AC Owners Club Forum > AC Weller Engine
Spark plugs
AC Ace Bristol:
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mmouss
Spark plugs have been discussed in depth on previous threads on the Ace, Aceca & Greyhound section of our Forum.
Granted both threads related to plug problems with higher compression Bristol 100D &100D2 engines, Might be worth making a cup of coffee and visiting
the thread below which also includes a link to the earlier thread.
https://www.acownersclub.co.uk/forum/index.php?topic=5144.0
Hopefully you find the content helpful in solving your problem with your AC engine. ;)
Keith
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mmouss:
--- Quote from: administrator on September 09, 2019, 09:25:04 ---A bit of a late reply, but I'm using Champion D9, which seem to work well. I was previously using NGK AB-6, which didn't like a combination of hot weather and stale petrol.
--- End quote ---
Thank you for your reply but don't D9s have a 18mm thread?
My cylinder head has 14mm threads, maybe 18mm were on older ones?
mmouss:
Thank you for your answer AC Ace Bristol, but my engine is an AC, not a Bristol...
administrator:
Yes, 18mm thread. Engine number is UMB 6 1/2 646, as far as I can see the last "pre-war" AC engine. I presumed that pre-war heads used 18mm threads as I'm sure 615 also has 18mm threads. I believe some owners fit adapters to reduce the threads to 14mm.
AC Ace Bristol:
--- Quote from: mmouss on September 10, 2019, 12:22:18 ---Thank you for your answer AC Ace Bristol, but my engine is an AC, not a Bristol...
--- End quote ---
mmouss.
I appreciate your engine is AC whereas mine is Bristol, I posted links as your original post referred to plug temperature ratings, so I thought the links
would be of interest and helpful.
According to NGK catalogue NGK's equivalent to Champion L85 / L86/ L86C/ L86CC & L87 is their B6HS not B5HS, Which is a hotter / softer plug .
Regards your latest question, reference 14mm & 18mm plugs, Brian is right , 14mm /18mm adaptors were ( are ? ) available so 14 mm plugs can be screwed into 18mm heads, Just be cautious regards over length thread reach into your cylinder head. / Combustion chamber.
B =14mm Thread pitch 1.25mm
6 = heat rating
H = thread pitch 12.7mm
S = Firing end construction ( Std super copper core centre electrode.)
A = 18mm thread pitch 1.50mm
NGK tel number 01442 281000 ( Hemel Hempstead, Hertfordshire. HP2 4SD
Keith
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