Hi there I've just bought NGK plugs for my 351 Cleveland, just wandering if anyone knows the factory plug gap sizes thanks,

 

I don't think the 351C was ever installed in a truck.
351M, from '80-'82 maybe?

Duraspark II ignitions called for .044" gap.
This should be shown on the sticker affixed to the radiator support.

 

He's in Australia. So he probably does have the cleveland heads on his truck. Would not have a clue what the Australian spec would be, but .044 or .045 would be a good place to start.

 

Just know the wider the gap the harder the box has to work to push the spark across it and could lead to the box failing.


Remember when HEI first came out the gap was .060? The modules would burn out so they closed the gap to .40-.045 I think it is.
Dave ----

 

Oh
I'm on my phone, so I don't see signatures or much identifying personal information.

Sorry about that.

 

Yep, Cleveland motor in the Aussie trucks, last of the Clevos I think in the late part of 1986.
.44 to .45 is what I run as stated above.

 

You seem to get *all the nice things*!

 

.40 to .45 gap will cause less stress on the module.
IMO, NGK are not the best plugs to use as they are a "high fire" plug traditionaly used in Asian built engines. I personally would try to source OEM Motorcraft plugs. And the nay-sayers chime in....3....2....1...

 

...0

I have bought WAY too many Motorcraft/Autolite plugs that were bad out of the box in recent years.

Moved to V-power and am not looking back.

 

Sorry to hear that....I have had good results being able to source OEM direct replacement Motorcraft spark plugs,wire sets,etc. direct from the manufacturer through authorized local distributors.

BTW.....What constitutes a "bad plug out of the box" ?

 

I would say not firing at idle or under load.
Dave ----

 

Bodies that are not crimped tight on the insulators, electrodes that are not sheared clean or square.

It's a sparkplug.
I don't want to have to pack up and go to the parts store to grab another one because of your complete lack of QC.

What is "high fire"???
Maybe I'm just too old to know these things.