Spark plugs

[deo]

I am rebuilding my XJ11 and have come across a really simple question. The PO had NGK BP 7ES plugs in it, I read that it was made to have the NGK BP 6 ES plug. When I went to the auto parts house they recommended theh R42XLS. Does anyone know why the difference in opinion on plugs? When I pulled the BP 7 plugs three were black and the 4th was rusty. The bike has been sitting for about 18 months in the Ocean air of OC Maryland.

[xssiveone]

I can't give any recomendation for type of plug, other then to use what the manufacturer recommends. If you find you have an oil burning problem that is fouling the plugs, go one or 2 higher in the heat range. Most importantly when experimenting with different plugs, check to ensure the reach of the plug, that is the length of the plug that will screw into the engine, including the tip and electrode, is the same. If it's too long, you might contact the top of a piston.

As for the 3 black ones and one rusty one, that's easy. It's impossible to stop an engine and have all the valves closed. One or more valves are left open, allowing air, and moisture, into the combustion chamber.

[deo]

Thanks Brian!

All of the plugs have the same reach so I guess I will go with the newest ones. The blackened ones from the PO are not fouled just black. There are not any heavy oil deposits on them so I guess when I go to start it I'll find out for sure.

dave

[chopper]

hi,i use ngk bpr7ev plugs.work fine for me.

[deo]

How does one know which plug is higher in the heat range? I looked at the box and didn't see any heat markings. Just interested incase I need to know.

[sixtysix]

Check out www.ngksparkplugs.com or the website of the plugs you are looking at. All the following good info came from the above site.

NGK Heat range 2(hot) - 10 (cold)

SPARK PLUG BASICS:
The spark plug has two primary functions:

To ignite the air/fuel mixture
To remove heat from the combustion chamber
Spark plugs transmit electrical energy that turns fuel into working energy. A sufficient amount of voltage must be supplied by the ignition system to cause it to spark across the spark plug's gap. This is called "Electrical Performance."

The temperature of the spark plug's firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called "Thermal Performance", and is determined by the heat range selected.

It is important to remember that spark plugs do not create heat, they can only remove heat. The spark plug works as a heat exchanger by pulling unwanted thermal energy away from the combustion chamber, and transferring the heat to the engine's cooling system. The heat range is defined as a plug's ability to dissipate heat.

The rate of heat transfer is determined by:

-The insulator nose length

-Gas volume around the insulator nose

-The materials/construction of the center electrode and porcelain insulator

A spark plug's heat range has no relationship to the actual voltage transferred though the spark plug. Rather, the heat range is a measure of the spark plug's ability to remove heat from the combustion chamber. The heat range measurement is determined by several factors; the length of the ceramic center insulator nose and its' ability to absorb and transfer combustion heat, the material composition of the insulator and center electrode material.

Heat rating and heat flow path of NGK Spark Plugs



The insulator nose length is the distance from the firing tip of the insulator to the point where insulator meets the metal shell. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and fouling. Whether the spark plugs are fitted in a lawnmower, boat, or a race car, the spark plug tip temperature must remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These accumulated deposits can result in spark plug fouling leading to misfire. If the tip temperature is higher than 850°C the spark plug will overheat which may cause the ceramic around the center electrode to blister and the electrodes to melt. This may lead to pre-ignition/detonation and expensive engine damage. In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber. A projected style spark plug firing tip temperature is increased by 10°C to 20°C.

Tip Temperature and Firing End Appearance



The firing end appearance also depends on the spark plug tip temperature. There are three basic diagnostic criteria for spark plugs: good, fouled and overheated. The borderline between the fouling and optimum operating regions (500&def;C) is called the spark plug self-cleaning temperature. The temperature at this point is where the accumulated carbon and combustion deposits are burned off.

Bearing in mind that the insulator nose length is a determining factor in the heat range of a spark plug, the longer the insulator nose, the less heat is absorbed, and the further the heat must travel into the cylinder head water journals. This means the plug has a higher internal temperature, and is said to be a hot plug. A hot spark plug maintains a higher internal operating temperature to burn off oil and carbon deposits, and has no relationship to spark quality or intensity.

Conversely, a cold spark plug has a shorter insulator nose and absorbs more combustion chamber heat. This heat travels a shorter distance, and allows the plug to operate at a lower internal temperature. A colder heat range is necessary when the engine is modified for performance, subjected to heavy loads, or is run at high rpms for a significant period of time. The colder type removes heat more quickly, and will reduce the chance of pre-ignition/detonation and melting or damage to the firing end. (Engine temperature can affect the spark plug's operating temperature, but not the spark plugs heat range).

[deo]

Gary,

You gave me a lot for my money on that one. But I like reading that stuff. So often it is easier to make valid decisions on why do something when you know the principles for it. My mother said cause I told you so and that never cut it with me. Maybe that is why I lived 7000 miles away from her for so many years, eh?

thanks again.

dave olson

[TopCatGr58]

Spark Plug Info

Hey Gary,

Is that info in the Tech tips section? I didn't try to look for it yet, but if it's NOT there, then it should be, perhaps along with a listing of other brands and #'s that folks can use vs. the NGK types. I have used Champion N9YC, had 11 but that is a hotter plug, and with my previous lean condition, felt a cooler plug was better protection.
T.C.

[sixtysix]

TC,

Not sure if it is there, but we really can't just steal copyrighted material and repost it here as our own. If somebody wanted to take the info and make a tip (in their own words) with a link to the article OR if permission was granted to reprint the info then we could do it. If you or anybody else is interested in making up a tech tip on this (or any) subject, please contact me or one of the other moderators.

[xsivebiker]

I went from the NGK BP6ES to the BPR6ES [resistor type]. I just thought I'd give them a try and since I have "tunes" installed on my XS, it couldn't hurt.
No performance difference. I didn't have any real electrical interference ploblems before, and since the change over, my "tunes" are still interference-free. 'Just my two cents worth.
Greg
1980 XS1100-G [fully dressed]
1982 CX500 Custom [Wife's ride]
1979 XL250-S

[Jerry]

I use the BP7ES (1 range cooler) in summer riding when pulling my trailer. I am about 240 pounds and and the trailer is about 180. Most of the riding is at highway (nterstate) speeds of 65 - 75 MPH. Result: engine is under heavier than normal load for quite a few hours at a time. For general trips the BP6ES seems to work very well.

Like most things, you have to try it a couple different ways and see what works best for you. Since you are new to the bike, start with the BP6ES plugs to establish a baseline.

[deo]

Jerry,

I had the BP7ES in the machine and changed them out today for the BP6ES. I think that I will watch for overheat this summer, as it gets hot here during the summer. I am about 240+ we wont go into the plus side of this, and should do a good bit of road work this summer.

Thanks for your comment.

dave