1973 Johnson 115hp power-pack assassins?

[JarFisch]

I recently acquired a 1973 Johnson 115hp motor from a fellow who had owned it himself for about 5 yrs. As the story goes..he got it from the first & original owner who was a state Parks & Wildlife employee. The supposition & superficial evidence was that the motor had been generally well cared for over the preceding years.

I was given a rudimentary maintenance history from the seller who disclosed having to replace the power-pack, plugs, impeller, & starter at some point; as well as having to deal with a relatively minor bendix-gear issue. Aside from that, the seller convincingly asserted that his experience with it was very good & stable; although he did confess that he hadn't run the engine in approximately 18 months or so.

Now I have virtually no reason to suspect any misrepresentation on the part of the previous seller. In fact, he handed over a box of miscellaneous used parts from which it's easy to see that he did apparently complete the various maintenance items claimed. ~~ However, . upon mounting the motor onto my boat and taking it down for a first-round shake-down test..., my buddy & I quickly discovered the motor was, in fact, only running on 2 cyls. Quick & dirty diagnostics at water's edge indicated the port-side bank wasn't firing at all. So back to the boat-barn we went.. to take a closer look. No, as of yet...we've not been able to take any electrical readings while the motor is running!

My boating buddy and I are long-time boat owners. We've both dealt with a variety of boat & motor 'issues' in the past. Nevertheless... neither of us can stake any claims as to being any kind of "marine-engine-expert". If anything, we're just well-experienced DIY amateurs. So after doing homework here on the forums, and following several troubleshooting procedures available elsewhere as well... our best evaluation is that the power-pack is likely bad. -- So an online order for a power-pack is in the works.. and soon it will be replaced.

So with all of the above run-up I'll finally get down to the the point of this post.

I'm hoping that the old&crusty (like me) outboard-motor experts (not like me).. can offer any of their insights & thoughts on what kinds of circumstances can, or have typically been found to, cause premature damage (burnouts etc) of outboard ignition power-packs.

The reason I ask about power-pack mortality...is that we've just recently discovered two (2) additional power-packs (presumably defunct) which were in the previously mentioned box of 'used parts'. Obviously, the elimination of any real causative problems are always preferred over just putting a bandaid on a symptom. At well over $100 apiece... I'd kinda' like to avoid having to replace another power-pack or two... simply because I failed to do the job right initially.

My background in is electronics and industrial electro-mechanical stuff & such.... - so I can't help but suspect there's some kind of electrical condition which may be operating either at the edge of, or outside of, design-spec range (actually I would think transient spikes would be more likely)... and which might could explain the (assumed) premature power-pack failures.

Please excuse this rather long-winded noobe posting..but in closing I'll try to offer the following as some kind of explanation:

My last Johnson 115hp (1978) was bought used in 1995. At the time it was already 17yrs old! Now aside from the occasional impeller and routine lube & seasonal maintenance etc. ... we NEVER EVER had to replace the power-pack(there's 2 of 'em). And that was true over the entire 15 YEARS we owned & operated that previously well-matured Die-Hard Beast! --- So I guess the inescapable question is... Why am I looking at what appears to be three (3) blown power-packs??


Thanks in advance,

Cheers! ~ Dave

 

[HighTrim]

Re: 1973 Johson 115hp power-pack assassins?

Re: 1973 Johson 115hp power-pack assassins?

Best said by Joe...

(MCD Powerpack Failures - 1973 +)
(Magneto Capacitance Discharge Systems)
(J. Reeves)

The usual cause of having those type powerpacks fail repeatedly is having a very small of voltage applied to the Black/Yellow wire at the pack. Test as follows.

Disconnect the Black/Yellow wire at the powerpack.

Insert either an ampere meter or a volt meter set to its lowest DC voltage reading between that Black Yellow wire and ground.

With the ignition key in the OFF position, observe the meter reading. Now turn the ignition key to the ON position and again observe the meter reading.

Any reading, movement of the meter needle, would indicate that battery voltage is being applied to that Black/Yellow wire. If a reading is present, remove the other end of that Black/Yellow from the raised terminal of the ignition switch.

If the reading ceases to exist when the Black/Yellow wire is removed from the ignition switch, replace the switch. If the reading continues to exist, there would be a short of some kind in either the engine or instrument wiring harness.... to determine which, simply unplug the large RED electrical plug at the engine which would eliminate the instrument cable.

 

[emdsapmgr]

Re: 1973 Johnson 115hp power-pack assassins?

You may have a third failed power pack on the engine, possibly over a 37 year period. For a potted electrical component that may amount to "normal" life expectancy. Having said that, the power pack is the most likely failure component in that ignition system.

 

[Tim Frank]

Re: 1973 Johnson 115hp power-pack assassins?

I recently acquired a 1973 Johnson 115hp motor from a fellow who had owned it himself for about 5 yrs. As the story goes..he got it from the first & original owner who was a state Parks & Wildlife employee. The supposition & superficial evidence was that the motor had been generally well cared for over the preceding years.

