Forum

[Steve T]

Hi all wondering if you could advise on the state of this plug this is after a 120 mile run on which the bike ran well does it look like its running rich or burning oil don't know how much oil its using as I have some oil leaks which is next question here's the plug

can oil come up from anywhere from this nut as it seems to have around this area
Thanks for any help as I've got have. The head off to fix the leaks and need to know whether I need to look at the h e valves etc.

[Beezabryan]

Plug looks sooty - rich
Oil is usually shinier on a plug

[Mark M]

I'd agree with Bryan, sooty=rich. Do be careful though, modern fuels burn much whiter/greyer than the old pictures in the back of Haynes Manuals which we used to use as a guide! Also that looks like an iridium plug which also tends to burn very hot and therefore clean. None of that means it isn't running rich but these factors may mask the true extent of the richness.

REgards, Mark

[PeteF]

A bit rich but not excessively so I would think. If you are removing the head it doesn't make sense NOT to check the valves and guides.

[Tim NZ]

Total lack of info....


Brand of plug? HEAT number of plug? At what speed was the ride taken? What carb and jetting? How long did the bike idle before the plug was pulled?


In use, the surface of Spark plugs is slowly coated with amorphous carbon, this is more so when the plug temp is below 200c, or the mixture is too rich. If it remains on the plug for periods of time, it is gradually converted into graphite; a good conductor or electricity, and also a ready absorber of water vapours. Such plugs will slowly build up increasing layers of carbon fouling, frequently wet in appearance, though not always, and are highly prone to misfiring issues. At plug temps between 200-400c, the fouling no longer accumulates, but neither does it dissipate. With out Lead in Petrol you need plug temps of between 400-500c to start to see this residue ‘burn off’ and keep the insulator clean.
The removal of Lead oxide, corrosive scavengers, and Lead from petrol has also removed the ‘self cleaning’ properties from petrol. No longer are there the coloured shades of yellow-orange-brown that once used to build up as a glaze on the central porcelain, the former generally accepted indication of ‘optimal’ air-fuel mixture. Which it never was either, it simply indicated optimal Plug operating temps!

[Tim NZ]

The typical CI barrel 500 bullet uses (burns) approx 1 - 3 cc of oil for every mile it travels, so unless you know what your oil consumption is prior to disassembly...


While you have the head off, check the piston and rings:


If ANY of the rings are tight in their grooves and do not freely pass right around the piston, or there is definite visual sign of wear to the oil ring, REPLACE THE PISTON and rings!
If there is ANY evidence of piston slap, (clear areas in the carbon staining, fore and aft, on top land) dimentionally check EVERY aspect of the piston


If the rings are tight in their groves DO NOT clean up the piston and fit new rings; your piston IS FAILING!


IF there is evidence of excessive ring blow-by (blackened piston skirt) or over heating of the piston (Blackened underside of piston crown)


REPLACE the piston! And then double check the ignition timing.


With the OEM pistons Top-land diameter is critical to life expectancy. The top-land dia must be at least 0.028" smaller in size than the nominal bore size or piston-slap and ring-land compaction is likely, and the risk of eventual crown separation is accelerated.


I have encountered far too many OEM pistons with too large a top-land and they are the ones that are prime indicates for 'Grenade of the Year' contest.

[Steve T]

Thanks for the replies guys, Tim will come back with relevant details thanks f

[jefrs]

I agree it looks too rich and sooty. It should be a brownish grey.
If you have a carburettor it is fairly easy to lean it up. With an Amal I tend to go more by ear and feel than science: "the bike ran well". A cold plug is for racing where the motor is constantly running hot (thicker ceramic = more cooling). Carbon fouling occurs when the plug does not reach optimal temperature, the plug is too cold, not much chance of that in a race engine. So if you run less enthusiastically you may want a hotter plug.
The only real way to assess plug colour is to take it for a thrash and stop the engine quickly without pottering in and letting it idle. If you do let it doddle before pulling the plug, it may blacken because the idle mix tends to be rich. It may be that your plug ran perfectly for 119 miles ...
I'd adjust the mix before the blur of spanners and pulling the engine apart.
Old Enfields leak oil, it will waterproof your boots.

[Tim NZ]

Cold - Hot, Rich - Lean. Both terms a relative, and the plugs visual appearance is not just affected by the ignition timing, but also the air temp and relative air density, as well as the applied load.


It is easy to make a 'Hot' plug look rich/cold, or a 'Cold' plug lean/hot.


A Plug chop is needed to be taken from the speed/load at which the view of the motor is required. Allow a motor to idle for only but a few seconds and the picture has changed. A plug chop is a LOT more than simply a Rich/Lean indicator.


And all that goes straight out the window IF the motor is using oil in excess of 2cc per mile?


If you are wanting to fix oil leaks, check the piston and rings too, as the 500 is notorious for suffering from premature piston failure.


If the Barrel/head nut adjacent to the pushrod tunnels has been over-torqued in a forlorn attempt to 'cure' oil leaking, the iron in the barrel is prone to distortion that will be revealed after a light hone as a 'hollow' in the bore perpendicular with that stud...

[Presto]

Tim will have his little joke! Why complicate life? To all intents and purposes that plug is running ‘rich’. That could be due to carburation or it could be due to an unsuitable grade of plug (too hard/cold, soft/hot) – or maybe burning more than 2cc of oil a mile (!!) – or something else . But whatever the cause in normal everyday biking that plug is running ‘rich’. To fix the ‘problem’ a few more details would help. (But a 'chop' won't tell you more than you can see now) Or am I wrong?