AC Owners Club Forum

AC Owners Club Forum => AC Weller Engine => Topic started by: mmouss on June 17, 2019, 12:56:49

Title: Spark plugs
Post by: mmouss on June 17, 2019, 12:56:49
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?
Title: Re: Spark plugs
Post by: mmouss on June 22, 2019, 23:05:51
Hello again,

So, nobody here has plugs on his AC engine and can help with advise about them??? :-[
Title: Re: Spark plugs
Post by: Flyinghorse on June 24, 2019, 09:28:30
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
Title: Re: Spark plugs
Post by: mmouss on June 24, 2019, 14:53:01
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
Title: Re: Spark plugs
Post by: 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.
Title: Re: Spark plugs
Post by: AC Ace Bristol on September 09, 2019, 15:52:54
.
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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Title: Re: Spark plugs
Post by: mmouss on September 10, 2019, 12:20:11
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?
Title: Re: Spark plugs
Post by: 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...
Title: Re: Spark plugs
Post by: administrator on September 11, 2019, 09:09:58
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.
Title: Re: Spark plugs
Post by: AC Ace Bristol on September 11, 2019, 14:37:55
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
.

 
Title: Re: Spark plugs
Post by: mmouss on September 11, 2019, 22:50:27
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… :-\
(http://)
Title: Re: Spark plugs
Post by: administrator on September 12, 2019, 08:46:14
Ouch!
Title: Re: Spark plugs
Post by: Robin A Woolmer on September 12, 2019, 10:05:26
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   
Title: Re: Spark plugs
Post by: mmouss on September 12, 2019, 14:06:03
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...
Title: Re: Spark plugs
Post by: Robin A Woolmer on September 12, 2019, 14:59:04
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
Title: Re: Spark plugs
Post by: administrator on September 13, 2019, 08:39:07
UMB 386 was originally fitted to L431, a 1936 2 seater DHC.  It suggests your engine is a pre-war block with a post-war cylinder head.
Title: Re: Spark plugs
Post by: mmouss on September 13, 2019, 19:44:46
Here it is Robin, so, post war isn't it?
Title: Re: Spark plugs
Post by: administrator on September 15, 2019, 10:07:55
That is a post-war block with the front engine mounts at the side, so it shouldn't be stamped 386.  Perhaps 1386 - probably from a 2 Litre saloon?
Title: Re: Spark plugs
Post by: Robin A Woolmer on September 15, 2019, 10:44:57
As has been said by the Administrator, it is a Post War engine, the water jacket looks fairly good but the picture does not give enough definition, if you are going to remove the head studs be very careful as they can be weakened at the junction of the head & block due to corrosion of the steel stud , effectively making a notch where they often shear!
Unfortunately the studs become tight due to them corroding down the stud drilling!
As you have a 16/80 it should have a Cats Paw block. Unfortunately these are very difficult to find & often very corroded!     
Title: Re: Spark plugs
Post by: mmouss on October 19, 2019, 09:17:42
Yes Robin, the water jacket is in very good condition and I do not think I will have to remove the head studs as the top face seems correct.
Even if it is not original, I will keep this block and fit it with new liners & pistons.

I checked and cleaned the cylinder head and noticed the ports castings were very rough from new, so I spent some time smoothing and adjusting them with the manifolds.
Also noticed the gas holes in the intake gaskets between manifolds and head were protruding 2 or 3 mm all round into the ports, which seems far from optimum in terms of efficiency!!!
 
Title: Re: Spark plugs
Post by: Robin A Woolmer on October 19, 2019, 14:12:14
You will clearly have improved performance when it is reassembled, hope all will go well.

Robin
Title: Re: Spark plugs
Post by: mmouss on November 10, 2019, 14:00:53
Hope so Robin, but still a lot of work to do in rebuilding it!
Title: Re: Spark plugs
Post by: mmouss on June 04, 2020, 23:41:48
So, after a lot of work done, the engine is now ready to be dropped again in the chassis.
The crank has been reground, rods & mains have been re-white metaled, small end bushes are new as well as liners & pistons.