CDI powerfull multi-spark

[Clarence L.Snyder]

Michael Farrugia wrote:
> 
> Unfortunately there are no O2 sensors fitted,  But before we engine blew
> we put out the plugs and realised that the mixture was a bit week.  We
> increased the size of the jets but it seems the harm has already been
> done.  It was loosing a bit of performance when it got to 5000 on top
> gear , on lower gears performance was better.
> I can understand that weak mixture can heat up the chamber but I have
> heard it from two sources that very powerful spark can melt the piston.
> Can this be true?
> thanks
> Michael
> 
> >> I have put a CDI which gives a fairly powerful multi-spark on a 2
> litre
> >>  Ford pinto engine.  This engine is tuned to go up to 8500 RPM.
> >>  However after some runs the engine broke.  When we opend the engine
> up
> >>  we found that on piston was melted.  A friend of mine told me that a
> >>  powerfull spark may be the cause.  Has anyone encountered such a
> >>  situation and how can it be rectified.
> >>  Thanks in advance
> >
> >That souinds more like (1.) lean mixture, or (2.) (less likely)
> retarded
> >timing.
> >  Either can cause combustion chamber temps to soar...But, retarded
> timing
> >will cause a serious reduction in performance, which wasn't mentioned,
> >so I'd wager the "lean-out" scenario is what took place...
> >Do you have any data such as O2 or (?) readings?
> >Mike V.
> >
> 
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A hot spark cannot melt a piston. Too high a spark plug heat range, on
the other hand, can cause detonation which can hole a piston in a hurry.
This is totally unrelated to the strength of the spark plug discharge.
So can over advanced spark. Retarded spark can also cause cyls to run
hot, but usually you will get general overheating as well if this is the
case. Exhaust manifolds can glow red hot, or even hotter.
Running too lean at high power settings is the most common cause,
however. Rather err on the rich side if you are going to be wrong at
all.