Outboard Motor Coils

[Rob Skala]

> 
> Yes, these are NGK plugs on my boat.  Now both two-strokes and rotaries have
> more power 'strokes' than four-stroke motors.  Is this significant?  What
> does it mean vis-a-vis four-stroke engines?
> 
> 
> Regards,
> 
> John
> 

I think the reason for these types of plugs, is not because of the power 
strokes but rather that both types of engines consume oil design. It is 
obvious with the two-strokes, but with the rotaries, oil is injected into 
the engine to lubricate the apex seals and provide some degree of gas 
sealing. For this reason, at low-speed operation, standard plugs would 
tend to foul from the oil during operation. Using these types of plugs 
will allow more reliable operation at low-speeds since there is more 
electrode surface area. I hope this makes sense.

By the way, the NGK SD-xx plugs used in the rotaries are fired by 
standard high energy igntion systems, not CDI systems, so they can be 
used in a normal engine provided you can find the right heat-range for 
your application. As an aside I once used one of these plugs in a 150cc 
McCulloch chainsaw and it ran really well.....much better than with the 
factory recommended plug !!!!

Regards,

Rob


Robert D Skala
Materials Research Group
School of Physical Science
Curtin University of Technology
GPO Box U1987
Perth	6001
WESTERN AUSTRALIA
Telephone: +61 9 351 2331
Fax:	   +61 9 351 2377
email: skala_rd at cc.curtin.edu.au