I was given a rudimentary maintenance history from the seller who disclosed having to replace the power-pack, plugs, impeller, & starter at some point; as well as having to deal with a relatively minor bendix-gear issue. Aside from that, the seller convincingly asserted that his experience with it was very good & stable; although he did confess that he hadn't run the engine in approximately 18 months or so.

Now I have virtually no reason to suspect any misrepresentation on the part of the previous seller. In fact, he handed over a box of miscellaneous used parts from which it's easy to see that he did apparently complete the various maintenance items claimed. ~~ However, . upon mounting the motor onto my boat and taking it down for a first-round shake-down test..., my buddy & I quickly discovered the motor was, in fact, only running on 2 cyls. Quick & dirty diagnostics at water's edge indicated the port-side bank wasn't firing at all. So back to the boat-barn we went.. to take a closer look. No, as of yet...we've not been able to take any electrical readings while the motor is running!

My boating buddy and I are long-time boat owners. We've both dealt with a variety of boat & motor 'issues' in the past. Nevertheless... neither of us can stake any claims as to being any kind of "marine-engine-expert". If anything, we're just well-experienced DIY amateurs. So after doing homework here on the forums, and following several troubleshooting procedures available elsewhere as well... our best evaluation is that the power-pack is likely bad. -- So an online order for a power-pack is in the works.. and soon it will be replaced.

So with all of the above run-up I'll finally get down to the the point of this post.

I'm hoping that the old&crusty (like me) outboard-motor experts (not like me).. can offer any of their insights & thoughts on what kinds of circumstances can, or have typically been found to, cause premature damage (burnouts etc) of outboard ignition power-packs.

The reason I ask about power-pack mortality...is that we've just recently discovered two (2) additional power-packs (presumably defunct) which were in the previously mentioned box of 'used parts'. Obviously, the elimination of any real causative problems are always preferred over just putting a bandaid on a symptom. At well over $100 apiece... I'd kinda' like to avoid having to replace another power-pack or two... simply because I failed to do the job right initially.

My background in is electronics and industrial electro-mechanical stuff & such.... - so I can't help but suspect there's some kind of electrical condition which may be operating either at the edge of, or outside of, design-spec range (actually I would think transient spikes would be more likely)... and which might could explain the (assumed) premature power-pack failures.

Please excuse this rather long-winded noobe posting..but in closing I'll try to offer the following as some kind of explanation:

My last Johnson 115hp (1978) was bought used in 1995. At the time it was already 17yrs old! Now aside from the occasional impeller and routine lube & seasonal maintenance etc. ... we NEVER EVER had to replace the power-pack(there's 2 of 'em). And that was true over the entire 15 YEARS we owned & operated that previously well-matured Die-Hard Beast! --- So I guess the inescapable question is... Why am I looking at what appears to be three (3) blown power-packs??


Thanks in advance,

Cheers! ~ Dave

If you are new to this forum, you will quickly find that the overwhelmingly most common first advice you are going to get is some variant of "Get yourself a $50- OEM service manual, it will pay for itself the first time you use it, and then go on saving you money for years".

I would add as #2, do NOT order a new power pack until you have done the troubleshooting sequence from the aforementioned manual; the major components in that ignition system could add up to many hundreds of $$$, and not be the problem. If you want to just change out parts until you luck into the right one, you might just as well take it to a shop...
3) Don't throw any of those "extra" power packs....I'd bet that "some" of them are OK and were installed to try to solve a problem that lay elsewhere. Do the proper troubleshooting and you may already have a usable power pack "in stock".

 

[JarFisch]

Re: 1973 Johnson 115hp power-pack assassins?

Well! -- After finally getting back to check in here... I find this is a nice surprise! ((a local thunderstorm took out our net-connection last night just after my posting!))

Thanks very much to you Chris (HighTrim).. for the information passed along from J.Reeves. That is just the kind of info needed. -- In reviewing the schematic sheets I see that the Black/Yellow wire turns out to be the the magneto-grounding 'shutoff' circuit loop. I can easily imagine why any stray (floating) potential on that power-pack input is NOT a good thing. We'll verify we've got a well-isolated and protected path for that wire all the way up to the ignition switch. Switch integrity will be checked as well.

@emdsapmgr : You know.. that's a very good point you make about our unspoken assumption regarding the 3 power packs. The fact is that we really have no way of knowing IF those units served their 'normal' life-expectancy roles over the entire 37 year span, OR IF... they are actually all rather later-date victims. Along with the truth of that uncertainty, there is always the risk of a false conclusion. ~ Thanks for the reminder and - Point taken!
What speaks more to my immediate focus however, is the helpful insight you provide with your closing statement.. " the power pack is the most likely failure component in that ignition system. " Actually... that's a bit of a relief in a way, for that reduces the chance of possible issues with the stator & related coils & stuff etc.

