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Spark plug gap

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2mgs4doors Avatar
2mgs4doors Harry Rathvon
Lancaster, PA, USA   USA
An original MGA workshop manual (1500) that I keep in my tool chest listed spark plug gap at .019 - .021 I checked several other sources and they all showed the gap to be .024-.026 for all models.....I know I've always used .025 Did very early cars use the .019-.021 gap even though the same type plugs are listed in each case?

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copernicus Avatar
copernicus Nick Kopernik
Springtime in, CT, USA   USA
Nice write-up on the MGAguru site re plugs & gap:

http://mgaguru.com/mgtech/ignition/ig101.htm

2mgs4doors Avatar
2mgs4doors Harry Rathvon
Lancaster, PA, USA   USA
The article doesn't explain why my manual recommends a plug gap of .019-.021

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copernicus Avatar
copernicus Nick Kopernik
Springtime in, CT, USA   USA
In reply to # 3199482 by 2mgs4doors The article doesn't explain why my manual recommends a plug gap of .019-.021

Don't know. .024-.026 is in everthing that I've seen.

Stevieg Avatar
Stevieg Steve Gyles
Church Crookham, Fleet, Hampshire, UK   GBR
1958 MG MGA
I just looked in the MG Workshop Manual for the Type M through to the MGTF 1500 (the book is known as 'Blowers'). Interesting that the MGTF, with the predecessor engine to the B-Series, was specified with the Champion NA8 as was the early MGA 1500. It lists the plug gap as 0.020 to 0.022. I wonder if it was one of those numerous specifications that technical authors transferred to the new MGA series for the first issue documents - only later to be amended with more testing and experience?

Steve

dipstick Avatar
dipstick Kenny Snyder
La Center, WA, USA   USA
1941 Ford N-Series
1958 MG MGA 1500 Coupe "Rosie"
1970 MG MGB GT "Pat's GT"
1971 MG MGB "Gifted To Me"    & more
My original hardcover "MG Series MGA Workshop Manual" specifies .024" - .026" gap, Champion N5, and that is what I use on my 1958 MGA Coupe. I have never seen any other factory specification.



Be safe out there.
Kenny


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MGA Workshop Manual.jpg    29.2 KB
MGA Workshop Manual.jpg

Stevieg Avatar
Stevieg Steve Gyles
Church Crookham, Fleet, Hampshire, UK   GBR
1958 MG MGA
Kenny

Same plug. Champion relabelled it.

Steve

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2mgs4doors Avatar
2mgs4doors Harry Rathvon
Lancaster, PA, USA   USA
Ok here is the text........original series MGA


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IMG_0991[1].JPG

2mgs4doors Avatar
2mgs4doors Harry Rathvon
Lancaster, PA, USA   USA
Text from section B ignition system page B8

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Blueosprey90 Avatar
Blueosprey90 Jeff Sienkiewicz
New Milford, CT, USA   USA
maybe weak coil ????

But does it make a difference? I run a gap of .30 with no ill effects.



Edited 1 time(s). Last edit at 2016-02-22 09:36 PM by Blueosprey90.

barneymg Avatar
barneymg Barney Gaylord
(Somewhere in USA), Pick one (or more), USA   USA
1958 MG MGA "MGA With An Attitude"
In reply to # 3200195 by 2mgs4doors Text from section B ignition system page B8

Wow. How early is that publication? In that paragraph,
my copy says, "see 'GENERAL DATA' for correct clearance".
The G.D. section says 0.024 - 0.026 in.

Of course my copy is the "latest and greatest".
The intro page is Issue 5 - 40954
Some other pages are as far as Issue 11 - 40954
That Ignition page is Issue 3 - 22142



Barney Gaylord - 1958 MGA with an attitude - http://MGAguru.com - barneymg@mgaguru.com

2mgs4doors Avatar
2mgs4doors Harry Rathvon
Lancaster, PA, USA   USA
intro page issue 2 ........8547 ignition page issue 2 ......1727

Stevieg Avatar
Stevieg Steve Gyles
Church Crookham, Fleet, Hampshire, UK   GBR
1958 MG MGA
There is no doubt that an early issue of the workshop manual had these numbers. The question has been asked how did those figures come about. IMHO I feel sure it would have been down to the technical authors of that first edition using archive and early trials data in front of them as they rushed to achieve the publication date. I was a fighter jet pilot in the RAF. One of my tours was to produce the handling and emergency procedures for the Tornado GR1 that was soon to enter service. The volume of paperwork from the test pilots and engineers was horrendous and I did the best I could to keep up. No sooner had issue 1 been printed when I would be presented with new data that had to be included as soon as possible. It was an almost impossible task and unvalidated (best guess) data often stayed in those early documents for some time.

On the subject of the plug gap, there was previously published data by Champion that the gap on this plug should be set at 0.020 to 0.022 inches. This could well have formed the basis of that early specification in the manual. What was not so obvious in that Champion data was in the small print that this was the gap for cars with magneto ignition. So, there we have a newly designed engine with coil ignition but specified with an 'old' but well respected plug. The engineers probably went for the gap of around 0.020 initially as that was all they had to go on, pending further trials. That figure would have been picked up by the technical authors and printed, only to be amended very soon after when the more common 0.025 was validated.

Steve

RJBrown Avatar
RJBrown Randy Brown
Queen Creek, AZ, USA   USA
I use NGK BP6ES gapped at .025. Not a fan of Champion plugs. Seen too many bad new ones in 33 years of owning an auto repair shop to ever choose them. B6ES plugs work also. Even with a hot coil you should not run a wider gap. The small size of the ignition rotor causes it to fail if a wide gap and ensuing higher voltage is run through it.

SPAMROD Avatar
SPAMROD Silver Member Mark Kemmerer
Clear Lake, IA, USA   USA
1954 MG TF "The Wife's"
I agree with Randy NGK just makes me sleep a little better at night and with a brand new engine (original) going in I will stick with what I think works best and like Randy I have been a Master MerCruiser Mech all my life and we see the same thing. But I am running BR6ES at .025 be cause I don't want static on AM with my marine stereo, you never know when you'll get caught in the rain and short out your radio!!! LOL



Edited 1 time(s). Last edit at 2018-03-10 10:45 AM by SPAMROD.

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