted 07-19-2001 10:48 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Maybe I had an 85 then.
jimh posted 07-19-2001 09:00 PM ET (US)     Profile for jimh  Send Email to jimh     
I hope you have better luck getting the flywheel off than I did.

After two weekends of frustration, I gave up and had the dealer yank the flywheel for me and change out my bum stator coil on my Yahama outboard.

Whalerdan posted 07-20-2001 07:35 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
Jimh - did you try to use an air impact wrench on the fly wheel puller? I have one and was considering using it but am a little worried about damaging things. Hoping if I go slow it will work out.
jimh posted 07-20-2001 08:48 AM ET (US)     Profile for jimh  Send Email to jimh     
I asked the mechanic how he got the flywheel nut loose: "Impact Wrench". I think that is the ONLY way to get them loose.
triblet posted 07-20-2001 10:25 AM ET (US)     Profile for triblet  Send Email to triblet     
The extra $160 gets you a regulated "12V"
(really 13.somethingV) instead of unregulated
somewhere between 10V and 18V depending on
RPM and load.

Chuck

Whalerdan posted 07-23-2001 07:28 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
Well, I got the flywheel off, changed the regulator/rectifier, and got it all back together. $205 plus about 20 for the 1 5/16 inch socket and 1/2 to 3/4 extension. THE TACH STILL DOESN'T WORK! I don't know if the battery is charging, since I worked on it all weekend I didn't get a chance to take it out for a long day. Any other ideas?
Whalerdan posted 08-14-2001 02:47 PM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
Well it seems my battery is charging properly but my tach still isn't working. I checked the wiring and I think its good. Is there a resistance check one can do looking into the tach? Has anyone ever seen a tach go bad.
Bigshot posted 08-14-2001 03:33 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
They go bad! Can you borrow one?
Whalerdan posted 08-15-2001 07:28 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
Good idea! I'll ask my buddy to borrow one off his boat.
Badluck posted 01-28-2007 01:24 PM ET (US)     Profile for Badluck  Send Email to Badluck     
Tach on my 1985 Evinrude 115 will not work,replace stator & reglator ref. and tach. All wires check out. Please help.

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