[OMC-Boats] Electric Shift Circuit Protection

There are probably some sound reason why OMC engineers did not choose
to provide specific fuse-protection on the isolated shift coil circuit.

a) The circuit is already protected by the 20-amp IGNITION circuit
fuse, as the the engine coil/distributor.

b) They use their 7-position fuse distribution panel, which was
already provisioned.

c) You want the "cleanest" least resistive circuit path. That means
the closet thing to a straight wire. That's because marine
environments can be brutal on electrical systems and wiring, and in
particular on connectors and junctions.
If you add two more fuses you add at least four more junction points,
at the very least. And the current drain of each shift coil is
relatively small. And the shift coil device design is well insulated
and protected in the lower unit.
The last thing you want is losing electrical power to the coil while
underway. If the current setup encounters a DEAD SHORT, it will blow
the IGNITION fuse and your engine will not over-rev in fact in will
shutdown immediately.
If you added a shifter fuse and it OPENED up while under way, you risk
a lot more than the shifter coil.

d) The mod you SHOULD all consider is this: Add a GROUND strap
between the lower unit and the intermediate case. Make sure your
intermediate case is well grounded to the engine block and the battery
ground. We tend to forget that ground paths are equally important to
operational efficiency. Also, clean and inspect the two KNIVE BLADE
connectors that feed the shifter coil and them seal them against
moisture intrusion with brush-on tape or RTV silicon. These
connectors are rather out of sight and out of mind. You will locate
them in the vicinity of the tilt motor near the transom on the Port
side.

Lee

On Aug 17, 2009, at 7:58 AM, Lee Shuster (lib1) wrote:

>
> First check the forward and reverse coils (one at a time with an
> ohmeter, out of circuit.)
>
> A good coil will read between 4.5 and 6.5 ohms.
>
> Most likely the electrical coil is okay but the spring tab has
> broken off.
>
> I wouldn't recommend fuse-protecting the coils, but you can
> calculate the current flow in amps using Ohm's law. I generally see
> 2 to 3 amps current draw on my digital ohmeter, when shifting with
> the motor not running and battery at approximately 12.3 volts.
>
> Lee
>
>
> On Aug 16, 2009, at 10:46 PM, jd wrote:
>
>> yikes. this strikes fear in the hearts of .......me.
>>
>> both the up and down wires are pretty accessible before they get to
>> the outdrive stuff.
>>
>> a) any technical reason why a person couldn't put an inline fuse on
>> both those wires just for situations like this? It would be
>> pretty easy to do.
>>
>> b) any technical reason why OMC didn't back in the day?
>>
>>
>> (there i go again, wanting to put fuses on everything)
>>
>>
>>
>>
>>
>>
>>
>> On Aug 16, 2009, at 7:54 PM, ANDY PERAKES wrote:
>>
>>> Yeah, that's what I was thinking too. I was a bit surprised there
>>> was no fuse -- at least not one outside the stern drive (I guess
>>> there could be one inside, but it doesn't show on the schematics
>>> and doesn't seem a likely place to put one). What I didn't get to
>>> do was test the resistance of the coils so I guess that's next,
>>> but barring any big surprises from the group, it looks like I'll
>>> be taking my first foray into the lower unit. It still seems odd
>>> to me that the coil would go so quickly like that, but I guess
>>> it's possible. There's no sound like something chunking around or
>>> loose when I turn the prop by hand or run in reverse.
>>>
>>>
>>> ----- Original Message -----
>>> From: "Don Mandelas" <dmandelas@...>
>>> To: "Evinrude & Johnson Boats of the 1960's and 70's" <omc-boats@...
>>> >
>>> Sent: Sunday, August 16, 2009 9:20:23 PM GMT -05:00 US/Canada
>>> Eastern
>>> Subject: Re: [OMC-Boats] Forward Clutch Won't Engage on Late-1967
>>> 3-wire Shifter - Update
>>>
>>> Since you have power all the way back then I guess its not a fuse
>>> which would protect the forward coil.
>>>
>>> Don
>>> 1697 Sportsman 155
>>>
>>>
>>> Date: Sun, 16 Aug 2009 18:17:09 -0400
>>> From: aperakes@...
>>> To: omc-boats@...
>>> Subject: Re: [OMC-Boats] Forward Clutch Won't Engage on Late-1967
>>> 3-wire Shifter - Update
>>>
>>> I was able to trace power all the way back to the stern drive so
>>> its not the shifter switch or another break in electrical power.
>>> At this point it doesn't appear to be something I can repair in
>>> the water so we're starting to paddle. Obviously a fried coil is
>>> one possibility; can anyone name any other high-probablility
>>> possibilities? Thanks!
>>>
>>>
>>> ----- Original Message -----
>>> From: "ANDY PERAKES" <aperakes@...>
>>> To: omc-boats@...
>>> Sent: Sunday, August 16, 2009 5:15:37 PM GMT -05:00 US/Canada
>>> Eastern
>>> Subject: [OMC-Boats] Forward Clutch Won't Engage on Late-1967 3-
>>> wire Shifter
>>>
>>>
>>> So once again I made the mistake of trusting someone else to
>>> ensure the ski
>>> line was clear of the drive and once again got a harness cable
>>> wrapped
>>> around the drive. Only a small ding in the prop and a slight bend
>>> in the
>>> shear pin (for which I had a spare and easily changed), but now my
>>> forward
>>> clutch won't engage (reverse work's fine). I have the late-1967 3-
>>> wire
>>> set-up out of the shifter, but unfortunately I can't see any more
>>> than that
>>> given the conditions. (I should add I'm on the water so I don't
>>> not have
>>> access to any manuals, limited tools, and its a bit too rocky to
>>> be poking
>>> around very much.) If anyone happens to see this and has any
>>> thoughts I can
>>> try before giving up and paddling back in, I'd sure appreciate
>>> it. Even
>>> though I have a 3-wire, I've already tried Lee's 5-wire trick of
>>> shutting
>>> down in neutral and backing in reverse; didn't work. Thanks!
>>>
>>> Andy
>>> 1967 Reveler
>>>
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Received on Monday, 17 August 2009