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5hp Mercury CD

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swamp

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"Can someone tell me the diffe

"Can someone tell me the difference for the CD between a 5hp Mercury 2 cycle and a 5hp Mercury 4 cycle outboard.
Thanks,
Swamp"
 
"Graham,
The 5hp Mercs are si

"Graham,
The 5hp Mercs are single cylinders and it is called a CD unit. It would be the same as the switchbox in a multi cylinders outboards."
 
The 4 stroke engine is a Tohat

The 4 stroke engine is a Tohatsu. The 2 stroke might be a Tohatsu; it depends on the year.
 
"Graham getting schooled by a

"Graham getting schooled by a newbie, love it..
lol.gif
Just kidding, happy hunting"
 
"No! No! JB, I am not trying t

"No! No! JB, I am not trying to school anyone. If I came across like that, then I am really sorry. I am trying to learn something. I see that the price for a CD unit for a 2cycle 5hp is almost 3 times as much, than a CD unit for a 4cycle 5hp. Both have the same setup, a trigger, stator and CD unit. What is the difference? If someone knows, please educate me.
Thanks"
 
"Regardless of what name you t

"Regardless of what name you tack on it, the SCR in a 4 stroke is different than a two stroke.

The SCR is a switch in "the box" that interprets the pulse from the trigger (or actually a pulsar coil in the case of single cylinders).

So I'll back up a little here now.

The trigger/pulsar produces a pulse each time the flywheel magnet passes it - on one revolution of the flywheel it produces a positive pulse and a negative on the next (then back and forth, etc etc).

On a single cylinder 2 stroke, the SCR releases the charge to the coil regardless of whether the pulse is positive or negative because the 2 stroke fires every revolution.

On a single cylinder 4 stroke, the SCR only releases a charge to the coil for every positive pulse - the negative pulse is ignored since that is the "exhaust stroke" and you don't want the cylinder firing.

So no, you can't mix the two. Your two stroke would run like crap with a 4 stroke box, only firing half the time and your 4 stroke would backfire like crazy if there was any residual fuel in the cylinder since it would be firing on the exhaust stroke..."
 
"My above explanation is a lit

"My above explanation is a little off above, a spark on a 4 stroke at top dead center of the exhaust stroke would not likely cause a backfire.

However, it's the guts of the CDI box that are different. SCR operates differently, they have different blocking diodes and the capactior itself is different between 2 and 4 stroke models.

As to the CD/Switchbox debate


In general CD or CDI is used to describe the switchbox on Japanese built motors and Switchbox is used to describe (the CDI unit) on Mercury's. If you talk to someone of OMC persuasion they will refer to the CDI as a "PowerPack" - just kinda avoids confusion - If you saw "powerpack", you would assume we were talking about a Johnson or an Evinrude....

CD simply stands for "Capacitor Discharge" - and regardless of what you call the box, it's capacitor(s) is/are discharged when the SCR gets the pulse that it's looking for from the Trigger or the Pulsar (or if you have a very old single cylinder you will find it listed as an "exciter coil") or the Sensor (which are all just triggers with different names)"
 
"Can someone tell me the d

"Can someone tell me the difference for the CD between a 5hp Mercury 2 cycle and a 5hp Mercury 4 cycle outboard"

The electrical values are completely different.
 
"So's the action: One zap

"So's the action: One zap per revolution (2 stroke) vs. one per every other revolution (4 stroke, unless it fires for nothing on the exhaust stroke).

Jeff"
 
"That's really a question

"That's really a question I have never looked at - I made a couple guesses there above as how possibly the trigger functions (based on Mercs T4 ignition on twins), but really have no idea and could find no explanation on it either...

Maybe someone will donate their (fully functional) 4 stroke single so we can do some "live tests"
"
 
"Once again, it depends on whe

"Once again, it depends on whether or not they are both Tohatsu engines. If they are, the CD units may very well be interchangeable. Both would be single cylinder engines, with ignition systems that are practically identical.

If we actually knew exactly what engines we were talking about this thread might have some relevance."
 
