There have been numerous questions about spark plugs, so I thought that the following might be useful:-
Most Minors probably left the factory with Champion spark plugs. I have seen these fitted in genuine original engines and most of the old Gold Seal “Factory Reconditioned” units, although some of these definitely had NGK plugs fitted. Let’s look at Champion:
The Champion recommendation is an N9Y. This is interpreted as:
N = 14mm thread, ¾ inch reach
9 = heat range
Y = projected core nose
An additional prefix “R” indicates that the plug has a built in resistor for suppressing interference on radios. These can use plain leads and caps, whilst plugs without a resistor may require a suppressed cap and/or lead – but suppression of interference on radios is a separate subject in its own right!
An additional suffix “C” indicates a copper cored plug.
So your standard Minor might use N9Y, RN9Y or RN9YC, all perfectly acceptable.
The heat range for normal automotive use is 1 (cool) to 25 (warm).
Engines with a low combustion chamber temperature use a hotter plug such as 14.
Engines with a higher combustion chamber temperature use a cooler plug such as 6.
Using different heat values may help with tuning, but again, that’s a separate subject.
Other manufacturers use their own reference system. For example:
Champion NGK
N6Y BP8ES
N7Y BP7ES
N8Y BP6ES
N9Y BP6ES
N10Y BP6ES
N11Y BP5ES
RN9Y BPR6ES
RN9YC BPR6ES
Note that the heat range numbers run in the opposite direction, the “R” appears in a different position, and that there is an overlap in heat values, not a direct one-to-one correlation.
Just to complicate things further, there are many different makes of spark plug, and not all cross reference guides give the same results. Consider the Champion N9YC which, depending on your source of reference, could be replaced by:
AC-Delco R41XLS
Bosch W5DC
Mighty M4G22
Motorcraft AGS12C
NGK BP7ES
Lastly, the recommendation for most A-series engines is the trusty N9Y, but it is a recommendation. Just as some engines need a different needle in the carburettor, and timing varies slightly between engines, so it may be necessary to try a hotter or cooler plug.
Spark Plugs
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mike.perry
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"L" = 14mm thread with 1/2 inch reach.
"N" as above.
"Y" as above.
"C" as above.
Heat range for L10 and B6HS,as above, suggesting that sidevale used hotter plugs, and that early "A" series used cooler, but the recommendation changed over time - possibly to do with fuel grades?
The L86 is interesting, a very hot plug, typically for two-stroke motors. It's listed for outboard motors such as British Anzani Seasprite, lawnmowers, and motorcycles such as Puch and Puegot. For interest:
1-25 Automotive, small engines, and ordnance
26-50 Aviation
51-75 Competition, racing (see my note about tuning)
76-99 Industrial and Special Features types.
It is possible that the L86 was a "Special Feature", but regretfully I do not have any further data on those.
My research is taken from Champion Application Guides of the 1970s-80s where virtually every A-series (948, 1100, 1800, Morris, Austin, Mini, Vandan Plas, MG, etc) is listed as N9Y (a couple of MGs were different).
I'd welcome comments from anyone who has access to earlier guides to see if we can get a changeover point for the recommendations.
"N" as above.
"Y" as above.
"C" as above.
Heat range for L10 and B6HS,as above, suggesting that sidevale used hotter plugs, and that early "A" series used cooler, but the recommendation changed over time - possibly to do with fuel grades?
The L86 is interesting, a very hot plug, typically for two-stroke motors. It's listed for outboard motors such as British Anzani Seasprite, lawnmowers, and motorcycles such as Puch and Puegot. For interest:
1-25 Automotive, small engines, and ordnance
26-50 Aviation
51-75 Competition, racing (see my note about tuning)
76-99 Industrial and Special Features types.
It is possible that the L86 was a "Special Feature", but regretfully I do not have any further data on those.
My research is taken from Champion Application Guides of the 1970s-80s where virtually every A-series (948, 1100, 1800, Morris, Austin, Mini, Vandan Plas, MG, etc) is listed as N9Y (a couple of MGs were different).
I'd welcome comments from anyone who has access to earlier guides to see if we can get a changeover point for the recommendations.
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mike.perry
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John, thanks for your comment.
