What exactly does The small coil do?

[johnyrude200]

These two powerheads have obvious problems with them, and are already torn down, so to split the crankcase won’t take much time. I’m sort of interested to see if my guesses are right or wrong…sort of like opening up a christmas present 🙂

[pappy]

Fleetwin is correct. Hardly ever a worn crank bearing issue.
The Delrin ring on those 74-76 15hp all the way up through the 35 hp. were the subject of a Service bulletin if memory serves me correct.
The new material replacing the original ones was much better.

[fleetwin]

quote johnyrude200:

These two powerheads have obvious problems with them, and are already torn down, so to split the crankcase won’t take much time. I’m sort of interested to see if my guesses are right or wrong…sort of like opening up a christmas present 🙂

let us know what you find!

[fleetwin]

quote Pappy:

Fleetwin is correct. Hardly ever a worn crank bearing issue.
The Delrin ring on those 74-76 15hp all the way up through the 35 hp. were the subject of a Service bulletin if memory serves me correct.
The new material replacing the original ones was much better.

yes, many bulletins, and changes in materials/lube procedures. Those del rin plastic bushings should be considered a wear item and replaced everytime the mag plate is removed.
There were also very expensive kits for engines with worn crankcase mag plate pilot bushings that included a new mag plate and attaching hardware.

[legendre]

quote fleetwin:

Yes, the single coil on the right of the picture is the driver coil on the electric start/alternator wiring diagram you posted.
While there is an alternator, it is only capable of about 4-5amps at WOT, I doubt it could keep up with the load presented by a conventional battery/coil ignition system.

Um yeah.. and if they didn’t have that driver coil hogging space, they’d have enough room to put a proper 15A alternator under there! 😛

quote :

Additionally, you would have to have some sort of mag system for manual start models.

And on the manual-start models, that +single+ driver coil put out more energy than a +pair+ of similarly-sized conventional magneto coils?

Oh.. let me guess: They were stuck with using the same dumb mag plate for both models, right? The manual-start had provisions for everything, but lacked the charging coils? Yeah, that’s a crap compromise.. good that they got rid of it. No wonder the Japanese were handing us our national ass at the time.

[fleetwin]

Someone here explained once that the low tension system was developed partially because of the desire to get an alternator winding under the flywheel. No room for alternator windings using the two coils on the conventional universal mag set up.
And while I won’t even pretend to like/defend the low tension/hybrid system, the OMC CD2 system competed favorably with the Japanese stuff.

[legendre]

quote fleetwin:

Someone here explained once that the low tension system was developed partially because of the desire to get an alternator winding under the flywheel. No room for alternator windings using the two coils on the conventional universal mag set up.

Oh yeah, if you approach it from that direction, it does make sense.. the engineers were working within managerial and philosophical constraints, and this was just a low-point in an otherwise successful design cycle.

My main point, is that I’ve worked with several low-tension mags like this (in the motorbike world) – but prior to this one, I’ve never once seen a low-tension mag system that ran +two+ alternately phased ignition coils off of +one+ exciter coil. It seems like it would be low on power, and apparently, it was.

BTW, this is essentially a two-cylinder moped ignition, for those who might care.

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