"Graham,
Sorry I am just gett

"Graham,
Sorry I am just getting back to the CD (switchbox) question. Like Fastjeff stated, the only difference in a single cylinder 2 stroke and 4 stroke is the revolution of the flywheel. One revolution for a 2 stroke and two for a 4 stroke. They both require a voltage of around 20,000 volts to fire the plug. The coils for both have the same resistance as do the triggers. The charging coils, I am pretty sure, are the same. I know that Tohatsu stated that they are different electrical, but I do not buy that. So I purchased a CD (switchbox) unit for a 4 stroke and put it in my 2 stroke. They are both the same in electrical wiring, the only difference, is the 4 stroke unit is ¼” longer. This was 1/3rd the price that I would have to pay for a 2 stroke CD. I have run it for over three hours up and down the Satilla River with no problems. I will let you know more when I get more hours on it. Thanks for all the replies.
Rick"
 
"There is a $35.00 price diffe

"There is a $35.00 price difference between the two and four-stroke CD module and do they have different values....Open up a service manual and see for yourself. If the pulse is too strong you will put a hole in your piston. If it is too weak you will prematurely foul a plug. Regardless, putting on an incorrect part is a mistake."
 
"I think it will be okay, but

"I think it will be okay, but I do not see why the price difference was so great."
 
"Tony,
The price is what star

"Tony,
The price is what started all this. My CD unit went out and I went to my Mercury dealer and they wanted $285.00 for one. I could not believe this so I started to look around. The part # for my CD is 16061T04 which I found for $243. I then looked at the 4 stroke to see what they wanted and found the part # 803558T02 for $84. So you can see why I ask the question. I purchase one and my motor right now runs great. I have got over 3hrs so far. Now if Tahatsu Guru can get my CD for $119 I'll will buy it. Also I would like to know what service manual would tell you that if you applied more voltage to a spark plug that it would put a hole in your piston. Back in the days of my hot roding, we use to put in colts for 50,000 volts to insure a better spark. Further more if they were less voltage for less spark, the engine would miss. So fouling the plug on a single cylinder is not an issue. You would have to fix the problem.
Thanks,
Rick"
 
"Tohatus Guru,
Thanks for the

"Tohatus Guru,
Thanks for the info. but I have a Mercury outboard not a Tohatus. Are you telling me that the parts for a Tohatu are interchangeable with a Mercury? Mine is a 2001 5hp Mercury. Thanks for the help
Rick"
 
"Rick, what the name says on t

"Rick, what the name says on the cover often has little to do with who actually built the motor.

Tohatsu builds all the small 4 stroke Mercs. They also built a run of 2 strokes a few years back (that are clearly marked "product of Japan" - but should not be confused with the Mariner line built by Yamaha (100%) for Merc prior to the early/mid 90's).

Tohatsu also builds ALL the Nissan outboards.

In years past, Yamaha built pretty much all the powerheads and gears for most Mercs (at least up to the 4 cylinder models).

Not that it was totally one way. For a good few years Merc built all the lower cases for Honda.

Suzuki built all the little 4 stroke Johnson's and there are numerous other examples.

So yes, there is a chance that you have a 100% Tohatsu motor that just happens to be painted "phantom black" and has Merc stickers on the side (which could have just as easily read Tohatsu or Nissan) and the motors would have been identical...."
 
"Graham,
Help me here, my mot

"Graham,
Help me here, my motor is a 2001 5hp serial# 0T022164 and the part# for my CD unit is 16061T4
the sierra part# is 18-5792. Here on MarineEngine.com, they want $224 for it and on Crowley Marine their are asking $274. I saw the sites that Tohatsu Guru gave me and the price is not that bad but how do you know that it will work? The unit I purchased for $84, that was for a Mercury 5hp 4 stroke, works great for the time being. There is a statement on the Tohatsu site that says that the 4 stroke CD unit will not fit on a 2 stroke.I am really confused, help me out please!
Rick"
 
"Rick not much I can add - I d

"Rick not much I can add - I don't do any work on 4 strokes at all and can't tell you more than the few notes on their ignition which is contained in the service manual.

Will that unit continue to work? Who knows - it could last a week, a month, a year or maybe forever.

From your serial (plus since it's a single cylinder) you do have a "product of Japan" outboard.

When I bought my entire collection of Merc service manuals it didn't even include a manual for the single cylinder 4 and 5 horse motors (which Merc had nothing to do with other than supplying the decals bascially).

Why not contact Tohatsu and ask them directly why they say that the unit will not work with a 2 stroke...."
 
"Rick,

You would be better

"Rick,

You would be better off buying replacement parts for both of those engines from Tohatsu. The price will be much less than from Mercury. The only differences are the color, the decals and the price of the engines. Tohatsu sells these engines for quite a bit less than the Mercury price tag.

Both of those CD units are available from Tohatsu for less than $150. Try this site;

www.tohatsu-nissan-parts.com"
 
"Tony,

I just don't se

"Tony,

I just don't see any reason to trade barbs. Whether its some sort of jealousy on your part or some sort of imagined wrong your righting I just don't see a need to feed you any reason to continue. If you want a fight, find someone else."
 
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