Mike,
D = 18mm 1/2 inch reach
J = 14mm 3/8 inch reach
Back on Minors, I have an Autobook Owners Workshop Manual (number 770) for the Minor, dated 1978, and a "Handybook" manual from 1974; and both of these recommend N5 plugs, which is at odds with Champion's own recommendation.
"Morris Cars" from 1966 by "T.B.D. Service" lists:
MM L10
Series II N5
1000 (948 & 1098) N5
Mini Cooper N9Y
What started as an attempt to give simple guidance has now become an intriguing detective story. Could the change in recommendation be due to improved cooling (better water pumps and water additives), changed fuel grades, changed range of plugs from Champion?
If anyone can post additional information, then I'll try to follow up and publish combined results. I did say originally that guides were only recommendations!
Mike,
D = 18mm 1/2 inch reach
J = 14mm 3/8 inch reach
Back on Minors, I have an Autobook Owners Workshop Manual (number 770) for the Minor, dated 1978, and a "Handybook" manual from 1974; and both of these recommend N5 plugs, which is at odds with Champion's own recommendation.
"Morris Cars" from 1966 by "T.B.D. Service" lists:
MM L10
Series II N5
1000 (948 & 1098) N5
Mini Cooper N9Y
What started as an attempt to give simple guidance has now become an intriguing detective story. Could the change in recommendation be due to improved cooling (better water pumps and water additives), changed fuel grades, changed range of plugs from Champion?
If anyone can post additional information, then I'll try to follow up and publish combined results. I did say originally that guides were only recommendations!
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mike.perry
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- Joined: Sun Jul 24, 2005 11:39 pm
- Location: Reading
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As my original post raised a couple of questions, I contacted Champion who have provided the following information:-
Over the years we have unfortunately lost much historical data & literature, therefore we cannot give exact dates when changes were made. We have also not catalogued the Minor for around 20 years.
I have, in investigation of your query, now defined the current production plugs for the Minor & it will be back in our next catalogue.
N5 for the 948cc was superseded by N5C
N9Y for the 1098cc was superseded by N9YC
N5 & N9Y were nickel electrode plugs, they were upgraded to N5C & N9YC copper core electrode plugs as the copper core provides longer plug life. Automotive plugs are now all copper core or higher technology to cover life/service interval demands. Nickel plugs remain for small engine (ie mower) applications.
So there we are, after 20 years, the Minor will be back in current Champion catalogues, and if using the copper electrodes, you can extend plug life to from 6,000 miles to 10,000 miles. I'd call that a result, and would like to thank Champion for their assistance. I recommend their plugs most heartily.
Over the years we have unfortunately lost much historical data & literature, therefore we cannot give exact dates when changes were made. We have also not catalogued the Minor for around 20 years.
I have, in investigation of your query, now defined the current production plugs for the Minor & it will be back in our next catalogue.
N5 for the 948cc was superseded by N5C
N9Y for the 1098cc was superseded by N9YC
N5 & N9Y were nickel electrode plugs, they were upgraded to N5C & N9YC copper core electrode plugs as the copper core provides longer plug life. Automotive plugs are now all copper core or higher technology to cover life/service interval demands. Nickel plugs remain for small engine (ie mower) applications.
So there we are, after 20 years, the Minor will be back in current Champion catalogues, and if using the copper electrodes, you can extend plug life to from 6,000 miles to 10,000 miles. I'd call that a result, and would like to thank Champion for their assistance. I recommend their plugs most heartily.
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Chris Morley
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xpress
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Re: Spark Plugs
oh rats, what have i got myself into? shoving all this information in my little head ..
:S
If the spark plug gap is set too small, the spark may discharge too early because it's easier to jump the gap, and it may not ignite the mixture. If the gap too wide, will affect high speed performance. The wider the gap, the harder it is to spark across it. Also, the narrower the gap, the faster the plug wear. So the moral is, MIND THE GAP!
:S
If the spark plug gap is set too small, the spark may discharge too early because it's easier to jump the gap, and it may not ignite the mixture. If the gap too wide, will affect high speed performance. The wider the gap, the harder it is to spark across it. Also, the narrower the gap, the faster the plug wear. So the moral is, MIND THE GAP!
