NGKD6EA

[JezzaPeach]

Hi all. I know the ideal is a top end rebuild BUT with only gradual sooting of the plugs, I have switched back from NGK D8EA to D7EA as I understand they run slightly hotter which I think should help. I expect it is pretty marginal, but to take it a step further has anyone used D6EA (which I think is the lowest number available)?

[Johnwebley]

Hi all. I know the ideal is a top end rebuild BUT with only gradual sooting of the plugs, I have switched back from NGK D8EA to D7EA as I understand they run slightly hotter which I think should help. I expect it is pretty marginal, but to take it a step further has anyone used D6EA (which I think is the lowest number available)?

It sounds like your not riding the bike enough,

They need to get hot and rev



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[K2-K6]

Although I can see the reasoning, the first response should be to reduce fuelling slightly to see if there's space there to clean up low speed mixture.

For no PD carb, the idle airshow adjustment can be moved OUT by 1/4 turn from where it is to then assess result.

I'd be more comfortable with not going below a NGK 7 grade on these if it were mine, that's without exceptional reason.

[deltarider]

In The Netherlands dealers and mecs advised the D8ES-L (or the ND equivalent). The "7" was considered the plug for break-in period only. This was advised because we used to ride at maintained high speeds. US riders usually have the 7. They prefer to ride at lower rpm's. The D8ES-L, halfway the  '7' and the '8', was also adviseded by Honda France for the CB500. They said it was auto-nettoyant selfcleaning. Many see the D8EA as a renamed D8ES-L
Sooty plugs. First suspect is the air intake. What filter do you run and what is its condition? Is air intake free from obstruction like a forgotten cloth underneath the seat? The Cb500 will get sooty plugs after too much idling. Honda meant this bike to be a workhorse, in other words: start engine and begin riding as soon as the chokes are opened. I have the  feeling that nowadays many CB500s are subjected to prolonged idling (doing maintenance). These bikes don't like that.

Concerning a top end rebuild. Let me say this: in general people have no idea how many miles you can ride these bikes, without needing one. Mine has done over 140.000 km and still has the original pistons. BTW, the other day I read about a Goldwing (1975-6) which had done 650.000kms and when opened for a rebuild, the mechanic judged that all what it needed was new rings. Pistons still good. I have knowledge of a CB500 owner, who had done 220.000 kms and thanks to his dayly rides, his engine had not been opened yet. Nine of ten issues I had, had to do with standing, not with riding.

[JezzaPeach]

Many thanks both. I ride it plenty, I guess it’s the valve guide oil seals, but it’s not bad enough for a top end overhaul. I’ll try the idle mixture anyway and see how that goes.

[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.