MGA Forum

Spark plug gap

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Don MGA 1600 Avatar
Don MGA 1600 Silver Member Don Tremblay
Rutland, Rutland, USA   USA
1960 MG MGA "My Oldest Friend"
1962 Jaguar E-Type "Rich Bitch"
I have an NOS copy of the very first edition of the MGA owner's manual with the Tyrolite Green Cover and multi-page fold out for lubrication and is also lists the plug gap as: .019-.021"

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SPAMROD Mark Kemmerer
Clear Lake, IA, USA   USA
1954 MG TF "The Wife's"
Then .020 it is.

Dandare Avatar
Dandare Danny H
Sydney, Australia   AUS
I've seen this apparent anomaly with other BMC vehicles. The first edition of my Wolseley Instruction Manual says .022 in.

Second Edition (Operation Manual) says .019 to .021 in. Every thing since is .025 in.

I used to think this was plain wrong but was it a fuel thing in1954-55 UK?


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oleanderjoe Avatar
oleanderjoe Gold Member Joseph Baba
Fresno, CA, USA   USA
Modern day cars now run gaps as wide as .040 -.045, You cant run an MG with that gap. Lucky to get it started. BUT, years back we messed around with plug gaps, and a lot of guys were even fabricating Spark Plug washers that would "CLOCK" the open part of the electrode 90 degrees to the combustion chamber. < Did it help, ????? We even tried starting the Racecar with plugs at .025 -.030, and after warm up, switch plugs to .045. A litter hotter spark. BUT< if there was a delay on GRID. WELL SWICHAROO AGAIN. I always thought that was a little dumb.

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ozieagle Avatar
ozieagle Gold Member Herb Adler
Geelong Victoria, Australia   AUS
1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"
Just a bit of sideways thinking, maybe wrong.

The plug gap directly affects the HT voltage, the bigger the gap, the higher the voltage required.

Now we come to system constraints, the early insulation on the HT wires may not reliably stand up to the voltage from a 0.25 or larger gap. The coil may also be in trouble.

Along came material improvements and the gap could be widened.

As to why one would want a wider gap? The wider the gao the better chance of the spark firing a charge, because the wider gap will have more mix in it.


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Gary E Avatar
Gary E Silver Member Gary Edwards
Kernersville, ,N.C., USA   USA
I've used .025 for years and never a problem.


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