Forum

[Michael]

So, on the advice of this forum I lobbed an NGK BPR6ES (I think! The new plug is whatever has been advised!) into my EFI because the Bosch plug I had been using soots up really quickly and the bike has been misfiring badly for a wee while now. this, I think, is mainly due to sooting of plug and there being next to no gap becuase of build up.




Started first kick... idled nicely in the garage, ran it until hot and never missed a beat. It was a chilly night last night so I didn't pull the plug again to check as I was outside for ages doing other things too, but I am pleased with the initial improvements.




However, maybe a learned forum-ite can give me some more info on a few questions I have. A plug soots up because of incomplete combustion right - so too much fuel, not enough air or not enough spark/heat. Given that this is an EFI bike, you would expect the fuel-air ratio to be correct unless there was an air leak (which there doesn't seem to be, I checked) so the sooty plug was most likely caused by the plug itself not generating enough heat or perhaps a poor spark (e.g. coil, dud plug)? Would that be right?




Second question... what if the soot was instead, oil - this would mean oil in the combustion chamber right? The ways for oil to get in there include: past the piston (i.e. rings/bore worn), through the valve/valve guides (i.e. guides/stems worn or stem seals kaput) or through the air filter/crankcase breather (check air filter for oilyness)... So what would cause too much oil to go out through the breather into the air filter then into the combustion chamber?




One final point to add... my bike is leaking oil very slightly from the exhaust rocker and an o-ring at the head gasket joint. Moreover, there is a slight carbon looking build-up at the head gasket joint itself, especially round the pushrod guides. Anything to be overly concerned about? I only mention because the main theme in this message is 'soot and oil where they shouldn't be.'

[apparently lucky eddie]

..or it could just be that the original fitment bosch is badly designed, ill-concieved, shoddily made, possibly snide-made-in-china etc., etc. Your bike is n't alone in having a problem eith these plugs, I doubt many owners persevere with them for too long when you can get a brand spanking new and superior NGK for less than a couple of squids (Beware of snide NGKs too, there are millions of them out there.). I'd just be happy there is a cheap and simple fix and don't go looking for more problems cos with an Enfield you'll sure as hell find them!

[Thack]

It's probably more accurate to say that a plug soots up because it's running too cold. There can be various reasons for this, including a rich mixture or the wrong plug for the engine. However, short runs in cold weather can have much the same effect and I wonder if this is probably what is happening here. Nobody really knows why the Bosch plug causes trouble in our engine (after all, Bosch is a good name), but they do.



It won't be burning oil, and it won't be running rich - I'm sure of it. Just ride and enjoy.

[Scalyback]

NOW GUYS...



Remember that the 'BOSCH' plugs are made under licence in India, out of recycled cooking pots and ground down old imperial dinner china.



As far as I remeber, if you look on the official (German) BOSCH lists, they don't list the plug at all.



For once, I'm 'doing a Norm', they are sh*t. Go get a (non fake) NGK plug. (if it had a ming dynasty stamp on it, then it's probably a chinese copy).



I fed my EFI an NGK, and it has thanked me every ride since!

[Presto]

The ideal operating temperature of the central electrode is between 400° and 800°c. If the plug tip temperature rises too high, say above 950°c, the tip becomes incandescent. The glowing plug may then ignite the mixture before the spark occurs. This effect is referred to as ‘pre-ignition’. Where pre-ignition occurs the fuel charge does not burn progressively and the combination of the extreme heat, typical of pre-ignition, and the shock wave from the uncontrolled explosion of the fuel charge may result in serve damage to the piston crown.

Plugs are designed to run at high temperatures. Failure to reach these temperatures often results in the plug ‘oiling-up’. A plug tip temperature below the optimum, below 400°c, will not allow the plug to self-clean, to burn off carbon and fuel deposits. Allowing an engine to idle for long periods may also result in plug oiling, for the level of heat generated, though comparatively high, will not be high in relation to the plug’s ideal working temperature.

Classic bikes are frequently ‘nursed’, often run at only very moderate speeds, and often over relatively short distances. This may prevent the plug from reaching its optimum temperature and is one common reason why plugs ‘die’ after only low mileage. This is not, as is often supposed, a fault of the plug. In these circumstances the heat range originally recommended by the manufacturer may be too ‘hard’ (or ‘cold’), and thus the recommended plug, being subjected to less heat than the manufactures envisaged, is unable to reach a self-cleaning temperature.

If the plug shows a tendency to oil-up it ought to be replaced by a plug of a ‘hotter’ (or ‘softer’) heat range than that originally recommended.

A fouled plug is liable to misfire. Electrical current is ‘lazy’, taking the most readily available route to earth. A fouled plug gives the current an escape route, allowing the current to track from the debris on the insulator before it reaches the electrode. The plug in an engine that misfires will fail to generate sufficient heat at the firing tip to self-clean, and this will create a vicious circle of failure.

[Scalyback]

Well done Presto!



That has to be the most concise, easy to understand and comprehensive plug explanation I have ever heard.



Pre-ignition had been something of a mystery to me, as I (my engines) have never suffered with it, but it sounds similar to the way that diesel glow plugs work. The plug is very hot, and the mixture fires when a certain compression point is reached, at a time before the plug actually fires! Now I understand it.



Thank you!

[Leon Novello]

Scaly: Pre-ignition, detonation, pinging and pinking, whatever you like to call it, all sound like a crate full of empty glass beer/ milk bottles rattling around in the back of a car on a corrugated dirt road. You cannot fail to hear it when it does occur.

[Bullet Whisperer]

For a plug to run black, I would be looking at something other than the plug as being the cause, unless your machine is misfiring to begin with, the fuelling, or something else is more likely the cause. An NGK B6/7/8 ES/HS is pretty much all you are likely to see in any of my Enfields, including the racers, I stopped kidding myself that iridium or platinum tipped plugs made any difference. I don't know where the plugs I get are made, but a duffer is quite a rare occurrence here, unless bits of piston wipe them out! As for pre-ignition and detonation, they are two very different things - I read this while trying to get to the bottom of my pre-ignition problems with the 350 Clipper racer, which took far to long to find the cause of, but it is ok again these days. Regards, Paul.
http://www.contactmagazine.com/Issue54/ ... asics.html

[Scalyback]

Head went round, but I see the difference.

[Presto]

Bullet Whisper is right – as usual, preignition is different from detonation.


DETONATION: an engine event in which combustion is initiated by the spark but where the flame speed is so high that the fuel mixture explodes (‘detonates’) rather than undergoing a normal progressive burn, creating a resonant ‘spike’ (cause of the ‘pinking’ sound). Also a secondary combustion may occur elsewhere in the combustion chamber, the two flame fronts collide, creating a resonant ‘spike’ (cause of the ‘pinking’ sound). This fault may be caused by an over-advanced ignition timing (the spark occurring too early in the cycle).


Detonation produces an extremely high and sharp pressure spike of short duration in the combustion chamber. This spike produces an audible ringing tone, as if the engine was hit with a steel hammer. The resonance occurs at about 6400 Hertz and the pinging (or ‘pinking’) heard is the engine’s structure reacting to these pressure spikes.


PREIGNITION: an engine event in which the combustion of fresh fuel/air mixture is caused by incandescence in the combustion chamber, the mixture being combusted by an area of excessive heat before normal ignition occurs. A secondary combustion occurs at the spark. The two flame fronts collide creating a resonant ‘spike’ (cause of the ‘pinking’ sound). A cause of this incandescence may be a heavy build-up of carbon deposit in the combustion chamber or a spark plug that glows with excessive heat.