SOHC.co.uk Forums > CB500/550

NGKD6EA

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deltarider:
I use oils that claim/have a reputation to keep rubber parts like seals supple. IMO for our vintage engines such characteristic is more important than the ppm of zinc.

McCabe-Thiele (Ted):
Not sure about engine oils these days but modern ATF's do contain plasicisers that help maintain seal integrity.

Looking at the original post about the plugs being sooty, were there any other symptoms?

I would only worry if there was some sort of engine misfire as well, I've always reminded myself that holes in pistons are caused by weak mixtures - whats a little carbon between friends.

A little excess carbon might be sorted by adding something like Redex that raises the burn temperature as well as being an upper cylinder lubricant.

K2-K6:
There's two problem here, which effectively overlap when looking at the plug colour.

Valve stem oil seals, nothing is going to change that from adjustment, or really running a different plug temperature grade. May keep the plug from fouling a little more at low load demand by heating the tip a small amount to higher residual point.

The risk for going too low on plug temperature specification is that the tip can't clear adequately the resulting combustion effect to surrounding metal fast enough. This is the highest risk as ultimately if it climbs above critical  level it will produce pre-ignition in that chamber, colloquially known as "knock" which will definitely melt the piston crown if not quenched fast. It's effectively trying to turn that cylinder backwards as it completes it's cycle as the pistom comes up on compression against a glowing plug, all before the ignition is even thought about. Catastrophic, and very quickly, under full load conditions.

Its a projection of mine, as most are set this way from just going defacto X turns out, that it'll be slow running a little too rich regardless of oil inclusion, hence the suggestion to just try it with small change.  That'll not compensate at for the other problem, but may not add unwanted soot to the whole ensemble  :) its free to try this, and easy to reverse too. If thst were too much, It'll show as a flat spot in response just as you bring the throttle up from low speed under load, which will tell if its inappropriate as a measure.

Valid assessment to see if just a little "optimisation" can nudge it to more satisfactory running in its current setup really.

JezzaPeach:
Many thanks Ted and K2.

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