And finally.. thanks very much Tim! You're preaching to the choir about service manuals Amigo! We've already got a SELOC manual for the motor. It's a helpful guide to be sure, but still "oem" is always best. Thanks for the reminder though! I'm about to order an original Johnson srvc manual listed as being for a 115ESL73 motor. Our motor is actually a 115ESL73M ! Now I don't suppose there's any concern about the letter-suffix "M" in this case. ~ is there??
----> As for throwing money at parts trying to fix any motor on a 'trial-&-error' basis...NO THANKS! Beentheredonethat!
In fact that's precisely what my original post is attempting to avoid. And I've already set about efforts to triple-verify the current power-pack's health status prior to installing another. -- Interestingly... one of the adjunct tasks will be to definitively verify the *actual* status of the other pair of (presumably defunct) power-packs.

The only other thing (& I know this is a long-shot...but...) - I don't suppose anyone has ever uncovered a *detailed* electrical schematic describing the ACTUAL circuitry & specific discreet components that go into the manufacture of one of these "power-packs"?? -- My background allows me a certain amount of leeway in making an educated guess. But it still would be just a 'guess'.

My sincere thanks to you all for providing your feedback & insightful suggestions. It's heart warming to find a group of other water-bugs who are so supportive and helpful with the challenges of troubleshooting tasks.

Cheers!
dave

 

[McGR]

Re: 1973 Johnson 115hp power-pack assassins?

I used to have a '76 85hp which had the same ignition system as your motor. I still have a factory manual for this motor. I was pleasantly surprised to find that the manual included a schematic diagram of the internal componentry of the power pack. I'll see if I can place a scanned copy of the diagram here for you. I've got to find the old manual first... it's somewhere in my basement.

 

[Tim Frank]

Re: 1973 Johnson 115hp power-pack assassins?

And finally.. thanks very much Tim! You're preaching to the choir about service manuals Amigo! We've already got a SELOC manual for the motor. It's a helpful guide to be sure, but still "oem" is always best. Thanks for the reminder though! I'm about to order an original Johnson srvc manual listed as being for a 115ESL73 motor. Our motor is actually a 115ESL73M ! Now I don't suppose there's any concern about the letter-suffix "M" in this case. ~ is there??
----> As for throwing money at parts trying to fix any motor on a 'trial-&-error' basis...NO THANKS! Beentheredonethat!
In fact that's precisely what my original post is attempting to avoid. And I've already set about efforts to triple-verify the current power-pack's health status prior to installing another. -- Interestingly... one of the adjunct tasks will be to definitively verify the *actual* status of the other pair of (presumably defunct) power-packs.


Cheers!
dave

They are available new from Ken Cook, but I just lucked into a good deal on eBay, so it's always worth a quick look there, first.

 

[McGR]

Re: 1973 Johnson 115hp power-pack assassins?

Here's the innards of your powerpack:



Uploaded with ImageShack.us

 

[JarFisch]

Re: 1973 Johnson 115hp power-pack assassins?

Hey there McGR!
Many many thanks to you for the ignition schematic!

I'm a bit surprised and impressed though. This design requires only two triggering inputs (only two sensor coils). I didn't realize that. Though I've never needed to replace a stator in the past... I have certainly used the electrical diagrams in my SELOC manual. And even though I understood there are only two charge coils... I've been mistaken in my assumption that there were actually 4 separate sensor/trigger coils; one for each cyl. --- Having referred to those electrical diagrams of our manual many times... it makes me wonder why I didn't notice only 2 sensor coil before.

Anyway... I've got a genuine Johnson service manual on its way. We'll see if it has the same or similar schematic in it.

In any case, I'd like to thank you again for taking the time & effort to go find your manual down in the basement! ~ If yours is anything at all like what my old basement used to be (dark & spooky) <<shudder!>> then you deserve 100 Kudos for gumption & bravery!

Cheers ~ Dave

 

[JarFisch]

Re: 1973 Johnson 115hp power-pack assassins?

They are available new from Ken Cook, but I just lucked into a good deal on eBay, so it's always worth a quick look there, first.

Yeah ..thanks for the tip Tim. -- And I actually found a reasonable deal on Ebay as well. -- About $24 delivered to my door. Can't argue with that!

Cheers,
Dave

 

[McGR]

Re: 1973 Johnson 115hp power-pack assassins?

I agree, the trigger coil design is quite elegant. If I remember correctly, there are two sets of magnets in the flywheel of opposing polarity. Basically, when one magnet whizzes past the sensor coil it pushes the current through in one direction and triggers the correctly polarized SCR. When the opposing magnet passes the coil it triggers the other SCR...

I actually decapsulated and repaired my power pack. I did manage to run the motor on the drive with my repaired pack, though I ended up buying a new one anyway. The repaired unit never did get a chance to run on the water. I still have the decapsulated/repaired pack, so if you have questions, let me know.