Spark plugs

[mmouss]

Hello, I thank you for admission on this interesting forum. :)

I recently bought a 1936 AC 16/80 and am wondering if the sparks plugs fitted are the correct type.
Those are NGKs B6HS and tend to get wet quite often.

I think of fitting slightly hotter ones like NGKs B5HS or equivalent Champions L86C but would of course avoid the risk of damaging pistons...

Can someone give me an advise about this please?

[mmouss]

Hello again,

So, nobody here has plugs on his AC engine and can help with advise about them??? :-[

[Flyinghorse]

Yes surprised you had no response.
The 2 litre saloon runs this engine and there's a good website that details engine / ignition maintenance and Leo Archibald wrote a good book on the 2 litre car  that has a engine / gearbox section - I would get a copy as it covers engine/ gearbox.
http://www.ac2litre.com/maintain4.html

The excerpt from the  site says lodge C14. These may be hard to get but if it were me call up Tim Green. My quick research suggests an equivalent is Ngk B5 which is hotter.
https://www.gsparkplug.com/
and discuss equivalents( and your issue)  with him. Incidentally many are starting to use iridium plugs now to combat many plug related issues ( wetting) (ace Bristol, CRS )
"Spark-plugs are specified in the manuals as Lodge C14, 14mm. The gap is specified as 0.015 to 0.018 inch (0.38 to 0.46mm). When low octane 2 star petrol was phased out in the UK (in 1989), I found that slight mis-firing occurred on partial throttle, and I followed advice of another classic car owner to widen the spark-plug gap. With a gap of about 0.025 inch (0.64mm) the trouble was solved."

Hope that helps.
Graham

[mmouss]

Thank you very much Flyinghorse for your kind answer.
The link you provided seems very interesting to me as many other important points are also detailed.

I will try Champion L86C which is equivalent to NGK B5 and let you know the result.
I am not sure iridium plugs would be of great help but I will try the 0.025" gap you suggest.

Thank you for your help :)
Michel

[administrator]

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.

[AC Ace Bristol]

.
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

.

[mmouss]

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.

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]

Thank you for your answer AC Ace Bristol, but my engine is an AC, not a Bristol...

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
.

[mmouss]

Thank you Keith for all those informations. My head has 14 mm plug threads.

Unfortunately, the plugs are not anymore my main concern with my engine... :-\

[administrator]

Ouch!

[Robin A Woolmer]

I thought i should let you know what plugs we now use on my new engines & heads, these are 14mm thread but a long series but the heat ranges can be used for reference, They Are NKG LFR5A & LFR6A, you should need 1/2" long threads Short thread type!
For reference the Saloon general instructions quote Lodge C14 plugs

I am sure a good Motor Factor can help you but The Green Plug Company should assist anyway

Robin   

[mmouss]

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.

In fact, I suspect my engine marked UMB 386 would be a post war one as the plugs are 14 mm and the bolt securing the front pulley is left hand threaded...

[Robin A Woolmer]

You may have a Post War head fitted to your engine, the best way to find out which period your head is is from the drilling formation on the front of the head!
PVT Cars all had 18mm plugs to my knowledge all Post War engines /Heads have 14mm plugs!
To determine if you have a PVT or Post War engine fitted you determine which way the front feet are facing, all PVT & Vintage engines have what is called ' Cats Paw Feet ' mountings forward of the engine block, Post War engines have side mounting front feet each side of the block just rearward of the block front!
If you have a 16/80 you should have Cats Paw engine mounting!

Robin